epidemiological transmission patterns of taenia solium ... · v list of tables table 1-1 synopsis...

Epidemiological transmission patterns of Taenia solium cysticercosis in endemic areas: The case of Ecuador

Marco Rafael Coral Almeida

Dissertation Submitted in fulfillment of the requirements for the degree of Doctor (PhD) in Veterinary

Sciences, 2015

Promoter:

Prof. Dr. Pierre Dorny

Co-Promoters:

Prof. Dr. Washington Benitez Dr. Sarah Gabriël

Dr. Emmanuel Nji Abatih

Laboratory of Parasitology

Department of Virology, Parasitology and Immunology Faculty of Veterinary Medicine, Ghent University

Salisburylaan 133, B-9820 Merelbeke

“Ecuadorians are strange and unique beings: they sleep peacefully surrounded by roaring volcanoes,

they live poor among incomparable riches and they become happy listening to sad music.”

― Alexander von Humboldt

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1 Acknowledgements

I would like to express my gratitude to all the people that contributed in many different ways to this dissertation.

First of all, I would like to express my sincere gratitude to my supervisor Prof. Pierre Dorny for all his support, patience and wisdom. His motivation and his guidance were of enormous support for my research.

I would like to express my special gratitude to Dr. Nicolas Praet and Dr. Sarah Gabriël for all their assistance, time, great work and comments that helped me to accomplish this dissertation.

My special and sincere Gratitude to Dr. Emmanuel Abatih for sharing all his knowledge and supporting me scientifically and at personal level.

I am very grateful to Prof. Dr. Washington Benitez for all his support and for his input in my science career, without him anything of this could be possible.

I would like to thank my colleagues Freddy, Lenin, Maritza, Jorge, Sandra, Ana, Graciela, Juan Carlos, Dr. Mena, Ernesto, Yess, Hector, Gabriela, Andrés and Richar for all their help and support.

I am very grateful to professors Dirk Berkvens, Niko Speybroek, Emmanuel Abatih, Vincent Delespaux, Tanguy Marcotty, Eric Thys, Maxime Madder, Redgi De Deken for their guidance and support when I was a Master’s student at the ITM.

My special gratitude to all the ITM staff at the campus Mortelmans, specially to Clémentine, Lynn, Leen, Björn, Véronique, Anke, Nadia, Danielle, Vincent, Karen, Géraldine, Housyanatou, Katja, Famke, Nele, Kim, Julie, Ko and Ellen.

My sincere gratitude to my former classmates and other Ph.D. students that I found in this long journey, specially to Angel Rosas, Francesa Barletta, Lionel Gbaguidi, Olivier Zannou, Esteban Londoño, Lenin Ron, Adam, Marvelous, Jules, Teresa Palomar, Nga, Maryse, Alicia and her class, the 2009 QRAs and my former M.Sc. classmates.

My gratitude to all my ITM and non ITM friends that are too many to name them here but I would like to name a few: Jeroen, Sanne, Sévérine, Lieselotte, Tim, Andy, Farah, Pierre, Catherine, Fahdi, Werner, Jos, Caroline et le petit Léon, Jeroen(2), Émilie, Élodie, Ildikó, Alexandra, Ariadna, Marlon, Yann, Bérangère, Caroline(2), Maryse, The Namasté and the Friday ITMs.

I am very grateful to all the ITM staff, specially to Annelies, Fiona, Patricia, Helga, Hilde, Goele, Fita, Mathieu and Myriam from the student service for all their great work.

I would like to express my gratitude to the Directorate General of Development Cooperation, Belgium for the financial support of this research. I would like to extend my gratitude to the Institute of Tropical Medicine in Antwerp with special thanks to the department of Biomedical Sciences, Unit of Veterinary Helminthology. My gratitude also goes to the Faculty of Veterinary Medicine, Department of virology, parasitology and immunology of Ghent University .

My special gratitude to my family, specially to my parents and my sisters for all the love, good vibe, energy and emotional support during these years.

Samanta, all my gratitude is not enough to thank you for all the love you give me every day and all your support during these years, you are the inspiration that makes me give my best all the time all the times. I love you with all my heart my love.

Finally, I would like to thank Nature and Music for having the best mysteries left uncover that feed my curiosity.

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Table of contents

1 Acknowledgements .......................................................................................................................... i

Table of contents .................................................................................................................................... iii

List of tables ............................................................................................................................................ v

List of figures ......................................................................................................................................... vi

Abbreviations ........................................................................................................................................ vii

1 General introduction & literature review ......................................................................................... 8

1.1 General Introduction ................................................................................................................ 9

1.2 Taenia solium life cycle ......................................................................................................... 10

1.3 Importance ............................................................................................................................. 11

1.4 Diagnosis ............................................................................................................................... 15

1.5 Epidemiology ......................................................................................................................... 20

1.6 Control programs ................................................................................................................... 30

Rationale & Objectives .......................................................................................................................... 36

2 Taenia solium exposure and active infections around the world: Characterization and variability in endemic communities ........................................................................................................................ 38

2.1 Chapter summary ................................................................................................................... 39

2.2 Introduction ............................................................................................................................ 40

2.3 Methods ................................................................................................................................. 41

2.4 Results .................................................................................................................................... 43

2.5 Discussion .............................................................................................................................. 56

3 Human neurocysticercosis and epilepsy in Ecuador: Distribution in space and time of hospitalized reported cases. ................................................................................................................... 64

3.1 Chapter summary ................................................................................................................... 65

3.2 Introduction ............................................................................................................................ 66

3.3 Materials and methods ........................................................................................................... 68

3.4 Results .................................................................................................................................... 72

3.5 Discussion .............................................................................................................................. 80

4 Serological dynamics of cysticercosis in an endemic area in Ecuador. ......................................... 85

4.1 Chapter summary ................................................................................................................... 86

4.2 Introduction ............................................................................................................................ 87

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4.3 Materials and methods ........................................................................................................... 87

4.4 Results .................................................................................................................................... 90

4.5 Discussion .............................................................................................................................. 95

5 Towards prioritization of intervention areas of Taenia solium taeniasis/cysticercosis in Ecuador 98

5.1 Introduction ............................................................................................................................ 99

5.2 Characterizing Taenia solium human cysticercosis transmission in endemic areas. ............. 99

5.3 Identifying priority areas of intervention within a country with special attention to Ecuador. 101

5.4 Considerations when designing control strategies ............................................................... 103

5.5 Perspectives in Ecuador ....................................................................................................... 109

5.6 Conclusions & recommendations ........................................................................................ 110

6 Summary ...................................................................................................................................... 112

7 Samenvatting ............................................................................................................................... 115

8 Publications .................................................................................................................................. 119

9 Abstracts and Posters ................................................................................................................... 119

10 Curriculum vitae ...................................................................................................................... 120

11 Bibliography ............................................................................................................................ 121

v

List of tables

Table 1-1 Synopsis of intervention strategies available for Taenia solium taeniasis/cysticercosis, adapted from Allan et al. (2002) [196] and updated from Thys et al. (2015) [197]; Carabin et al. (2014) [14]; Braae et al. (2015) [179]; Gilman et al. (2012) [198]; Bulaya et al. (2015) [199]; Miwunda et al. (2015) [200]. ................................................................................................................. 31

Table 2-1. Sero-epidemiological studies using Ag-ELISA and/or EITB for human cysticercosis in Africa. .................................................................................................................................................... 46

Table 2-2. Sero-epidemiological studies using Ag-ELISA and/or EITB for human cysticercosis in Latin America ........................................................................................................................................ 48

Table 2-3. Sero-epidemiological studies using Ag-ELISA and/or EITB for human cysticercosis in Asia ........................................................................................................................................................ 51

Table 2-4. Taeniasis reports from Africa, Latin America and Asia ...................................................... 53

Table 2-5. Factors affecting serological variations of human cysticercosis infection and exposure to T. solium eggs. ........................................................................................................................................... 59

Table 3-1 Socio-economic and demographic factors used to model the incidence risk of hospitalized human cases of epilepsy and neurocysticercosis in Ecuador from 1996 to 2008. ................................. 70

Table 3-2 Municipalities having the highest incidence of hospitalized cases (/100,000 inhabitants) of neurocysticercosis and of epilepsy from 1996 to 2008. ......................................................................... 75

Table 3-3: Indicator factors associated with the incidence of hospitalized epilepsy cases in Ecuador from 1996 to 2008 (negative binomial model chosen by AIC criterion). .............................................. 78

Table 3-4: Indicator factors associated with the incidence of hospitalized epilepsy cases in Ecuador from 1996 to 2008 based on Bayesian model averaging (BMA). ......................................................... 79

Table 3-5: Factors involved in the incidence of hospitalized neurocysticercosis cases in Ecuador from 1996 to 2008 based on a zero-inflated negative binomial regression model. ........................................ 79

Table 4-1. Antigen and antibody seroprevalence figures (as based on the results of the Ag-ELISA and the EITB, respectively) by sex and by sampling round. ........................................................................ 92

Table 4-2. Proportions of antigen and antibody positive and/or negative individuals who participated in the 3 sampling rounds. ....................................................................................................................... 93

Table 4-3. Antigen change to seropositivity/seronegativity test result, Antibody seroconversions/seroreversion figures (as based on the results of Ag-ELISA and EITB respectively) by period. ............................................................................................................................................... 93

Table 4-4. Yearly incidence rates for infection and exposure (as based on the results of Ag-ELISA and EITB,respectively) of individuals who participated in two sampling rounds by period. ...................... 94

vi

List of figures

Figure 1-1: Taenia solium life cycle and human cysticercosis. Adapted from Del Brutto (2013) [22] and Kraft (2007)[23] .............................................................................................................................. 11

Figure 1-2 circulating antigen and antibody detection in serological samples. ..................................... 18

Figure 1-3 Areas at risk of Human cysticercosis in 2011 (WHO, 2012 [118]) ..................................... 21

Figure 1-4 Geographical regions of Ecuador ......................................................................................... 25

Figure 1-5 Factors contributing to the transmission dynamics of the taeniid zoonoses. Adapted from Gemmell (1989) [165]. .......................................................................................................................... 28

Figure 1-6 The cysticercosis cycle: intervention points [201] ............................................................... 34

Figure 2-1. Flow diagram describing literature search and selection of studies (PRISMA 2009 Flow chart). ..................................................................................................................................................... 44

Figure 2-2. Global distribution of the endemic countries where Ag-ELISA and/or EITB based epidemiological studies were held. ........................................................................................................ 52

Figure 3-1: Neurocysticercosis and epilepsy reporting flow chart in the Ecuadorian health system .... 68

Figure 3-2: Histogram of the incidence of hospitalized epilepsy cases per 100,000 inhabitants between 1996 and 2008 in Ecuadorian municipalities. ........................................................................................ 73

Figure 3-3: Histogram of the incidence of hospitalized neurocysticercosis cases per 100,000 inhabitants between 1996 and 2008 in Ecuadorian municipalities. ....................................................... 73

Figure 3-4: Incidence of hospitalized neurocysticercosis and epilepsy cases per 100,000 inhabitants in Ecuador between 1996 and 2008. .......................................................................................................... 74

Figure 3-5 Significant space-time clusters of hospitalized epilepsy cases with up to a maximum of 25% of the total centroids included in the scanning window between 1996 and 2008. ........................ 76

Figure 3-6: Significant space-time clusters of hospitalized NCC cases with up to a maximum of 25% of the total centroids included in the scanning window between 1996 and 2008. ................................ 77

Figure 4-1. Sera availability and individual participation during the three sampling rounds. .............. 91

Figure 4-2. Proportions of Ab seroconversion and seroreversion by time period ................................. 94

Figure 4-3. Results of the change point analysis with a change point at 30 years old .......................... 95

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Abbreviations

Ab Antibody

Ag Antigen

BOD Burden of disease

CSF Cerebrospinal fluid

CI Confidence Interval

CLTS Community led total sanitation

CNS Central nervous system

CR Confidence Region

CrI Credibility Interval

CT-Scan Computer tomography scan

DALY Disability-Adjusted Life Year

EITB Enzyme-linked Electroimmunotransfer blot assay

ELISA Enzyme-linked immunosorbent assay

GBD Global Burden of Disease

HCC Human cysticercosis

HIV Human immunodeficiency virus

IHC Incidence of hospitalized cases

MDA Mass drug administration

MRI Magnetic resonance imaging

NCC Neurocysticercosis

NTD Neglected tropical disease

PCC Porcine cysticercosis

PCR Polymerase chain reaction

USD United States of America Dollars

WHO World Health Organization

YLD Years Lived with Disability

YLL Years of Life Lost

Chapter 1 1 General introduction & literature review

General introduction & literature review

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General Introduction & Literature Review “Science is a way of thinking much more than it is a body of knowledge.”

― Carl Sagan

1.1 General Introduction

Taenia solium is a cestode that is transmitted between humans, the definite host in which it causes

intestinal tapeworm infection (taeniasis), and pigs, the natural intermediate host in which it causes

cysticercosis. Humans can also act as accidental dead-end intermediate hosts. Human cysticercosis

(HCC) is a neglected zoonotic parasitic disease caused by the development of the metacestode larval

stage of T. solium in different tissues. In humans the disease is responsible for different clinical

manifestations that can be very severe and even cause death [1]. The parasite can establish in the

central nervous system (CNS), called neurocysticercosis (NCC), which is the most important cause of

acquired epilepsy in developing countries [2;3].

Other impacts of this disease include economic burden caused by the costs of medical care and

disability, as well as economic losses for vulnerable traditional pig raisers in endemic countries

caused by the devaluation and/or condemnation of infected pig carcasses [4]. Endemic areas of HCC

are located in Latin America, Asia and Africa [5-7]. The presence of the parasite is related to poor

sanitary conditions, inadequate hygiene, open defecation, presence of free roaming pigs and poverty

[8;9]. However, HCC occurs in all the 6 WHO (World Health Organization) regions [10]. The disease

was eliminated in the past century in most developed countries, but imported cases of HCC and

taeniasis have been reported; new data suggests that immigration together with specific farming

practices could lead to the re-introduction of the disease in these non-endemic areas [11-13].

While the life cycle of T. solium is well known and different approaches to interrupt transmission are

available, there is no scientific evidence that supports elimination of HCC in endemic countries in the

near future [14]. Better efforts are needed to understand the factors that affect the transmission

dynamics of the parasite in order to design adequate interventions that can be integrated in national

control programs.

Ecuador is a South American country considered as endemic for cysticercosis with some areas

considered as hyperendemic such as the Andean region of the country [15]. Human and porcine

cysticercosis cases are regularly reported in Ecuador and all the conditions related to the presence of

the parasite are met within its borders. Studies conducted in the country, demonstrated the dynamic

nature of the transmission of the parasite [16;17]. However, to date no national control program has

been conducted in Ecuador.


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The present chapter aims to present an overview of the current knowledge on T. solium infections,

emphasizing its impact on public health and economy, and focusing on diagnosis, epidemiology and

control programs with an special attention to Ecuador. The chapters 2, 3 and 4 present the analysis of

data from the global to the local epidemiology of HCC in Ecuador. In chapter 5 the results from this

research are discussed and conclusions and recommendations are presented.

1.2 Taenia solium life cycle

The natural life cycle of T. solium includes humans as the definitive hosts harboring the intestinal

adult tapeworm, which causes taeniasis, and pigs as the intermediate hosts infected with the

metacestode larval stage (cysticercus), generally in the muscular tissue [18;19].

Humans acquire the tapeworm through consumption of improperly cooked infected pork containing

viable cysticerci. The cysticerci will evaginate in the small intestine liberating the scolex composed of

suckers and hooks, will use these organs to effectively attach to the intestinal walls, and subsequently

develop into an adult tapeworm.

The intermediate pig host gets infected by ingestion of parasite eggs containing the oncosphere larval

stage, passed in the stool of a tapeworm carrier. In the intestine, the eggs hatch, liberating the

embryos, which cross the intestinal mucosa to reach the bloodstream and are transported to different

tissues.

Once established in the tissue of the intermediate host, the cysticercus develops into the viable stage,

which is composed of a scolex visible through vesicular fluid and an opaline membrane inside a cyst

[20]. The metacestode larval stage establishes in the pig’s muscles, brain and other tissues causing

porcine cysticercosis (PCC) [19]. Unfortunately, humans can also serve as dead-end intermediate

hosts by accidentally ingesting parasite eggs and develop the metacestode larval stage in their body

tissues [21] (Figure 1).


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Figure 1-1: Taenia solium life cycle and human cysticercosis. Adapted from Del Brutto (2013) [22] and Kraft (2007)[23]

1.3 Importance

The zoonotic nature of T. solium taeniasis/cysticercosis and the involvement of a productive animal

species make this disease both a public health and a social agro-economic problem.

1.3.1 Clinical importance

While human taeniasis presents almost no clinical signs or mild and non-specific symptoms, HCC can

cause severe clinical manifestations and in severe cases even death [1]. In humans the parasite tends

to locate in the central nervous system (CNS) (neurocysticercosis (NCC)) causing a variety of

neurological disorders [24].

HCC can also involve skeletal muscular tissue, myocardium, the eye and subcutaneous tissue [25-27],

but these types of manifestations are considered less common or pathogenic compared to NCC [28].

The most frequent clinical disorders described for NCC include epilepsy and seizures, followed by

headaches, focal neurological deficits and disorders related to increased intracranial pressure such as,


12

hydrocephalus or papilledema. Other not so frequent manifestations are: meningitis, visual disorders,

cognitive disorders, and other psychiatric manifestations related to altered mental states [29].

NCC is the most severe presentation of the infection and is considered the most important parasitic

disease of the neural system and the main cause of acquired epilepsy in T. solium endemic areas,

where NCC is associated with 14.2 to 50% of the acquired epilepsy cases [30;31].

Most of the disorders related to HCC appear after several months or even years after infection due to

the ability of the cyst to evade the immune response of the host, thus preventing the inflammatory

reaction, associated with the presence of the viable parasite in an asymptomatic phase [32]. When the

cysticercus starts degenerating, which can be a few months to years after infection, the vesicular fluid

becomes dense and opaque, the cyst loses its regular shape and becomes smaller. Finally, the

cysticercus undergoes the stage of calcification in which it ends as a round white calcified nodule

[28]. During this degeneration process, an inflammatory response is generated by the hosts’ immune

system, resulting in a symptomatic phase [33]. Other elements influencing the gravity of these lesions

and the appearance of symptoms are the localization of the cyst, number of larvae, type of cysticerci

(racemose or vesicular) and the implication of the mechanical pressure caused by the cysts [34;35].

In pigs, the evolution of the infection is similar to HCC, however, the most frequent tissues infested

are the skeletal muscles and the myocardium, and less frequently, the brain and other organs. In most

cases no clinical manifestations are present but it is worth to mention that this may be due to the short

life period of the pigs until they are slaughtered and the long period needed to develop symptoms

[36;37]. However, some clinical manifestations such as, excessive salivation, tearing, fever, ataxia,

excessive blinking and/or a subjunctival nodule were observed after experimental infections in

pigs[38]. In other studies, it has been observed that when the CNS is compromised in infected pigs,

seizures and/or stereotypic walk in circles can occur [39]. Unfortunately, these manifestations are

inconclusive on their own to diagnose PCC and must be accompanied by other diagnostic tests to

confirm the infection [38;40].

1.3.2 Public Health and Socio-Economic importance

The first attempts to make a global estimation of deaths caused by HCC reported 50,000 fatalities per

year [41;42], but more recent estimations in the Global Burden of Disease studies (GBD) for 2010 and

2013 calculated that between 1,200 and 700 yearly deaths, respectively are due to HCC [43;44].

However, accounting only for mortality data does not describe the real impact of a disease in the

health status of a population. In fact, the most important impact caused by HCC is represented by the

disability that affects the symptomatic patients and contributes to the burden of the disease (BOD) in a

population.


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1.3.2.1 The non-monetary burden of HCC

To quantify the non-monetary BOD, the DALY (Disability-Adjusted Life Year) metric was

introduced in the early 1990’s and it has been widely accepted and used by the WHO and other

organizations involved in the local and global estimation of the BOD. The DALY metric combines

the morbidity and mortality components of a disease [45-47]. The DALYs are the result of the

addition of the YLD (Years lost due to disability) and the YLL (Years of life lost due to a premature

death). This data is derived from the demographic data, epidemiological data and the information

available about the severity of a disease [48], which makes the use of DALYs a better representation

of BOD, making it less abstract, more manageable and helps to make comparisons of BOD among

geographical locations or among diseases. In other words, each DALY represents a year of full health

lost due to a disease.

In the GBD 2010 study, it was calculated that HCC was responsible for 503,000 DALYs or 0.07

DALYs per 1,000 individuals worldwide every year [49], but the number of DALYs associated with

epilepsy that should derive from NCC and should be included in this calculation is unknown, which

suggests an underestimation of the burden associated with HCC [50]. In the most recent GBD study

(2013), HCC was estimated to be responsible for 310,400 YLDs (95%CI [212,200-409,500]) only for

that year, YLLs and DALYs estimations from the 2013 GBD study are not yet published [51]. For the

2010 GBD study HCC ranked as the 13th neglected tropical disease (NTD) responsible of the DALYs

attributed to all the NTDs for that year; HCC also accounted as the 9th NTD responsible for the YLDs

and 8th for the YLLs attributed to all the NTDs for that year [52]. For the 2013 GBD study the

estimated number of YLDs due to HCC was higher than the sum of the YLDs attributed to Chagas

disease, leishmaniasis (visceral, cutaneous and mucocutaneous), African trypanosomiasis, and cystic

echinococcosis together [51]. These estimations reveal the great contribution of HCC to the GBD, but

also show that a global assessment of the GBD of HCC is challenged because of underestimations due

to the characteristics of the clinical expressions of the disease, and because of the lack of quality data.

Torgerson and McPherson (2011) gave a crude estimation of between 2 and 5 million DALYs

associated with HCC yearly [53].

Only few studies estimated the BOD related to HCC in individual endemic countries. In 2009 in West

Cameroon (Africa), it was estimated that 9 DALYs per 1,000 person-years (95% CrI [2.8–20.4]) are

caused by HCC and the major monetary burden was related to the professional inactivity caused by

the clinical manifestation of the disease [4]. In 2012 in Mexico (Latin America), the estimated BOD

of HCC was 0.25 DALYs per 1,000 person-years (95% CR [0.12–0.46]) [54] and one year later, in

Nepal (Asia) the BOD associated with HCC was estimated to be 0.543 DALYs per 1,000 persons per

year (95% CrI [0.207–1.054]) [55]. It is worth mentioning that most of these estimations used


14

different methodologies; for example, the study conducted in Cameroon only took into account NCC-

related epilepsy cases while the Mexican study incorporated chronic headaches and NCC-related

epilepsy cases. However, despite of the variation in the methodologies, it can be observed that the

BOD estimated for HCC in endemic countries is much higher than the BOD estimated by the GBD

studies. In addition, the variability of the estimates between the studies suggests a variation on how

the disease impacts the BOD in different populations [4;54].

The impact of the stigma that epilepsy carries in certain populations should be added to the non-

monetary BOD as it increases the societal cost of the disease. The stigmatization of epilepsy patients

leads to discrimination when applying for work, isolation and psychological pressure [4;56;57]. In

children, this stigma leads to their exclusion from school and social activities. Sometimes, epileptic

children are locked in their houses and because of the stigmatization have an increased risk of being

malnourished. The mothers of epileptic children are also not well seen in many cultures and may be

victims of stigmatization, all of it compromising in many ways the future of these children and their

mothers [58-60].

1.3.2.2 The monetary burden of cysticercosis

The financial impact of HCC is difficult to measure at a global level. On the one hand there are the

costs of health care and treatment. Depending on the health care system in a country, these costs are

subsidized or not. Therefore, the financial impact can go directly to the patient or to the public system.

On the other hand, there are monetary losses due to losses in productivity, for which estimations are

relative, depending on the salaries and the cost per hour lost in every country [61].

To date, the global financial cost of porcine cysticercosis is unknown [53]. Porcine cysticercosis in

most cases does not present clinical manifestations or presents symptoms that do not substantially

affect the productivity of the pig [38;39]. The financial losses due to porcine cysticercosis are caused

by the total or partial condemnation of carcasses, also, in endemic countries where pigs are

slaughtered without meat inspection, pork showing physical lesions which include the presence of

cysts are sold at a lower price. However, clandestine markets and abattoirs plus the backyard

slaughtering of pigs for local consumption are regular practices in endemic countries, which limits the

availability of accurate data on this matter [5;62;63].

Another consequence of the informal slaughtering of pigs is that while veterinary inspection is

avoided, the infected meat is still sold, thus the risk of taeniasis infections continues [5;62;64;65]. In

other cases, pig traders use the tongue inspection before buying pigs; infected pigs are not bought

which implies economic loss for the pig owner [66]. However, infected pigs that are not sold will be

slaughtered at the village and consumed anyway [67].


15

In Cameroon the economic burden of cysticercosis was estimated to be 10.3 million Euros per year

with 95% of this burden attributable to HCC only in 2009 and it was estimated that treating a NCC

patient costs 194 € yearly [4]. In the Eastern Cape Province in South Africa it was estimated that

between 15 and 27.5 million € are lost per year (18.4-34.2 millions of USD (2004 currency exchange

adjusted)) due to cysticercosis depending on the methods used for the estimation. HCC was

responsible for 73-85% of these costs [68]. In Peru the cost estimated for the first two years of

treatment for one NCC case was estimated at 996 USD (2007 currency exchange adjusted), the costs

in the first year of treatment represented 54% of the minimum wage [69].

As these studies detail, it is clear that the monetary impact is more important on the public health level

than on the agricultural level. It has to be taken into account that the population that is affected by T.

solium infections usually belongs to the poorer strata. Because poorer people have less resources to

access proper health care, the impact of NCC can be higher than in the wealthier part of the

population [53;69].

Also, even if the agricultural economic impact seems to be lower when compared to public health

costs, it has to be taken into consideration that this impact goes directly to the economy of poor

traditional pig farmers who keep free roaming pigs and have very limited resources, thus the impact of

a carcass condemned or sold at a lower price can greatly affect their household economy aggravating

the socio-economic problem of NCC [70].

1.4 Diagnosis

Different tools are available for the diagnosis of taeniasis and cysticercosis. To date there is not a

single test that can correctly identify all the cases of cysticercosis in a simple and practical way. There

are many diagnostic techniques, which differ in the type of sample analyzed, test format, sensitivity,

specificity, cost, availability and ease of use.

1.4.1 Clinical diagnostic tools

Human cysticercosis has multiple clinical manifestations depending on the organ affected, with the

majority of the manifestations related to the infection of the CNS. However, there are no specific

pathognomonic signs or symptoms that could guide to a specific NCC diagnosis [22]. Therefore,

diagnosis is based on the clinical presentation, supported by neuroimaging, immunodiagnosis and

epidemiological information. Neuroimaging tools such as, CT-Scan (Computer tomography) and MRI

(Magnetic resonance imaging), are essential tools when symptomatology is compatible with neural

lesions; but images on their own are inconclusive if specific parasite structures are not present [34].

Immunodetection methods on CSF (Cerebrospinal fluid) or serum can contribute to the clinical

diagnosis of NCC but they are generally not sufficient on their own to allow for an accurate diagnosis.


16

For instance, detection of specific antibodies or circulating parasite antigens does not indicate the

location and the number of the cysticerci [71;72]. Antibody detection can overestimate the presence of

the parasite because anti-T. solium antibodies can be detected in serum from patients that have been

exposed to the parasite and not necessarily carry the cysts [73]. Detection of circulating antigens can

efficiently diagnose active infection (presence of viable cysts) but its efficacy is limited in the case of

calcified or highly degenerated cysts, which can pass undetected with this technique. Direct collection

of cysticerci from the host’ tissues for morphological identification and/or molecular analysis is the

most accurate way to diagnose cysticercosis, however, the proper extraction of the cyst involves the

risks of any invasive method, except for subcutaneous cysticercosis [34;74;75].

In order to correctly diagnose NCC, the use of multiple diagnostic tools and criteria has been

proposed. Del Brutto et al. introduced in 1996 a set of diagnostic criteria, which has been revised and

updated until recent years [76-78]. Their diagnostic criteria prioritize the results from the different

diagnostic tests/tools available; four categories are distinguished: absolute, major, minor and

epidemiological criteria, depending on the power of each test to correctly identify the presence of the

parasite [78]. These criteria are based on clinical, imaging, immunological and epidemiological data

[79].

An absolute criterion corresponds to the evidence of the undeniable presence of the parasite in the

CNS such as, a cystic lesion showing the parasite scolex or the demonstration of the parasite from a

biopsy. Major and minor criteria are applied when there is evidence suggesting the presence of the

parasite, the difference between the two will depend on how powerful the evidence is of the presence

of the parasite to confirm NCC. Epidemiological criteria are applied when there is evidence that the

patient was or lives in an environment where T. solium is present such as, an endemic area or a

household with a history of a tapeworm carrier. The presence/absence of the criteria leads to two

degrees of diagnostic certainty: Definitive and probable, which depend on the number, type and

combination of the other diagnostic criteria present in a patient [78].

The main disadvantage when applying the diagnostic criteria proposed by del Brutto et al., is that to

achieve a satisfactory result the use of multiple tools is requested [79]. In endemic countries, these are

often either unavailable or involve high costs, are complex to perform, need trained personnel and

specific equipment, which limits their use in field conditions. For these reasons, some authors suggest

the inclusion of the detection of circulating antigens as a major criterion in order to add more

confident elements to the diagnosis of NCC and a revision of the diagnostic criteria proposed by del

Brutto et al. for use in endemic countries [71].


17

1.4.2 Epidemiological diagnostic tools

Serology has the big advantage of being relatively accessible, not difficult to use in large numbers of

samples and at a relatively low cost when compared to other techniques. For these reasons, serology

for immunodiagnosis has become an important tool in epidemiological studies, notwithstanding its

limitations [75].

Immunodiagnosis can be performed either on serum samples, CSF, urine and saliva. However, for

epidemiological surveys the diagnosis on CSF is impractical, while tests on urine and saliva tests still

need to be better validated. The available serological tools can be classified into antibody detection

methods and circulating antigen detection methods. For the former, several tools have been developed

over the years (complement fixation test, haemagglutination, radioimmunoassay, ELISA, dipstick

ELISA, latex agglutination and immunoblot) but the most used and accepted test for epidemiological

studies is the Enzyme-linked Electroimmunotransfer blot assay (EITB), which is an immunoblot using

seven lentil-lectin-purified glycoproteins isolated from cysticerci, with a reported sensitivity ranging

from 97 to 98% and a specificity ranging from 97 to 100% to detect circulating antibodies to T. solium

in human serum [72;75;80].

For the circulating antigen detection methods the monoclonal antibody-based ELISAs directed at

specific Taenia antigens (Ag-ELISA) present the most accurate results [75;81-83]. The B158/B60 Ag-

ELISA and the HP10 Ag-ELISA are the most representative tests for epidemiological studies for the

detection of circulating antigens. The B158/B60 Ag-ELISA has a reported sensitivity of 90% (95%

CI: [80-99%]) and a specificity of 98% (95% CI: [97-99%]) to detect circulating antigens released by

T. solium metacestodes in humans, with no cross-reactions reported in humans to date [72;80;84]. For

the HP10 Ag-ELISA the reported sensitivity ranges from 84.8% to 86% and the specificity is

estimated at 94% to detect circulating antigens in human serum [85;86].

Circulating antigen detection and antibody detection differ in their interpretation. On the one hand, the

detection of circulating antigens shows the presence of viable cysts or the active disease in an

individual leaving calcified lesions undetected, while the detection of anti-T. solium antibodies

indicates the exposure to the parasite, which means that viable cysts can be present or not, a positive

detection can be the result of an aborted infection or even a past infection already healed, which can

lead to overestimation of the prevalence of HCC [72;73;75]. A high seroprevalence of antibodies is

indicative of a “hot spot” in a population, to which effective control measures should be directed. The

information gathered from the use of these techniques provides valuable information on the potential

risk factors for HCC [18;75;87]. The simultaneous use of both techniques provides a better

understanding of the transmission of the parasite [72].


18

Figure 2 describes the stages of the T. solium larval infection detected by an antibody test and antigen

test.

Figure 1-2 circulating antigen and antibody detection in serological samples.

It is worth mentioning that other techniques to detect HCC are under development such as the

detection of cellular response in serum [88] as an alternative to the antibody and/or antigen detection;

and the detection of antigens in urine, which can help to avoid invasive sampling methods [89-91].

1.4.3 PCC diagnostic tools

The diagnosis of PCC can be performed ante-mortem and post-mortem. Ante-mortem diagnosis can

be useful for the purchase of live pigs and for epidemiological purposes such as prevalence and

intervention surveys [81]. One of the most used diagnostic techniques is the tongue inspection, which

consists in the examination of the pig tongue in search of cysticerci by visual inspection or by

palpation. This technique is highly specific, quick to perform and does not involve any specific cost in

reagent or laboratory usage. However, this technique has a low sensitivity since not all infected pigs

will present lesions in the tongue. The sensitivity of this technique has been reported to vary from 21

to 70% and is greatly dependent on the intensity of the infection [92;93].

Immunological tools are also important ante-mortem techniques, which have been adapted in most of

the cases from HCC or bovine cysticercosis serological techniques to detect both circulating antigens

[82;94] and anti-T. solium antibodies [80;95]. Immunodiagnosis in pigs is widely used in

epidemiological surveys and provides important information in live pigs at a relatively low cost [81].

However, the use of immunological tools for PCC present some disadvantages: they have similar

drawbacks as for diagnosis of HCC [96], and have shown to be ineffective to detect light infections in


19

rural pigs [97]. Also, Ag-ELISAs are genus specific, thus false positives can arise because of cross

reaction with infections caused by other Taenia species such as the non-zoonotic Taenia hydatigena

[75]. The substitution of conventional antibodies by nanobodies for capturing antigens in these

techniques seems promising for increasing species specificity but needs to be validated [98]. On the

other hand, antibody detection techniques such as EITB do not cross react with T. hydatigena but the

confidence of these tests to detect porcine cysticercosis in naturally infected pigs still needs to be fine-

tuned [92;99]. Other ante-mortem techniques for PCC are 1) molecular diagnosis in serum and 2) the

use of ProteinChip technology for detection of biomarkers in serum samples; however, both

techniques are still under development and need to be validated [100;101].

Total dissection of the carcass can be considered as a “gold standard” test to detect PCC with a

sensitivity close to 100% but only if meticulous manual slicing of all meat is conducted. However,

this technique involves high costs because of the purchase of the pigs and the payment of trained

personnel to perform the dissection. An alternative to this procedure is the partial or targeted

dissection of the carcass, which reduces the time and cost of the test but has the disadvantage of

lowering the sensitivity of the test [102].

Post-mortem diagnosis corresponds to the veterinary inspection of the carcasses and is routinely used

in abattoirs. However, there exist different protocols of meat inspection that vary between countries

and abattoirs. The sensitivity of meat inspection depends on the number of cuts, muscles targeted and

the level of infection of the pigs; it has been estimated to be as low as 22.1% in abattoirs in Zambia

and can be a cause of underestimation of the prevalence [81;93]. In endemic countries not all pigs are

slaughtered in abattoirs, which contributes to an underestimation of the prevalence of PCC, thus limits

its validity for epidemiological estimations [62;63].

The use of sentinel pigs in endemic areas combined with diagnostic techniques described for PCC

including molecular tools, can give important information on the transmission dynamics of PCC,

environmental contamination with T. solium eggs, human risk to infection and can help to assess the

efficacy of control programs [103-105].

1.4.4 Taeniasis diagnosis

The questioning and self-detection/report technique is based on the auto-detection of expelled

proglottids that can be found in feces. While it has the advantage of being low cost, this technique is

not very efficient for the detection of T. solium since the expulsion of the proglottids is passive unlike

T. saginata and the technique lacks specificity because the distinction between proglottids and other

helminths and artifacts can be very difficult for the patient [81].


20

Conventional coprological examination can be applied at 1) macroscopic level if proglottids are found

in feces or 2) microscopic level using concentration techniques such as, sedimentation or flotation

methods to detect T. solium eggs in feces; or the use of the Graham test, which consists of the use of

an adhesive tape to collect T. solium eggs from the perianal region. The advantages of these

techniques are: the relatively low cost, and the fact that they are easy to perform. The drawbacks are

the considerable lack of sensitivity, the need to apply these techniques several times for satisfactory

results, and the fact that tests are genus specific, thus the differentiation of T. solium, T. saginata and

T. asiatica is not possible [81;106-108].

More advanced diagnostic tests are the copro-antigen detection, molecular methods and serological

antibody detection. Copro-antigen detection relies on the use of a polyclonal antibody-based sandwich

ELISA to detect specific Taenia coproantigens. It is more sensitive than conventional coprological

methods [109], it can detect early stages of infection, coproantigens disappear briefly after a

successful treatment of taeniasis, and it can be used on formalin preserved stool samples, which is

useful in field conditions [110]. The major drawback of this test is its genus specificity, thus in areas

where T. saginata or T. asiatica are sympatric the prevalence of T. solium tapeworm carriers can be

overestimated [81;107]. However, a novel T. solium species-specific coproantigen technique has been

developed [111].

Molecular methods have been used for identification and differentiation of parasites when proglottids

or other parts of the parasite can be recovered. They can also be used for taeniasis diagnosis on stool

samples. Copro-PCR is highly sensitive and specific, but the costs involving DNA extraction from

human feces for analysis is high, and PCR involves the use of a specialized lab, which limits its use

for routine purposes [81;108;112]. Finally, an EITB on serum samples for taeniasis diagnosis using

excretory-secretory antigens from adult T. solium has been developed. This technique is T. solium

species-specific and has the advantage of avoiding handling of feces, which can put the personnel at

risk. Its main drawback is the persistence of antibodies after treatment and elimination of the

tapeworm [110;113;114].

1.5 Epidemiology

1.5.1 Global epidemiology

HCC is a disease transmitted between humans. Infection occurs when a tapeworm carrier

contaminates the direct environment, water or food with parasite eggs, which are subsequently

ingested by a susceptible individual [115]. Based on the Multicriteria-based ranking for risk

management of food-borne parasites, which measured criteria such as the number of food-borne

illnesses, geographical distribution, acute and chronic morbidity and socio-economic impact amongst


21

others, HCC and T. solium taeniasis are ranked together as the most important food-borne parasitic

diseases [116;117]. The 2013 GBD study estimated that there exist 1,030,800 (95% CI [901,400 –

1,185,600]) prevalent cases of HCC worldwide [51]. T. solium infections are distributed in all the 6

WHO regions [10]. Figure 1-3 describes the global distribution of HCC around the world.

Figure 1-3 Areas at risk of Human cysticercosis in 2011 (WHO, 2012 [118])

HCC can be found from the poorer rural settings to the more developed and industrialized countries,

however, to maintain the full life cycle of the parasite, conditions such as, poor sanitation, lack of

hygiene, open defecation and traditional pig rearing systems allowing free roaming of the animals are

needed. Tapeworm carriers are the only source of HCC but the adult parasite can only be acquired by

consumption of infected undercooked pork. These particular conditions divide the affected countries

into three main categories, 1) endemic countries in which all conditions for completion of the life

cycle exist and all the infections with T. solium are confirmed (HCC, PCC and taeniasis), 2) the non-

endemic countries in which the conditions for the full life cycle are not met but which present cases of

HCC and 3) the suspected endemic countries in which the existence of the full cycle of T. solium is

probable but has not been proven consistently and some HCC cases have been reported. Endemic

areas have been identified in Asia, Africa and Latin America [5;6;119;120].

Ito et al. describe HCC as a societal disease [115], they classified human societies in three groups: 1)

societies where pork is not eaten because of cultural and religious beliefs, thus adult tapeworm free, 2)

societies where pork is consumed but are PCC free, such as developed countries with improved


22

husbandry and rigorous sanitation measures and 3) societies where infected pork meat is present and

consumed (endemic countries). Traditionally, societies in the third category are the societies carrying

the higher burden of HCC. However, through the years the interaction between these three societies

has increased and the transmission enhanced, thus increasing HCC infections in societies were pork is

safe to consume or is not consumed at all. Globalization and (im)migration seem to be the greatest

contributors to this evolution [12]. This historical evolution emphasizes the huge importance of

mobility and contact with tapeworm carriers in the transmission of HCC and breaks the paradigms

surrounding pig keeping and pork consumption as principal determinants for HCC [121]. In fact, in

non-endemic countries two types of infections can be found, 1) imported cases of HCC when the

infection was acquired in an endemic country, this could affect tourist travelers as well as immigrants

from endemic countries [1;122-124] and 2) the infections in situ which are the result of imported

cases of taeniasis and human-to-human transmission. HCC is a clustered mobile disease linked to the

presence of a tapeworm carrier [12;125-127]. The infection in situ with adult tapeworms in non-

endemic countries seems unlikely due to the strict restriction applied to pork trade [12]. However,

new data suggests that Europe can return to an endemic state. Organic farming with outdoor access is

becoming more common because of the increasing demand of organic products and animal welfare

concerns. Another contribution to this matter is the increasing number of immigrants and travelers

from endemic countries [12;13]. It has to be taken into account that until the first half of last century,

Europe still had endemic cases within its borders. Cysticercosis was eradicated at that time due to

improved meat inspection, sanitary conditions and pig farming [128]. In the USA, the number of HCC

cases is increasing in the last decades. Between 2003 and 2012, 18,584 hospitalized cases were

recorded nationwide, the costs of hospitalization of these cases surpassed USD 908 million. Most

cases were reported in Latin American communities. From these figures, some authors consider that

the disease should be a nationally reportable disease in the USA [129;130].

Despite the efforts to estimate a global prevalence of HCC, it is difficult to have a real estimate of the

actual distribution of HCC. Most of the cases remain cryptic until appearance of clinical

manifestations, or are diagnosed under research conditions as it happens in poor areas, thus the correct

diagnosis of HCC is practically accidental [115]. These characteristics of the disease may imply that

actual global figures are underestimating the real burden of HCC [50].

To date there is not a reliable estimate on the number of prevalent cases of taeniasis, an accurate

detection of tapeworm carriers is almost impossible due to the main limitations of taeniasis diagnosis

described in the section 1.4.4. [81;106]. For PCC there is a similar picture due to the diagnostic

limitations described in the section 1.4.3. Furthermore, most of the pigs at risk to develop PCC are

slaughtered in the backyard for local consumption, and serological tests available to date are

confronted with problems of cost, non-adapted format for field use and cross-reactions to other


23

parasites; thus the prevalence of PCC at a global level is unknown [53;62;63;93]. However, in field

studies in endemic areas using the B158/B60 Ag-ELISA, apparent prevalences ranged from 9.01-

11.5% in Ecuador and Tanzania to 57.1% in Zambia [93;131;132].

The more reliable data for HCC are the figures obtained from epidemiological field studies and

clinical data, though they only give a partial picture of the transmission of the disease. On the one

hand, clinical data reflects the “tip of the iceberg” because they present only symptomatic patients

[36]; on the other hand, epidemiological field studies rely on the sensitivity and specificity of the tests

that are used. To date the best tools for epidemiological studies rely on immunodiagnosis provided by

serology [75;133]. The prevalence of circulating antigens of T. solium metacestodes using the

B158/B60 Ag-ELISA in endemic communities ranges from 0.57% in a rural community in Viet Nam

to 21.63% in a rural community in the Democratic Republic of Congo [134;135]. The seroprevalence

of anti-T. solium antibodies using the EITB technique in endemic communities ranges from 3.07% in

Colombia to more than 30% in Ecuador, Peru and Zambia [17;73;136].

The variability of the prevalence and seroprevalence of HCC, PCC and taeniasis in endemic areas

needs to be understood in order to obtain better estimates of the real impact of T. solium at a global

level. Also, understanding the origin of this variability could help identifying important information

that could be used to design different strategies to control T. solium in endemic areas.

1.5.2 T. solium taeniasis/cysticercosis in Latin America

Published data on HCC in Latin America show a significantly consistent association between

cysticercosis and epilepsy with more than 12% of NCC cases among urban epileptic patients and

more than 23% in rural settings [2]. Furthermore, it is estimated that there are 5 million people living

with epilepsy in Latin America [137], suggesting that only in Latin America there are between

500,000 and more than 1 million cases of symptomatic HCC. These rough estimations contrast with

the GBD 2013 estimations of around 1 million HCC cases worldwide [51]. Another study estimated

that 75 million people in Latin America are at risk for HCC and that there are 400,000 cases of

symptomatic NCC, based on the conditions observed in clinical and serological studies conducted in

Peru [138]. The discrepancy among these estimates could be the reflection of a high variability of the

epidemiology and the transmission dynamics within endemic regions [139].

Epidemiological studies using the EITB test for anti-T. solium antibodies, conducted in endemic areas

in several countries in Latin America revealed seroprevalences varying from 1.59% in Brazil to

31.22% in Ecuador [17;140]. Studies using Ag-ELISAs found circulating T. solium metacestode

antigens ranging from 0.94% in an endemic area in Ecuador (B158/B60 Ag-ELISA) to 9.12% in

Venezuela (HP10 Ag-ELISA) [17;141]. These results also showed a significant difference between


24

anti-T. solium antibodies seroprevalence and circulating T. solium metacestode antigens

seroprevalence, indicating a significantly higher exposure to the parasite and a relatively low

prevalence of active infections [139].

The major risk factors studied for the presence of HCC in endemic areas of Latin America were

mostly related to the lack of proper hygienic/sanitary conditions, the presence and proximity of

tapeworm carriers, presence of infected pigs, pig farming/consumption and an increased risk of

infection with increasing age [139].

The prevalences obtained for taeniasis in Latin America are very dissimilar and depend on the

sensitivity and specificity of the tests; figures range from 0% to 17.5% in Ecuador and Guatemala,

respectively. The techniques used were formalin-ether and magnesium sulphate flotation techniques

for Ecuador and formalin-ether technique and copro Ag-ELISA for Guatemala [16;142].

Porcine cysticercosis has been found ranging from 0% to 33% in villages in a same endemic area in

Mexico using a low sensitive test as tongue inspection. In Peru, serological studies using EITB report

seroprevalences in pigs as high as 61% in small villages in endemic areas [143;144].

1.5.3 Epidemiology of T. solium taeniasis/cysticercosis in Ecuador

Ecuador is a South American country, located at the Pacific Coast between the latitudes 2 °N and 5

°S. The country has a surface of 283,560 square kilometres; its borders are Colombia in the North,

Peru in the East and South, and the Pacific Ocean in the West. It has a population of around 16

million. The country has 4 different geographical regions, the insular region of Galapagos, which is a

group of islands declared national park and is a protected area, the coastal region with a typical

tropical and sub-tropical weather and landscape, also known as Costa region, the Andean region or

Highlands also known as the Sierra region with cooler temperatures and a mountainous landscape and

the Amazonia region characterized by its hot and humid weather and dense rainforest (Fig. 1.4). The

rural population of Ecuador accounts for 38% of the total population of the country and is composed

in its majority by the indigenous communities dedicated to agricultural labours. The Sierra region and

the coast region comprise most of the active agricultural zones [145-147].


25

Figure 1-4 Geographical regions of Ecuador

Human and porcine cysticercosis occurrences are regularly reported to the OIE, the diseases are listed

as present in the country [148]. Official reports from the Ministry of Public Health in Ecuador

reported 67 new cases of cysticercosis in 2013 or 0.42 cases per 100,000 persons. Most of these cases

correspond to symptomatic NCC hospitalized patients in public hospitals only, which suggests a large

underestimation. The data show a decreasing trend since 1994 with 400 new cases or 3,6 cases per

100,000 habitants at that time. The Sierra region seems to carry the majority of the burden, with

Pichincha and Loja provinces showing the highest numbers of reported cases and cases per 100,000

persons [149]. The decreasing trend over time is compatible with what has been observed by

specialists in large hospitals in Ecuador and might be caused by the improvement of general life

conditions, such as better sanitation and better access to health care [150;151]. However, this does not

mean that these conditions have significantly changed in rural areas and that elimination or

spontaneous regulation of the disease has occurred. In fact, the highlands of Ecuador have been

considered hyper-endemic for HCC since a long time [15]. Possibly, the observed decreasing trend in

part represents a decrease in the severity of symptomatic NCC cases. With the general improvements

in the health care system in Ecuador, it is possible that symptomatic patients are properly diagnosed

and treated in an early stage of the disease avoiding the progression of the disease and reducing the

number of hospitalized cases, while the number of asymptomatic or non-hospitalized cases remains


26

stable [151;152]. However, the causes of this decreasing trend have to be further studied. On the other

hand, the Ministry of Public Health reports a totally different picture for taeniasis: cases of taeniasis

vary from 400 to 125 cases per year in 1994 and 2013, respectively, but there is not a clear trend

during that period. For example, in 2002, 2006 and 2011 the number of reported cases was 94, 103

and 59, respectively, but in 2000, 2004, 2009 and 2012 there were 320, 475, 396 and 216 cases

reported, respectively. In addition, there is no geographical trend in the reporting of taeniasis; the

cases are reported from all regions of the country without a specific pattern [149]. Considering that

the diagnosis of human taeniasis is difficult and the prevalence of tapeworm carriers recorded in most

of the epidemiological studies in Ecuador is lower than the prevalence of HCC [16;106;131;153],

either the reported cases of tapeworm infection are misdiagnosed and a proportion of the cases

possibly corresponds to T. saginata infections, which is also present in Ecuador [131], or there is a

serious underreporting of HCC cases.

Reports from epidemiological studies during the last decade demonstrated that HCC is still present in

rural areas in the highlands and that the population is highly exposed to the disease. Indeed,

epidemiological studies in rural areas of Loja province in the Southern Sierra geographical zone,

reported antibody seroprevalences as high as 34.1% (95% CI [29.2–39.2]) [17]. Active HCC,

measured by the detection of circulating antigens was found to be 4.99% in rural areas of the north of

the country (95% CI [4.36-5.69]) [131]. T. solium taeniasis has been confirmed by different methods

in epidemiological studies in different rural areas of the country ranging from 0% (95% CI [0-0.5]) to

1.63% (95% CI [0.89-2.72]) in two villages of the same province of Loja, 0.41% (95% CI [0.18-

0.81]) in the northern provinces of Imbabura and Pichincha and 1.55% (95%CI [1.31-1.82]) in a large

study conducted in several communities of the southern province of Loja and the coastal province El

Oro, bordering with the province of Loja [15;16;131;153]. Similarly, for PCC, meat inspection

detected metacestodes in 0.52% (95% CI [0.29-0.0.85]) of carcasses in the abattoir of Imbabura; the

seroprevalence of T. solium circulating antigens for the same pigs was reported to be 9.01% (95% CI

[7.33-10.92])[131]. In a rural village in Loja, PCC diagnosed by tongue inspection was found in

3.56% of the pigs (95% CI [2.27-5.29]) while EITB demonstrated a seroprevalence of 73% (95% CI

[63.20-81.39]) [153].

In the rural environment of Ecuador risk factors for taeniasis/cysticercosis such as open defecation,

lack of latrines, poor hygiene, keeping free roaming pigs and eating under-cooked pork are commonly

present [16;153]. Additionally, some studies found that the risk of infection with HCC in rural areas

of Ecuador increases with age [16;17]. The presence of HCC has also been documented in urban

environments of the country and it was found that in cities not only low income social classes are at

risk of infection, but also middle to upper classes, which contrasts with the general statement that

links cysticercosis mostly to the economically poorer social classes. Risk factors for infection in urban


27

areas were, working in manual labour, eating frequently outside and a history of other NCC patients

in the same household [154;155].

Clinical manifestations of neurological disorders such as, epilepsy, migraine and chronic headache in

Ecuador present a strong correlation with NCC [156-158]. For most of the NCC patients in Ecuador

the cysticerci are located in the brain parenchyma and the single, small, enhancing CT lesion is the

most common presentation of NCC, which is a common lesion found in patients with seizures in

endemic countries [151;159-163]. Subcutaneous cysticercosis is practically absent (or not reported) in

the country [156-158;160].

From the experiences gathered from these studies, it can be assumed that HCC is still an important

public health problem in Ecuador that does not discriminate from poorer to richer social strata, neither

from urban to rural settings. Also, a considerable gap between epidemiological studies and official

data is present. To date no national control program for T. solium has been conducted in Ecuador.

While a decreasing trend is observed in the number of hospitalized cases of NCC in Ecuador,

epidemiological studies show that there are no signs that the risk factors for T. solium life cycle

maintenance in rural communities have disappeared. Neither there are signs that the transmission of

HCC has been effectively interrupted in urban settings. The official reports of taeniasis show

fluctuations in the number of detected cases along the years. However, there are no clear patterns of

the geographical location of the most affected areas for both conditions. PCC is still reported in the

country but accurate data from traditional pig holders is unavailable. Data from epidemiological

studies conducted in endemic areas of the country partially detail the situation of T. solium human

infections. There is an urgent need to better understand the information gathered from these studies

about how, when and where the transmission occurs in order to design appropriate control strategies.

1.5.4 Transmission dynamics

HCC is the result of human-to-human transmission. The level of the parasitic infection and the

distribution of the parasite in an area are the result of the interaction between parasite, environmental

and host-related factors [164]. To understand the transmission dynamics of HCC, it is important to

have a complete view of the dynamics including also the adult tapeworm infection and PCC. Figure 1-

5 represents the factors contributing to the transmission dynamics of the taeniid zoonoses.


28

Figure 1-5 Factors contributing to the transmission dynamics of the taeniid zoonoses. Adapted

from Gemmell (1989) [165].

Adult tapeworms are capable of producing tens of thousands of eggs daily that are fecally shed by the

tapeworm carriers. These carriers are the sole source of infection for pigs and other humans and they

are capable of widely spreading eggs in the environment, depending on their behaviour. Egg dispersal

from stools in the environment can be affected by different mechanisms such as; wind, rainfall,

sewage systems, fertilizing systems, arthropods, and other warm-blooded animals. Eggs can rapidly

be dispersed in a radius of 100 meters around a defecation site. This reflects the high biotic potential

of the parasite [19;164-168]. The dispersion of eggs by arthropods is still debated. Flies have failed to

prove to be mechanical vectors of T. solium eggs because the coprophagic behaviour of pigs does not

allow enough time for flies to be impregnated with T. solium eggs [169]. On the other hand, dung

beetles can play an important role in the transmission of T. solium eggs and subsequent infection in

pigs [170;171].

Infection with T. solium may be regulated by the presence of other Taenia species in the same

environment competing for both intermediate and definitive hosts. For adult tapeworms, the

“crowding effect” when more than one adult parasite is present in a host reduces the fitness of the

parasite which affects negatively the size of the parasite and subsequently the egg output. Also, the

presence of an already established infection with an adult tapeworm from other Taenia species seems

to be protective for the host preventing the infection with T. solium tapeworms. For infections with

the metacestode, it seems that acquired immunity after exposure to Taenia spp. eggs or transferred


29

immunity from mother to the offspring may have a modulatory effect. The mechanisms of this

regulation are not completely understood but it may be that cross-resistance plays a role; also, an

interspecific competition in the host is plausible. This competition results in the limitation of the

number of infections by limiting the number of susceptible hosts [168;172]. On the other hand,

molecular studies have identified two main genotypes of T. solium, an Asian genotype and a Latin

American/African genotype, the difference in their infective capability has to be further studied. For

instance, the lack of subcutaneous HCC clinical manifestations in Latin America differ with

commonly found subcutaneous HCC manifestations in Asia and some parts of Africa. Studying the

infection patterns in epidemiological studies conducted in different geographical settings where each

genotype is present could help characterizing possible differences between the infective capability of

these types [115;173-175].

Field studies demonstrated that there is an increased seroprevalence of HCC surrounding tapeworm

carriers. This seems to be moderated by the distance to the tapeworm carrier forming clusters, thus the

level of infections in a population seems also to be regulated by the number of clusters present and the

number of susceptible individuals living in proximity to tapeworm carriers. [18].

Climatic conditions affect the infectivity and the dispersal of the eggs in the environment. The effects

of humidity, desiccation and temperature have an important impact on the survival and distribution of

Taenia spp. eggs. Temperatures between 10º and room temperature and high humidity favour egg

survival, while extreme temperatures and desiccation diminish the survival and infectivity of the eggs.

The longevity of Taenia spp. eggs in the environment is variable depending on the species studied. It

has been reported that in certain conditions of humidity and temperature Taenia spp. eggs can survive

from 21 to 413 days (T. saginata) or from 0 to 300 days (Taenia pisiformis). Specifically for T.

solium, information on the survival and viability of the eggs in the environment is not yet available.

Most of the current knowledge comes from studies on other Taenia species. It has to be taken into

account that extrapolating such information is hazardous because of the biological differences among

Taenia spp. [164;176;177]. Yet, seasonal fluctuations of the prevalence of PCC suggest that

environmental factors influence the transmission of the disease [178]. The maintenance of the

infections in confined pigs also suggests that environmental contamination happens even when pigs

have no direct access to infected feces. How environment influences PCC transmission still needs to

be elucidated [178;179].

The presence of other pathogens in the same area seems to affect the hosts’ resistance to the parasite.

In the case of HCC, debilitating infections such as tuberculosis and HIV, affecting the immune system

of the host seem to increase the susceptibility to HCC [104;180-184]. In the case of PCC, the presence

of other pathogens in the area indirectly affects the transmission of the disease. When African swine

fever is present, farmers tend to keep their pigs penned to avoid infection. This change in the


30

production system may reduce the pigs’ exposure to human feces, thus negatively affecting the

transmission of PCC [178]. The combination of these elements with a conditional exposure to eggs

due to a lack of hygiene and behavioural, cooking and agricultural practices may greatly influence the

pattern of infections [179;185].

The intrinsic factors of the human host are the final barrier that regulates the level of infection.

Different immune profiles will allow or prevent infection. Age-related immunity plays a role in the

susceptibility to infection in humans; older age groups appear to be more prone to HCC, and this

phenomenon was attributed to immune senescence [16;17;136]. Hormonal profiles related to gender

that have an effect on the immunity, nutritional status, ethnic susceptibility and innate or acquired

immunity are also elements capable of influencing the susceptibility [104;186-188]. Similarly, for

PCC the breed type, hormonal profile, acquired immunity, possible resistance through passively

transferred maternal antibodies, pregnancy and castrated status influence the susceptibility to infection

[189-193]. For human taeniasis there is no evidence suggesting development of immunity, however,

transmission seems to be regulated by the competition with other Taenia species [167;172]. The

regulatory capacity of these elements and their interaction need to be well understood to proficiently

achieve the design of specific control strategies.

1.6 Control programs

In 1993 the International task Force for Disease Eradication (ITFDE) stated that HCC was a

potentially eradicable disease. This statement was based on the fact that human tapeworm carriers are

the only source of infection for HCC, pigs are the reservoir but have a rather short lifespan, there are

no significant reservoirs in the wildlife, treatments for HCC and taeniasis are available and Europe

was presented as an example where previously endemic T. solium was eradicated [194]. Following

this approach, the preventive and control measures against T. solium infections that were the

responsibility of the veterinary services alone, became also the responsibility of the medical services

[195]. However, to date there is no indication that eradication of T. solium can be achieved in the near

future in endemic areas [14].

The strategies proposed to control T. solium infections are based on interrupting the life cycle of the

parasite, some of them are adapted from the experiences learned in developed countries where the

disease was efficiently eradicated. Table 1-1 details the intervention strategies available for T. solium

taeniasis with their advantages and disadvantages.


31

Table 1-1 Synopsis of intervention strategies available for Taenia solium taeniasis/cysticercosis, adapted from Allan et al. (2002) [196] and updated from Thys et al. (2015) [197]; Carabin et al. (2014) [14]; Braae et al. (2015) [179]; Gilman et al. (2012) [198]; Bulaya et al. (2015) [199]; Miwunda et al. (2015) [200].

Intervention strategy Advantages Disadvantages

Elimination of infected pig carcasses (meat inspection)

• Known contribution to elimination of parasite from several developed countries

• Relatively easy to integrate with meat inspection for several other important diseases

• Low cost intervention

• Pigs in many endemic countries do not go to formal slaughter

• Infected pigs can be diagnosed ante mortem (tongue inspection) and slaughtered outside regulated system to avoid condemnation of carcasses

• Low sensitivity

• Economical problem, especially for poor rural communities

Freezing meat • Freezing meat can kill the parasite cysts

• Long periods of time are required to kill the cysts in frozen meat

• Infrastructure to freeze the meat is not always available

Improvement of cooking practices • Proper heat treatment of meat can kill the cysts

• Some cultures consume dishes containing raw or poorly cooked meat

• Difficult to assess when large pieces of meat are cooked or boiled

Improved sanitation, hygiene, community led total sanitation (CLTS)

• Known contribution to elimination of parasite from several developed countries

• Provides benefits beyond control of T. solium

• Economically difficult in many existing endemic areas

• Resistance to use the latrines for cultural or practical reasons

• CLTS requires monitoring over a long period of time

• Results from current field works failed to prove a decrease in PCC

• Require maintenance of latrines

• CLTS must be accompanied by a health education program to increase awareness about the disease and the benefits of latrine use

Health education • Provides benefits beyond control of T. solium

• New media now widely available

• Improved knowledge does not always result in change of practices

• Require long time follow-ups

Table continues on the next page


32

Table continued from previous page Intervention strategy Advantages Disadvantages

Treatment of intestinal taeniasis (Targeted interventions)

• Highly efficacious drugs available now (some generically produced niclosamide may have low efficacy)

• Demonstrated short-term benefits

• Removes known significant transmission risk

• Reduced price when compared to MDA

• Would require repeated interventions for long-term control

• Requires specific infrastructure; not self-sustainable

• Praziquantel should be used with caution in cases of NCC

• Targeted interventions are difficult to perform due to reluctance to collect stool samples for diagnosis and because of lack of sensitivity of diagnostic tests

Treatment of intestinal taeniasis (Mass drug administration (MDA))

• Highly efficacious drugs available now

• Demonstrated short-term benefits

• Removes known significant transmission risk

• Reduced logistic cost when compared to other strategies

• Increased feasibility when compared to targeted interventions

• Could be paired with current treatments for geohelminths

• Some generically produced niclosamide may have low efficacy

• Transmission is recovered quickly after stopping the treatment

• Environmental contamination with Taenia eggs

• Niclosamide and praziquantel are not always available in endemic areas

• Praziquantel should be used with caution in cases of NCC

Improved pig husbandry • Known contribution to elimination of parasite from several developed countries

• Provides benefits beyond control of T. solium

• Pigs are still infected even in confined environment

• Too expensive for poor farmers

• Free roaming is a practice to save money by avoiding having to feed the pigs

Vaccination of pigs • Long-term protection

• Possible to integrate with existing veterinary and/or pig husbandry practices

• Provides economic benefit to end user (avoidance of carcass condemnation)

• Compliance monitoring possible (serological testing)

• Many existing producers in endemic areas do not currently vaccinate against other diseases with high economic impact on pig production

• Vaccines not available now (other than at experimental level)

• Immunization schedule impractical in field conditions

• Not accessible for poor farmers who do not even have money to feed their pigs



33

Table continued from previous page Intervention strategy Advantages Disadvantages

Chemotherapy of infected pigs • Effective drugs available

• Highly effective

• Producers have economic motivation (avoidance of carcass condemnation)

• Other production benefits: can affect other economically important parasites of pigs

• Not all drugs can be found in endemic areas

• Producers often do not treat for other economically important parasites despite economic benefits

• Existing systems of avoiding meat inspection reduce economic advantages

• Long withdrawal time

• Drugs other than oxfendazole require more than one dose

• 3 months for complete disappearance of the cysts when using oxfendazole


34

Figure 1-6 shows a proposal for the integration of control strategies with the use of diagnostic tests

according to the T. solium life cycle [201]. There is consensus among scientists that the best approach

is a combination of different intervention strategies, in this case veterinary and medical services as

well as other health related scientists should join forces and follow the One Health approach

[198;202-204]. An integrated control program should include the use of diagnostic tools, for correct

diagnosis and for assessment of the control program [204].

Figure 1-6 The cysticercosis cycle: intervention points [201]

Studies conducted in China, Mexico, Peru, Tanzania and Ecuador, demonstrated that a significant

reduction of T. solium infections is achievable through the application of different intervention

strategies. The interventions conducted in China, Mexico, Tanzania and Ecuador aimed to control T.

solium in specific areas, while the intervention in Peru aimed at eliminating T. solium from a province

[15;198;205-207]. The strategies applied in China consisted of health education, health promotion and

chemotherapy of tapeworm carriers. These strategies significantly decreased infections with T. solium

after 6 years of efforts [206]. In Mexico interventions consisted of either 1) health education only or

2) mass drug administration (MDA) in humans to treat taeniasis. Evaluation 6 and 42 months after

intervention resulted in a significant reduction of the seroprevalence of cysticercosis in humans and

pigs [205;207]. The intervention in Ecuador was based on the use of MDA. One year later PCC was


35

significantly reduced in pigs and no new tapeworm infections were recorded [15]. In Tanzania, the

strategy applied was a health and pig management intervention. The results were measured one year

later by using sentinel pigs. A considerable decrease in the seroprevalence of circulating antigens in

these pigs was shown [208]. The elimination program in Peru was composed of combinations of

different strategies. These included repeated chemotherapy for both humans and pigs and pig

vaccination. This program achieved a focal elimination [198]. However, sustainability of elimination

over time has yet to be evaluated. On the other hand, not all the experimental strategies have been

successful in the field, in 2015 an intervention in Zambia using CLTS only, failed to reduce PCC

[199].

A lesson learned from these intervention studies is that social and environmental differences in

endemic areas have to be taken into account in order to adopt the best control program. Successful

strategies may not work in all settings because of cultural taboos, occupational activities or behavioral

practices [197-199]. Other concerns raised from these studies were the sustainability and the long-

term results of these measures and the cost-efficiency of these.

The development and use of mathematical simulation models can guide the selection of the best

control strategy, thus saving resources and time [209]. The use of simulation models can help to rank

the control strategies depending on their relative effectiveness. To do so, the simulation models take

into account the transmission dynamics of the disease and all known measurable parameters

influencing it. In addition, simulation models can help to fill the gaps in the absence of convincing

evidence from field trials [14]. However, to achieve these the model should be fed with correct

parameters [14;165;209]. The current transmission dynamic model available for T. solium generates

estimates for human taeniasis and porcine cysticercosis. From this study it was observed that the

effective control of the parasite relies on the improvement of sanitation and the improvement of pig

management practices [14;209]. To date there is no published transmission model for human

cysticercosis.

Rationale & Objectives

Rationale & Objectives

37

Rationale

T. solium cysticercosis is considered a potentially eradicable disease. However, to date, there is no

scientific evidence supporting eradication in the short term. Different interventions designed to reduce

the number of infections had promising results in some endemic areas, but these results were not

always reproducible in other areas. Gaps in the understanding of the transmission dynamics of the

disease probably contributed to the limited success or to the failure of interventions implemented.

There is a need to create feasible and cost-effective control programs adapted to the current situation

in T. solium endemic countries.

In Ecuador, T. solium cysticercosis/taeniasis are endemic and are responsible for public health,

agricultural and socio-economic problems. Epidemiological studies and official reports show that T.

solium infections are present both in rural and urban settings. An experimental intervention strategy

conducted in the country achieved promising results showing that control of parasite transmission can

be achieved. However, to date, no control program has been put in practice to control/eliminate the

parasite in any part of the country and official reports keep on showing occurrence of new cases of

HCC.

When designing control programs in endemic countries, it is critical to evaluate the general conditions

that enhance the transmission, maintenance and negative health outcomes of a disease. This will help

to identify and prioritize areas of intervention and consequently choose the adequate strategy for an

effective control and elimination.

Additionally, in order to assess the success or failure of an applied strategy, it is important to

understand the meaning of epidemiological patterns that can be obtained by field surveys or by

hospital reports. It is crucial for policymakers and decision takers to have a correct interpretation of

epidemiological data in dynamic conditions such as multiple affected communities located in different

socio-economical, geographical and agro-ecologic settings within a region or country.

Objectives:

For these reasons, the main objective of this research is to contribute to the understanding of

epidemiological patterns of the infection and exposure to T. solium in Ecuador and to contribute to the

design of control programs.

To achieve this goal, 4 specific objectives were defined.

1) Characterize active infections and exposure to T. solium in endemic zones around the world.

2) Study the distribution in time and space of NCC hospitalized cases in Ecuador.

3) Identify potential indicators of NCC hospitalized cases in Ecuador.

4) Study the dynamics of active infections and exposure to T. solium in an endemic area in Ecuador.

Chapter 2 2 Taenia solium exposure and active infections around the world: Characterization

and variability in endemic communities

Adapted from:

Coral-Almeida M, Gabriël S, Abatih EN, Praet N, Benitez W, Dorny P. Taenia solium Human Cysticercosis: A Systematic Review of Sero-epidemiological Data from Endemic Zones around the World. PLoS Negl Trop Dis 2015 Jul;9(7):e0003919.

Taenia solium exposure and active infections around the world: Characterization and variability in endemic communities

39

2.1 Chapter summary

Taenia solium cysticercosis is a zoonotic neglected disease responsible for severe health disorders

such as seizures and death. T. solium cysticercosis is endemic in countries in Africa, Latin America

and Asia where conditions such as inadequate hygiene, poor sanitary conditions, open defecation, free

roaming pigs and poverty permit the transmission of the disease. Understanding the epidemiology of

human cysticercosis (HCC) in endemic regions will help to expose critical information about the

transmission of the disease, which could be used to design efficient control programs. Current

serological diagnostic tools are capable of detecting exposure to eggs and infection levels in a

population through antibody and antigen detection, respectively. This review gathered serological data

on apparent prevalence of T. solium circulating antigens and/or seroprevalence of T. solium

antibodies, apparent prevalence of human taeniasis and risk factors for HCC from endemic

communities in order to understand the differences in exposure to the parasite and active infections

with T. solium metacestodes patterns in endemic areas around the world. Three databases were used to

search sero-epidemiological data from community-based studies conducted between 1989 and 2014 in

cysticercosis endemic communities worldwide. The search focused on data obtained from T. solium

circulating antigen detection by monoclonal antibody-based sandwich ELISA and/or T. solium

antibody seroprevalence determined by Enzyme-linked Immunoelectrotransfer Blot (EITB). A meta-

analysis was performed per continent. A total of 39,271 participants from 19 countries, described in

37 articles were studied. The estimates for the prevalence of circulating T. solium antigens for Africa,

Latin America and Asia were: 7.30% (95% CI [4.23- 12.31]), 4.08% (95% CI [2.77-5.95]) and 3.98%

(95% CI [2.81-5.61]), respectively. Seroprevalence estimates of T. solium antibodies were 17.37%

(95% CI [3.33-56.20]), 13.03% (95% CI [9.95-16.88]) and 15.68% (95% CI [10.25-23.24])

respectively. Taeniasis reported prevalences ranged from 0 (95% CI [0.00-1.62]) to 17.25% (95% CI

[14.55-20.23]). A significant variation in the sero-epidemiological data was observed within each

continent with African countries reporting the highest apparent prevalences of active infections.

Intrinsic factors in the human host such as age and immunity were main determinants for the

occurrence of infections while exposure was mostly related to environmental factors, which varied

from community to community. Understanding the epidemiology of cysticercosis in endemic regions

will help exposing information on the transmission, which could in turn be used to design appropriate

control programs.


40

2.2 Introduction

“The most dangerous worldview is the worldview of those who have not viewed the world”

― Alexander von Humboldt

Taenia solium human cysticercosis (HCC) is a zoonotic parasitic disease causing severe health and

economic problems in endemic areas in Latin America, Africa and Asia [2;4;31;53]. Even though

HCC is considered potentially eradicable, it is still highly prevalent in developing countries [210].

Different intervention measures have to be integrated to interrupt transmission of T. solium. Effective

control programs will reduce the incidence and prevalence of the disease leading to acceptable and

manageable levels, which could therefore become a first step towards elimination and eradication of

the disease. Understanding the conditions for transmission is required for developing appropriate

interventions [209]. This mainly involves accurate estimations of exposure and infection patterns in

communities, which can be obtained by laboratory tests [17;209]. Current immunological tools used

in HCC diagnosis can be classified into: 1) Tests detecting antibodies directed against T. solium

cysticerci, identifying exposure to the parasite, and 2) Tests detecting circulating antigens produced

by living cysticerci, identifying current infection with viable cysticerci [72]. Measuring the level of

adult tapeworm infections in a population can be used as a support for results obtained from

immunological tests to measure exposure. To understand exposure and infection patterns it is also

important to have a correct interpretation of risk factors, information that can be provided by studying

the correlation between host, environment and parasite factors and serological results for

cysticercosis.

Similar sero-epidemiological studies conducted in two endemic communities in Africa and Latin

America, presented comparable serological results for exposure to T. solium eggs with exposure levels

of 34.55% and 31.22%, respectively but presented significant differences when reporting active

infections with almost 12 times more infections in the African than in the Latin American community

[17;136], suggesting that there were significant variations in the conditions for transmission and in the

establishment of infection in each community. For this reason, extrapolating results from a single

community to a regional or even global level can be a hazardous exercise.

The aim of this review is to systematically collect serological data on apparent prevalence of T. solium

circulating antigens and/or seroprevalence of T. solium antibodies, apparent prevalence of human

taeniasis and risk factors for HCC from endemic communities in order to understand the differences

in exposure to the parasite and active infections with T. solium metacestodes in endemic areas around

the world.


41

2.3 Methods

A systematic literature search on T. solium HCC seroprevalence in community-based studies

performed in endemic countries in Africa, Asia, Latin America and the Caribbean was conducted on

indexed literature published during the period from 1989 to 2014. In order to have comparable data,

this search focused on the articles in which data was obtained using the following techniques and

protocols: 1) Enzyme-linked Immunoelectrotransfer Blot (EITB) from Tsang et al. (1989) [80] for

detection of antibodies directed against seven specific glycoproteins from T. solium metacestodes

and/or 2) Enzyme Linked Immunosorbent Assay detecting circulating antigens from the T. solium

metacestode (B158/B60 Ag-ELISA or HP10 Ag-ELISA) from Brandt et al. (1992) [82], Van

Kerckhoven et al. (1998) [211], Dorny et al. (2000) [94] and Harrison et al. (1989) [83]. Selection was

restricted to both EITB and Ag-ELISA because of their performance, frequent use and acceptance as

highly sensitive and specific tests in community-based studies when compared to other techniques.

The EITB has a sensitivity ranging from 97 to 98% and a specificity ranging from 97 to 100% to

detect circulating antibodies to T. solium in human serum. The EITB is considered positive when at

least one of the seven specific glycoproteins from T. solium metacestodes is recognized by the serum

The B158/B60 Ag-ELISA has a sensitivity of 90% (95% CI:[80-99%]) and a specificity of 98% (95%

CI:[97-99%]) to detect circulating antigens released by T. solium metacestodes in humans, with no

cross-reactions reported to date [72;80;84]. For the HP10 Ag-ELISA the reported sensitivity ranges

from 84.8% to 86% and the specificity is estimated at 94% to detect circulating antigens in human

serum [85;86]. For the studies where the EITB was performed, either the Centers for Disease Control

and Prevention (CDC) test or commercial kits were accepted for selection. Taeniasis apparent

prevalence data was collected when available in the selected articles and no restrictions for the

diagnostic method was made. It was anticipated that the taeniasis data would be influenced by the

technique used because coprology, coproantigen ELISA and molecular methods have wide

differences in their diagnostic performances. The estimated sensitivities of these tests were: 52.5%

(95% CI:[11.1-96.5]) for coprology, 84.5% (95% CI:[61.9-98]) for coproantigen ELISA and 82.7%

(95% CI:[57-97.6]) for real-time polymerase chain reaction assay (copro-PCR) and their specificities

were: 99.9% (95% CI:[99.5-100]) for coprology, 92% (95% CI:[ 90-93.8]) for coproantigen ELISA

and 99% (95% CI:[98.2-99.6]) for copro-PCR [108]. The wide confidence interval for the estimated

value for the sensitivity of coprology is due to the low number of positive cases found by this method,

which does not allow a more accurate estimation, however is in line with previous studies

[81;107;212]. Language restriction was applied when the article was written in a language other than

those spoken or understood by the authors of this review. The considered languages were English,

Spanish, French, Portuguese and Dutch.


42

The selected databases for this study were: PubMed (http://www.ncbi.nlm.nih.gov/pubmed/),

LILACS (Latin American and Caribbean Health Sciences Literature, lilacs.bvsalud.org/en/) and Web

Of Science (http://wok.mimas.ac.uk/). The search was performed from September 1st 2013 until

October 31st 2014.

2.3.1 Search

The following search strategy was applied: In PubMed, using the Boolean operator AND, the terms

“cysticercosis” AND “Taenia solium” AND “epidemiology” were introduced in the main search bar

and the filters were activated for the period from 1988/12/31 to 2014/10/31. In Web of Science, the

strategy applied was introducing in the basic search bar the topic “cysticercosis” adding fields with

the correspondent Boolean operators: AND Topic=(Taenia solium) AND Topic=(epidemiology). In

LILACS, the strategy adopted consisted in introducing in the main search bar the terms “cysticercosis

Taenia solium”. In the latter case the term “epidemiology” was excluded to obtain the maximum

return of articles since LILACS is a smaller targeted database when compared to PubMed and Web

Of Science. Additionally, relevant articles were included that were not found with this search strategy

but matched the selection criteria after manual search or expert recommendation.

2.3.2 Study selection

The articles were selected following three phases: The first phase consisted in the removal of all

repeated studies from the title selection and all studies performed before 1989. The second phase

consisted in the exclusion of articles from the title and abstract review as for the following exclusion

criteria: 1) Wrong parasite species, 2) Studies performed in non-endemic countries, 3) Studies

performed only in animals, 4) Clinical studies, 5) Studies which focused only on human taeniasis, 6)

Studies carried out for assessing laboratory tests performance, 7) Studies that focused on NCC, 8)

Studies conducted in specific targeted types of individuals (e.g. schoolchildren, refugees or soldiers),

9) Articles written in languages other than those spoken or understood by the authors of this review,

10) Interviews, letters, reviews or editorials not presenting original data and/or the techniques and

protocols performed on their studies, 11) Studies not related to T. solium epidemiology. The third

phase was applied when full texts were read and consisted in the study selection according to the

following selection criteria: 1) Community-based studies, 2) Original HCC prevalence reports

available, 3) Protocols applied for HCC diagnosis using the EITB and Ag-ELISA protocols

mentioned previously in this document, 4) Random sampling method for selection of participants in

the study or/and population representative voluntary participation. 5) Coverage of most age groups

(young, adults and elderly).


43

2.3.3 Data collection

From every selected article the following items were collected and introduced in a data base:

Author(s), year the article was published, country, number of participants for Ag-ELISA survey,

number of Ag-ELISA positive detected cases, number of participants for EITB survey, number of

EITB positive detected cases (when specified in the article, the EITB positive cases were considered

when at least one band had a visible reaction [80]), estimated apparent prevalence expressed in

percentage. When applicable, identified risk factors were also included in the database. For

longitudinal studies where two or more sampling rounds were organized in a community, only data

from the first round were taken into account in order to avoid any possible bias caused after contact

with the teams collecting the samples. Additionally, if the study was conducted in parallel with a

survey on human taeniasis, the prevalence and the method used to diagnose taeniasis were also

gathered. All countries where the selected studies took place were visualized using QGIS software

(version2.8).

2.3.4 Statistical analysis

A meta-analysis was conducted using the “meta” package in R [213] to estimate the prevalence of

circulating antigens for T. solium and the seroprevalence of antibodies in each continent based on a

random effects model. A global prevalence estimation was not performed as it was not the intention of

this study. Ninety five % exact binomial Confidence Intervals (95% CI) were calculated for every

reported prevalence. The significant differences in estimated prevalences were evaluated using their

95% confidence intervals. The difference in prevalence between two regions was considered to be

statistically significant if their 95% confidence intervals do not overlap.

2.4 Results

2.4.1 Study selection

Figure 2-1 describes the review process and the number of articles selected at each stage of the

review. From an initial number of 696 articles, only 37 studies were included in this review; 9 studies

were selected for the African region [134;136;186;214-219], 22 studies for Latin America [16-

18;73;109;131;140-142;144;153;185;205;220-228] and 6 for the Asian region .


44

Figure 2-1. Flow diagram describing literature search and selection of studies (PRISMA 2009 Flow chart).


45

2.4.2 Human cysticercosis in Africa

From the 9 sero-epidemiological studies from 7 countries selected for the African region, 7 studies

[134;186;214-216;218;219] used Ag-ELISA and two studies [136;217] used both Ag-ELISA and

EITB. The total number of individuals sampled for serological testing in this region was 12,596.

Prevalence of circulating antigens ranged from 0.68% to 21.63%, while seroprevalence of antibodies

ranged from 7.69 to 34.55%. Detailed descriptions of each study are given in Table 2-1.


46

Table 2-1. Sero-epidemiological studies using Ag-ELISA and/or EITB for human cysticercosis in Africa.

Author YOP Country Location Circulating Ag positive cases/total participants

Circulating Ag prevalence (%) [95%CI]

Ab positive cases/total participants

Ab seroprevalence (%) [95%CI]

Nguekam et al. 2003 Cameroon West province 34a/4993 0.68 [0.47-0.95]

Carabin et al. 2009 Burkina Faso Sanguié, Kadogo, Oubritenga 48a/763 6.29 [4.67-8.25]

Kanobana et al. 2011 Dem. Rep. of Congo Bas-Congo 204a/943 21.63 [19-24.4]

Secka et al. 2011 Senegal Ziguinchor 31a/403 7.69 [5.28-10.74] 31/403 7.69 [5.28-10.74]

Nitiéma et al. 2012 Burkina Faso Sanguié, Kadogo, Oubritenga 45a/734 6.13 [4.50-8.12]

Mwape et al. 2012 Zambia Estern Province 41a/707 5.80 [4.19-7.8]

Mwape et al. 2013 Zambia Eastern Province 141a/1129 12.49 [10.61-14.56] 57/165 34.55 [27.32-47.33]

Mwanjali et al. 2013 Tanzania Mbeya 139a/830 16.75 [14.27-19.46]

Thomas 2014 Kenya Western and Nyanza 169b/2094 8.07 [6.94-9.32]

Total 852/12596 6.76 [6.33-7.22] 88/568 15.49 [12.61-18.73]

REMEP: 7.30 [4.23-12.31] 17.37 [3.33-56.20]

Legend: YOP: Year of publication; Location: Corresponds to the Province, State, Region or Department in which the communities where the studies took place are located; Ag: Antigen detection based on Ag-ELISA results; Ab: Antibody detection based on EITB results; 95% CI: 95% Confidence Intervals; REMEP: Random Effects Model Estimated Prevalence; a : Results obtained from B158/B60 Ag-ELISA; b : Results obtained from HP10 Ag-ELISA. Dem. Rep. of Congo: Democratic Republic of Congo.


47

2.4.3 Human cysticercosis in Latin America

Information on HCC in Latin America was obtained from 22 studies from 8 countries with two

studies performing only Ag-ELISA [131;141], 17 studies performing EITB only

[18;73;109;140;142;144;185;205;220-228] and three studies performing both Ag-ELISA and EITB

[16;17;153]. The total number of individuals sampled was 21,911. Active T. solium infection ranged

from 0.94 to 9.12% and antibody seroprevalence ranged from 1.82 to 31.22%. A detailed description

of each study is given in Table 2-2.


48

Table 2-2. Sero-epidemiological studies using Ag-ELISA and/or EITB for human cysticercosis in Latin America

Author YOP Country Location Circulating Ag positive cases/Total participants

Circulating Ag Prevalence (%) [95%CI]

Ab positive cases/Total participants


Díaz et al. 1992 Peru San Martin 30/371 8.09 [5.52-11.34]

Sarti et al. 1992 Mexico Morelos 167/1546 10.80 [9.3-12.46]

Sarti et al. 1994 Mexico Michoacan 49/1005 4.88 [3.63-6.39]

García-Noval et al. 1996 Guatemala Jutiapa 207/1542 13.42 [11.76-15.23]

Sanchez et al. 1998 Honduras Francisco Morazán 63/404 15.59 [12.2- 19.5]

García et al. 1998 Peru Cusco 24/102 23.8 [15.69-32.96]

Sanchez et al. 1999 Honduras Olancho 80/480 16.67 [13.44-20.31]

García et al. 1999 Peru Cusco 14/108 12.96 [7.27-20.8]

Sarti et al. 2000 Mexico Morelos 91/1603 5.68 [4.59-6.92]

García et al. 2001 Peru Piura 76/482 15.77 [12.63-19.33]

Peru Junín 140/398 35.18 [30.48-40.1]

Colombia N.A. 23/750 3.07 [1.95-4.57]

Gomes et al. 2002 Brazil Bahia 11/694 1.59 [0.79-2.82]

García et al. 2003 Peru Junín 355/2583 13.74 [12.44-15.13]



49

Table continued from previous page Ferrer et al. 2003 Venezuela Carabobo 27b/296 9.12 [6.10-12.99]

Venezuela Lara 37b/608 6.08 [4.32-8.29]

Venezuela Lara 20b/305 6.56 [4.05-9.95]

Agudelo-Flores & Palacio 2003 Colombia Antioquia 12/661 1.82 [0.94-3.15]

Moro et al. 2003 Peru Lima 66/316 20.89 [16.54-25.79]

Rodriguez et al. 2003 Ecuador Pichincha & Imbabura 215a/4306 4.99 [4.36-5.69]

Montano et al. 2005 Peru Tumbes 200/825 24.24 [21.35 -27.32]

Rodriguez et al. 2006 Ecuador Loja 18a/800 2.25 [1.34-3.53] 40/100 40.00 [30.33-50.23]

Agudelo-Flores et al. 2009 Colombia Chocó 4/46 8.70 [2.42-20.79]

Lescano et al. 2009 Peru Tumbes 196/803 24.41 [21.47 -27.53]

Praet et al. 2010 Ecuador Loja 23a/794 2.90 [1.84-4.31] 202/807 25.03 [22.08-28.17]

Coral et al. 2014 Ecuador Loja 7a/744 0.94 [0.38-1.93] 232/743 31.22 [27.9-34.69]

Total 347/7853 4.42 [3.97-4.90] 2282/16369 13.94 [13.41-14.48]

REMEP: 4.08 [2.77-5.95] 13.03 [9.95- 16.88]

Legend: YOP: Year of publication; Location: Corresponds to the Province, State, Region or Department in which the communities are located where the studies took place; Ag: Antigen detection based on Ag-ELISA results; Ab: Antibody detection based on EITB results; 95% CI: 95% Confidence Intervals; REMEP: Random Effects Model Estimated Prevalence; a : Results obtained from B158/B60 Ag-ELISA; b : Results obtained from HP10 Ag-ELISA; N.A.: Not available.


50

2.4.4 Human cysticercosis in Asia

The data obtained for HCC in Asia resulted from 6 studies from 4 countries organized in 4 studies

performing Ag-ELISA only [84;135;172;229], one study performing EITB only [230] and one study

performing both Ag-ELISA and EITB [231]. The total number of individuals sampled was 4,764.

Seroprevalence varied from 0.57 to 5.71% for circulating T. solium metacestode antigens and from

12.60 to 19.17% for T. solium antibody seroprevalence. Detailed descriptions of each study are given

in Table 2-3.


51

Table 2-3. Sero-epidemiological studies using Ag-ELISA and/or EITB for human cysticercosis in Asia

Author YOP Country Location Circulating Ag positive cases/total participants

Circulating Ag prevalence (%) [95%CI]

Ab positive cases/total participants


Theis et al. 1994 Indonesia Bali 94/746 12.60 [10.3-15.2]

Erhart et al. 2002 Viet Nam Bac Ninh 12a/210 5.71 [2.99-9.77] Somers et al. 2006 Viet Nam Bac Kan 16a/303 5.28 [3.05-8.43]

Viet Nam Ha Tinh 1a/175 0.57 [0.01-3.14]

Raghava et al. 2010 India Tamil Nadu 46a/960 4.79 [3.53-6.34] 184/960 19.17 [16.72-21.8]

Jayaraman et al. 2011 India Tamil Nadu 48a/1064 4.51 [3.34-5.94]

Conlan et al. 2012 Laos Oudomxay, Luangprabang, Huaphan, and Xiengkhuang

29a/1306 2.22 [1.49-3.17]

Total 152/4018 3.78 [3.21-4.42] 278/1706 16.29 [14.57-18.13]

REMEP 3.98 [2.81-5.61] 15.68 [10.25-23.24]

Legend: YOP: Year of publication; Location: Corresponds to the Province, State, Region or Department in which the communities are located where the studies took place; Ag: Antigen detection based on Ag-ELISA results; Ab: Antibody detection based on EITB results; 95% CI: 95% Confidence Intervals; REMEP: Random Effects Model Estimated Prevalence; a : Results obtained from B158/B60 Ag-ELISA.


52

Globally, 39,271 participants from 19 countries were included in 37 studies, from which 24,467 were

studied for circulating T. solium antigen with 5.52% (1,351/24,467) positive cases (95% CI [5.24-

5.82]) and 18,643 were studied for anti T. solium antibodies with a crude seroprevalence of 14.20%

(2,648/18,643) (95% CI [13.70-14.71]). Figure 2-2 represents the global distribution of the countries

where the serological studies took place.

Figure 2-2. Global distribution of the endemic countries where Ag-ELISA and/or EITB based epidemiological studies were held.

Light yellow represents the countries confirmed as endemic by the World Health Organization (WHO) until 2012 [118]. Circles represent the countries where Ag-ELISA based studies took place. Each color represents the average prevalence per country found from the selected articles in this review classified in 0 to 5 percent; 5 to 10 percent and more than 10 percent. Triangles represent the countries where EITB based studies took place. Each color represents the average prevalence per country found from the selected articles in this review classified in 0 to 5 percent; 5 to 10 percent and more than 10 percent.

2.4.5 Taeniasis

Within the examined reports, twenty-four studies from 14 countries in Africa (6 studies), Latin

America (13 studies) and Asia (5 studies) reported adult T. solium data, using different diagnostic

techniques. In these studies, 4,682 African, 13,782 Latin American and 3,437 Asian subjects

participated; with a global participation of 21,901 individuals. Apparent prevalence on taeniasis

varied from 0 to 17.25%. Results are shown in table 2-4.


53

Table 2-4. Taeniasis reports from Africa, Latin America and Asia

Continent Author Year of publication

Country Diagnostic Technique Positive cases/ Total participantsa

Prevalence (%) [95%CI]

Africa Kanobana et al. 2011 Dem. Rep. of Congo

Coprology† 3/816 0.37 [0.08-1.07]

Secka et al. 2011 Senegal Direct fecal examination 2/43** 4.65 [0.57-15.81]

FECT 4/43** 9.30 [2.59-22.14]

worm expulsion and morphological identification

1/43** 2.33 [0.06-12.29]

Mwape et al. 2012 Zambia FECT 2/718 0.28 [0.03-1.00]

Copro-Ag ELISA 45/712 6.32 [4.65-8.37]

Mwanjali et al. 2013 Tanzania Copro-Ag ELISA 43/820 5.24 [3.82-7.00]

EITB (rES38) 34/820 4.15 [2.89-5.75]

FECT 9/820 1.10 [0.50-2.07]

Mwape et al. 2013 Zambia FECT 0/226 0.00 [0.00-1.62*]

Copro-Ag ELISA 27/226 11.95 [8.02-16.90]

Thomas 2014 Kenya Copro-Ag ELISA 278/2003 13.88 [12.39-15.47]

FECT 4/2059 0.19 [0.05-0.50]



54

Table continued from previous page Continent Author Year of

publication Country Diagnostic Technique Positive cases/

Total participantsa


Latin America

Diaz et al. 1992 Peru microscopy, both directly and after FECT 1/305 0.33 [0.01-1.81] Sarti et al. 1992 Mexico FECT 4/1531 0.26 [0.07-0.67] Sarti et al. 1994 Mexico FECT 2/828 0.24 [0.03-0.87] García-Noval et al.

1996 Guatemala FECT & Copro-Ag ELISA 27/995 2.71 [1.80-3.92] Guatemala FECT& Copro-Ag ELISA 123/713 17.25 [14.55-20.23]

Sanchez et al. 1998 Honduras FECT 2/404 0.50 [0.06-1.78] Sanchez et al. 1999 Honduras FECT 12/480 2.50 [1.30-4.33] Sarti et al. 2000 Mexico Copro-Ag ELISA 16/1865 0.86 [0.49-1.39]

FECT 11/1865 0.59 [0.29-1.05] Gomes et al. 2002 Brazil Copro-Ag ELISA 26/577 4.51 [2.96-6.53] Rodriguez et al. 2003 Ecuador FECT 30/1935 1.55 [1.05-2.21]

PCR-RFLP (identification) 8/29 27.59 [12.73-47.24] García et al. 2003 Peru microscopy, both directly and after FECT 8/1317 0.61 [0.26-1.19]

Copro-Ag ELISA 45/1619 2.78 [2.03-3.70] Lescano et al. 2009 Peru FECT 11/898 1.22 [0.61-2.18] Praet et al. 2010 Ecuador FECT 0/674 0.00 [0.00-0.55*]

MSFT 0/674 0.00 [0.00-0.55*] Rodriguez et al. 2006 Ecuador FECT 14/958 1.46 [0.80-2.44]

PCR-RFLP (identification) 12/12 100 [73.54-100*]



55

Table continued from previous page Continent Author Year of

publication Country Diagnostic Technique Positive cases/

Total participantsa


Asia Erhart et al. 2002 Viet Nam FECT 0/210 0.00 [0.00-1.74*]

Somers et al. 2006 Viet Nam Copro-Ag ELISA 1/297 0.34 [0.01-1.86]

KATO 1/297 0.34 [0.01-1.86]

Worm expulsion & PCR-RFLP for identification

1/297 0.34 [0.01-1.86]

Viet Nam Copro-Ag ELISA 3/166 1.81 [0.37-5.19]

KATO 2/166 1.20 [0.15-4.28]

Worm expulsion and PCR-RFLP for identification

1/166 0.60 [0.01-3.31]

Raghava et al. 2010 India Copro-Ag ELISA 22/729 3.02 [1.90-4.53]

Jayaraman et al. 2011 India Copro-Ag ELISA 6/729 0.82 [0.30- 1.78]

Conlan et al. 2012 Laos FECT and self-report 110/1306 8.42 [6.97-10.06]

Legend: a: Fecal samples were provided voluntarily from participants when not specified otherwise; *: One sided 97.5% confidence interval; **: Technique applied in fecal samples from seropositive subjects for T. solium antibodies or circulating antigens; Coprology†: Technique not defined; FECT: Formalin-ether concentration technique; KATO: Kato-Katz technique; MSFT: Magnesium sulphate flotation technique; PCR-RFLP: Polymerase chain reaction-restriction fragment length polymorphism; ELISA: Enzyme-Linked Immunosorbent Assay; Copro-Ag ELISA: Coproantigen ELISA; EITB: Enzyme-linked Immunoelectrotransfer Blot; Dem. Rep. of Congo: Democratic Republic of Congo.


56

2.4.6 Risk factors for human cysticercosis

Twenty-three articles out of the 37 selected articles reported statistically significant risk factors for the

presence of T. solium circulating antigens or T. solium antibodies. The identified risk factors for the

presence of T. solium circulating antigens in Africa were: insufficient latrines or sanitary toilets [217],

washing hands by dipping method [219], history of taeniasis or proximity to tapeworm carriers

[186;219], being male [134] and increased risk with age [134;136;186;214;217;219], while the

identified risk factors for presence of anti T. solium antibodies were: insufficient latrines or sanitary

toilets, and increased risk with age [217]. In Latin America the only identified risk factor for presence

of T. solium circulating antigens was associated with increased age [16], while the identified risk

factors for presence of T. solium antibodies were: insufficient latrines or sanitary toilets

[222;225;228], lack of potable water [222], poor personal hygiene [185], deficient house hygiene

[185], earthen floor [222], presence of infected pigs [109;144], pig owning [109;222;225;228], pork

consumption [185;228], history of taeniasis/proximity to tapeworms carriers [18;109;140;142;185],

being female [142;223;228], age (risk increased with age) [16;17;220;221;227], increased risk at

younger age [226], low education level [222;226], presence of a sewage system [227]. In Asia the

only risk factor for the presence of T. solium circulating antigens was the ownership of pigs [229].

2.4.7 Meta-analysis

The random effects model used in the meta-analysis gave an overall estimated prevalence for

circulating T. solium antigens in Africa of 7.30% (95% CI [4.23- 12.31]) from 9 studies. The overall

estimated prevalence for circulating T. solium antigens in Latin America was 4.08% (95% CI [2.77-

5.95]) from 5 studies and 3.98% (95% CI [2.81-5.61]) for Asia from 5 studies. For the anti T. solium

antibodies seroprevalence, the overall estimated seroprevalence in Africa was 17.37% (95%CI [3.33-

56.20]) from 2 studies, while in Latin America it was 13.03% (95% CI [9.95-16.88]) from 20 studies

and in Asia 15.68% (95% CI [10.25-23.24]) from 2 studies. The prevalence of circulating T. solium

antigens was not significantly different between continents and neither was the anti T. solium

antibodies seroprevalence. The prevalence of circulating T. solium antigens was significantly lower

than the T. solium antibodies seroprevalence in Latin America and Asia but not in Africa.

2.5 Discussion

The results of this review allowed us to characterize and compare estimates of active infections with

T. solium metacestodes and exposure to the parasite in endemic communities of different countries in

three continents. The estimated seroprevalence of anti T. solium antibodies in Africa (17.37%), Latin

America (13.03%) and Asia (15.68%) was not significantly different, which could be interpreted as a


57

similar exposure to T. solium eggs in these regions, though, within each continent a visible

heterogeneity was observed, with seroprevalence for antibodies ranging from 1.82% to 40% as shown

in tables 2-1, 2-2 and 2-3.

The estimated prevalence of T. solium circulating antigens was higher in endemic areas of Africa

(7.30%) compared to Latin America and Asia (4.08% and 3.98%, respectively), though this difference

was not statistically significant. When studied in detail, all the African studies but one showed a

higher prevalence of active infections than the studies in Latin America and Asia: the prevalence of

circulating antigens reported in Latin America and Asia ranged from 0.57 to 9.12%, while the

prevalence in Africa ranged from 6.13 to 21.63%, excluding one study from West Cameroon in 2003

reporting a prevalence of 0.68% [214]. The figures observed in tables 2-1, 2-2 and 2-3 demonstrate

big variations in prevalence of active infection with T. solium cysticerci, similar as observed for

seroprevalence of antibodies.

Studies from the Democratic Republic of Congo, Zambia and Tanzania [134;136;219] revealed very

high prevalence figures of circulating antigens not registered in any other part of the world (21.63%,

12.49% and 16.75%, respectively). These figures suggest a higher occurrence of HCC in Africa when

compared to Latin America and Asia. The estimated prevalence of T. solium circulating antigens in

each continent was lower than the estimated seroprevalence for T. solium antibodies in the same

continent, but this difference was only statistically significant for Latin America and Asia and not for

Africa.

In studies that carried out both antigen and antibody detection tests [16;17;136;153;231] a

significantly higher seroprevalence of T. solium antibodies was observed (Tables 2-1, 2-2 and 2-3)

except for one study performed in Senegal [217] in which the number of positive cases for Ag-ELISA

and the number of EITB positive cases were similar. However, in that study only a fraction of the

positive cases was positive in both tests. This marked difference in the prevalence of circulating

antigens and of antibodies has already been observed by Praet et al. (2010) [72]: exposure expressed

by antibody seroprevalence could be interpreted as the result of a past infection, current infection or

the result of a failed infection, while circulating antigens can only be detected if viable cysticerci are

present.

Findings in this review from sero-epidemiological studies have shown that T. solium transmission

varied from one geographical location to another, which raised several questions on the causes of

these differences. It is reasonable to think that the variations in the figures observed in this study

could be the result of a combination of more than one element capable of affecting the presence of T.

solium cysticercosis in a zone, such as individual host characteristics, parasite singularities and

environmental properties each of them prone to change depending on the geographical situation.


58

Table 2-5 summarizes the potential factors contributing to the variations observed in serology from

endemic communities.


59

Table 2-5. Factors affecting serological variations of human cysticercosis infection and exposure to T. solium eggs. Human host

(Accidental intermediate host) Parasite (Taenia solium) Environment

Factors affecting exposure in a population (Presence of detectable antibodies)

Age (time exposed to the parasite)[214] Number of adult parasites present (tapeworm carriers, hotspots) [18;188]

Gender (Role played in different cultures) Number of eggs dispersed in the environment [164;177]

Occupation Egg survival (egg viability) on climatic conditions: Temperature, Humidity, seasonality[164;177]

Hygiene, sanitation, behavioral practices, agricultural & cooking practices[185]

Area (endemic)

Factors affecting active infections in a population (Presence of circulating antigens)

Age (Immunosenescence) [16] T. solium genotype : Asian or African/Latin American [173;174;232]

Egg survival (egg viability) on climatic conditions: Temperature, Humidity, seasonality[164;177]

Gender (Hormonal profile)[188] Presence of other Taenia species (within host) [168;172] Frequency and Intensity of exposure [188]

Ethnicity (Immune characteristics) [158;188;233] Presence of other Taenia species (cross-resistance) [168;172]:

Nutritional status [186] Presence of other pathogens [183;184;186]

Acquired immunity [187]

Innate immunity [17;173;229]

Immune profile [187;234]

Level of exposure

Presence of concurrent infections [183;184;186]


60

In this review, age was reported as a significant risk factor both for the presence of circulating

antigens and/or antibodies, studied reports are compatible with what is described in table 2-5. The

effect of gender on prevalence is less clear: the studies in Latin America [142;223;228] indicated

female to be more likely to have antibodies, while in Africa, in one study, male were more likely to

present circulating antigens [134]. The effect of gender on transmission should be further studied to

determine whether there is a real difference in physiological gender susceptibility to T. solium

infections [187], or rather a difference associated with the role gender plays in every culture, resulting

in different exposure. It is clear that immunity plays a huge role in the host susceptibility/resistance to

the parasite but the underlying mechanisms are not well understood. In some cases, the origin of the

type of immune resistance/susceptibility present in a population is characterized by the surrounding

environment more than of an intrinsic factor in the host. This is the case for low immunity related to

the poor nutritive status, which could be a consequence of poverty [186].

Surprisingly, only for the studies from Latin America included in this review, the presence of pigs and

the consumption of pork were identified as important risk factors for exposure. In one study from Asia

this risk factor was associated with the presence of circulating antigens. In contrast, none on the

African studies revealed an association between pig ownership and pork consumption and infection or

exposure. These results are compatible with the results from Mwape et al. (2015) [121], reporting

other risk factors as the number of inhabitants and age as determinants when studying and ranking T.

solium infections determinants by classification trees. In fact, HCC is the result of the ingestion of

eggs coming from tapeworm carriers that could have acquired the adult tapeworm from pork meat

either locally produced or transported from other endemic regions [219], thus, presence of pigs in this

case is not as relevant for HCC transmission than the local prevalence of tapeworm carriers. HCC is

considered a “clustered” disease; some studies have pointed out the importance of the presence of

tapeworm carriers in a household triggering HCC in endemic and non-endemic

communities[125;235]. Twenty three out of 24 studies reporting taeniasis identified at least one

tapeworm carrier, however the diversity of methods used to diagnose taeniasis did not allow to make

adequate comparisons between studies, even more, parasitological tests are considered having a low

sensitivity, suggesting underestimation of the prevalences. Nevertheless, tapeworm carrier

identification can be an important tool to recognize endemicity, in a zone, to identify the sources of

infection and to support serological results.

Other important risk factors reported from Africa and Latin America were related to poor sanitary

conditions, the deficient handling of human feces, the presence or history of adult tapeworms near the

positive cases and low educational level. In the latter case, educational level could be interpreted also

as an indicator of rural environment and/or poor household income in endemic communities. An

interesting finding is the association of the presence of sewage installations in the house and positivity


61

to EITB in a village in northern Peru [227]. Usually, sewage systems could be interpreted as a sanitary

improvement, but in the Peruvian study, sewage installations were present only in some houses, which

could result in the concentrated use of hygienic systems, and if they are not handled properly, they can

turn the house into a “hotspot” for HCC [18].

Little is known about T. solium eggs survival in the environment. Some studies have been done on

related cestodes like Taenia saginata and Echinococcus spp. [164], however, extrapolating knowledge

from those studies could result in inadequate interpretations because of biological differences between

these species. In addition, flies may play a role in the transmission of eggs of some Taenia spp.

[236;237]; in the case of T. solium, however, flies were found not to be important because of the

coprophagic behavior of pigs that left not enough time after defecation to allow flies to get

impregnated with T. solium eggs [169]. Dung beetles were also shown to carry infective T. solium

eggs in their bodies making them capable of transmitting the parasite [170;171]; however, ingestion of

the beetles is needed for effective transmission of the parasite, which makes this route of transmission

more likely for porcine cysticercosis than for HCC. Nevertheless, from the experiences acquired in

these studies [164;169-171;236;237], it is clear that climatic factors have a direct impact on the

viability of taeniids eggs. Thus climatic factors can have a direct influence on the variations observed

in the prevalence of active infections and exposure to T. solium in different climatic settings.

The results observed in the studies performing both Ag-ELISA and EITB could be interpreted as

indicating a higher occurrence of active infection in African communities, under a similar exposure to

the parasite, suggesting that in this continent there are factors enhancing the human infection

regardless of the level of exposure. At a population level, variations and similarities in exposure could

be the result of the environmental or behavioral conditions enhancing or disfavoring egg dispersal and

survival. The presence of circulating antigens at a population level is the outcome of viable cysticerci,

which reflects successful establishment of infection after exposure to T. solium eggs. This would

indicate exposure to infectious eggs and human behavior ensuring the uptake of eggs. Another factor

triggering infection is the contact with a large number of eggs, increasing the probability of breaking

the immune barrier raising the chance of the cysticerci to establish. A high prevalence of active

infections could be as well an indicator of weak immune responses due to multiple factors as

described in table 2-5. Also, the level of active infections in a population could be inversely

proportional to the level of intrinsic factors in the human hosts permitting the presence of innate or

acquired resistance to the parasite.

To have a complete picture on the human-to-human transmission for T. solium cysticercosis, more

longitudinal studies should be carried out following strict protocols in order to make them

comparable. In the present review, only three studies were found that contributed incidence data, two

from the Latin American region [17;73] and one from the African region [136]. The results from


62

Ecuador and Zambia [17;136] reported at least one change between positivity and negativity in their

EITB for T. solium antibodies in 20-32% of the population studied at one point during a year. For the

circulating antigen detection, the percentage of subjects showing a similar phenomenon was about

11.5% of the studied population in Zambia. These results suggest that the number of subjects that are

actually exposed to T. solium eggs or are infected with cysticerci every year is higher than what is

reported in prevalence studies. Incidence data could help to explain the interactions of the different

components for transmission and their evolution over time. Data obtained from these studies

contribute enormous knowledge on how seroprevalence estimation is affected because of the dynamic

nature of the infection and of the presence of transient antibodies and possibly transient antigens.

Studying the fluctuations of the humoral response over time can also provide information about the

level of individual susceptibility by measuring the establishment rate of cysticerci following infection

[238].The information obtained from longitudinal studies can also help deciding on the duration of

control programs to effectively have an impact in the reduction on the prevalence of the disease.

When designing control programs and strategies, the correct interpretation of exposure patterns can

show which factors affect the egg dispersal in the environment and to locate the potential

“hotspots”[18;125;235]. By doing so, it will provide the necessary information to create targeted

interventions to avoid the spread of the disease taking into account that these patterns vary from one

location to another [125;235]. Interpreting the different infection patterns observed in every

community will help to prioritize which strategy should be better adapted to the demo-geographical

setting in order to decrease the number of new negative health outcomes.

Variations in exposure to the parasite and active infection with T. solium cysticerci in endemic

communities present a challenge when implementing control programs. For these reasons, more

studies searching in parallel the presence of antibodies directed against T. solium metacestodes and

the presence of circulating antigens need to be conducted in other endemic communities around the

world with detailed characteristics of potential risk factors. It is also recommended that these studies

be paired with the study of the adult T. solium prevalence that can provide another element of the

transmission of the parasite.

The main limitation of this study was the lack of a standardized protocol in community-based studies,

which made comparable data scarce [75;113]. Moreover, the reliance on only one serological test

(EITB or Ag-ELISA) in most of the current sero-epidemiological studies gives only a partial view of

the current status of T. solium infection/exposure in the communities in which they were carried out.

Another limitation is that B158/B60 Ag-ELISA and HP10 Ag-ELISA have not been compared in

human samples, which could lead to different results given the fact that the monoclonal antibodies

used are directed against different antigens in each test. On the other hand, the large time period that

elapsed (22 years from 1989 to 2014) between the oldest and the most recent studies may also imply a


63

certain bias in the health, sanitary and educational conditions that may have changed and may have

had a direct impact on the T. solium life cycle, thus affecting its transmission dynamics and

prevalence. Another important drawback is the fact that not all the studies selected for this review

reported the presence of adult tapeworms. Additionally, the methods used in the studies reporting the

presence of tapeworms were diverse and considered with a low sensitivity and specificity,

complicating comparisons between studies. Moreover, not all the studies presented details of the

studied population such as representativeness of each age group, health status or the presence of other

pathogens that could have interfered when characterizing and comparing prevalence figures.

In conclusion, this review demonstrated the variability on the occurrence of active T. solium

infections and exposure to the parasite in endemic zones with some African communities reporting

the highest prevalence levels for cysticercosis active infection around the world with results bordering

20%. Several significant risk factors were listed for both active T. solium infections and exposure to

the parasite, some of them being determinant depending on the geographical location, climatic,

economic and socio-cultural conditions. The findings in this review should be taken into account in

order to help defining priority areas for intervention and control of T. solium.

Chapter 3 3 Human neurocysticercosis and epilepsy in Ecuador: Distribution in space and time

of hospitalized reported cases.

Adapted from:

Lenin Ron-Garrido*, Marco Coral-Almeida*, Sarah Gabriël, Washington Benitez, Claude Saegerman, Pierre Dorny, Dirk Berkvens, Emmanuel Abatih. Distribution and Potential Indicators of Hospitalized cases of Neurocysticercosis and Epilepsy in Ecuador from 1996 to 2008 (2015) . PLoS Negl Trop Dis 2015 Nov;9(11):e0004236.

*Joint first authorship

Human neurocysticercosis and epilepsy in Ecuador: Distribution in space and time of hospitalized reported cases.

65

3.1 Chapter summary

T. solium neurocysticercosis (NCC) is considered the most important parasitic disease of the central

nervous system in humans; it is estimated to be responsible for at least one third of acquired epilepsies

in developing countries. In Ecuador, the relationship between acquired epilepsy and NCC remains

unclear due to different factors such as, the lack of specialized health care personnel, appropriate

diagnostic techniques and the fact that acquired epilepsy is characteristic of many other infectious and

non-infectious diseases in the endemic zones of the country. In this chapter, spatial and temporal

variations in the incidence of hospitalized cases of epilepsy and NCC in Ecuadorian municipalities

were analyzed in order to locate and characterize important clusters in space and time. Additionally,

potential socio-economic and landscape indicators were evaluated to understand in part the macro-

epidemiology of the Taenia solium taeniasis/cysticercosis complex.

Data on the number of hospitalized epilepsy and NCC cases by municipality of residence were

obtained from morbidity-hospital systems in Ecuador. SatScan software was used to determine

whether variations in the incidence of hospitalized epilepsy and NCC cases were clustered in space

and time. In addition, several socio-economic and landscape variables at municipality level were used

to study factors intervening in the macro-epidemiology of these diseases. Negative Binomial

regression models through stepwise selection and Bayesian Model Averaging (BMA) were used to

explain the variations in the incidence of hospitalized epilepsy and NCC cases.

This study identified traditional endemic clusters in the highlands for both conditions as well as new

clusters appearing in recent years in other zones not considered endemic. An increase in the

implementation of systems for eliminating excrements would help to reduce the incidence of

hospitalized cases of epilepsy by 1.00% (IC95%; 0.2% - 1.8%) and by 5.12% (IC95%; 3.63%-6.59%) for

NCC. For epilepsy, the percentage of dwellings with piped water and the number of physicians per

100,000 inhabitants were associated with an increase in the number of cases hospitalized. Pig

population was related to NCC emergence. Some variables were related to some development

indicators in services which could have poor quality in developing countries. The presence of clusters

of municipalities with high incidence of hospitalized epilepsy cases could be the result of a high

incidence of NCC cases or other acquired epilepsy cases. Both disorders were related to the lack of an

efficient system for eliminating excrements. Given the appearance of recent epilepsy clusters, these

locations should be studied in depth to discriminate epilepsies due to NCC from epilepsies due to

other causes. More specific studies are needed to evaluate the true prevalence of cysticercosis in

humans and pigs in different zones of the country in order to better implement and manage prevention

and/or control campaigns.


66

3.2 Introduction

“A hospital bed is a parked taxi with the meter running.”

― Groucho Marx

T. solium NCC has been found to be the leading cause of acquired epilepsy in endemic countries. In

fact, NCC was found to be responsible for at least half or a third of acquired epilepsy cases [31;156].

In developing countries, NCC is often an underrecognized and neglected disease [4;239]. The large

variety of clinical signs and symptoms, and the inaccessibility of highly sensitive tests, like

Computerized Tomography (CT) or Magnetic Resonance Imaging (MRI) (due to high costs involved

and the unavailability of neuroimaging facilities), have contributed to the underreporting of NCC.

In Ecuador, an average of 480 and 1670 patients are hospitalized each year because of NCC and

epilepsy, respectively [147]. Notification of hospitalized cases for both disorders is mandatory in

Ecuador. Tools for diagnosing causes of acquired epilepsy, including parasitic and infectious diseases

are available in the country; however, these diagnostic tools are not regularly used because of their

high costs, thus, as in other NCC endemic countries, in Ecuador more than 82% of epilepsies do not

have definitive diagnosis and the cause remains unknown [30;147;240;241].

Different measures such as education, improvement of household sanitation, changes in meat

inspection practices, identification and treatment of tapeworm carriers, mass drug administration and

modifications in pig-rearing methods have proven, at least at short term, to be effective in lowering

levels of transmission of NCC [143;205;242]. However, practices like free roaming pig management,

clandestine marketing of living pigs and pork, open defecation, and the use of residual waters in

irrigation [143;167], make the disease still prevalent in many regions.

Symptomatic and asymptomatic cases of NCC have been studied in urban [151;154;155] and rural

[15-17;131;153;156] areas of Ecuador in different epidemiological studies. Endemic areas were found

mostly in the highlands, where the population has a high exposure to the parasite as measured by

specific antibody detection. Up to one third of the population is seropositive in some of these areas

[17]. In some endemic communities in these highland areas, human cysticercosis active infections, as

measured by antigen detection are present in up to five percent of the population [131]. However, in

the past three decades, a decreasing trend in the incidence of hospitalized cases (IHC) of NCC has

been observed in the country, apparently due to an improvement in sanitary conditions and the use of

better diagnostic tools [151].


67

Epidemiological surveillance data in the Ecuadorian health status reports only include ambulatory

cases from the public health care system. The public registers from the Ministry of Public Health are

the only official health reports available. The consultations at any level attended in the public health

system have been estimated to be around 30% of all the medical consultations in the country [243].

However, for the ambulatory cases the reporting is not always done properly, mainly due to the lack

of synchronization among the different types of health care services in Ecuador [244]. Figure 3-1

explains the reporting system for NCC and epilepsy cases in Ecuador. Additionally, and in a parallel

way, the National office of Statistics (INEC) collects all information on morbidity registered in

hospitals and clinical centres (from public, private or social security systems) where patients are

attended at the secondary health care level and also in case of emergencies irrespective of their

underlying sources. In these registers, both NCC and epilepsy are frequent causes of hospitalization.

Thus, epidemiological data generated by the Ecuadorian office of statistics offers the possibility of

studying important variables related to the macro-epidemiology of NCC and epilepsy in Ecuador.

Here, we use macro-epidemiology in terms of the determinants of disease, including economic, social,

and climatological factors into national patterns in risk assessment [245].


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Figure 3-1: Neurocysticercosis and epilepsy reporting flow chart in the Ecuadorian health system

Legend: NGO: Non-governmental organization.

In this study we aimed at identifying areas (municipalities) with a high IHC of NCC and epilepsy

between 1996 and 2008. In addition, given the fact that the IHC of NCC and epilepsy have been

related to several socio-economic, and landscape variables, we evaluated the macro-epidemiology of

epilepsy and NCC in Ecuador at the municipality level. Finally, spatio-temporal analysis was

implemented in order to investigate the distribution of the IHC of epilepsy and NCC in Ecuador.

3.3 Materials and methods

3.3.1 Ethics statement

Ethical approval was not required for this study. All information used in this study came from public

sources freely available on the referenced websites. Reports of human cases belonged to the public

health surveillance system, the anonymity of clinical histories is guaranteed by legal mandate.


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3.3.2 Study region and data

The study unit was the municipality. The number of patients hospitalized in different institutions with

diagnosis of epilepsy and NCC, from 1996 to 2008 was obtained from hospital morbidity and

mortality databases managed by the National Office of Statistics (INEC)[147]. This time period was

chosen because of the availability of digitized morbidity data (www.inec.gob.ec), and because data on

agricultural and life conditions of the population were available for that time period [147;246].

Additionally, we did not consider the data of the period after 2008 because biases in the number of

cases were expected given the fact that public health systems increased their coverage and became

more accessible and free of charge, including the distribution of parasitic drugs [247].. The cases were

identified through the ICD-10 codes for disease classification [248]. In Ecuador, the protocol to

declare a patient with NCC is defined by the neurology department of hospitals. Briefly, the diagnosis

of NCC follows the directions of the Del Brutto (2012) criteria. The diagnosis is based on patient’

clinical symptoms and signs (seizures, headache, dementia, hydrocephalous, among other

neurological disorders), serology (detection of antibodies directed to T. solium metacestodes and/or

circulating antigens of T. solium metacestodes in serum or cerebrospinal fluid) and imaging (CT,

MRI) [78]. In the public sector there exist 39 neuroimaging facilities (CT-Scans) the majority of them

are in the provincial capital cities (24 provinces). The private sector also has neuroimaging capacity

but the number of scanners is unknown. The database has information about each hospitalized patient

with cause-specific morbidity, hospital of attendance, and the place (parish or municipality) where the

patient lives (access to official databases are included in S2).

All municipalities in the continental part of the country were included in this study (217

municipalities). The registers of the Galapagos Islands were excluded because they might distort the

spatial analysis, although both disorders have also been reported there. Each record was designed to

contain the total number of NCC and epilepsy cases, the total population, the year and the

geographical coordinates of the centroid of each municipality. Time trends of hospitalized reported

cases for both disorders were tested using Negative Binomial regression models. Furthermore, the

relationship between the number of hospitalized cases of epilepsy and NCC was evaluated using

correlation analysis on Log transformed data.

Additionally, data on several explanatory variables were gathered using governmental databases about

several socio-economic indices, information from the agricultural census conducted in 2000, and

climatological information from the National Hydrometeorological Service [249]. The information on

explanatory variables possibly associated with NCC and epilepsy at municipality level were grouped

into different classes. Climatic variables: (tropical or highlands) (ZONE), rainfall (RAIN) and number

of days without precipitations (DRYD). For each municipality, values of RAIN and DRYD were

inferred on the basis of 205 weather stations, and ordinary Kriging was used to interpolate values. The


70

similarity with rainfall maps published by the National Hydrometeorological Service (INAMHI) let us

choose the proper model [249]. Population variables: population number (POPULATION),

percentage of indigenous population (%INDG), and percentage of rural population (%RURAL);

Educational level: mean number of years of schooling (SCHOOL), mean number of years of

schooling for farmers in the municipality (FSCHOOL), and percentage of farms receiving technical

assistance (TECHASSIS); Sanitary conditions: % of families with piped water (TUBWAT), % of

dwellings with systems for eliminating excrements (EXCR), and physicians per 10,000 inhabitants

(PHYS); Poverty indices such as: percentage of families with unsatisfied basic necessities (UBN)

(Number of people or families that live under poverty conditions with respect to the population in a

specific year, referring to the lack of dwelling, health, education and employment [246]), and

percentage of people under extreme poverty (EXTPOOV); Livestock: percentage of agriculture land

dedicated to pastures (%GLS) and pig population (PIG) [246]. In Ecuador, the majority (58.8%) of

the pig population is raised under the traditional husbandry system if we consider smallholder

producers in Ecuador as those farmers owning ≤10 pigs [145]. The agricultural office of geographical

information systems provided the map showing the political division of the country at municipality

level. A description of all the variables considered for this study is presented in Table 3-1.

Table 3-1 Socio-economic and demographic factors used to model the incidence risk of hospitalized human cases of epilepsy and neurocysticercosis in Ecuador from 1996 to 2008.

Variable Description

POPULATION Population EPI Number of epilepsy cases (1996-2008) CYS Number of NCC cases (1996-2008) Zone Tropical (1) or temperate zone(0) RAIN Rainfall during the year DRYD Number of days during a year with precipitations ≤ 1mm %GLS Percentage of agriculture land dedicate to pastures PIG Number of pigs (Criollo breed) SCHOOL Average number of years on formal education in people >=24 years

old PHYS Number of physicians per 10,000 inhabitants TUBWAT Percentage of dwellings with piped water EXCR Percentage of dwellings with some kind of system for eliminating

excrements. UBN Percentage of families with unsatisfied basic necessities EXTPOOV Percentage of extreme poverty %INDG Percentage of indigenous population %RURAL Percentage of rural population. TECHASSIS Percentage of land with technical assistance FSCHOOL Years of education of farmers> 24 years N 217 municipalities

3.3.3 Space-time analysis

Space-time analysis was used to determine whether municipalities with high incidence of hospitalized

cases (IHC) of epilepsy and NCC are clustered in space and in time [250;251]. The space-time scan


71

software [250] was used to search, and test for significance and identify approximate locations of

areas with an increased risk for the occurrence of NCC and epilepsy cases. The analysis was run in

SatScan Software v9.4, with case file as the number of hospitalized reported cases, population file as

the estimated total number of individuals in each municipality per year and as the coordinate file, the

latitudes and longitudes of the centroids of each municipality. The spatial dimension varied from 0 up

to 25% of the total number of centroids in the study region. The temporal dimension was established

with a maximum of up to 50% of the study period with a time precision of 1 year. Poisson-distribution

was used to contrast the number of cases in the scanning of areas. Space-time clustering was assessed

by comparing the iRR (incidence rate ratio) of epilepsy and NCC IHC within a specific area and time

in contrast to an expected iRR of hospitalized NCC and epilepsy cases if their incidences were

randomly distributed. The cylinder with the maximum likelihood ratio was selected as the most likely

cluster (Primary cluster), and others no overlapping significant clusters were also selected. The

significance of identified space-time clusters was tested using the likelihood ratio test statistic and p-

values of the test were obtained through Monte Carlo simulations (999). The significance was

arbitrated at the 5% level. All significant clusters were visualized using QGIS software (version 2.8).

3.3.4 Regression analysis

Multivariable-count regression models were used to assess the relative contribution of different socio-

economic and demographic variables to the IHC of epilepsy and NCC from 1996 to 2008 across the

country. For the case of hospitalized NCC cases, an excess of zero cases were observed. For this

reason, Zero inflated negative binomial models (ZINB) were used to explain the over-abundance of

zero cases [252].

A manual forward stepwise procedure was implemented to select the set of independent variables that

describe the number of NCC hospitalized cases or the probability of not observing any hospitalized

case of NCC using the zinb command in STATA, version 12 software (StataCorp LP, College Station,

Texas). The procedure started with the null model (with no covariates), and subsequently, covariates

were added and evaluated for their importance. The Akaike Information Criteria (AIC) was used as

the calibrating parameter and models with lower AIC values and few parameters were preferred. Two

models were considered to be significantly different whenever the difference in AIC was greater than

3 [253]. In the forward selection procedure, each covariate was added in either the linear predictor for

the count part or in the logit function for the absence of the disease, and the covariate with the best

explanation preserved for the second round. If the addition of a covariate improved the model

explanation through the reduction in AIC, the variable was captured and the process was repeated

until the AIC value could not be reduced further [254]. The significance level for the covariates in the

model was set at 0.05. For the case of NCC Vuong’s test was applied in order to evaluate if zero-

inflation was more appropriate as compared to the standard negative binomial model.


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To assess the influence of the selected indicators on the IHC of epilepsy, a Poisson regression model

was used, and due to the presence of over-dispersion, Negative Binomial models were also evaluated

through a likelihood ratio test for over-dispersion using the function odTest (in pscl package, in the R

software) to test the null hypothesis that the restriction implicit in the Poisson model is true [255]. The

approach of bidirectional elimination of variables was applied for variable selection, which also used

the AIC as calibrating parameter. The functions glm.nb and stepAIC, in the MASS package under the

R environment were used [256].

In addition, for the study of epilepsy, Bayesian model averaging (BMA) was used in order to deal

with the uncertainty about the “correct” model [257]. BMA chooses the better model according to the

best posterior probabilities among the models using the Occam’s window principle [253]. The

inference about the explanatory variables in the best model is expressed as posterior effect

probabilities, which indicate evidence of the importance of the effects of each variable in the model.

The function bic.glm() in the BMA package of the R software was used [258] with the specification

that counts follow a quasi-Poisson distribution, and that variance increases with the square of the

mean: an equivalent version of NB regression [259]. No explicit prior distributions for models and

model parameters were assumed implying that all models were equally likely.

3.4 Results

3.4.1 Space-time analysis

Figures 3-2 and 3-3 display the histogram of the cumulative incidence of hospitalized epilepsy (Figure

3-2) and NCC (Figure 3-3) cases, during the study period (between 1996 and 2008) over all the

municipalities. For epilepsy, the distribution is more uniform compared to that of NCC; however, for

NCC there are high proportions of zero cases throughout the municipalities. Figure 3-4 presents the

Incidence of hospitalized cases (IHC) with both health problems over time in Ecuador. In the case of

NCC, from 1996 to 2008, there was an overall decreasing trend with around 5 cases per 100,000

inhabitants in 1996 to around 3 cases per 100,000 inhabitants in 2008. The decreasing trend was

statistically significant (p<0.001); thus, annually a reduction of 5.68% (IC95%: 4.5%-6.4%) in hospital

cases is expected. In contrast, for the case of epilepsy, the incidence appeared to be slowly and

steadily increasing from 1996 to 2008. The increasing trend was statistically significant (p<0.001).

Annually an increase of 4.7% (%(IC95%: 3.7%-5.7%) in reported cases is expected. It was also

observed that as long as the incidence of epilepsy increased through time, the annual IHC of NCC

appeared to decrease slowly; and the IHC for epilepsy was always higher than that of NCC.


73

Figure 3-2: Histogram of the incidence of hospitalized epilepsy cases per 100,000 inhabitants between 1996 and 2008 in Ecuadorian municipalities.

Figure 3-3: Histogram of the incidence of hospitalized neurocysticercosis cases per 100,000 inhabitants between 1996 and 2008 in Ecuadorian municipalities.


74

Figure 3-4: Incidence of hospitalized neurocysticercosis and epilepsy cases per 100,000

inhabitants in Ecuador between 1996 and 2008.

Table 3-2 presents a list of the top 15 municipalities with the highest IHC of epilepsy and NCC. It can

be observed that municipalities with a high IHC of epilepsy did not necessarily have a high IHC of

NCC. However, an overall (all years combined for each municipality), highly significant positive

linear correlation (r=0.78, IC95%(0.72-1.00), p<0.0001) was found on log(x+1) transformed number of

hospitalized cases of epilepsy and NCC reported in each municipality. Similar significant positive

linear trends within municipalities were observed for each year evaluated separately. The IHC of

epilepsy varied from 0 to 505 cases per 100,000 with an average number of 127.1 cases. On the other

hand, for NCC, the IHC varied from 0 to 282.54, and the average number of cases was 35.1. Out of

the top 15 municipalities with high IHC for epilepsy, six also featured amongst the top 15 for

municipalities with high IHC for NCC. It should be highlighted that Quito (capital city) presented the

highest number of patients (1829 and 3123) in hospitals for NCC and epilepsy during the study

period, but the rates were diluted because of the city’s large population size.


75

Table 3-2 Municipalities having the highest incidence of hospitalized cases (/100,000 inhabitants) of neurocysticercosis and of epilepsy from 1996 to 2008.

Municipality Highest IHC for NCC Municipality Highest IHC for epilepsy

IHC NCC IHC epilepsy IHC NCC IHC Epilepsy

Chinchipe 282.5 494.4 Paulo VI 0.0 505.0

Loja 241.6 327.4 Chinchipe * *

Quilanga 218.2 43.6 Zamora * *

Espíndola 215.8 273.0 Sta. Clara 0.0 396.2

El Tambo 206.0 218.2 El Chaco 130.4 391.3

Azogues 204.9 359.0 Sucúa 13.8 381.6

Zamora 183.6 472.7 Santiago 0.0 375.9

Cañar 171.7 268.1 Baños 0.0 367.1

Paltas 165.9 206.4 Azogues * *

Calvas 159.4 282.6 Sta. Rosa 28.1 341.1

Biblian 144.7 328.1 Biblian * *

Gonzanama 140.1 126.8 Loja * *

Cuenca 138.8 288.8 Morona 51.0 321.8

Riobamba 135.5 320.7 Riobamba * *

Ibarra 134.4 204.2 Penipe 61.0 308.0

Legend: NCC: Neurocysticercosis; IHC: Incidence of hospitalized cases *: Data reported in the previous column

3.4.2 Significant space-time clusters

Four clusters were detected for the iRR of epilepsy when up to a maximum of 25% of centroids were

included in the scanning window (Figure 3-5). The most likely cluster extended from the center to the

northern part of the country, involving municipalities from Tungurahua, Cotopaxi, Napo and

Pichincha provinces. This cluster lasted between 2003 and 2008 with an iRR of 1.57 in contrast to

centroids outside the cluster (p =0.001). A secondary cluster was located in the Guayaquil

municipality in Guayas province in the Southern coast of the country with an iRR of 1.69 (p=0.001).

This cluster existed between 2005 and 2008 with 1745 hospitalized cases when only 1070 cases were

expected. A third secondary cluster was located in the southern part of the country in municipalities in

the provinces of El Oro, Loja Zamora, Cañar, Azuay, Morona Santiago, and Chimborazo. This cluster

was the biggest cluster found, and the iRR was 1.60 (p=0.001) compared to the municipalities outside

the cluster. This cluster existed from 2002 to 2007. Finally, in the western coast of the country, a

secondary cluster covering 11 municipalities of Manabí province was detected in 2008, which had an

iRR of 1.62 (p=0.001).


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Figure 3-5 Significant space-time clusters of hospitalized epilepsy cases with up to a maximum of 25% of the total centroids included in the scanning window between 1996 and 2008.


77

Figure 3-6: Significant space-time clusters of hospitalized NCC cases with up to a maximum of 25% of the total centroids included in the scanning window between 1996 and 2008.

Like for epilepsy, four significant clusters were identified for NCC. A main cluster was found in the

southern part of the country, which existed from 1996 to 2001 with an iRR of 3.78 (p=0.001) (Figure

3-6). Municipalities of El Oro, Loja, Zamora, Azuay and Morona Santiago provinces were part of this

cluster within the given time frame. Likewise, in the central-northern part of the country, some

municipalities from Imbabura, and Pichincha provinces were part of an important secondary cluster

that lasted from 1996 to 2001. The iRR for the municipalities within this cluster was 2.75 (p=0.001).

Additionally, there was a secondary cluster in the municipality of Riobamba in Chimborazo Province

in the middle of the country that lasted between 2000 and 2005. The iRR for this cluster was 3.15

(p=0.001). Finally, besides the last zone, some municipalities from Cotopaxi and Tungurahua

provinces were part of an additional cluster that had an iRR of 2.09 (p=0.001) and had a relatively

high incidence starting in 1996 until 1997.


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3.4.3 Potential indicators associated with the incidence of hospitalized epilepsy and neurocysticercosis cases.

The analysis of several socio-economic and demographic variables affecting the IHC of epilepsy

between 1996 and 2008 is presented in Tables 3-3 and 3-4. Table 3-3 presents the set of covariates

selected by stepwise procedure and Table 3-4 presents the total set of variables included in this set of

potential indicators and their partial contribution according to the BMA methodology. Posterior effect

probabilities (P(β≠ 0|D)) were included to show the evidence of an effect for each covariate when

model uncertainty was incorporated. According to the results, the variables that significantly

increased the IHC of epilepsy in municipalities were: the number of physicians per 10,000 inhabitants

(PHYS) iRR=1.045 (IC95%: 1.031-1.059), and the percentage of families having piped water

(TUBWAT, not necessarily drinking water) iRR=1.022 (IC95%: 1.014-1.029). On the other hand, the

only variable that apparently led to a significant reduction in the IHC of epilepsy in municipalities

was the percentage of houses having any kind of system to eliminate excrements (EXCR) iRR=0.986

(IC95%: 0.979-0.993). The climatic variable (Zone) showed that municipalities located in the highlands

presented an increased risk of epilepsy in contrast to municipalities located in tropical zones

(iRR=1.02 (IC95%: 0.855-1.207)) even though it was not statistically significant at a 5% level. For the

BMA variable selection, out of 15 variables evaluated, 3 had substantial evidence (P(β≠ 0|D)>90%)

of being different from zero (Table 5); PHYS, TUBWAT, and EXCR. Overall, the BMA and stepwise

selection methods yielded similar results.

Table 3-3: Indicator factors associated with the incidence of hospitalized epilepsy cases in Ecuador from 1996 to 2008 (negative binomial model chosen by AIC criterion).

Coefficients: Estimate Std. Error z value P-value

(Intercept) -6.77 0.199 -33.95 <0.001

Zone (Tropical) -0.16 0.088 -1.82 0.069

PHYS 0.04 0.007 6.37 <0.001

TUBWAT 0.02 0.004 5.53 <0.001

EXCR -0.01 0.004 -3.85 <0.001

Dispersion parameter for Negative Binomial (3.50)

AIC: 1769.8

Legend: PHYS: Number of physicians per 10,000 inhabitants; TUBWAT: Percentage of dwellings with piped water; EXCR: Percentage of dwellings with some kind of system for eliminating excrements; AIC: Akaike Information Criterion; Std. Error: Standard Error.


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Table 3-4: Indicator factors associated with the incidence of hospitalized epilepsy cases in Ecuador from 1996 to 2008 based on Bayesian model averaging (BMA).

Coefficients: P(β≠ 0|D) Mean SD

Intercept 100 -6.84 0.699

PHYS 100 0.05 0.008

TUBWAT 96.7 0.02 0.006

EXCR 94.0 -0.01 0.005

Legend: TUBWAT: Percentage of dwellings with piped water; PHYS: Number of physicians per 10,000 inhabitants; EXCR: Percentage of dwellings with some kind of system for eliminating excrements; SD: Standard deviation; P(β≠0|D): Posterior effects probability.

Table 3-5 presents the results of the potential indicator factors associated with NCC in hospitals. In

the binary part, three covariates were chosen (EXCR, PIG, %RURAL). According to this selection

procedure, the covariates that positively influenced the odds of hospitalized NCC cases in the

communities were the implementation of systems for eliminating excrements (EXCR) (OR=0.94;

IC95%: 0.89 - 1.0), and pig population (PIG) (OR=0.999; IC95%: 0.999-1.0). In contrast, the higher the

proportion of rural population in a community the lower the odds ratio of reporting NCC hospitalized

cases (OR=1.073 (IC95%: 1.01 - 1.14)).

Table 3-5: Factors involved in the incidence of hospitalized neurocysticercosis cases in Ecuador from 1996 to 2008 based on a zero-inflated negative binomial regression model.

Count model Coef. Std. Err. Z P>|z| [95% Conf. Interval]

Intercept -4.32 1.29 -3.35 0.001 [-6.843 - -1.790]

ZONE (Tropical) -1.72 0.170 -9.69 <0.001 [-2.070 - -1.37]

SCHOOL 0.19 0.092 2.09 0.037 [0.012 - 0.372]

EXCR -0.05 0.008 -6.62 <0.001 [-0.068 - -0.037]

TUBWAT 0.02 0.008 1.98 0.047 [0.0002 - 0.030]

TECHASSIS 0.05 0.015 3.46 0.001 [0.0222 - 0.080]

%GLS 0.01 0.004 2.52 0.012 [0.0024 - 0.019]

EXTPOOV -0.02 0.008 -2.33 0.020 [-0.0362 - -0.003]

%RURAL -0.01 0.005 -2.03 0.042 [-0.0192 - -0.0001]

Zero inflation

Intercept -1.97 3.099 -0.64 0.525 [-8.0451 - 4.102]

EXCR -0.06 0.028 -2.09 0.036 [-0.1134 - -0.003]

PIG -0.001 0.0003 -2.46 0.014 [-0.0011 - -0.0001]

%RURAL 0.07 0.032 2.13 0.033 [0.0056 - 0.131]

log(alpha) -0.70 0.1453 -4.74 <0.001 [-0.9734 - -0.403]

Alpha 0.50 0.0730 [0.3777 - 0.667]

Legend: SCHOOL: Average number of years on formal education in people >=24 years old; EXCR: Percentage of dwellings with some kind of system for eliminating excrements; TUBWAT: Percentage of dwellings with piped water; TECHASSIS: Percentage of land with technical assistance; %GLS Percentage of agriculture land dedicated to pastures; EXTPOOV: Percentage of extreme poverty; %RURAL: Percentage of rural population; PIG: Number of pigs (Criollo breed); Coef: coefficient; Std. Err.: Standard Error.


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On the other hand, for the count model, the variables that positively influenced the number of

hospitalized cases were SCHOOL, TUBWAT, TECHASSIS, and %GLS, and the variables that were

associated with a decrease in the number of hospitalized cases were Zone (Tropical), EXCR,

EXTPOOV, and %RURAL. The temperate zone (highlands) had by far higher NCC cases compared

to the tropical zones, so that the possibility of having a NCC diagnosis in Andean zone hospitals is

higher (iRR=5.6 times (IC95%: 3.95-7.92)). Variables such as, the schooling in municipalities

(SCHOOL) (iRR=1.212; IC95%: 1.012-1.451), the percentage of dwellings having piped water

(TUBWAT), (iRR=1.020;IC95%: 1.001 - 1.031), the proportion of farms with technical assistance

(TECHASSIST) (iRR= 1.051; IC95%: 1.022 - 1.084), and the percentage of land dedicated to pastures

(%GLS) (iRR=1.010; IC95%: 1.002 - 1.019) were positively associated with an increase in the IHC of

NCC. In contrast, covariates that negatively affected the number of NCC hospitalized cases in

hospitals were: the percentage of dwellings having any system for eliminating excrements (EXCR)

(iRR=0.951; 0.934 - 0.964), extreme poverty (EXTPOOV) (iRR=0.980; IC95%: 0.965 - 0.997); and

%RURAL population (iRR=0.990; IC95%: 0.9812- 0.999). The implementation of systems for

eliminating excrements (EXCR) reduced the IHC of NCC in average by 4.87% (IC95%: 3.6% - 6.6%).

The model chosen for the iRR of epilepsy fitted better than the model without over-dispersion. The

likelihood-ratio test for the over-dispersion parameter was significantly different from zero (p<0.001),

meaning that Negative binomial regression was preferred over Poisson regression. For the case of

NCC, when the zero-inflated negative binomial model was contrasted against the zero-inflated

Poisson model, the likelihood-ratio test was significant in favour of taking into account the

overdispersion (different from zero) (p<0.0001). In the same way, Vuong’s test confirmed that the

assumption of zero inflation in the model for NCC was preferred over a model without this

assumption (p=0.02).

3.5 Discussion

During the study period, NCC still had an impact on the general health status of the population in

Ecuador. Our findings indicate that 6294 cases of NCC and 19821 cases of epilepsy were hospitalized

between 1996 and 2008. Additionally, there was a significant increasing time-trend for IHC of

epilepsy, but a decreasing time-trend for IHC of NCC overall. In contrast, within municipalities a

positive linear relationship between both disorders was found. Also, the number of hospitalized cases

(both for epilepsy and NCC) was related to some potential indicators evaluated. A general reduction

in the IHC of both conditions was observed with an increasing percentage of systems to eliminate

excrements. . Moreover, the presence of pig production was related to the IHC of NCC.


81

3.5.1 Epilepsy

In the case of epilepsy, according to the spatio-temporal analysis, all significant clusters of

municipalities with high incidence of epilepsy existed between 2002 and 2008. The incidence risk

ratio (iRR) of the epilepsy clusters were not so high (they ranged from 1.57 to 1.69), meaning that

epilepsy can be almost classified as an endemic disorder in Ecuador. A possible explanation for the

epilepsy clusters since 2002 is that during these years, health facilities could have improved in

municipalities leading to a better coverage of hospitalization.

Clustered epilepsy municipalities were located in the Sierra region, mainly in the southern and some

in the central-northern part of the country. Some of those municipalities were known as endemic for

epilepsy and as epilepsy-NCC related zones, with some new clusters in the Sierra region that have not

been pointed out before as endemic areas in previous studies [15;131;153;160]. The appearance of

this new epilepsy cluster could also be related to the presence of other infectious and non-infectious

diseases present in coastal tropical zones [260], but the evaluation of the newer clusters become

urgent as this could be a strong predictor for NCC [261].

Based on two selection methods, there was a positive association between number of physicians and

number of hospitalized cases of epilepsy. This effect occurs mainly in provincial capital cities where

more health services exist and consequently specialized physicians are available to people. The

implementation of systems for eliminating excrements, such as latrines, septic tanks, or sewage

systems, seemed to have an impact on the occurrence of epilepsy, which suggests that a part of

hospitalized epilepsy cases might be due to NCC or other fecal-related causes of epilepsy [262].. In

this study period, the majority of the epilepsy cases were classified as non-specific cases (ICD codes:

G408 and G409), and they were between 81% and 92% every year. As in other places, the majority of

epilepsy cases apparently do not have a recognized etiological origin well identified [30;241].

However, not all types of acquired epilepsy can be attributed to NCC [30;261;262]. Other causes

related to poverty, such as poor nutrition, neurological sequels due to infectious agents, and head

traumas related to occupational accidents and violence can also contribute to the number of

hospitalized epileptic cases [231;262-264]. The other variable was the percentage of dwellings with

piped water. Having piped water not necessarily refers to water that is drinkable. According to

estimations, in Ecuador, 30% of the piped water in urban zones is not potable water. [265].

3.5.2 NCC

In Ecuador, the protocol to declare a patient with NCC depends on the diagnostic capacity of the

neurology department, which in many cases, only exists in the main cities [77]. Based on national

hospital data, 35.5% of the NCC cases were reported by the public sector, 39.4% were reported by the

private sector and 23% by the systems of social security insurance. Furthermore, the appearance of


82

clinical signs of NCC in patients might occur several months or even years after infection, so that

some etiological factors could not have been measured correctly at the beginning of this study.

Likewise, it is worth to mention that only a part of the cases of human cysticercosis are symptomatic,

and therefore the statistical relationships found in this study are valid only for the hospitalized cases

reported. A wider spectrum might be found with the addition of asymptomatic cases and people

suffering from chronic headaches who do not often consult physicians, which only can be found in

field studies[14;54;261;266;267].

NCC clusters in Ecuador apparently appeared earlier compared to epilepsy clusters and the majority

of them existed between 1996 and 2001. Only one of them was identified from 2000 to 2005 in

Chimborazo province and in some surrounding municipalities in Bolívar Province. This area presents

ideal conditions for the T. solium life cycle, as it is located in the highlands with a high percentage of

rural population and lack of basic services. In this cluster, more than 90% of the pig producers are

smallholders [147]. According to the last Agricultural National Census carried out in 2000, 80.5% of

the smallholders (≤10 pigs) are located in the Sierra region and 18.6% in the Coastal region. Porcine

Cysticercosis has not been reported in slaughterhouses by the National Veterinary Services

(Agrocalidad) since 2001 [268]. However, only 30% of slaughtered pigs in these facilities is provided

by smallholder. [269].

Based on a zero-inflated negative binomial model, the percentage of rural population in municipalities

was associated with a reduction in the IHC of NCC; so that urban zones increased their incidence in

contrast with previous studies published [270]. Nowadays, the rural population in Ecuador accounts

for less than 38% of the total population, which is a significant reduction compared to previous

decades when the rural population was over 50%. Translocated rural communities tend to settle in

slum zones of big cities [271]. However, rural and sometimes poor communities might have not been

well represented in the data, as they may refrain from hospitalization due to the high costs of

diagnosis and treatments [272]. This concern is a limitation of hospital-based registers [231]. In our

study only 7% of patients appeared to belong to rural communities, although, if we consider the

patients not living in the provincial capital cities this percentage increases to 26.7%. The structure of

the data makes it difficult to differentiate people from peri-urban zones or slums, or semi-rural towns

and communities from urbanized areas. On the other hand, housemaids and food vendors coming

from endemic rural zones have a higher chance to be tapeworm carriers and can be at the origin of

spreading T. solium infection among the urban population [154;223;273]. Another possible

explanation is that traditional livestock systems are still preserved on a small scale in urban slums,

although this presumption has not been quantified.

The presence of pigs was the most important positively associated with the appearance of

hospitalized-symptomatic NCC cases. Industrialization of pig production, in many cases is not


83

responsible for the increase in NCC cases. On the other hand, the presence of free roaming pigs has

been associated with an increased risk for the occurrence of cysticercosis [153;274]. In Ecuador,

despite 58.8% of pigs are raised in traditional production systems it has been estimated, that it only

represents nearly 30% (50% in year 2000) of pork available in markets. [269].

In the negative binomial count model, eight variables were associated with the IHC of NCC. As in the

case of epilepsy, the implementation of systems for eliminating excrements was involved in a

reduction in the IHC of NCC. More in depth studies are needed to evaluate the real scale of those

variables in the macro epidemiology of NCC, although some of them express the lack of quality in

offering services.

3.5.3 NCC & epilepsy

It has been mentioned that the difficulties of identifying the etiology of epilepsy could play an

important role in the sub-notification of NCC [15;275;276]. The condition most commonly associated

with NCC is epilepsy, but many cases of NCC are asymptomatic or manifest chronic headaches or

other neurological disorders [14;54;261;267]. In T. solium endemic communities in Ecuador an

important proportion of acquired epilepsy cases were due to NCC [15;160]. Although extrapolating

this quantity to the current reality in the country may be biased; zones with an apparent increase of

epilepsy cases may elucidate the origin of new suspected NCC cases [19;261]. Additionally, epilepsy

and NCC in developing countries have been reported to be clustered [18;231;235], but the presence of

imported cases has also been mentioned as an important factor in urban zones.

NCC underreporting might be due to a misdiagnosis in the epilepsy etiology. However, in our case

both disorders were linearly related. This positive relationship is an indicator of an apparent constant

relationship between epilepsy and NCC. This relationship has to be further studied and the meaning of

this pattern has to be elucidated.

Additionally, given that the lack of sewage systems was demonstrated to be associated with an

increase in the incidence of both conditions. Increasing the sewage systems could be used as an

important control tool to reduce the incidence of the hospitalized cases.. The installation of these

systems, at municipal level varied from 20.6% to 96.3% of coverage with a median value of 68.5%,

so there are still many municipalities that lack basic services.

The zone where the municipality was located was one of the principal indicators affecting the IHC of

NCC and epilepsy. Municipalities located in temperate zones (highlands) had a significantly higher

number of hospitalized NCC cases. From the BMA procedure, in the case of epilepsy, the posterior

effect had a small probability (11.8%), so we argue that in tropical zones lack of appropriate

diagnostic tools and specialized knowledge of health staff might make it difficult to properly identify


84

NCC cases [263]. Likewise, the levels of coverage of basic services is lower in tropical zones of

Ecuador [147]. Thus, the presence of the life cycle of T. solium in these zones traditionally considered

to be NCC free cannot be ruled out.

A limitation of this study was that peri-urban zones where poverty belts of cities are frequently

located could not be analyzed separately given that records do not use this residence category for

patients. The conditions in peripheral zones can differ from city to city, thus the assumption that the

origin of the hospitalized cases in big cities come from peripheral zones should not be extrapolated in

all cases. As in other studies based on hospital data, rural communities might not be appropriately

represented in the sample. This could be a major limitation of our study, and also because of the

asymptomatic human cysticercosis cases, migraine-type and chronic headaches [54;261;267].

However, due to the fact that ambulatory cases do not offer reliable data, hospital data is a better

attempt to represent the situation of the disease in a municipality.. Another limitation ins this study

might be the presence of duplicated cases in the data base. These cases might be due to the fact that a

patient was hospitalized more than once, or because some NCC cases were diagnosed as epilepsy

before. But given the mentioned limitations, the present results are still reliable due to their apparent

representation of the municipalities in Ecuador, and because they are based on the appropriate

statistical tools. So given the data constraints, the methods used to identify risk indicators and/or areas

based on available data presents valuable results for veterinary and public health sectors at no cost.

There is a need to re-evaluate the current situation for both disorders throughout the country as life

conditions have been changing over time [243;247;277]. Given the recent changes in the organization

of the public health sector, new trends need enough data collection-time to be evaluated again.

In conclusion, NCC might still have a relevant presence in Ecuador and might play an important role

as a cause of acquired epilepsy in Ecuador [160]. Although the real burden of NCC is still unknown,

we found that the hospitalization rate of patients with epilepsy has been increasing in recent years

(Figure 3-4). Traditional NCC and epileptic endemic zones were recognized as high risk zones even

though more recent clusters of both diseases seem to have appeared. Although the lack quality of

basic services was related to the IHC in both disorders, one important finding of this study was that

the implementation of systems for eliminating excrements helped to reduce the incidence of

hospitalized cases of both epilepsy and NCC, which could be used as an indicator strategy for

planning control programs. More specific studies linking human NCC with epilepsy and their

respective factors in field conditions are needed to evaluate the prevalence of the disease in humans

throughout the country and generate data that could be used for estimation of the burden disease.

Chapter 4 4 Serological dynamics of cysticercosis in an endemic area in Ecuador.

Adapted from:

Marco Coral-Almeida, Richar Rodríguez-Hidalgo, Maritza Celi-Erazo, Héctor Hugo García, Silvia Rodríguez, Brecht Devleesschauwer, Washington Benítez-Ortiz, Pierre Dorny, Nicolas Praet. Incidence of Human Taenia solium Larval Infections in an Ecuadorian Endemic Area: Implications for Disease Burden Assessment and Control. PLoS Negl Trop Dis 2014 May;8(5):e2887.

Serological dynamics of cysticercosis in an endemic area in Ecuador.

86

4.1 Chapter summary

While human cysticercosis (HCC) prevalence data become available worldwide, incidence rate and

cumulative incidence figures are lacking, which limits the understanding of the Taenia solium

epidemiology. The present chapter describes the dynamic nature of human Taenia solium larval

infections in an Ecuadorian endemic community. In this study it is reported for the first time incidence

rate and cumulative incidence figures of human T. solium larval infections in Latin America. The

simultaneous use of antibody and antigen serological detections allowed estimating both parasite

exposure and infection rates, respectively. A sero-epidemiological cohort study was conducted in a

south-Ecuadorian community to estimate the incidence rate of infection with and the incidence rate of

exposure to T. solium based on antigen and antibody detections, respectively. The incidence rate of

infection was 333.6 per 100,000 person-years (95% CI: [8.4-1,858] per 100,000 person-years)

contrasting with a higher incidence rate of exposure 13,370 per 100,000 person-years (95% CI:

[8,730-19,591] per 100,000 person-years). The proportion of infected individuals remained low and

stable during the whole study year while more than 25% of the population showed at least one

antibody seroconversion/seroreversion during the same time period. While about 13% of the

inhabitants were exposed to T. solium eggs, less than 1% of the population became yearly infected

with the parasite. This contrast between exposure and infection may be linked to an effective

resistance to the parasite acquired through long-term exposure of the population and differs from the

African situation, where much higher levels of infection have been observed. These estimates are of

high importance to understand the epidemiology of T. solium in order to develop ad hoc cost-effective

prevention and control programs. They are also essential to assess the burden of T. solium

cysticercosis since longitudinal data are needed to make regional and global projections of morbidity

and mortality related to cysticercosis. The estimates generated here may now be incorporated in

epidemiological models to simulate the temporal transmission of the parasite and the effects of control

interventions on its life cycle.


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4.2 Introduction

“Art is not a handicraft, it is the transmission of feeling the artist has experienced.”

― Leo Tolstoy

In Latin America human cysticercosis has been reported in at least 18 countries and is considered a

major public health problem, especially in poor rural areas [6;119]. The Andean region of Ecuador

and neighboring countries is hyper-endemic for cysticercosis [15]. While reliable prevalence data

become available worldwide, they may considerably vary depending on the diagnostic test used

[72;81;113]. Serological antigen and antibody detections are valuable tools when conducting

epidemiological studies, since they inform on infection with and exposure to the parasite,

respectively. Taking the latter distinction into account, studies conducted in Ecuadorian endemic rural

communities have shown an exposure to the parasite ranging from 25 to 40% and a proportion of

infected individuals ranging from 2.25 to 4.99% [16;131;153]. However, prevalence figures do not

inform on the evolution of the number of positive cases over time and estimates for human

cysticercosis incidence rate and cumulative incidence are lacking, which limits the understanding of

the transmission dynamics of T. solium and does not allow a precise estimation of its disease burden.

García et al. (2001) [73] conducted longitudinal studies in endemic areas of Peru and Colombia and

demonstrated the presence of transient antibody responses suggesting a high number of antibody

seroconverted cases per year ranging from 8 to 25% of the population depending on the studied area.

Through rule-based modeling, Praet et al. (2010) [16] simulated the annual antibody seroconversion

rate in an endemic area of Ecuador. They estimated an annual incidence rate of exposure of people

becoming seropositive of 14 per 100 person-years. On the other hand, studies estimating both

incidence rate of infection and cumulative incidence are scarce [16;73;209]. Mwape et al. (2013)

[136] reported an incidence rate of infection of 6,300 per 100,000 person-years in a rural community

of eastern Zambia. Such estimates for Latin America are inexistent. For this reason, the present study

aims at estimating the cumulative incidence and the incidence rate of human CC in an endemic area of

Ecuador. A sero-epidemiological cohort study was conducted to investigate the transmission

dynamics of T. solium among individuals living in a southern Ecuadorian rural community. This

paper reports estimates of the incidence rates, cumulative incidences of active infection and exposure

rates to T. solium and discusses the implications for the disease burden assessment and control.

4.3 Materials and methods

4.3.1 Ethical clearance

The protocol used in this study was approved by the Ethical Committee of the Central University of

Ecuador (IRB 00002438) and by the Ethical Committee of The University Hospital of Antwerp,


88

Belgium. Written informed consent was obtained from each individual willing to participate in the

study. For participants aged less than 18 years old written informed consent was also obtained from a

parent or a legal adult representative. Individuals testing positive for T. solium cysticercosis antigens

were referred to the local health center for follow-up.

4.3.2 Study area, population and design

The study was conducted in the rural parish of Sabanilla (4º 12´ S, 80º 8´ W) belonging to the Celica

canton in the Southern Ecuadorian province of Loja. The parish has 1145 inhabitants; most of them

are farmers involved in activities related to agriculture and animal husbandry. The climate is semi-

arid, and the altitude is 700 meters above sea level. The region is endemic for T. solium cysticercosis

and presents the risk factors for the transmission of the parasite [153;278]. A sero-epidemiological

community-based cohort study was performed. Three blood sampling rounds were organized in

Sabanilla in a period of 13 months: the first sampling round took place in June 2009 (SR1), the second

in November 2009 (SR2) and the third one in July 2010 (SR3). Based on the three sampling rounds,

three periods of time were defined as follows: a six-month period from June 2009 to November 2009

(P1), a seven-month period from November 2009 to July 2010 (P2), and a total 13-month period from

June 2009 to July 2010 (P3).

First, an informative meeting inviting the population to participate took place at the beginning of the

study in collaboration with the local authorities. Then, a census of the population was conducted

based on a door-to-door survey, including collection of information on age and sex of the inhabitants.

After informed consent, all individuals older than one year willing to participate and present at the

time were blood sampled.

4.3.3 Samples collection and analyses

At each sampling round, 10 ml of blood was collected in dry tubes. After coagulation and

centrifugation, serum was collected and stored at -20°C until analysis. Two serological diagnostic

tests were performed. (1) The Enzyme Linked Immunosorbent Assay for the detection of circulating

antigens of the metacestode of T. solium (Ag-ELISA) [84;93;133]. The sensitivity and specificity of

the Ag-ELISA for detecting active infection in humans are 90% (95% CI: [80-99%]) and 98% (95%

CI: [97-99%]), respectively. No cross-reaction with other parasites has been reported [72;84]. (2) The

Enzyme-Linked Immunoelectrotransfer Blot (EITB) for the detection of antibodies directed against

seven specific T. solium metacestode glycoproteins [80]. The sensitivity and specificity of the EITB

for detecting exposure to the parasite range from 97% to 98% and from 97% to 100%, respectively

[72;80].


89

4.3.4 Antigen and antibody seroprevalence

The antigen and antibody seroprevalence (Ag and Ab seroprevalence), as based on the results of the

Ag-ELISA and of the EITB, respectively, were calculated for each sampling round for the whole

population and by sex.

A multinomial Bayesian model adapted from Berkvens et al. (2006) [279] was used to estimate the

true prevalence of T. solium larval infections for each sampling round based on the antigen

seroprevalence data and on prior information on the test characteristics (sensitivity and specificity of

the Ag-ELISA). Prior information was extracted from the available literature [72]. A uniform

distribution with lower and upper limits of 0.80 and 1.00, and 0.97 and 1.00 were used to constrain the

sensitivity and the specificity of the test, respectively. The analysis was conducted in WinBUGS and

R [280;281]. Three chains, 20,000 iterations, following a burn-in of 5,000 were used to assess the

convergence of the results. Criteria assessing the fit between prior information and the seroprevalence

data were evaluated, i.e. the Bayesian p-value (Bayesp), the Deviance Information Criterion (DIC)

and the number of parameter effectively estimated by the model (pD) [279;281].

4.3.5 Seroconversion, seroreversion and incidence rate

First, proportion of change to antigen seropositivity/seronegativity (change to Ag

seropositivity/seronegativity) and proportion of antibody seroconversion and seroreversion (Ab

seroconversion and seroreversion) were calculated to characterize the transmission dynamics of the

disease.

Seroconversion is defined as the change from a negative to a positive serological test result between 2

sampling rounds; the opposite is defined as seroreversion [282]. The proportion of Ab seroconversion

and the proportion of change to Ag seropositivity reflect the cumulative incidence for a defined time

period. They were calculated by dividing the number of new cases by the number of susceptible

individuals (having a negative test result at the previous sampling round) during a given time. The

proportion of Ab seroreversion and the proportion of change to Ag seronegativity were calculated by

dividing the number of positive tests that turned negative by the number of positive tests at the

previous sampling round.

The incidence rate of infection with the larval stage of T. solium and the incidence rate of exposure to

T. solium eggs were also calculated based on the results of the antigen and antibody detection tests,

respectively.

The incidence rate was calculated as the number of new (change from seronegativity to seropositivity)

cases in a defined time period divided by the number of person-time units at risk during the time-

period. Yearly incidence rates were multiplied by 100,000 to be expressed by 100,000 person-years


90

[283;284]. The person-time unit represents one person for a defined period of time. The latter was

calculated as described in Ngowi et al. (2008) assuming that the infection occurs uniformly over time

and considering halfway the period between two sampling rounds [208]. For example, if a person is

followed up for six months and does not seroconvert during this time, this person will contribute 0.5

person-year to the person-time at risk. If a person that is followed up for the same period but

seroconverts during that period, this person will contribute 0.25 person-year to the person-time at risk.

Yearly incidence rates were calculated based on this calculation method . Ninety-five % exact Poisson

confidence intervals were calculated using the epitools package in R for all incidence rates [285].

4.3.6 Data management and statistical analyses

Data were entered in Excel 2010 (Microsoft Office 2010). Statistical analyses were performed in Stata

(Stata Corp., College Station, TX) and in R:[213]

Fisher exact test was used to compare (1) Ag/Ab seroprevalence between sex within each sampling

round and (2) Ag seroprevalence with Ab seroprevalence within each sampling rounds. Also,

McNemar test was performed to compare the sero-Ag and sero-Ab prevalence between rounds.

Multivariateble logistic regression analysis was used to study the association between sero-Ag/Ab

prevalence and age and sex, and this for the three samplings rounds. The significance level was set at

0.05.Fisher exact test was used to compare (1) the proportion of Ab seroconversion with the

proportion of antibody seroreversion and the proportion of change to Ag seropositivity with the

proportion of change to Ag seronegativity within periods, (2) the proportions of Ab

seroconversion/seroreversion and the proportions of Ag change to seropositivity/seronegativity

between sexes, (3) the proportions of Ab seroconversion/seroreversion and the proportions of change

to Ag seropositivity/seronegativity between periods.

In addition, a change point analysis was used to compare the proportion of Ab seroconversion with

the proportion of Ab seroreversion in function of age. The change point analysis classifies the

population into 2 age groups at different age points (10, 20, 30, 40, 50, 60, 70, 80 years old). The

Fisher exact test was then used on both age groups in order to identify any change of significance

when comparing the proportions of Ab seroconversion and seroreversion [16;136;286]. The

significance level was set at 0.05 for all statistical analyses.

4.4 Results

A total of 967 (84.45%) individuals from the 1145 inhabitants listed in the census participated in the

study. Depending on the willingness of the individuals to participate, their presence at the time of

sampling and on the quantity of serum available, EITB was performed on 743 (64.9%), 538 (47%)

and 518 (45.2%) sera for June, November and July, respectively. Ag-ELISA was performed on 744


91

(65%), 538 (47%) and 514 (44.9%) sera for the same time periods. Figure 4-1 describes in detail sera

availability and individual participation during the three sampling rounds.

Figure 4-1. Sera availability and individual participation during the three sampling rounds. (Format adapted from Mwape et al., 2013[136] ). S1, S2 and S3 stand for first, second and third sampling rounds, Ag-ELISA: Enzyme Linked ImmunosSorbent Assay for the detection of circulating antigens of the metacestode of T. solium, EITB: Enzyme-Linked Immunoelectrotransfer Blot for the detection of antibodies directed against seven specific T. solium metacestode glycoproteins.

4.4.1 Antigen and antibody seroprevalence

The Ag and Ab seroprevalence for each sampling round for the whole population and by sex are

presented in Table 4-1. The prevalence adjusted for misclassification error of T. solium larval

infections was 0.7% (95% Credibility Interval (CI): [0.03-1.75]), 0.7% (95% CI: [0.03-2.00]) and

1.1% (95% CI: [0.05-2.84]) for SR1, SR2 and SR3, respectively. All except one Ag positive

individuals were also Ab positive in the 3 sampling rounds. Fisher exact test did not reveal any

significant difference of Ag and Ab seroprevalence between sexes, McNemar test did not reveal any

significant difference of Ag and Ab seroprevalence between rounds. Ab seroprevalence was

significantly higher than Ag seroprevalence within each sampling round. Multivariate logistic

regression analysis showed a significant positive correlation between Ab seroprevalence and age.


92

Table 4-1. Antigen and antibody seroprevalence figures (as based on the results of the Ag-ELISA and the EITB, respectively) by sex and by sampling round.

Seroprevalence Sampling

round Sex

Number of positive cases/Total number of

individuals

Percentage of

positive cases

[95%CI]a

Antigen SR 1b Female 2/367 0.5 [0.1-2]

Male 5/377 1.3 [0.4-3.1]

Total 7/744 0.9 [0.4-1.9]

SR 2c Female 1/293 0.3 [0-1.9]

Male 4/245 1.6 [0.4-4.1]

Total 5/538 0.9 [0.3-2.2]

SR 3d Female 3/265 1.1 [0.2-3.3]

Male 5/249 2 [0.7-4.6]

Total 8/518 1.5 [0.7-3]

Antibody SR 1b Female 124/364 34.1 [29.2-39.2]

Male 108/379 28.5 [24-33.3]

Total 232/743 31.2 [27.9-34.7]

SR 2c Female 100/293 34.1 [28.7-39.9]

Male 83/245 33.9 [28-40.2]

Total 183/538 34 [30-38.2]

SR 3d Female 80/270 29.6 [24.2-35.5]

Male 77/248 31 [25.3-37.2]

Total 157/518 30.3 [26.4-34.5]

aCI= Binomial exact 95% Confidence Intervals; SR=sampling round; bSR 1= June 2009 sampling, cSR 2= November 2009 Sampling; dSR 3= July 2010 Sampling

.

Table 4-2 shows the proportions of antigen and antibody seropositive and/or seronegative individuals

who participated in all 3 sampling rounds and whose sera were available for both tests (n = 277). Only

one individual changed to antigen seropositivity status throughout the entire study period. Eighteen

percent of this restricted population remained antibody positive throughout the entire study period

while about 20% of the individuals showed at least 1 change of antibody positivity status.


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Table 4-2. Proportions of antigen and antibody positive and/or negative individuals who participated in the 3 sampling rounds.

Test result per sampling round

Number of individuals (antibody detection)

Percentage of individuals (antibody detection; [95%CI]a)

Number of individuals

(antigen detection)

Percentage of individuals (antigen detection;

[95%CI]a)

SR 1b SR 2c SR 3d - - - 169 61 [54.99-66.7] 276 99.63 [98-99.99] - - + 9 3.24 [1.49-0.6] 1 0.36 [0.01-1.99]

- + - 8 2.89 [1.25-5.61] 0 …

- + + 9 3.24 [1.49-6.07] 0 …

+ - - 13 4.69 [2.52-7.89] 0 …

+ - + 4 1.44 [0.36-3.66] 0 …

+ + - 14 5.05 [2.79-8.33] 0 …

+ + + 51 18.4 [14.02-23.49] 0 … Total 277 277

aCI= Binomial exact 95% Confidence Intervals; SR=sampling round; bSR 1= June 2009 sampling, cSR 2= November 2009 Sampling; dSR 3= July 2010 Sampling.

4.4.2 Seroconversion, seroreversion and incidence rate

The overall incidence rate of human T. solium larval infection based on -antigen detection was 333.6

per 100,000 person-years (95% exact Poisson CI: [8.4-1,858] per 100,000 person-years). The overall

incidence rate of exposure to T. solium based on antibody detection was 13,370 per 100,000 person-

years (95% exact Poisson CI: [8,730-19,591] per 100,000 person-years). Ag proportion of changes to

seropositivity/seronegativity and proportion of Ab seroconversion/seroreversion by period are

represented in Table 4-3. Incidence rates estimates for individuals who participated in at least two of

the sampling rounds are given in Table 4-4.

Table 4-3. Antigen change to seropositivity/seronegativity test result, Antibody seroconversions/seroreversion figures (as based on the results of Ag-ELISA and EITB respectively) by period.

Test Period Parameter

Number of individuals

Percentage of individuals ( [95%CI]a)

Antigen P1c Change to seropositivity for 6 months 0/421 0 [0-0.9]b Change to seronegativity for 6 months 0/3 0 [0-70.8]b

P2d Change to seropositivity for 7 months 1/317 0.3 [0-1.7] Change to seronegativity for 7 months 0/1 0 [0- 97.5]b

P3e Change to seropositivity for 13 months 2/373 0.5 [0.1-1.9] Change to seronegativity for 13 months 1/1 1 [2.5- 100]b Antibody P1c Seroconversions 26/288 9 [6-12.9] Seroreversions 25/135 18.5 [12.4-26.1] P2d Seroconversions 17/226 7.5 [4.4-11.8] Seroreversions 26/101 25.7 [17.6-35.4] P3e Seroconversions 24/264 9.1 [5.9-13.2] Seroreversions 34/120 28.3 [20.5-37.3]

aCI= Binomial exact 95% Confidence Intervals;b =one-sided, 97.5% confidence interval; cP1=June-November period; dP2=November-July period; eP3=June-July period.


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Table 4-4. Yearly incidence rates for infection and exposure (as based on the results of Ag-ELISA and EITB,respectively) of individuals who participated in two sampling rounds by period.

Test Period between

samplings Number of individuals

Yearly incidence rate ( [95% Poisson CI]a) per 100,000

person-years Antigen P1c (6 months) 0/421 0[0-1790.7]

P2d (7 months) 1/317 541.6[13.7-3018] P3e (13 months) 2/373 496.3 [60.1-1792.7]

Antibody P1c (6 months) 26/288 18,909.1[12,352-27,706.2] P2d (7 months) 17/226 13,399[7,805.4-21,453.1] P3e (13 months) 24/264 8,791.2[5,632.7-13,080.6]

aCI= Poisson exact 95% Confidence Intervals; bP1=June-November period; cP2=November-July period; dP3=June-July period.

Fisher exact test did not show any difference of proportion of Ab seroconversion/seroreversion and

proportions of change to Ag seropositivity/seronegativity between sexes, nor between periods.

Proportion of Ab seroreversion was significantly higher than proportion of Ab seroconversion for

each period (Figure 4-2). The change point analysis showed that the proportion of Ab seroreversion

was significantly higher than proportion of Ab seroconversion until the age of 30 years. After this

change point, the difference was not significant (Figure 4-3).

Figure 4-2. Proportions of Ab seroconversion and seroreversion by time period

Legend: white bars represent proportions of Ab seroconversion whereas grey bars represent proportions of Ab seroreversion; vertical error bars represent the upper and lower limits for the 95% binomial exact confidence interval; Period 1 stands for the period between Sampling round 1 and sampling round 2 (June-November 2009); Period 2 stands for the period between sampling round 2


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and sampling round 3 (November 2009-July 2010) and Period 3 stands for the period between sampling round 1 and sampling round 3 (June 2009-July 2010).

Figure 4-3. Results of the change point analysis with a change point at 30 years old

Legend: The vertical dotted/lined line represents the change point at 30 years old; white bars represent proportions of Ab seroconversion whereas grey bars represent proportions of Ab seroreversion; vertical error bars represent the upper and lower limits for the 95% binomial exact confidence interval.

4.5 Discussion

This is the first study reporting cumulative incidence and incidence rate figures of human T. solium

larval infection in Latin America. The overall incidence rate of infection in the endemic rural

community of Sabanilla, was 333.6 per 100,000 person-years (95% exact Poisson CI: [8.4-1,858] per

100,000 person-years), which suggests that less than 1% of the population becomes infected yearly

with the parasite. In contrast, the incidence rate of exposure to T. solium is much higher: about 14 %

of the population has a yearly contact with the parasite. The latter estimates are in line with observed

and simulated antibody seroconversion rates ranging from 8 to 25% in Peru, Colombia and Ecuador

[16;73]. Proportions of change to Ag seropositivity/seronegativity and Ab seroconversion and

seroreversion were identical in males and females indicating that both genders get equally infected

with cysticercosis and are equally exposed to the parasite. Moreover, these proportions did not

significantly vary in time (one year period). On the other hand, proportion of Ab seroreversion was

significantly higher than proportion of seroconversion Ab for each period and a change point analysis


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showed that proportion of Ab seroreversion was significantly higher than proportion of Ab

seroconversion until the age of 30 years. After this change point, the difference was not significant.

These results corroborate the findings of Praet et al. (2010) [16] suggesting a higher proportion of

seroreversion before the age of 40 years due to a higher number of primary immune responses before

this age. In other words, individuals will serorevert more rapidly before the age of 30-40 years

because primary humoral response is shorter and weaker than secondary response. Thus, the

proportion of seroreversions depends on the immunological status of the individuals.

The dynamics of infection and exposure in the population, represented by the proportions of antigen

and antibody results from the individuals who participated in all 3 sampling rounds, showed that the

proportion of infected individuals remains low and stable during the whole study year, while the

proportion of exposed individuals is remarkably higher. Of note is the high level of serological status

variation with more than 20% of the population showing at least one antibody

seroconversion/seroreversion during the year. Together with the prevalence estimates presented by

period, these longitudinal data corroborates the findings of other studies conducted in Latin America

highlighting a high prevalence of exposure to the parasite but a low prevalence of active infections.

This contrast between exposure and infection may be linked to an effective resistance to the parasite

acquired through long-term exposure of the population. In addition, these results confirm the

occurrence of transient antibody responses in individuals living in T. solium endemic areas and

suggest exposure to the parasite without infection or mild infections that are aborted by the natural

immunity of the individual [136]. Mwape et al. (2013) [136] conducted a similar community-based

longitudinal study in the Eastern Province of Zambia. While a much higher incidence rate was

observed in the African endemic area, similar higher proportion of Ab seroreversion than Ab

seroconversion and the presence of transient antibody responses were described. Further studies are

needed to unravel the difference of parasite transmission patterns in different epidemiological settings.

Specifically, research should focus on identifying the causes for differences in infection levels. In this

context, the identification of tapeworm carriers in a community should be based on improved

methods, because sensitivity and specificity of conventional coprological methods are low [108].

Our study has limitations that are mainly due to the inhabitant proportion of participation. Although

967 individuals from a total of 1045 inhabitants provided at least one blood sample, 396 provided

only one sample and another 283 provided two blood samples. Compliance in participating in all 3

sampling rounds was of 288 volunteers despite extensive information sessions prior to the sampling

procedure. The main reason for irregular participation was the absence of the individuals for

professional duties. Reduced participation can have an impact on the precision of the estimation of the

incidence rate, however, the participation on the three sampling rounds is still representative of the

total population and all the participants selected for the incidence rate estimation match all the


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selection criteria for this calculation (n=288 (27.6% (95% CI: [24.9-30.4]))). Another limitation of the

study is the limited number of samplings and the relatively long sampling intervals depending on

logistic, economic and ethical constraints. In other words, much more information could have been

produced if more sampling had been organized at shorter time intervals, i.e. the positivity status of the

participants would have been more accurately monitored over time. The incidence rate estimation for

both infection and exposure is likely to be lower with increasing intervals between samplings: a

proportion of the new infections may be undetected and the time of occurrence of a new infection

overestimated. A quicker detection of new infections will result in a decrease of the number of

person-years at risk and consequently in higher estimates of the incidence rate. Finally, even though

the tests used in this study have shown high sensitivity and specificity, false positive and negative

individuals may bias the prevalence and the incidence rate estimates. Bayesian estimation of infection

with T. solium larva prevalence has been used to estimate the true prevalence of infection with an

exposure to T. solium. The Bayesian estimation corrects the apparent prevalence at, but does not allow

to know the true infection status at the individual level. Consequently, it does not allow to estimating

the true incidence rate.

In conclusion, the present study underlines the importance of conducting longitudinal serological

follow-up allowing generating incidence rather than prevalence data to fully understand the

transmission dynamics of the infection and to avoid under/overestimation of the occurrence of the

parasite. Similar cohort studies assessing the effect of risk factors such as development of immunity

and behavioral factors should be conducted to identify all the parameters that may influence parasite

transmission. Understanding the transmission dynamics of T. solium is essential to develop ad hoc

cost-effective prevention and control programs. The estimates generated here may now be

incorporated in epidemiological models to simulate the temporal transmission of the parasite and the

effects of control interventions on its life cycle [209]. These estimates are also of high importance to

assess the burden of T. solium cysticercosis since incidence data are needed to make regional and

global projections of morbidity and mortality related to cysticercosis. To this end, the link between the

incidence rate of infection and health outcomes related to human cysticercosis, such as epilepsy and

chronic headache, as well as the case-fatality ratio still need to be estimated.

Chapter 5 5 Towards prioritization of intervention areas of Taenia solium taeniasis/cysticercosis

in Ecuador.

Towards prioritization of intervention areas of Taenia solium taeniasis/cysticercosis in Ecuador.

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“We may brave human laws, but we cannot resist natural ones.”

― Jules Verne

5.1 Introduction

The main objective of this dissertation was to better understand the epidemiological patterns that

affect the exposure to and infection with T. solium in endemic areas, with special reference to

Ecuador, in order to provide significant information that would assist in the formulation of appropriate

control strategies.

In this chapter, the findings of this thesis will be discussed in a broader context and the limitations of

the studies will be explored to give recommendations and conclusions from the knowledge acquired.

5.2 Characterizing Taenia solium human cysticercosis transmission in endemic areas.

Sero-epidemiological data from endemic communities show a high variability between and within

regions. In endemic areas the epidemiological situation can be categorized in: (1) areas where high

exposure and high numbers of active infections predominate; (2) areas with high exposure but rather

low numbers of active infections; (3) areas with low exposure and low numbers of active infections.

From the systematic review on epidemiological studies it appeared that the category 1 situation was

significantly more prevalent in Africa than in Asia and Latin America. For instance, in Ecuadorian

rural communities, seroprevalence of antibodies measured by EITB was very high, indicating high

exposure to T. solium eggs, while the proportion of active cysticercosis cases in the population,

measured by Ag-ELISA was low (category 2). In some African countries, like Zambia, the proportion

of both EITB and Ag-ELISA was high (category 1). The reasons for these marked differences are not

clear but are probably multifactorial, as discussed in chapter 4. It is evident that the causes of these

epidemiological variations must be better understood before implementing interventions. The study of

risk factors can greatly contribute to a better understanding of the local transmission factors. Indeed,

different climatic, economic and socio-cultural conditions in endemic communities can significantly

affect transmission. However, one must be cautious when interpreting data from risk factor studies.

Sometimes, expected risk factors in endemic areas are not significant because they are masked by

other factors. For example, latrine use has been found to be a risk factor for both PCC and HCC while

in other studies it was identified as a protective factor [179;217;220;287]. These contradictory

findings are probably related to the proper use and maintenance of such facilities, cultural taboos or

the effect of environmental contamination. Additionally, in some studies the latrine use has not been

found to be a significant risk factor due to the fact that most of the households did not have latrines;

also, some households in rural settings often share their latrines with neighbors and other villagers,


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therefore the relationship between latrine use and HCC cannot be determined [139;197;227;287-289].

Studies on exposure and infection heavily rely on serology and the performances of serological

methods and on the way the results are interpreted have been contested [102]. However, in this thesis

we only selected and used serological tests that have shown to be most reliable, such as the EITB and

B158/B60 ELISA for measuring specific antibodies and circulating antigens, respectively.

The variability within each region and country should be better represented. The use of maps

extrapolating the situation of HCC (e.g. the WHO world map of cysticercosis, page 20) from one area

to the whole country might hide important elements that could wrongly influence decision takers,

policy makers and the public in general. For example, in some countries there are areas where active

transmission occurs but also areas in which transmission of T. solium is rare due to religious beliefs

and the subsequent feeding habits (e.g. Burkina Faso that is considered endemic on the WHO map). In

Ecuador we used hospital records to identify areas with higher numbers of HCC and these appeared to

be unevenly distributed in the country. Thus, a global or regional characterization of an endemic area

is likely to be inaccurate, the term “endemic area for cysticercosis” should be updated and the

characteristics of the area should be taken into account for a better classification.

A more accurate classification would discriminate highly endemic countries from countries where the

disease is present but only in specific locations. To properly do so, it would be recommended to

categorize each country depending on the geographical distribution, number and level of prevalence

of HCC of affected areas within each country. A first attempt to provide a more detailed description

of the situation of cysticercosis in Africa was published by Braae et al. (2015) [290]; In their work,

the authors presented maps in which the districts where the presence of T. solium is recorded are

highlighted over the countries in which T. solium is considered as present based on literature or by

reports from the OIE. Also they presented maps in which the approximate simple size and the

prevalence of taeniasis and porcine cysticercosis are represented graphically and located

geographically accordingly. Burden estimations and global projections of the prevalence of HCC

would greatly benefit from this approach, avoiding overestimations.

Global estimates available for HCC seem to be affected by the large variability in the epidemiological

data; indeed, depending on the source and the method, the local, regional and global projections for

HCC seem to differ widely [41;42;44;50;51;138;291]. Future estimations should analyze more in

detail the impact of this variability before making extrapolations of particular situations and correct

accordingly in the calculations for better estimates with the appropriate methodology.

The characterization of endemic areas is challenged by different problems. There is a general lack of

data. Official country reports rely on hospital-based symptomatic cases that are just the pinnacle of a

bigger problem [36;115]. The more reliable data relies on epidemiological studies in the field.


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However, it has to be taken into account that: 1) The diagnostic arsenal available for human T. solium

infections is limited as a result of the cost, availability, acceptance of communities to participate, low

sensitivity and specificity, especially for tapeworm carrier detection, although new promising tools

are being developed [110;111;113;114]; 2) diagnosis of PCC is difficult because of imperfect

diagnostic methods and because many slaughtered pigs are escaping meat inspection [75;81;92;93]; 3)

different study designs and diagnostic tools used do not allow accurate comparisons of results; 4)

there is almost no knowledge on the environmental component, though new evidence highlights the

importance of the environment in the transmission of T. solium infections [178].

To overcome these difficulties, we suggest to: 1) develop a standard protocol for epidemiological

field-studies. This protocol should recommend the use of validated serological tests and

questionnaires for identifying key risk factors; 2) develop cheap, sensitive and specific tests to detect

taeniasis and PCC and include these in the previously suggested protocol; 3) use sentinel pigs to better

characterize transmission [104;105;178]; 4) promote research to understand the influence of

environment in the transmission of HCC and PCC; 5) declare HCC and PCC reportable diseases

worldwide [41]. In order to develop an efficient protocol for epidemiological field-studies, it would be

recommended to incorporate elements from other protocols already standardized that have been used

for other helminths such as Schistosoma spp. and soil transmitted helminths. These protocols have

been used to determine the prevalence of the infections and additionally helped to select the type of

MDA to be applied, identifying the target population and the frequency of interventions [292].

5.3 Identifying priority areas of intervention within a country with special attention to

Ecuador.

The identification of priority areas is important for focal interventions. HCC is a “clustered disease”

and this means that interventions should focus on priority areas. In the epidemiological studies

performed in Ecuador, high estimates of exposure to the parasite and non-negligible levels of active

infections were found. However, these studies alone are not sufficient to represent the situation of the

whole country, neither to identify all the priority areas for intervention. Official data in Ecuador

reports the incidence of hospitalized cases of NCC as well as for other neurological disorders such as

epilepsy, which are strong predictors of NCC in endemic areas [261]. These data are represented

geographically by the municipality of residence of the patient and are available for each individual

year. Additionally, data on different socio-economic and landscape variables are also available at

municipality level and per year. Analyzing these data together allowed us: 1) to identify priority areas

for intervention in space and time and 2) to fine-tune the knowledge about these areas.


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Traditional and new clusters were identified, as well as urban and rural clusters. These findings

showed that despite the apparent decreasing trend of NCC cases [150;151], the disease is still present

and is extending geographically. These clusters are priority areas of intervention. It is plausible that

the presence of urban cases of NCC is the result of the import of tapeworm carriers from rural

settings, highlighting the importance of the rural to urban migration in the transmission of NCC

[273;293]. The problem of this event is that it becomes more difficult to detect and treat a tapeworm

carrier in an urban setting. Studies conducted in urban settings in Ecuador failed to detect tapeworm

carriers among NCC symptomatic patients, suggesting that most infections were acquired by contact

with other individuals or by a contaminated environment [154]. In the cities, mobility is high and

usually the distances between the workplace, house, markets and eating places are not comparable to

the ones found in rural settings; also, public transportation and crowding in public places increases the

contact with tapeworm carriers. The tapeworm can survive for several years and spread the disease

when the tapeworm carrier remains untreated. All these elements added to the high cost of conducting

a massive survey to detect specific antibodies in a city, makes that identifying “hot spots” in urban

centers is complicated. Also, in Ecuador, both T. saginata and T. solium have been reported and these

species cannot be differentiated by routine diagnostic tools [131]. In any case, identification of a

tapeworm carrier in urban centers should be done when a NCC case is suspected. In those cases

tapeworm diagnosis should be directed in the first place to the people surrounding the NCC patient

such as his/her family living in the same house and house workers. In addition, when taeniasis is

accidentally detected by a routine coprological examination, differentiation of the species should be

requested and if T. solium is detected, people surrounding the tapeworm carrier should be examined

for HCC.

Despite the many different causes of epilepsy [262], indicators of hospitalized cases for both NCC

and epilepsy were similar, highlighting the relationship of these two conditions and indicating the

priority factors that should be tackled or enforced to prevent these negative health outcomes. For

example, one indicator for the increase of both epilepsy and NCC hospitalized cases was the lack of

services for elimination of excrements. However, even if NCC is not the only fecal related cause of

epilepsy, this suggest that controlling T. solium and other fecal related conditions through the

improvement of these services is possible [294].

The presence of these clusters fall into the definition of “ T. solium infection focus” for intervention

purposes [261], indeed, some authors consider that the more appropriate term to be used for the

control of T. solium should be “control of taeniasis/neurocysticercosis (T/NCC)” instead of the

commonly used “control of taeniasis/cysticercosis (T/CC)” based on the fact that the clinical features

that justify the control of T. solium are the ones involving neurological disorders [294]. However,

neurological disorders derived from NCC are only the “tip of the iceberg” [36], many asymptomatic


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cases are not diagnosed until appearance of clinical evidence of NCC; also, the results of any control

strategy on NCC will be observed in long-term due to the long period between the infection and

development of clinical signs.

Thus, identifying and characterizing NCC clusters is a valid and powerful methodology to identify

and characterize priority areas of intervention, but it should be complemented with the analysis of

data from other areas where no NCC cases are reported but where risk factors such as, the lack of

hygienic services, presence of PCC and/or free roaming pigs, among others, are present. Also, it has

to be taken into account that the efficacy of the use of IHC to detect priority areas depends on the

quality of data.

5.4 Considerations when designing control strategies

HCC was previously declared as potentially eradicable, however, despite the apparent feasibility, this

statement has changed over the years. To date, elimination was achieved only focally in Peru as a

result of an intensive integrated program.. Other strategies applied in field trials and pilot projects do

not provide enough scientific material to suggest that the disease can be eradicated in the foreseeable

future, but suggest that control is feasible at a large scale [14;198;295]. Mixed results observed on the

different strategies applied to control T. solium in different settings are probably derived from the

variability in the factors affecting the transmission dynamics in every area [296]. Every control

strategy aims to attack a certain point in the life cycle of T. solium in order to interrupt it, but the

feasibility of these interventions or the impact that the strategy would have in the complete life cycle

depend of the situation in every setting.

To implement a national control program for T. solium, the first step should be the identification of

priority areas of intervention. Active and passive surveillance can provide most of the necessary

indicators to identify priority areas. Passive surveillance would provide the first approach to identify

the most critical areas to intervene at national level. For this, passive surveillance would be done at

ministerial levels by both the ministry of public health and the ministry of agriculture through the

routine reporting of HCC and PCC cases from health facilities, abattoirs and veterinary centers.

Active surveillance would be required for the areas where information is not available but where the

presence of the parasite is suspected. Active surveillance in this case would be done by the municipal

public health and veterinary centers or by synchronized activities with research centers, such as

universities and national institutes of public health. However, to achieve this the development of a

coordination system is necessary to synchronize, update, process and ensure a routine analysis of all

the obtained data, and a clear procedure on how this processed information should reach the relevant

authorities who should act upon the reception of this information if required[195]. Also, the support of

a legislation to approve the compulsory reporting of T. solium taeniasis/cysticercosis at any level is


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necessary. As such, interventions could be focused on priority areas only. However, synchronized

actions are required in order to avoid the reintroduction of the disease in an intervened area.

Hospital data of T. solium infection cases would be the most obvious indicator to prioritize an area of

intervention, however, as mentioned in the previous chapters, this information is not sufficient to

characterize the whole situation of T. solium due to many factors such as the silent course of the

disease in early stages of infection, asymptomatic cases, sensitivity of diagnostic tools and mild

symptomatology (if any symptom is present) in the case of taeniasis, among other factors. For these

reasons the indicators that could be paired with the analysis of hospital data of T. solium infection

cases could be: 1) reports from PCC cases in abattoirs with their respective traceability; 2)

independent veterinary reports of suspected PCC areas; 3) reports from epidemiological studies in

rural or urban areas; 4) identification of areas combining high occurrence of epilepsy and other

neurological disorders with risk factors such as, pigs kept in free ranging systems, lack of basic

services such as sewage, potable water and latrines.

Once the priority areas of intervention are identified, classification of these areas should be done in

order to apply the most suitable strategy. In this case the most evident step would be the

discrimination between rural and urban zones. The approach for control interventions at urban and

rural level should be adapted accordingly. In urban settings of Ecuador, tapeworm infections are not

as common as in rural settings, because pork sold usually comes from official abattoirs where

veterinary inspection is mandatory. Also, the slaughtered pigs usually come from improved pig farms

where contact of pigs with human excrements is not possible. Therefore, most efforts in urban areas

should target at the interruption of the human-to-human transmission. To interrupt this transmission in

urban areas, the strategies should be directed to 1) raise awareness about the parasite, how it is

transmitted (including self-detection) and the urgency to contact a physician for proper diagnosis and

treatment in case of suspicion of infection; 2) highlight the importance of personal hygiene to avoid

HCC; 3) identification and treatment of tapeworm carriers and HCC patients; 4) identification of

possible pig rearing in slums or in peri-urban areas.

In urban centers, mass media, such as television, radio and newspapers are more available. These

media can be used to transmit health education messages and awareness about the disease. In rural

areas health education would be rather transmitted through conferences, meetings with the citizens,

information campaigns and interventions in schools. A national campaign of health education to

prevent T. solium infections has to include both approaches and it would be recommended to include

the interventions in both rural and urban schools. These type of campaigns can be paired with other

health campaigns, such as dengue prevention or vaccination campaigns.


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The social security system in urban centers could apply strategies, such as mandatory parasitological

diagnosis and treatment as a requirement to access to the benefits of this system. This type of strategy

would not be applicable in rural centers in Ecuador where only few people are in the social security

system. Knowing that taeniasis is acquired more commonly in rural settings, targeted studies to detect

and treat tapeworm carriers in urban settings, can be directed to groups where immigration from the

rural areas is high, such as housemaids, traders of agricultural products, construction workers and

refugees, among others [273;293]. In priority areas (urban and rural), it would also be recommended

to include serological diagnosis for HCC and taeniasis in routine laboratory analysis.

The municipalities of each big city should create special units to periodically visit slums and peri-

urban areas in search of pig rearing and other farm practices. The approach of these units to the peri-

urban farmers should be initially as advisors on how to improve sanitary conditions, but in a next

stage as a regulatory organism if sanitary conditions in these areas do not improve.

Interventions in priority endemic rural areas may have an impact on the macro-epidemiology of T.

solium. Prioritizing the treatment of tapeworm carriers in rural settings and then interrupting the

infection in pigs should decrease gradually the number of HCC infections in urban settings. A high

proportion of infections occurring in urban centers are concentrated around tapeworm carriers

migrating from rural endemic populations [12;125;293;297].

In rural settings, the strategies are directed to interrupt the life cycle of the parasite. These include: 1)

improvement of sanitary conditions; 2) restriction of pigs to access human feces; 3) identification of

PCC and sanitary sacrifice of infected pigs; 4) improvement of farming practices; 5) identification and

treatment of tapeworm carriers and HCC patients; 6) health education.

The improvement of sanitary conditions was shown as an indicator of the reduction of NCC cases in

Ecuador. This improvement was based on an increased coverage of systems to eliminate excrements.

This strategy has to be financed and directed by the affected municipalities with the support of the

government. This strategy has also to be paired with health education to avoid open defecation.

However, in field conditions it has to be taken into account that latrines and toilets are often far from

the work places. As a result, a fraction of the population that will practice open defecation will

remain. For these cases the use of mobile latrines with a proper system of excrement disposal could be

recommended.

Pig penning should be encouraged to avoid access of pigs to human feces, although, this practice does

not always avoid PCC [179]. In rural areas, pigs are kept in a free roaming system, mainly because the

owners do not need to invest in the construction of a pig pen and in animal feed. Veterinary services

should encourage pig owners to join forces and to develop common pig pens and feeders with a

sanitary maintenance system to reduce the costs of the pig keeping. Also, veterinary services could


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introduce alternatives to pig farming, such as farming of original species like the south American

camelid Lama glama (lama), the rodent Cavia porcellus (guinea pig or “cuy”), or even the capybara

(Hydrochoerus hydrochaeris). The advantages of farming these species is that they could partially

reduce pork consumption, therefore reducing taeniasis infections. This type of farming can also

increase the economy of the farmers because these species can also provide fur, wool and leather and

the productivity is high, mainly in the case of guinea pigs. This increase in the economy of farmers

could probably lead to an increase of the sanitary conditions of their households. Also, farming these

species has a low ecological impact due to the fact that these species were originally living in these

areas before the introduction of pigs. These species are resistant to many diseases but it is advised to

encourage the veterinary services to regularly visit and monitor these farms to reduce the risk of

introduction of other zoonotic diseases. However, benefits of this proposed change in animal species

can only be expected on a longer term.

Identification of PCC can be done at post-mortem inspection and in living pigs. Post mortem-

inspection can lead to the total or partial condemnation of pigs, but if the sanctions are too high,

farmers will avoid taking their animals to official abattoirs and escape the control. Therefore, it would

be necessary to introduce a compensation system that will not discourage official inspection but at the

same time will not encourage the intentionally infection of pigs. It has to be taken into account that in

rural settings, slaughter of pigs is often done in a house or backyard in the village [62;63]. It would be

interesting to explore the possibility of training some villagers for tongue inspection and inspection of

the carcasses [298]. The inspection reports, both from abattoirs and villages, must be addressed to the

local veterinary services in order to send an official report to the authorities of public health and

agriculture ministries. These authorities must coordinate the interventions in the affected areas.

The identification of PCC in living pigs can be done through surveys in coordination with the public

health and veterinary services. This kind of surveys has to be directed to identified priority areas in

order to reduce costs. These surveys are limited mainly by the characteristics of the available

diagnostic tools, such as low sensitivity (tongue inspection) and specificity (circulating antigens

detection). Nevertheless, new improvements have been done in this field and it is anticipated that

better diagnostic tools will become available in the near future. Another strategy that has to be

explored is the use of sentinel pigs, taking into account all the complexities described by

Devleesschauwer et al. (2013) [104;105]; however this strategy should be further studied in

independent studies in order to assess its feasibility and usefulness in a control program.

Treatment with oxfendazole and vaccination of pigs as intervention methods to interrupt transmission

should be further studied for applicability in Ecuadorian conditions. Both strategies have proven to be

promising in Peru [198]; however, the success of these strategies depends on the combined efforts

with the identification and treatment of tapeworm carriers [198;295].


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Identification of tapeworm carriers and HCC patients in rural settings of Ecuador is only done by

epidemiological research interventions or in the presence of symptomatic cases. To get over this

situation, the inclusion of serological diagnosis for both HCC and taeniasis in the priority areas in

routine laboratory analysis, is a strategy that should be explored. CDC Atlanta is currently developing

a point of care test for simultaneous serological diagnosis of HCC and taeniasis that will be evaluated

on a large scale in the field (P. Dorny, personal communication).

Health education in rural settings has to be much more elaborated than the message given in urban

settings. In rural areas, messages on the improvement of pig farming and sanitary conditions, in

addition to the awareness of the disease have to be clear and feasible. Also, in rural areas different

groups can be targeted with different priority messages. Meetings with pig owners should focus on the

importance of good disposal of human waste and the importance of impeding the access of pigs to

these; meetings with school children have to highlight the importance of hygiene and the use and

maintenance of latrines and toilets [200]; meetings with the general townspeople should highlight the

awareness about the parasite, its consequences and what are the basic procedures to avoid the

infections. Meetings with the authorities and representatives must highlight the importance of

reporting T. solium taeniasis/cysticercosis cases.

Understanding the transmission dynamics in rural settings is a necessary step to implement an

effective control measure in these areas. The longitudinal study conducted in an endemic area of

Ecuador showed the dynamic nature of the HCC infection and exposure. Prevalence data on exposure

showed that more than 30% of the population is exposed to the disease at a specific time, but the

longitudinal analysis revealed that yearly, around 40% of the population is effectively producing

antibodies against T. solium. Such figures suggest that there is a part of the population that is

constantly exposed to the parasite, probably surrounding the tapeworm carrier(s) and another part of

the population that has sporadic close contact with these individuals. Identifying the individuals

permanently exposed could lead to detect the tapeworm carriers or “hot spots” [18;75], using this

approach the targeted drug therapy of the suspected tapeworm carriers and the people surrounding

him/her could be useful to save efforts and resources. Targeted interventions as suggested here have

been tested in rural communities in Peru with promising results [299].

The low number of infections in this Ecuadorian rural community, contrasting to a high exposure

suggests that exposed individuals are at high risk of infection but that there is an unknown factor

avoiding this to happen. Some authors suggest that this presentation of high exposure/ low infections

is the result of acquired immunity in high prevalence areas [154;300]. Another hypothesis is the

presence of cross-resistance due to the presence of other Taenia species in the same area [168;172].

However, the validity of these hypotheses still needs to be studied further.


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In general, if the understanding of the epidemiological transmission patterns in epidemiological

studies is well achieved, the control strategies derived from them could be extrapolated to similar

endemic settings in priority areas of intervention.

The estimates generated from longitudinal data may be used to simulate the temporal transmission of

the parasite and the effects of control interventions on its life cycle [209]. These type of simulations

would be useful to make fine-tuned estimations of cost-effectiveness of the interventions/control

programs, to help to fill the gaps in the absence of convincing evidence from field trials and to rank

the control strategies depending on their relative efficacy [14]. Another advantage of such simulations

is the estimation of the duration of the effect of an intervention. Estimating the duration of the effect

of an intervention is important to assess the sustainability of a program, also, it will help to estimate

how many interventions and when they should be applied for the efficient control of a disease.

To date, the only simulation models available are the model published by Kyvsgaard et al (2007), and

the agent based model by Braae et al (2015) presented at the first CYSTINET (European network on

taeniasis/cysticercosis) conference held in Belgrade [209;301]. However, these models do not include

HCC in the simulations. The current data from longitudinal studies allows an approximate estimation

of the human-to-human probability of transmission. This probability can be included in the cited

models to add the HCC component in the simulations. As a result, the impact of the simulated control

measures in the transmission of HCC could be represented.

This updated simulation model could be used to calculate the burden of the disease. However, there is

still a gap between the infection rates (HCC), and the appearance of the clinical disease (mainly due to

NCC) and the mortality that should be filled. Also, the influence of the environment in the

transmission has not yet been well documented [178].

In conclusion, the implementation of a control program for T. solium in Ecuador should synchronize

efforts from different sectors of the society. The government represented by the Ministries of Public

Health and Agriculture and its Veterinary services should act in the first instance in the identification

of priority areas of intervention. To achieve this, an appropriate legislation has to be created to

support any effort on this matter such as mandatory reporting of any cases and routine diagnosis of T.

solium infections in priority areas or suspected areas. Once the affected areas are identified, the

control strategies to be applied should be designed accordingly depending on the type of area to be

intervened. In urban areas, the more feasible strategies are the ones involving the social security

system, education at schools and the mass media, also, these strategies could be part of other control

strategies for other diseases or sanitary campaigns. These efforts could be managed at municipal level

with the support of the government. In rural areas, the control strategies to be applied should be

carried out joining forces of the Ministry of Agriculture and its Veterinary Services, the Ministry of


109

Public Health and the authorities of rural municipalities. Pig farming has to be improved, pig access to

human waste has to be eliminated and the proper elimination of infected pigs has to be encouraged.

Municipalities have to develop proper systems to eliminate excrements where it is possible. The

Ministry of public Health, represented by the local health care centers should take action with targeted

interventions of tapeworm carriers every time HCC and eventually PCC are detected and reported.

Also, health education has to be promoted at any level. Research centers such as universities and

health institutes, should also participate with the support of the concerned authorities. The inclusion of

these centers would help in the fine-tuning of the strategies applied and would bring new information

that could be incorporated in the design of control strategies. Finally, the results of this control

program should be assessed at governmental level by the regular measuring of indicators such as

prevalence of HCC, PCC and taeniasis.

5.5 Perspectives in Ecuador

Official data and clinical studies present a decreasing trend of hospitalized cases of NCC without any

specific national program for control of HCC. However, this data reflects only partially the situation

of the country. Sanitary and health conditions have improved in most of the country in the last decade,

reducing the transmission of T. solium and lowering the incidence of HCC [150;151]. But the problem

will persist if no control measures are taken in rural settings. The life cycle of T. solium continues to

exist in rural areas despite the improvement of general conditions. The movement of tapeworm

carriers between rural and urban settings is impossible to prevent, thus intervening at a rural level to

interrupt the cysticercosis/taeniasis cycle is a must.

The monitoring and assessment at a country level of control programs for T. solium could be done

through the continuous analysis of hospital data [295]. The hospital reports for NCC and neurological

disorders is made continuously and is mandatory, but an improvement to the actual reporting system

in Ecuador is necessary to generate more accurate figures. However, results of the intervention

strategies would only be reflected on the long-term in this kind of reports. Reports from hospital cases

are not immediately available and there is a long period between the infection and the appearance of

symptoms. Monitoring and assessment of control programs for T. solium must be supported by other

sources of data, such as reports from veterinary services, abattoirs and periodical coordinated

epidemiological surveys in priority areas.

It would be necessary to enlarge the status of mandatory reporting of NCC and epilepsy ambulatory

cases from private and social security hospitals, which are not included in the reports of the Ministry

of public health. Also, monitoring of control programs for T. solium would benefit from a legislation

that supports the compulsory diagnosis of HCC and taeniasis (with species identification) through the


110

social security system. Veterinary services should direct efforts in the traceability of PCC and increase

the attention to informal pig rearing and slaughter.

Recently, Ecuador was capable to eradicate onchocerciasis being the second country in the world to

achieve so [302]. In the animal health field, Ecuador was declared in 2014 free of Food and Mouth

disease [303]. Educational campaigns have been successful in the country to control seasonal diseases

such as dengue fever. Also, focused elimination of T. solium in Peru achieved promising results,

giving some examples of strategies that could be applied in Ecuador given the similarities with this

neighboring country [198]. Therefore, if Ecuadorian authorities dedicate enough attention to T. solium

taeniasis/cysticercosis, control of the parasite is achievable.

If control measures are not taken in time, elimination of T. solium in Ecuador will not be achievable in

a near future. The Ecuadorian authorities must conduct a control program integrating veterinary

services, and public health agencies to act in rural areas to interrupt the life cycle of T. solium. The

approach used in this thesis can guide the design of control programs involving simultaneous targeted

interventions in priority communities. The application of such strategies at a large scale (provincial or

country level) could have a measurable impact on the overall prevalence and incidence of the disease

that if turned successful could be an example for other endemic countries.

5.6 Conclusions & recommendations

The existing variability in endemic areas affects the global estimates and control programs but

studying the geographical distribution of high and low HCC prevalence areas can be used to identify

priority areas of intervention. Ecuador appeared as one of the countries where HCC transmission

dynamics could be further studied being a priority zone with high estimates for exposure to the

parasite and non-negligible levels of active infections.

Spatio-temporal analysis with hospital data at country level is an important tool that should be

incorporated when designing national/large scale control programs. The use of spatio-temporal tools

with hospital data in Ecuador allowed to: 1) identify priority areas of intervention and 2) identify the

indicators enhancing or preventing the appearance of negative health outcomes. Also, spatio-temporal

tools could be used for the monitoring of the disease and for the assessment of control programs. A

better reporting system should increase the power of the analysis of official databases. This kind of

approach should be paired with reports from the veterinary services and epidemiological surveys to

increase the coverage when identifying priority areas of intervention or monitoring control programs.

Studying longitudinal data in an endemic community in Ecuador permitted to obtain incidence

estimates. These estimates can be incorporated in epidemiological simulation models to calculate the

burden of the disease and the cost-effectiveness of an intervention. The results from this study also


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revealed specific characteristics in this community that could be taken into account when designing

control strategies.

To design an effective control program, the availability of quality epidemiological data is essential.

Appropriate reporting should be encouraged at rural level and mandatory at health care centers at any

level as well as in abattoirs. Sero-epidemiological monitoring of HCC and taeniasis should be

incorporated in existing health campaigns. Better diagnostic tools that are more affordable, available

and less invasive should be developed for both HCC and taeniasis diagnosis. An attractive

compensation program should be developed for smallholders that should be enough to avoid

underreporting but also not too high as to encourage the intentional infection of pigs. Pig husbandry in

endemic communities has to be improved taking into account the economic issues for smallholders.

Health education has to be continued at many levels in priority areas of intervention.

Given the experiences from neighboring countries when controlling T. solium taeniasis/cysticercosis,

and given the recent success in Ecuador to control some other infectious and parasitic diseases,

Ecuador can be one of the first countries to effectively achieve the control of T. solium

taeniasis/cysticercosis if the respective authorities direct the necessary efforts to achieve this. To

ensure the success in this integrated fight, it is necessary that veterinary and medical services as well

as other health related scientists join forces following the One Health approach.

Global projections for the burden and the prevalence of HCC should take into account the variability

in endemic areas and within. A correct methodology should be developed to correct this matter.

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6 Summary

Taenia solium taeniasis/cysticercosis is a neglected zoonotic parasitic disease complex that causes

public health and socio-economic problems in rural communities in many developing countries. It has

become of increasing concern in developed countries due to globalization and human migration.

Taenia solium is a cestode that is transmitted between humans, the definitive host in which it causes

intestinal tapeworm infection (taeniasis), and pigs, the natural intermediate host in which it causes

cysticercosis; but humans can also act as an accidental dead-end intermediate host. Human

cysticercosis occurs when T. solium eggs that are fecally shed by tapeworm carriers are accidentally

ingested. The disease is characterized by the development of the metacestode larval stage of T.

solium, the cysticercus, in different tissues. Human cysticercosis (HCC) presents a wide variety of

signs and symptoms that include several important neurological disorders (neurocysticercosis), in

most severe cases cysticercosis can even cause death. Porcine cysticercosis is responsible for

economic losses among vulnerable traditional pig farmers mainly due to the condemnation of

carcasses and decreased carcass value.

Despite the wide knowledge about the biology and life cycle of the parasite, and the risk factors for

infection, control of T. solium has received little attention from governments of endemic countries.

Pilot control strategies have been tested in the field achieving varying results. Better efforts are

needed to understand the factors that affect the transmission dynamics of the parasite in order to

design adequate interventions that can be integrated in national control programs. To date, no national

control program has been implemented in Ecuador although the country is considered endemic for

HCC.

The objective of this thesis was to study the transmission patterns of T. solium taeniasis/cysticercosis

in order to design appropriate and effective control strategies for this Neglected Zoonotic disease in

endemic areas, with special reference to Ecuador. To achieve this goal, four specific objectives were

identified: (1) to characterize active infections of and exposure to T. solium in endemic zones around

the world; (2) to study the distribution in time and space of NCC hospitalized cases in Ecuador; (3) to

identify potential indicators of NCC hospitalized cases in Ecuador; (4) to study the dynamics of active

infections and exposure to T. solium in an endemic rural area in Ecuador.

The first chapter of this thesis presents an overview of the current knowledge of T. solium including

the life cycle of the parasite, the implications in public health and the economic impact of the disease,

its diagnosis, epidemiology with an emphasis on Latin America, with particular attention to the

situation in Ecuador. In addition, the current control measures available for T. solium

taeniasis/cysticercosis are described.

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In the second chapter, serological data on apparent prevalence of T. solium circulating antigens and/or

seroprevalence of T. solium antibodies, apparent prevalence of human taeniasis and risk factors for

HCC from endemic communities were gathered in order to understand the differences in patterns of

exposure to the parasite and active infections with T. solium metacestodes in endemic areas around

the world. A total of 39,271 participants from 19 countries, described in 37 articles were studied. The

estimates for the prevalence of circulating T. solium antigens for Africa, Latin America and Asia

were: 7.30% (95% CI [4.23 - 12.31]), 4.08% (95% CI [2.77 - 5.95]) and 3.98% (95% CI [2.81 -

5.61]), respectively. Seroprevalence estimates of T. solium antibodies were 17.37% (95% CI [3.33 -

56.20]), 13.03% (95% CI [9.95 - 16.88]) and 15.68% (95% CI [10.25 - 23.24]), respectively.

Taeniasis reported prevalences ranged from 0 (95% CI [0.00 - 1.62]) to 17.25% (95% CI [14.55 -

20.23]). A significant variation in the sero-epidemiological data was observed within each continent

with African countries reporting the highest apparent prevalences of active infections. Intrinsic factors

in the human host such as age and immunity were the main determinants for the occurrence of

infections while exposure was mostly related to environmental factors, which varied from community

to community.

In the third chapter, spatial and temporal variations in the incidence of hospitalized cases of epilepsy

and NCC in Ecuadorian municipalities were analyzed in order to locate and characterize important

clusters in space and time. Additionally, potential socio-economic and landscape indicators were

evaluated to understand in part the macro-epidemiology of the T. solium taeniasis/cysticercosis

complex. Data on the number of hospitalized epilepsy and NCC cases by municipality of residence

were obtained from morbidity-hospital systems in Ecuador. This study identified traditional endemic

clusters in the highlands for both conditions as well as new clusters appearing in recent years in other

zones considered non-endemic. An increase in the implementation of systems for eliminating

excrements would help to reduce the incidence of hospitalized cases of epilepsy by 1.00% (95% CI;

0.2% - 1.8%) and by 5.12% (95% CI; 3.63%-6.59%) for NCC. For epilepsy, the percentage of

dwellings with piped water and the number of physicians per 100,000 inhabitants were associated

with an increase in the number of hospitalized cases, whereas pig keeping was related to NCC

emergence. The presence of clusters of municipalities with high incidence of hospitalized epilepsy

cases could be the result of a high incidence of NCC cases or other acquired epilepsy cases. Given the

appearance of recent epilepsy clusters, these locations should be studied in depth to discriminate

epilepsies due to NCC from epilepsies due to other causes.

The fourth chapter describes the dynamic nature of human T. solium larval infections in an

Ecuadorian endemic community. In this study incidence rate and cumulative incidence figures of

human T. solium larval infections are reported for the first time in Latin America. A sero-

epidemiological cohort study was conducted in a south-Ecuadorian community to estimate the

Summary

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incidence rate of active cysticercosis and the incidence rate of exposure to T. solium, based on antigen

and antibody detections, respectively. The incidence rate of infection was 333.6 per 100,000 person-

years (95% CI: [8.4-1,858] per 100,000 person-years) contrasting with a higher incidence rate of

exposure 13,370 per 100,000 person-years (95% CI: [8,730-19,591] per 100,000 person-years). The

proportion of infected individuals remained low and stable during the whole study year while more

than 25% of the population showed at least one antibody seroconversion/seroreversion during the

same time period. While about 13% of the inhabitants were exposed to T. solium eggs, less than 1% of

the population became infected yearly with the parasite. This contrast between exposure and infection

may be linked to an effective resistance to the parasite acquired through long-term exposure of the

population and differs from the situation in African countries, where much higher levels of infection

have been observed. These estimates are of high importance to understand the epidemiology of T.

solium in order to develop ad hoc cost-effective prevention and control programs. They are also

essential to assess the burden of T. solium cysticercosis since longitudinal data are needed to make

regional and global projections of morbidity and mortality related to cysticercosis. The estimates

generated here may now be incorporated in epidemiological models to simulate the temporal

transmission of the parasite and the effects of control interventions on its life cycle.

In the fifth and final chapter of this thesis, the findings of this research are discussed in the context of

their contribution to the design of control strategies for T. solium with special attention to the case of

Ecuador. This research showed the implication of the variability of epidemiological patterns of T.

solium in different endemic areas in the design of control strategies. Also, some tools were provided

that could be used to help in the identification of priority areas of intervention within a country. The

transmission dynamics of human cysticercosis was analyzed in order to give further recommendations

when applying control measures in endemic rural and in urban areas of Ecuador. The approach given

in this research could be used to fine-tune the current control strategies of T. solium. However, further

studies are needed to fill in the gaps in the epidemiology of T. solium such as understanding the role

of the environment in the transmission of taeniasis/cysticercosis.

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7 Samenvatting

Taenia solium taeniasis/cysticercosis is een verwaarloosd zoönotisch ziektecomplex met belangrijke

gevolgen voor de volksgezondheid en met socio-economische impact op de landbouwsector in vele

ontwikkelingslanden. Het is ook een toenemend probleem in industrielanden als gevolg van de

globalisatie en menselijke migratie. Taenia solium is een cestode die wordt overgedragen tussen de

mens, de eindgastheer bij de welke het een intestinale lintworm infectie veroorzaakt (taeniasis), en het

varken, de natuurlijke tussengastheer waarbij de parasiet cysticercose veroorzaakt. De mens kan

echter ook accidentele tussengastheer zijn waarbij de infectie dan blind eindigt. Humane cysticercose

is het gevolg van de toevallige opname van T. solium eieren die door een lintwormdrager in de

stoelgang worden uitgescheiden. De ziekte wordt gekenmerkt door de ontwikkeling van het

metacestode larvaal stadium van T. solium, de cysticerc, in verschillende weefsels. Humane

cysticercose kan zich in verschillende ziektetekenen en symptomen uiten. De meest ernstige vorm van

cysticercose ontstaat bij ontwikkeling van cysticercen in het centraal zenuwstelsel

(neurocysticercose), die zelfs tot de dood kan leiden. Porciene cysticercose is verantwoordelijk voor

economische verliezen als gevolg van het afkeuren van besmette karkassen. Vooral traditionele

varkenshouders in endemische gebieden worden hierdoor getroffen.

Ondanks de goede kennis van de biologie en de levenscyclus van de parasiet, en van de risicofactoren

voor besmetting, heeft de bestrijding van T. solium weinig aandacht gekregen in endemische landen.

Piloot bestrijdingsstrategieën werden in het veld uitgetest met wisselende resultaten. Meer

inspanningen zouden moeten gedaan worden om de factoren die de transmissiedynamiek van de

parasiet bepalen beter te begrijpen, zodat aangepaste interventiestrategieën kunnen opgenomen

worden in nationale bestrijdingsprogramma’s. Tot op heden werd geen nationaal controleprogramma

geïmplementeerd in Ecuador, alhoewel dit land beschouwd wordt als endemisch voor humane

cysticercose.

Het objectief van deze thesis was om de transmissiepatronen van het T. solium taeniasis/cysticercosis

complex te bestuderen zodat aangepaste en efficiënte strategieën kunnen uitgewerkt worden ter

bestrijding van deze verwaarloosde zoönotische ziekte in endemische gebieden, met focus op

Ecuador. Om dit te realiseren werden vier specifieke objectieven geïdentificeerd: (1) het

karakteriseren van actieve cysticercose en blootstelling aan T. solium in endemische gebieden van de

wereld; (2) de studie van de spatio-temporale distributie van gehospitaliseerde gevallen van

neurocysticercose in Ecuador; (3) het identificeren van potentiële indicatoren van gehospitaliseerde

gevallen van neurocysticercose in Ecuador; (4) de studie van de dynamiek van actieve cysticercose en

blootstelling aan T. solium in een endemisch ruraal gebied in Ecuador.

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In het eerste hoofdstuk van deze thesis wordt een overzicht gegeven van de huidige kennis van T.

solium, namelijk, de levenscyclus van de parasiet, de implicaties voor de volksgezondheid en de

economische impact van deze parasiet, de diagnosis en de epidemiologie met nadruk op Latijns

Amerika, met daarbij de focus op de situatie in Ecuador. Tenslotte worden de beschikbare

bestrijdingsmethodes van T. solium taeniasis/cysticercose beschreven.

In het tweede hoofdstuk werden gepubliceerde gegevens verzameld van endemische gebieden in de

wereld, over serologische resultaten van de schijnbare prevalentie van circulerende antigenen van T.

solium en/of de seroprevalentie van antistoffen gericht tegen T. solium bij de mens, de schijnbare

prevalentie van humane taeniasis, en de risicofactoren van humane cysticercose. Het doel was om

verschillen in patronen van blootstelling aan de parasiet en infectie met cysticercen bij de mens in

verschillende gebieden beter te begrijpen. In totaal werden 37 wetenschappelijke publicaties

weerhouden met daarin gegevens over 39271 studiedeelnemers in 19 landen. De schattingen van de

prevalentie van circulerende antigenen van T. solium voor Afrika, Latijns Amerika en Azië waren

respectievelijk, 7,30% (95% CI [4,23 - 12,31]), 4,08% (95% CI [2,77 - 595]) en 3,98% (95% CI [2,81

- 5,61]). Schattingen van de seroprevalentie van antistoffen gericht tegen T. solium waren

respectievelijk, 17,37% (95% CI [3,33 - 56,20]), 13,03% (95% CI [9,95 - 16,88]) en 15,68% (95% CI

[10,25 - 23,24]). De gerapporteerde prevalentie van humane taeniasis varieerde van 0 (95% CI [0,00 -

1,62]) tot 17,25% (95% CI [14,55 - 20,23]). Significante verschillen in sero-epidemiologische data

werden gemeten binnen elk continent. De hoogste schijnbare prevalentie van actieve infectie werd

waargenomen in Afrikaanse landen. Intrinsieke factoren gebonden aan de menselijke gastheer, zoals

leeftijd en immuniteit waren de voornaamste determinanten van infectie, terwijl blootstelling aan de

parasiet eerder gerelateerd was aan omgevingsfactoren die varieerden tussen de studiegebieden.

In het derde hoofdstuk werden spatiale en temporale variaties in de incidentie van gehospitaliseerde

gevallen van epilepsie en neurocysticercose in Ecuadoriaanse gemeentes geanalyseerd met als doel

belangrijke clusters die zich geografisch en in tijd voordeden te karakteriseren. Bovendien werden

potentiële socio-economische en landschapsindicatoren geëvalueerd om de macro-epidemiologie van

het T. solium taeniasis/cysticercosis complex te begrijpen. Gegevens over het aantal

ziekenhuisopnames van epilepsie en neurocysticercose gevallen per gemeente werden verkregen van

hospitaal-morbiditeit systemen in Ecuador. De studie identificeerde naast de traditionele endemische

clusters voor beide aandoeningen in bergachtige gebieden, ook recentere nieuwe clusters in zones die

als niet-endemisch werden beschouwd. Een verbetering van de systemen voor de eliminatie van

fecaliën zou de incidentie van ziekenhuisopnames voor epilepsie met 1,00% (95%CI; 0,2% - 1,8%) en

voor neurocysticercose met 5,12% (95%CI; 3,63% - 6,59%) verminderen. Voor epilepsie waren, het

percentage van woningen met aansluiting aan het drinkwaternet en het aantal dokters per 100000

inwoners, geassocieerd waren met een toename van het aantal ziekenhuisopnames, terwijl dit voor

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neurocysticercose het houden van varkens was. De aanwezigheid van clusters van gemeentes met

hoge incidentie van ziekenhuisopnames voor epilepsie kunnen veroorzaakt zijn door een hoge

incidentie van neurocysticercose of van andere oorzaken van verworven epilepsie. Het ontstaan van

nieuwe epilepsie clusters vereist een grondige studie naar de oorzaak ervan en van de potentiële rol

van neurocysticercose.

In het vierde hoofdstuk wordt het dynamische karakter van humane cysticercose in een Ecuadoriaanse

endemische gemeenschap beschreven. Voor het eerst in Latijns Amerika konden we in deze studie

gegevens over incidentie en cumulatieve incidentie van humane cysticercose verzamelen. De sero-

epidemiologische cohortstudie werd uitgevoerd in een Zuid-Ecuadoriaanse gemeenschap waar we

door middel van antistof en antigeen detectie gegevens bekwamen over respectievelijk, de incidentie

van blootstelling aan de parasiet en actieve cysticercose. De incidentie van actieve infectie was 333,6

per 100000 personen-jaren (95% CI: [8,4 - 1858] per 100000 personen-jaren); dit contrasteerde met

de hogere blootstelling aan de parasiet van 13370 per 100000 personen-jaren (95% CI: [8730-19591]

per 100000 personen-jaren). De proportie van geïnfecteerde individuen bleef laag en stabiel

gedurende de ganse studieperiode, terwijl meer dan 25% van de bevolking minstens één antistof

seroconversie/seroreversie vertoonde tijdens die periode. Terwijl ongeveer 13% van de inwoners per

jaar blootgesteld werd aan T. solium eieren, werd actieve infectie op jaarbasis slechts bij 1% van de

bevolking vastgesteld. Het waargenomen contrast tussen blootstelling en infectie kan te wijten zijn

aan de opbouw van beschermende immuniteit tegen de parasiet als gevolg van langdurige

blootstelling. Deze observatie verschilt van de situatie in Afrikaanse landen, waar voor een

vergelijkbare blootstelling veel meer actieve cysticercose wordt gemeten. Deze bevindingen zijn van

groot belang voor het begrijpen van de epidemiologie van T. solium en voor het ontwikkelen van ad-

hoc kosten-efficiënte preventie en controleprogramma’s. Ze zijn ook essentieel voor het bepalen van

de ziektelast van T. solium cysticercose omdat longitudinale data vereist zijn om regionale en globale

projecties van cysticercose-gerelateerde morbiditeit en mortaliteit te kunnen maken. De schattingen

bekomen uit deze studies kunnen gebruikt worden in mathematische epidemiologische modellen om

de temporale transmissie van de parasiet en de effecten van controlemaatregelen op de levenscyclus te

genereren.

In het vijfde en laatste hoofdstuk van deze thesis worden de belangrijkste bevindingen van dit

onderzoek besproken in de context van het ontwikkelen van strategieën voor de bestrijding van T.

solium, met speciale aandacht voor het toepassen in Ecuador. Het onderzoek toonde de implicaties

aan van de variabiliteit van epidemiologische situaties van T. solium in verschillende endemische

gebieden op de ontwikkeling van bestrijdingsmethoden. We brachten ook werkmiddelen aan die

kunnen helpen om gebieden in het land te identificeren waar interventies prioritair zijn. De

transmissie dynamiek van humane cysticercose werd geanalyseerd om recommandaties te geven voor

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interventie maatregelen in endemische rurale en in stedelijke gebieden in Ecuador. De aanpak

beschreven in ons onderzoek kan ook gebruikt worden om bestaande controle strategieën in andere

gebieden te verfijnen. Tenslotte identificeerden we ook lacunes in onze kennis van de epidemiologie

van T. solium, zoals onder andere de rol van het milieu in de transmissie van taeniasis/cysticercose.

Publications

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8 Publications

Coral-Almeida M, Gabriel S, Abatih EN, Praet N, Benitez W, Dorny P. Taenia solium Human Cysticercosis: A Systematic Review of Sero-epidemiological Data from Endemic Zones around the World. PLoS Negl Trop Dis 2015 Jul;9(7):e0003919.

Coral-Almeida M, Rodríguez-Hidalgo R, Celi-Erazo M, García HH, Rodríguez S, Devleesschauwer B, Benítez-Ortiz W, Dorny P, Praet N. (2014) Incidence of human Taenia solium larval Infections in an Ecuadorian endemic area: implications for disease burden assessment and control. PLoS Negl Trop Dis. 2014 May 22;8(5):e2887. doi: 10.1371/journal.pntd.0002887.

Lenin Ron-Garrido*, Marco Coral-Almeida*, Sarah Gabriël, Washington Benitez, Claude Saegerman, Pierre Dorny, Dirk Berkvens, Emmanuel Abatih. Distribution and Potential Indicators of Hospitalized cases of Neurocysticercosis and Epilepsy in Ecuador from 1996 to 2008 (2015) . PLoS Negl Trop Dis 2015 Nov;9(11):e0004236.

*Joint first authorship

Proaño-Pérez F, Benitez-Ortiz W, Desmecht D, Coral M, Ortiz J, Ron L, Portaels F, Rigouts L, Linden A. (2011) Post-mortem examination and laboratory-based analysis for the diagnosis of bovine tuberculosis among dairy cattle in Ecuador. Prev Vet Med. 2011 Aug 1;101(1-2):65-72. doi: 10.1016/j.prevetmed.2011.04.018. Epub 2011 Jun 8.

9 Abstracts and Posters

S Enríquez, R Rodríguez-Hidalgo, F Vaca-Moyano, L Ron, J Ron, M Coral, E Villacrés, P Lahuatte, V Guasumba y W Benítez-Ortiz. (2013) Altitudinal and spatial distribution of Rhipicephalus (Boophilus) microplus (Canestrini, 1888), Amblyomma spp. and Ixodes boliviensis Neumann, 1904 (Acari: Ixodidae) in Ecuador. In: 14th International Conference of the Association of Institutions for Tropical Veterinary Medicine. Johannesburg, South Africa.

N Praet, M Coral-Almeida, W Benitez-Ortiz, R Rodriguez-Hidalgo, M Celi, Sarah Gabriël, N Speybroeck and Pierre Dorny (2011) Incidence of Taenia solium cysticercosis in southern Ecuador: a longitudinal community-based study. TROPICAL MEDICINE & INTERNATIONAL HEALTH. 16(suppl. 1). p.170-170. In: 7th European congress on Tropical Medicine and International Health. Barcelona, Spain

Curriculum vitae

120

10 Curriculum vitae

Born in Quito, Ecuador on 6 January 1980

Education

2011 Master of Science in Tropical Animal Health (MSTAH), option: Epidemiology; Institute of Tropical Medicine, Antwerp, Belgium.

2010 Bachelor in Veterinary Science and Animal Husbandry; Central University, Quito, Ecuador.

1999 Diplôme du Baccalauréat Général Français, option Scientifique, Lycée Franco-Équatorien La Condamine, Académie de la Martinique, Quito, Ecuador (French High-School diploma). Mention Assez bien.

1999 Ecuadorian High-School diploma in Sciences, Lycée Franco-Équatorien La Condamine, Quito, Ecuador. Mention Assez bien.

Additional Education

2009 Quantitative Risk Assessment for Medical and Veterinary Public Health Officers and Researchers. Institute of Tropical Medicine, Antwerp, Belgium

Professional Experience

2014- to date Assistant Lecturer in the Faculty of Health Sciences in the Veterinary Medicine and Animal Husbandry department of the Universidad de las Américas (UDLA) Quito, Ecuador.

2014- to date Researcher in the Faculty of Health Sciences in the Veterinary Medicine and Animal Husbandry department of the Universidad de las Américas (UDLA) Quito, Ecuador.

2014 Assistant lecturer in the Faculty of Veterinary Medicine of the Universidad Central del Ecuador (UCE) Quito, Ecuador.

2014 Responsible of the laboratory of parasitology in the Faculty of Veterinary Medicine and Animal Husbandry of the Universidad Central del Ecuador (UCE) Quito, Ecuador.

2008- to date Researcher at the Centro Internacional de Zoonosis (CIZ) Quito, Ecuador.

2007-2008 Internship at the Centro Internacional de Zoonosis (CIZ) Quito, Ecuador.

2008-2009 Research collaborator at the project PIC (Étude de deux anthropozoonoses présentes en Équateur, la fasciolose et la tuberculose : aspects épidémiologiques, diagnostic et lutte intégrée) in field and laboratory work.

Bibliography

121

11 Bibliography

1. Sorvillo FJ, DeGiorgio C, Waterman SH. Deaths from cysticercosis, United States. Emerg Infect Dis 2007 Feb;13(2):230-5.

2. Bruno E, Bartoloni A, Zammarchi L, Strohmeyer M, Bartalesi F, Bustos JA, et al. Epilepsy and neurocysticercosis in Latin America: a systematic review and meta-analysis. PLoS Negl Trop Dis 2013;7(10):e2480.

3. White AC, Jr. Neurocysticercosis: a major cause of neurological disease worldwide. Clin Infect Dis 1997 Feb;24(2):101-13.

4. Praet N, Speybroeck N, Manzanedo R, Berkvens D, Nsame ND, Zoli A, et al. The disease burden of Taenia solium cysticercosis in Cameroon. PLoS Negl Trop Dis 2009;3(3):e406.

5. Zoli A, Shey-Njila O, Assana E, Nguekam JP, Dorny P, Brandt J, et al. Regional status, epidemiology and impact of Taenia solium cysticercosis in Western and Central Africa. Acta Trop 2003 Jun;87(1):35-42.

6. Flisser A, Sarti E, Lightowlers M, Schantz P. Neurocysticercosis: regional status, epidemiology, impact and control measures in the Americas. Acta Trop 2003 Jun;87(1):43-51.

7. Welburn SC, Beange I, Ducrotoy MJ, Okello AL. The neglected zoonoses-the case for integrated control and advocacy. Clin Microbiol Infect 2015 May;21(5):433-43.

8. Flisser A, Rodriguez-Canul R, Willingham AL, III. Control of the taeniosis/cysticercosis complex: future developments. Vet Parasitol 2006 Jul 31;139(4):283-92.

9. Lustigman S, Prichard RK, Gazzinelli A, Grant WN, Boatin BA, McCarthy JS, et al. A research agenda for helminth diseases of humans: the problem of helminthiases. PLoS Negl Trop Dis 2012;6(4):e1582.

10. World Health Organization (WHO), World. Accelerating work to overcome the global impact of neglected tropical diseases-a roadmap for implementation. Geneva-Switzerland; Printed in France: World Health Organization (WHO); 2012.

11. DeGiorgio C, Pietsch-Escueta S, Tsang V, Corral-Leyva G, Ng L, Medina MT, et al. Sero-prevalence of Taenia solium cysticercosis and Taenia solium taeniasis in California, USA. Acta Neurol Scand 2005 Feb;111(2):84-8.

12. Gabriël S, Johansen MV, Pozio E, Smit GS, Devleesschauwer B, Allepuz A, et al. Human migration and pig/pork import in the European Union: What are the implications for Taenia solium infections? Vet Parasitol In press Available On line 2015 Mar 20.

13. Devleesschauwer B, Allepuz A, Dermauw V, Johansen MV, Laranjo-Gonzalez M, Smit GS, et al. Taenia solium in Europe: Still endemic? Acta Trop 2015 Aug 11.

14. Carabin H, Traore AA. taeniasis and cysticercosis control and elimination through community-based interventions. Curr Trop Med Rep 2014 Dec 1;1(4):181-93.

15. Cruz M, Davis A, Dixon H, Pawlowski ZS, Proano J. Operational studies on the control of Taenia solium taeniasis/cysticercosis in Ecuador. Bull World Health Organ 1989;67(4):401-7.

Bibliography

122

16. Praet N, Speybroeck N, Rodriguez-Hidalgo R, Benitez-Ortiz W, Berkvens D, Brandt J, et al. Age-related infection and transmission patterns of human cysticercosis. Int J Parasitol 2010 Jan;40(1):85-90.

17. Coral-Almeida M, Rodriguez-Hidalgo R, Celi-Erazo M, Garcia HH, Rodriguez S, Devleesschauwer B, et al. Incidence of human Taenia solium larval Infections in an Ecuadorian endemic area: implications for disease burden assessment and control. PLoS Negl Trop Dis 2014 May;8(5):e2887.

18. Lescano AG, Garcia HH, Gilman RH, Gavidia CM, Tsang VC, Rodriguez S, et al. Taenia solium cysticercosis hotspots surrounding tapeworm carriers: clustering on human seroprevalence but not on seizures. PLoS Negl Trop Dis 2009;3(1):e371.

19. Flisser A, Correa D, Avila G, Maravilla P. Biology of Taenia solium, Taenia saginata and Taenia saginata asiatica. In: Murrell KD, editor. FAO/WHO/OIE Guidelines for the surveillance, prevention and control of taeniosis/cysticercosis.Paris: 2005. p. 1-9.

20. Rabiela MT, Hornelas Y, Garcia-Allan C, Rodriguez-del-Rosal E, Flisser A. Evagination of Taenia solium cysticerci: a histologic and electron microscopy study. Arch Med Res 2000 Nov;31(6):605-7.

21. Del Brutto OH. Neurocysticercosis: a review. ScientificWorldJournal 2012;2012:159821.

22. Del Brutto OH. Human cysticercosis (Taenia solium). Trop Parasitol 2013 Jul;3(2):100-3.

23. Kraft R. Cysticercosis: an emerging parasitic disease. Am Fam Physician 2007 Jul 1;76(1):91-6.

24. Garcia HH, Modi M. Helminthic parasites and seizures. Epilepsia 2008 Aug;49 Suppl 6:25-32.

25. Takayanagui OM, Chimelli L. Disseminated muscular cysticercosis with myositis induced by praziquantel therapy. Am J Trop Med Hyg 1998 Dec;59(6):1002-3.

26. Kadhiravan T, Soneja M, Hari S, Sharma SK. Images in clinical tropical medicine: disseminated cysticercosis. Am J Trop Med Hyg 2009 May;80(5):699.

27. Tappe D, Demmer P, Echterhoff U, Weskamp R. Two cases of presumably travel-related subcutaneous cysticercosis. Infection 2010 Apr;38(2):152-3.

28. Garcia HH, Gonzalez AE, Rodriguez S, Tsang VC, Pretell EJ, Gonzales I, et al. Neurocysticercosis: unraveling the nature of the single cysticercal granuloma. Neurology 2010 Aug 17;75(7):654-8.

29. Carabin H, Ndimubanzi PC, Budke CM, Nguyen H, Qian Y, Cowan LD, et al. Clinical manifestations associated with neurocysticercosis: a systematic review. PLoS Negl Trop Dis 2011 May;5(5):e1152.

30. Preux PM, Druet-Cabanac M. Epidemiology and aetiology of epilepsy in sub-Saharan Africa. Lancet Neurol 2005 Jan;4(1):21-31.

31. Ndimubanzi PC, Carabin H, Budke CM, Nguyen H, Qian YJ, Rainwater E, et al. A systematic review of the frequency of neurocyticercosis with a focus on people with epilepsy. PLoS Negl Trop Dis 2010;4(11):e870.

Bibliography

123

32. Chauhan A, Quenum FZ, Abbas A, Bradley DS, Nechaev S, Singh BB, et al. Epigenetic Modulation of Microglial Inflammatory Gene Loci in Helminth-Induced Immune Suppression: Implications for Immune Regulation in Neurocysticercosis. ASN Neuro 2015 Jul;7(4).

33. Sciutto E, Chavarria A, Fragoso G, Fleury A, Larralde C. The immune response in Taenia solium cysticercosis: protection and injury. Parasite Immunol 2007 Dec;29(12):621-36.

34. Ito A, Takayanagui OM, Sako Y, Sato MO, Odashima NS, Yamasaki H, et al. Neurocysticercosis: clinical manifestation, neuroimaging, serology and molecular confirmation of histopathologic specimens. Southeast Asian J Trop Med Public Health 2006;37 Suppl 3:74-81.

35. Garcia HH, Nash TE, Del Brutto OH. Clinical symptoms, diagnosis, and treatment of neurocysticercosis. Lancet Neurol 2014 Dec;13(12):1202-15.

36. Garcia HH, Gonzalez AE, Evans CA, Gilman RH. Taenia solium cysticercosis. Lancet 2003 Aug 16;362(9383):547-56.

37. Sciutto E, Fragoso G, Fleury A, Laclette JP, Sotelo J, Aluja A, et al. Taenia solium disease in humans and pigs: an ancient parasitosis disease rooted in developing countries and emerging as a major health problem of global dimensions. Microbes Infect 2000 Dec;2(15):1875-90.

38. Prasad KN, Chawla S, Prasad A, Tripathi M, Husain N, Gupta RK. Clinical signs for identification of neurocysticercosis in swine naturally infected with Taenia solium. Parasitol Int 2006 Jun;55(2):151-4.

39. Trevisan Ch, Mkupasi E, Ngowi HA, Forkman B, Johansen MV. Severe seizures in pigs naturally infected with Taenia solium. 1st Cystinet International Conference taeniosis And Cysticercosis: A One Health Challenge - Belgrade 2015: University of Belgrade Institute for Medical Research; 2015.

40. Fleury A, Trejo A, Cisneros H, Garcia-Navarrete R, Villalobos N, Hernandez M, et al. Taenia solium: Development of an Experimental Model of Porcine Neurocysticercosis. PLoS Negl Trop Dis 2015 Aug;9(8):e0003980.

41. Roman G, Sotelo J, Del BO, Flisser A, Dumas M, Wadia N, et al. A proposal to declare neurocysticercosis an international reportable disease. Bull World Health Organ 2000;78(3):399-406.

42. Gemmell M, Matyas Z, Pawlowsky Z, Soulsby E. Guideliness for Surveillance, Prevention andControl of Taeniasis/Cysticercosis. Geneva: WHO, 1983.

43. Lozano R, Naghavi M, Foreman K, Lim S, Shibuya K, Aboyans V, et al. Global and regional mortality from 235 causes of death for 20 age groups in 1990 and 2010: a systematic analysis for the Global Burden of Disease Study 2010. Lancet 2012 Dec 15;380(9859):2095-128.

44. Global, regional, and national age-sex specific all-cause and cause-specific mortality for 240 causes of death, 1990-2013: a systematic analysis for the Global Burden of Disease Study 2013. Lancet 2015 Jan 10;385(9963):117-71.

45. Devleesschauwer B, Maertens de NC, Smit GS, Duchateau L, Dorny P, Stein C, et al. Quantifying burden of disease to support public health policy in Belgium: opportunities and constraints. BMC Public Health 2014;14:1196.

Bibliography

124

46. The World Bank. World Development Report 1993: Investing in Health. New York: Oxford University Press, 1993.

47. Murray CJ, Lopez AD. Quantifying disability: data, methods and results. Bull World Health Organ 1994;72(3):481-94.

48. Devleesschauwer B, Havelaar AH, Maertens de NC, Haagsma JA, Praet N, Dorny P, et al. Calculating disability-adjusted life years to quantify burden of disease. Int J Public Health 2014 Jun;59(3):565-9.

49. Murray CJ, Vos T, Lozano R, Naghavi M, Flaxman AD, Michaud C, et al. Disability-adjusted life years (DALYs) for 291 diseases and injuries in 21 regions, 1990-2010: a systematic analysis for the Global Burden of Disease Study 2010. Lancet 2012 Dec 15;380(9859):2197-223.

50. Torgerson PR, de Silva NR, Fevre EM, Kasuga F, Rokni MB, Zhou XN, et al. The global burden of foodborne parasitic diseases: an update. Trends Parasitol 2014 Jan;30(1):20-6.

51. Global, regional, and national incidence, prevalence, and years lived with disability for 301 acute and chronic diseases and injuries in 188 countries, 1990-2013: a systematic analysis for the Global Burden of Disease Study 2013. Lancet 2015 Jun 7.

52. Hotez PJ, Alvarado M, Basanez MG, Bolliger I, Bourne R, Boussinesq M, et al. The global burden of disease study 2010: interpretation and implications for the neglected tropical diseases. PLoS Negl Trop Dis 2014 Jul;8(7):e2865.

53. Torgerson PR, Macpherson CN. The socioeconomic burden of parasitic zoonoses: global trends. Vet Parasitol 2011 Nov 24;182(1):79-95.

54. Bhattarai R, Budke CM, Carabin H, Proano JV, Flores-Rivera J, Corona T, et al. Estimating the non-monetary burden of neurocysticercosis in Mexico. PLoS Negl Trop Dis 2012;6(2):e1521.

55. Devleesschauwer B, Ale A, Torgerson P, Praet N, Maertens de NC, Pandey BD, et al. The burden of parasitic zoonoses in Nepal: a systematic review. PLoS Negl Trop Dis 2014;8(1):e2634.

56. Sebera F, Munyandamutsa N, Teuwen DE, Ndiaye IP, Diop AG, Tofighy A, et al. Addressing the treatment gap and societal impact of epilepsy in Rwanda--Results of a survey conducted in 2005 and subsequent actions. Epilepsy Behav 2015 May;46:126-32.

57. Baker GA. The psychosocial burden of epilepsy. Epilepsia 2002;43 Suppl 6:26-30.

58. Crepin S, Houinato D, Nawana B, Avode GD, Preux PM, Desport JC. Link between epilepsy and malnutrition in a rural area of Benin. Epilepsia 2007 Oct;48(10):1926-33.

59. Baskind R, Birbeck GL. Epilepsy-associated stigma in sub-Saharan Africa: the social landscape of a disease. Epilepsy Behav 2005 Aug;7(1):68-73.

60. Ali DB, Tomek M, Lisk DR. The effects of epilepsy on child education in Sierra Leone. Epilepsy Behav 2014 Aug;37:236-40.

61. Carabin H, Budke CM, Cowan LD, Willingham AL, III, Torgerson PR. Methods for assessing the burden of parasitic zoonoses: echinococcosis and cysticercosis. Trends Parasitol 2005 Jul;21(7):327-33.

Bibliography

125

62. The marketing of cysticercotic pigs in the Sierra of Peru. The Cysticercosis Working Group in Peru. Bull World Health Organ 1993;71(2):223-8.

63. Joshi DD, Maharjan M, Johansen MV, Willingham AL, Sharma M. Improving meat inspection and control in resource-poor communities: the Nepal example. Acta Trop 2003 Jun;87(1):119-27.

64. Sikasunge CS, Phiri IK, Phiri AM, Dorny P, Siziya S, Willingham AL, III. Risk factors associated with porcine cysticercosis in selected districts of Eastern and Southern provinces of Zambia. Vet Parasitol 2007 Jan 19;143(1):59-66.

65. Eshitera EE, Githigia SM, Kitala P, Thomas LF, Fevre EM, Harrison LJ, et al. Prevalence of porcine cysticercosis and associated risk factors in Homa Bay District, Kenya. BMC Vet Res 2012;8:234.

66. Ngowi HA, Kassuku AA, Maeda GE, Boa ME, Willingham AL. A slaughter slab survey for extra-intestinal porcine helminth infections in northern Tanzania. Trop Anim Health Prod 2004 May;36(4):335-40.

67. Praet N, Kanobana K, Kabwe C, Maketa V, Lukanu P, Lutumba P, et al. Taenia solium cysticercosis in the Democratic Republic of Congo: how does pork trade affect the transmission of the parasite? PLoS Negl Trop Dis 2010;4(9).

68. Carabin H, Krecek RC, Cowan LD, Michael L, Foyaca-Sibat H, Nash T, et al. Estimation of the cost of Taenia solium cysticercosis in Eastern Cape Province, South Africa. Trop Med Int Health 2006 Jun;11(6):906-16.

69. Rajkotia Y, Lescano AG, Gilman RH, Cornejo C, Garcia HH. Economic burden of neurocysticercosis: results from Peru. Trans R Soc Trop Med Hyg 2007 Aug;101(8):840-6.

70. Mkupasi EM, Ngowi HA, Nonga HE. Prevalence of extra-intestinal porcine helminth infections and assessment of sanitary conditions of pig slaughter slabs in Dar es Salaam city, Tanzania. Trop Anim Health Prod 2011 Feb;43(2):417-23.

71. Gabriel S, Blocher J, Dorny P, Abatih EN, Schmutzhard E, Ombay M, et al. Added value of antigen ELISA in the diagnosis of neurocysticercosis in resource poor settings. PLoS Negl Trop Dis 2012 Oct;6(10):e1851.

72. Praet N, Rodriguez-Hidalgo R, Speybroeck N, Ahounou S, Benitez-Ortiz W, Berkvens D, et al. Infection with versus exposure to Taenia solium: what do serological test results tell us? Am J Trop Med Hyg 2010 Aug;83(2):413-5.

73. Garcia HH, Gonzalez AE, Gilman RH, Palacios LG, Jimenez I, Rodriguez S, et al. Short report: transient antibody response in Taenia solium infection in field conditions-a major contributor to high seroprevalence. Am J Trop Med Hyg 2001 Jul;65(1):31-2.

74. Carpio A, Escobar A, Hauser WA. Cysticercosis and epilepsy: a critical review. Epilepsia 1998 Oct;39(10):1025-40.

75. Dorny P, Brandt J, Zoli A, Geerts S. Immunodiagnostic tools for human and porcine cysticercosis. Acta Trop 2003 Jun;87(1):79-86.

76. Del Brutto OH, Wadia NH, Dumas M, Cruz M, Tsang VC, Schantz PM. Proposal of diagnostic criteria for human cysticercosis and neurocysticercosis. J Neurol Sci 1996 Oct;142(1-2):1-6.

Bibliography

126

77. Del Brutto OH, Rajshekhar V, White AC, Jr., Tsang VC, Nash TE, Takayanagui OM, et al. Proposed diagnostic criteria for neurocysticercosis. Neurology 2001 Jul 24;57(2):177-83.

78. Del Brutto OH. Diagnostic criteria for neurocysticercosis, revisited. Pathog Glob Health 2012 Sep;106(5):299-304.

79. Garcia HH, Evans CA, Nash TE, Takayanagui OM, White AC, Jr., Botero D, et al. Current consensus guidelines for treatment of neurocysticercosis. Clin Microbiol Rev 2002 Oct;15(4):747-56.

80. Tsang VC, Brand JA, Boyer AE. An enzyme-linked immunoelectrotransfer blot assay and glycoprotein antigens for diagnosing human cysticercosis (Taenia solium). J Infect Dis 1989 Jan;159(1):50-9.

81. Dorny P, Brandt J, Geerts S. Detection and Diagnosis. In: Murrell K, editor. WHO/FAO/OIE Guidelines for the Surveillance, Prevention and Control of Taeniasis/cysticercosis.Paris, France: OIE/FAO/WHO; 2005. p. 45-55.

82. Brandt JR, Geerts S, de DR, Kumar V, Ceulemans F, Brijs L, et al. A monoclonal antibody-based ELISA for the detection of circulating excretory-secretory antigens in Taenia saginata cysticercosis. Int J Parasitol 1992 Jul;22(4):471-7.

83. Harrison LJ, Joshua GW, Wright SH, Parkhouse RM. Specific detection of circulating surface/secreted glycoproteins of viable cysticerci in Taenia saginata cysticercosis. Parasite Immunol 1989 Jul;11(4):351-70.

84. Erhart A, Dorny P, Van DN, Vien HV, Thach DC, Toan ND, et al. Taenia solium cysticercosis in a village in northern Viet Nam: seroprevalence study using an ELISA for detecting circulating antigen. Trans R Soc Trop Med Hyg 2002 May;96(3):270-2.

85. Garcia HH, Harrison LJ, Parkhouse RM, Montenegro T, Martinez SM, Tsang VC, et al. A specific antigen-detection ELISA for the diagnosis of human neurocysticercosis. The Cysticercosis Working Group in Peru. Trans R Soc Trop Med Hyg 1998 Jul;92(4):411-4.

86. Fleury A, Hernandez M, Avila M, Cardenas G, Bobes RJ, Huerta M, et al. Detection of HP10 antigen in serum for diagnosis and follow-up of subarachnoidal and intraventricular human neurocysticercosis. J Neurol Neurosurg Psychiatry 2007 Sep;78(9):970-4.

87. Lescano AG, Garcia HH, Gilman RH, Guezala MC, Tsang VC, Gavidia CM, et al. Swine cysticercosis hotspots surrounding Taenia solium tapeworm carriers. Am J Trop Med Hyg 2007 Feb;76(2):376-83.

88. Prasad A, Prasad KN, Yadav A, Gupta RK, Pradhan S, Jha S, et al. Lymphocyte transformation test: a new method for diagnosis of neurocysticercosis. Diagn Microbiol Infect Dis 2008 Jun;61(2):198-202.

89. Castillo Y, Rodriguez S, Garcia HH, Brandt J, Van HA, Silva M, et al. Urine antigen detection for the diagnosis of human neurocysticercosis. Am J Trop Med Hyg 2009 Mar;80(3):379-83.

90. Mwape KE, Praet N, Benitez-Ortiz W, Muma JB, Zulu G, Celi-Erazo M, et al. Field evaluation of urine antigen detection for diagnosis of Taenia solium cysticercosis. Trans R Soc Trop Med Hyg 2011 Oct;105(10):574-8.

Bibliography

127

91. Parija M, Biswas R, Harish BN, Parija SC. Detection of specific cysticercus antigen in the urine for diagnosis of neurocysticercosis. Acta Trop 2004 Nov;92(3):253-60.

92. Gonzalez AE, Cama V, Gilman RH, Tsang VC, Pilcher JB, Chavera A, et al. Prevalence and comparison of serologic assays, necropsy, and tongue examination for the diagnosis of porcine cysticercosis in Peru. Am J Trop Med Hyg 1990 Aug;43(2):194-9.

93. Dorny P, Phiri IK, Vercruysse J, Gabriel S, Willingham AL, III, Brandt J, et al. A Bayesian approach for estimating values for prevalence and diagnostic test characteristics of porcine cysticercosis. Int J Parasitol 2004 Apr;34(5):569-76.

94. Dorny P, Vercammen F, Brandt J, Vansteenkiste W, Berkvens D, Geerts S. Sero-epidemiological study of Taenia saginata cysticercosis in Belgian cattle. Vet Parasitol 2000 Feb 29;88(1-2):43-9.

95. Sato MO, Yamasaki H, Sako Y, Nakao M, Nakaya K, Plancarte A, et al. Evaluation of tongue inspection and serology for diagnosis of Taenia solium cysticercosis in swine: usefulness of ELISA using purified glycoproteins and recombinant antigen. Vet Parasitol 2003 Feb 27;111(4):309-22.

96. Gavidia CM, Verastegui MR, Garcia HH, Lopez-Urbina T, Tsang VC, Pan W, et al. Relationship between Serum Antibodies and Taenia solium Larvae Burden in Pigs Raised in Field Conditions. PLoS Negl Trop Dis 2013 May;7(5):e2192.

97. Sciutto E, Martinez JJ, Villalobos NM, Hernandez M, Jose MV, Beltran C, et al. Limitations of current diagnostic procedures for the diagnosis of Taenia solium cysticercosis in rural pigs. Vet Parasitol 1998 Nov 27;79(4):299-313.

98. Deckers N, Saerens D, Kanobana K, Conrath K, Victor B, Wernery U, et al. Nanobodies, a promising tool for species-specific diagnosis of Taenia solium cysticercosis. Int J Parasitol 2009 Apr;39(5):625-33.

99. Jayashi CM, Gonzalez AE, Castillo NR, Rodriguez S, Garcia HH, Lightowlers MW. Validity of the Enzyme-linked Immunoelectrotransfer Blot (EITB) for naturally acquired porcine cysticercosis. Vet Parasitol 2014 Jan 17;199(1-2):42-9.

100. Deckers N, Dorny P, Kanobana K, Vercruysse J, Gonzalez AE, Ward B, et al. Use of ProteinChip technology for identifying biomarkers of parasitic diseases: the example of porcine cysticercosis (Taenia solium). Exp Parasitol 2008 Dec;120(4):320-9.

101. Ramahefarisoa RM, Rakotondrazaka M, Jambou R, Carod JF. Comparison of ELISA and PCR assays for the diagnosis of porcine cysticercosis. Vet Parasitol 2010 Oct 29;173(3-4):336-9.

102. Lightowlers MW, Garcia HH, Gauci CG, Donadeu M, Abela-Ridder B. Monitoring the outcomes of interventions against Taenia solium: options and suggestions. Parasite Immunol 2015 Nov 5.

103. Deckers N, Kanobana K, Silva M, Gonzalez AE, Garcia HH, Gilman RH, et al. Serological responses in porcine cysticercosis: a link with the parasitological outcome of infection. Int J Parasitol 2008 Aug;38(10):1191-8.

104. Devleesschauwer B, Aryal A, Tharmalingam J, Joshi DD, Rijal S, Speybroeck N, et al. Complexities in using sentinel pigs to study Taenia solium transmission dynamics under field conditions. Vet Parasitol 2013 Mar 31;193(1-3):172-8.

Bibliography

128

105. Gonzalez AE, Gilman R, Garcia HH, McDonald J, Kacena K, Tsang VC, et al. Use of sentinel pigs to monitor environmental Taenia solium contamination. The Cysticercosis Working Group in Peru (CWG). Am J Trop Med Hyg 1994 Dec;51(6):847-50.

106. Flisser A. Where are the tapeworms? Parasitol Int 2006;55 Suppl:S117-S120.

107. Allan JC, Velasquez-Tohom M, Torres-Alvarez R, Yurrita P, Garcia-Noval J. Field trial of the coproantigen-based diagnosis of Taenia solium taeniasis by enzyme-linked immunosorbent assay. Am J Trop Med Hyg 1996 Apr;54(4):352-6.

108. Praet N, Verweij JJ, Mwape KE, Phiri IK, Muma JB, Zulu G, et al. Bayesian modelling to estimate the test characteristics of coprology, coproantigen ELISA and a novel real-time PCR for the diagnosis of taeniasis. Trop Med Int Health 2013 May;18(5):608-14.

109. Garcia HH, Gilman RH, Gonzalez AE, Verastegui M, Rodriguez S, Gavidia C, et al. Hyperendemic human and porcine Taenia solium infection in Peru. Am J Trop Med Hyg 2003 Mar;68(3):268-75.

110. Allan JC, Wilkins PP, Tsang VC, Craig PS. Immunodiagnostic tools for taeniasis. Acta Trop 2003 Jun;87(1):87-93.

111. Guezala MC, Rodriguez S, Zamora H, Garcia HH, Gonzalez AE, Tembo A, et al. Development of a species-specific coproantigen ELISA for human Taenia solium taeniasis. Am J Trop Med Hyg 2009 Sep;81(3):433-7.

112. Mwape K, Gabriël S. The Parasitological, Immunological, and Molecular Diagnosis of Human Taeniasis with Special Emphasis on Taenia solium Taeniasis. Curr Trop Med Rep 2014;1(4):173-80.

113. Deckers N, Dorny P. Immunodiagnosis of Taenia solium taeniosis/cysticercosis. Trends Parasitol 2010 Mar;26(3):137-44.

114. Wilkins PP, Allan JC, Verastegui M, Acosta M, Eason AG, Garcia HH, et al. Development of a serologic assay to detect Taenia solium taeniasis. Am J Trop Med Hyg 1999 Feb;60(2):199-204.

115. Ito A, Yanagida T, Nakao M. Recent advances and perspectives in molecular epidemiology of Taenia solium cysticercosis. Infect Genet Evol 2015 Jun 23.

116. WHO, FAO. Multicriteria-based ranking for risk management of food-borne parasites. Rome: FAO; 2014. Report No.: 23.

117. Robertson LJ, van der Giessen JW, Batz MB, Kojima M, Cahill S. Have foodborne parasites finally become a global concern? Trends Parasitol 2013 Mar;29(3):101-3.

118. Countries and areas at risk of cysticercosis, 2011 World Health Organization; 2012.

119. Schantz PM. Taenia solium Cysticercosis: an Overview of Global Distribution and Transmission. In: Singh G, Prabhakar S., editors. Taenia solium Cysticercosis From Basic to Clinical Science.UK: CABI; 2002. p. 63-73.

120. Raccurt CP, Agnamey P, Boncy J, Henrys JH, Totet A. Seroprevalence of human Taenia solium cysticercosis in Haiti. J Helminthol 2009 Jun;83(2):113-6.

Bibliography

129

121. Mwape KE, Phiri IK, Praet N, Dorny P, Muma JB, Zulu G, et al. Study and Ranking of Determinants of Taenia solium Infections by Classification Tree Models. Am J Trop Med Hyg 2015 Jan 7;92(1):56-63.

122. De la GY, Graviss EA, Daver NG, Gambarin KJ, Shandera WX, Schantz PM, et al. Epidemiology of neurocysticercosis in Houston, Texas. Am J Trop Med Hyg 2005 Oct;73(4):766-70.

123. Ehnert KL, Roberto RR, Barrett L, Sorvillo FJ, Rutherford GW, III. Cysticercosis: first 12 months of reporting in California. Bull Pan Am Health Organ 1992;26(2):165-72.

124. Townes JM, Hoffmann CJ, Kohn MA. Neurocysticercosis in Oregon, 1995-2000. Emerg Infect Dis 2004 Mar;10(3):508-10.

125. Schantz PM, Moore AC, Munoz JL, Hartman BJ, Schaefer JA, Aron AM, et al. Neurocysticercosis in an Orthodox Jewish community in New York City. N Engl J Med 1992 Sep 3;327(10):692-5.

126. Moore AC, Lutwick LI, Schantz PM, Pilcher JB, Wilson M, Hightower AW, et al. Seroprevalence of cysticercosis in an Orthodox Jewish community. Am J Trop Med Hyg 1995 Nov;53(5):439-42.

127. Sorvillo FJ, Waterman SH, Richards FO, Schantz PM. Cysticercosis surveillance: locally acquired and travel-related infections and detection of intestinal tapeworm carriers in Los Angeles County. Am J Trop Med Hyg 1992 Sep;47(3):365-71.

128. Hinz E. Current status of food-borne parasitic zoonoses in West Germany. Southeast Asian J Trop Med Public Health 1991 Dec;22 Suppl:78-84.

129. O'Keefe KA, Eberhard ML, Shafir SC, Wilkins P, Ash LR, Sorvillo FJ. Cysticercosis-related hospitalizations in the United States, 1998-2011. Am J Trop Med Hyg 2015 Feb;92(2):354-9.

130. O'Neal SE, Flecker RH. Hospitalization frequency and charges for neurocysticercosis, United States, 2003-2012. Emerg Infect Dis 2015 Jun;21(6):969-76.

131. Rodriguez-Hidalgo R, Benitez-Ortiz W, Dorny P, Geerts S, Geysen D, Ron-Roman J, et al. Taeniosis-cysticercosis in man and animals in the Sierra of Northern Ecuador. Vet Parasitol 2003 Dec 1;118(1-2):51-60.

132. Kabululu ML, Ngowi HA, Kimera SI, Lekule FP, Kimbi EC, Johansen MV. Risk factors for prevalence of pig parasitoses in Mbeya Region, Tanzania. Vet Parasitol 2015 Aug 12.

133. Dorny P, Brandt J, Geerts S. Immunodiagnostic approaches for detecting Taenia solium. Trends Parasitol 2004 Jun;20(6):259-60.

134. Kanobana K, Praet N, Kabwe C, Dorny P, Lukanu P, Madinga J, et al. High prevalence of Taenia solium cysticerosis in a village community of Bas-Congo, Democratic Republic of Congo. Int J Parasitol 2011 Aug 15;41(10):1015-8.

135. Somers R, Dorny P, Nguyen VK, Dang TC, Goddeeris B, Craig PS, et al. Taenia solium taeniasis and cysticercosis in three communities in north Vietnam. Trop Med Int Health 2006 Jan;11(1):65-72.

Bibliography

130

136. Mwape KE, Phiri IK, Praet N, Speybroeck N, Muma JB, Dorny P, et al. The incidence of human cysticercosis in a rural community of Eastern Zambia. PLoS Negl Trop Dis 2013 Mar;7(3):e2142.

137. Declaration of Santiago on epilepsy in Latin America. Epilepsia 2002;43 Suppl 6:42.

138. Bern C, Garcia HH, Evans C, Gonzalez AE, Verastegui M, Tsang VC, et al. Magnitude of the disease burden from neurocysticercosis in a developing country. Clin Infect Dis 1999 Nov;29(5):1203-9.

139. Coral-Almeida M, Gabriel S, Abatih EN, Praet N, Benitez W, Dorny P. Taenia solium Human Cysticercosis: A Systematic Review of Sero-epidemiological Data from Endemic Zones around the World. PLoS Negl Trop Dis 2015 Jul;9(7):e0003919.

140. Gomes I, Veiga M, Embirucu EK, Rabelo R, Mota B, Meza-Lucas A, et al. Taeniasis and cysticercosis prevalence in a small village from Northeastern Brazil. Arq Neuropsiquiatr 2002 Jun;60(2-A):219-23.

141. Ferrer E, Cabrera Z, Rojas G, Lares M, Vera A, de Noya BA, et al. Evidence for high seroprevalence of Taenia solium cysticercosis in individuals from three rural communities in Venezuela. Trans R Soc Trop Med Hyg 2003 Sep;97(5):522-6.

142. Garcia-Noval J, Allan JC, Fletes C, Moreno E, DeMata F, Torres-Alvarez R, et al. Epidemiology of Taenia solium taeniasis and cysticercosis in two rural Guatemalan communities. Am J Trop Med Hyg 1996 Sep;55(3):282-9.

143. Morales J, Martinez JJ, Rosetti M, Fleury A, Maza V, Hernandez M, et al. Spatial distribution of Taenia solium porcine cysticercosis within a rural area of Mexico. PLoS Negl Trop Dis 2008;2(9):e284.

144. Garcia HH, Gilman RH, Gonzalez AE, Pacheco R, Verastegui M, Tsang VC. Human and porcine Taenia solium infection in a village in the highlands of Cusco, Peru. The Cysticercosis Working Group in Peru. Acta Trop 1999 May 25;73(1):31-6.

145. Instituto Nacional de Estadísticas y Censos (INEC). III Censo Nacional Agropecuario. 1 ed. Quito Ecuador: Ministerio de Agricultura; 2002.

146. Población Indígena del Ecuador. Instituto Nacional de Estadísticas y Censos (INEC); 2006.

147. Instituto Nacional de Estadísticas y Censos (INEC). 2015. Ref Type: Online SourceAvailable: http://www.ecuadorencifras.gob.ec/ ; http://www.inec.gob.ec

148. OIE. World Animal Health Information Database. 2015. Ref Type: Online SourceAvailable: http://www.oie.int/wahid-prod/public.php?page=home

149. Ministerio de Salud Pública del Ecuador (MSP). Anuario de vigilancia epidemiológica 1994 - 2013 enfermedades zoonóticas. Ministerio de Salud Pública del Ecuador (MSP) . 2015. 27-8-0015. Ref Type: Online SourceAvailable: http://public.tableau.com/profile/manco.suxio#!/vizhome/zoonoticas/ANUARIO

150. Del Brutto OH, Del Brutto VJ. Changing pattern of neurocysticercosis in an urban endemic center (Guayaquil, Ecuador). J Neurol Sci 2012 Apr 15;315(1-2):64-6.

Bibliography

131

151. Alarcon TA, Del Brutto OH. Neurocysticercosis: declining incidence among patients admitted to a large public hospital in Guayaquil, Ecuador. Pathog Glob Health 2012 Sep;106(5):310-1.

152. Fleury A, Moreno GJ, Valdez AP, de Sayve DM, Becerril RP, Larralde C, et al. Neurocysticercosis, a persisting health problem in Mexico. PLoS Negl Trop Dis 2010;4(8):e805.

153. Rodriguez-Hidalgo R, Benitez-Ortiz W, Praet N, Saa LR, Vercruysse J, Brandt J, et al. Taeniasis-cysticercosis in Southern Ecuador: assessment of infection status using multiple laboratory diagnostic tools. Mem Inst Oswaldo Cruz 2006 Nov;101(7):779-82.

154. Kelvin EA, Yung J, Fong MW, Carpio A, Bagiella E, Leslie D, et al. The association of living conditions and lifestyle factors with burden of cysts among neurocysticercosis patients in Ecuador. Trans R Soc Trop Med Hyg 2012 Dec;106(12):763-9.

155. Goodman KA, Ballagh SA, Carpio A. Case-control study of seropositivity for cysticercosis in Cuenca, Ecuador. Am J Trop Med Hyg 1999 Jan;60(1):70-4.

156. Cruz ME, Schantz PM, Cruz I, Espinosa P, Preux PM, Cruz A, et al. Epilepsy and neurocysticercosis in an Andean community. Int J Epidemiol 1999 Aug;28(4):799-803.

157. Cruz ME, Preux PM, Debrock C, Cruz I, Schantz PM, Tsang VC, et al. [Epidemiology of cerebral cysticercosis in an Andean community in Ecuador]. Bull Soc Pathol Exot 1999 Feb;92(1):38-41.

158. Cruz I, Cruz ME, Teran W, Schantz PM, Tsang V, Barry M. Human subcutaneous Taenia solium cysticercosis in an Andean population with neurocysticercosis. Am J Trop Med Hyg 1994 Oct;51(4):405-7.

159. Nash T, Garcia H, Rajshekhar V, Del Brutto OH. Clinical Cysticercosis: Diagnosis and treatment. In: Murrell KD, Dorny P, Flisser A, Geerts S, Kyvsgaard NC, McManus D, et al., editors. Guidelines for the surveillance, prevention and control of taeniosis/cyticercosis. WHO/FAO/OIE; 2005. p. 11-27.

160. Del Brutto OH, Santibanez R, Idrovo L, Rodriguez S, Diaz-Calderon E, Navas C, et al. Epilepsy and neurocysticercosis in Atahualpa: a door-to-door survey in rural coastal Ecuador. Epilepsia 2005 Apr;46(4):583-7.

161. Del Brutto OH. Solitary cysticercal granuloma in Latin America. In: Rajshekhar V, Chandy MJ, editors. Solitary Cysticercus Granuloma: The Disappearing Lesion.London: Sangam Books; 2000.

162. Del Brutto OH. Single parenchymal brain cysticercus in the acute encephalitic phase: definition of a distinct form of neurocysticercosis with a benign prognosis. J Neurol Neurosurg Psychiatry 1995 Feb;58(2):247-9.

163. Carpio A. Neurocysticercosis: an update. Lancet Infect Dis 2002 Dec;2(12):751-62.

164. Lawson JR, Gemmell MA. Hydatidosis and cysticercosis: the dynamics of transmission. Adv Parasitol 1983;22:261-308.

165. Gemmell MA, Lawson JR. The ovine cysticercosis as models for research into the epidemiology and control of the human and porcine cysticercosis Taenia solium: I. Epidemiological considerations. Acta Leiden 1989;57(2):165-72.

Bibliography

132

166. Gemmell MA, Johnstone PD. Factors regulating tapeworm populations: dispersion of eggs of Taenia hydatigena on pasture. Ann Trop Med Parasitol 1976 Dec;70(4):431-4.

167. Murrell KD. Epidemiology of Taeniosis and Cysticercosis. In: Murrell KD, Dorny P, Flisser A, Geerts S, Kyvsgaard NC, McManus D, et al., editors. Guidelines for the surveillance, prevention and control of taeniosis/cyticercosis.Paris: WHO/FAO/OIE; 2005. p. 73-92.

168. Conlan JV, Vongxay K, Fenwick S, Blacksell SD, Thompson RC. Does interspecific competition have a moderating effect on Taenia solium transmission dynamics in Southeast Asia? Trends Parasitol 2009 Sep;25(9):398-403.

169. Martinez MJ, de Aluja AS, Gemmell M. Failure to incriminate domestic flies (Diptera: Muscidae) as mechanical vectors of Taenia eggs (Cyclophyllidea: Taeniidae) in rural Mexico. J Med Entomol 2000 Jul;37(4):489-91.

170. Arriola CS, Gonzalez AE, Gomez-Puerta LA, Lopez-Urbina MT, Garcia HH, Gilman RH. New insights in cysticercosis transmission. PLoS Negl Trop Dis 2014 Oct;8(10):e3247.

171. Gomez-Puerta LA, Lopez-Urbina MT, Garcia HH, Gonzalez AE. Longevity and viability of Taenia solium eggs in the digestive system of the beetle Ammophorus rubripes. Rev Bras Parasitol Vet 2014 Mar;23(1):94-7.

172. Conlan JV, Vongxay K, Khamlome B, Dorny P, Sripa B, Elliot A, et al. A Cross-Sectional Study of Taenia solium in a Multiple Taeniid-Endemic Region Reveals Competition May be Protective. Am J Trop Med Hyg 2012 Aug;87(2):281-91.

173. Ito A, Yamasaki H, Nakao M, Sako Y, Okamoto M, Sato MO, et al. Multiple genotypes of Taenia solium--ramifications for diagnosis, treatment and control. Acta Trop 2003 Jun;87(1):95-101.

174. Nakao M, Okamoto M, Sako Y, Yamasaki H, Nakaya K, Ito A. A phylogenetic hypothesis for the distribution of two genotypes of the pig tapeworm Taenia solium worldwide. Parasitology 2002 Jun;124(Pt 6):657-62.

175. Sato MO, Sako Y, Nakao M, Wandra T, Nakaya K, Yanagida T, et al. A possible nuclear DNA marker to differentiate the two geographic genotypes of Taenia solium tapeworms. Parasitol Int 2011 Jan;60(1):108-10.

176. Pawlowski Z. Taenia solium: Basic Biology and Transmission. In: Singh G, Prabhakar S., editors. Taenia solium Cysticercosis From Basic to Clinical Science.UK: CABI Publishing; 2002. p. 1-13.

177. Huerta M, Avila R, Jimenez HI, Diaz R, Diaz J, Diaz Huerta ME, et al. Parasite contamination of soil in households of a Mexican rural community endemic for neurocysticercosis. Trans R Soc Trop Med Hyg 2008 Apr;102(4):374-9.

178. Braae UC, Magnussen P, Lekule F, Harrison W, Johansen MV. Temporal fluctuations in the sero-prevalence of Taenia solium cysticercosis in pigs in Mbeya Region, Tanzania. Parasit Vectors 2014;7(1).

179. Braae UC, Harrison W, Lekule F, Magnussen P, Johansen MV. Feedstuff and poor latrines may put pigs at risk of cysticercosis - A case-control study. Vet Parasitol 2015 Aug 12.

180. Serpa JA, Moran A, Goodman JC, Giordano TP, White AC, Jr. Neurocysticercosis in the HIV era: a case report and review of the literature. Am J Trop Med Hyg 2007 Jul;77(1):113-7.

Bibliography

133

181. Rani A, Pushker N, Kulkarni A, Rajpal, Balasubramanya R, Bajaj MS. Simultaneous ocular and systemic cysticercosis and tuberculosis. Infection 2006 Jun;34(3):169-72.

182. Soto Hernandez JL, Ostrosky ZL, Tavera G, Gomez AA. Neurocysticercosis and HIV infection: report of two cases and review. Surg Neurol 1996 Jan;45(1):57-61.

183. Faleiros AC, Lino-Junior R, Lima V, Cavellani C, Correa RR, Llaguno M, et al. [Epidemiological analysis of patients coinfected with Chagas disease and cysticercosis]. Biomedica 2009 Mar;29(1):127-32.

184. Parija SC, Gireesh AR. A serological study of cysticercosis in patients with HIV. Rev Inst Med Trop Sao Paulo 2009 Jul;51(4):185-9.

185. Sarti E, Schantz PM, Plancarte A, Wilson M, Gutierrez IO, Lopez AS, et al. Prevalence and risk factors for Taenia solium taeniasis and cysticercosis in humans and pigs in a village in Morelos, Mexico. Am J Trop Med Hyg 1992 Jun;46(6):677-85.

186. Mwape KE, Phiri IK, Praet N, Muma JB, Zulu G, Van den Bossche P, et al. Taenia solium Infections in a rural area of Eastern Zambia-a community based study. PLoS Negl Trop Dis 2012;6(3):e1594.

187. Sciutto E, Cardenas G, Adalid-Peralta L, Fragoso G, Larralde C, Fleury A. Human neurocysticercosis: immunological features involved in the host's susceptibility to become infected and to develop disease. Microbes Infect 2013 Jun;15(6-7):524-30.

188. Fleury A, Escobar A, Fragoso G, Sciutto E, Larralde C. Clinical heterogeneity of human neurocysticercosis results from complex interactions among parasite, host and environmental factors. Trans R Soc Trop Med Hyg 2010 Apr;104(4):243-50.

189. Pondja A, Neves L, Mlangwa J, Afonso S, Fafetine J, Willingham AL, III, et al. Prevalence and risk factors of porcine cysticercosis in Angonia District, Mozambique. PLoS Negl Trop Dis 2010;4(2):e594.

190. Sikasunge CS, Phiri IK, Willingham AL, III, Johansen MV. Dynamics and longevity of maternally-acquired antibodies to Taenia solium in piglets born to naturally infected sows. Vet J 2010 Jun;184(3):318-21.

191. Gonzalez AE, Verastegui M, Noh JC, Gavidia C, Falcon N, Bernal T, et al. Persistence of passively transferred antibodies in porcine Taenia solium cysticercosis. Cysticercosis Working Group in Peru. Vet Parasitol 1999 Sep 30;86(2):113-8.

192. Morales J, Martinez JJ, Garcia-Castella J, Pena N, Maza V, Villalobos N, et al. Taenia solium: the complex interactions, of biological, social, geographical and commercial factors, involved in the transmission dynamics of pig cysticercosis in highly endemic areas. Ann Trop Med Parasitol 2006 Mar;100(2):123-35.

193. Morales J, Velasco T, Tovar V, Fragoso G, Fleury A, Beltran C, et al. Castration and pregnancy of rural pigs significantly increase the prevalence of naturally acquired Taenia solium cysticercosis. Vet Parasitol 2002 Aug 30;108(1):41-8.

194. Recommendations of the International Task Force for Disease Eradication. MMWR Recomm Rep 1993 Dec 31;42(RR-16):1-38.

195. Pawlowski Z, Allan JC, Meinardi H. Control measures for taeniosis and cysticercosis. In: Murrell KD, Dorny P, Flisser A, Geerts S, Kyvsgaard NC, McManus D, et al., editors.

Bibliography

134

Guidelines for the surveillance, prevention and control of taeniosis/cyticercosis.Paris: WHO/FAO/OIE; 2005. p. 73-99.

196. Allan JC, Craig P, Pawlowski Z. Control of Taenia solium with emphasis of taeniasis. In: Singh G, Prabhakar S., editors. Taenia solium Cysticercosis From Basic to Clinical Science.UK: CABI Publishing; 2002. p. 411-20.

197. Thys S, Mwape KE, Lefevre P, Dorny P, Marcotty T, Phiri AM, et al. Why latrines are not used: communities' perceptions and practices regarding latrines in a Taenia solium endemic rural area in Eastern Zambia. PLoS Negl Trop Dis 2015 Mar;9(3):e0003570.

198. Gilman RH, Gonzalez AE, Llanos-Zavalaga F, Tsang VC, Garcia HH. Prevention and control of Taenia solium taeniasis/cysticercosis in Peru. Pathog Glob Health 2012 Sep;106(5):312-8.

199. Bulaya C, Mwape KE, Michelo C, Sikasunge CS, Makungu C, Gabriel S, et al. Preliminary evaluation of Community-Led Total Sanitation for the control of Taenia solium cysticercosis in Katete District of Zambia. Vet Parasitol 2015 Jan 30;207(3-4):241-8.

200. Mwidunda SA, Carabin H, Matuja WB, Winkler AS, Ngowi HA. A school based cluster randomised health education intervention trial for improving knowledge and attitudes related to Taenia solium cysticercosis and taeniasis in Mbulu district, northern Tanzania. PLoS One 2015;10(2):e0118541.

201. World Health Organization (WHO). WHO seeks united approach to eliminate tapeworm infection. FAO and OIE join WHO to devise framework for tackling leading cause of epilepsy

10 July 2014 | Geneva. WHO . 2015. WHO. Ref Type: Online SourceAvailable: http://www.who.int/neglected_diseases/cysticercosis_meeting_2014/en/

202. Gonzalez AE, Garcia HH, Gilman R, Tsang VC, Cysticercosis Working Group in Peru. Control of Taenia solium. Acta Trop 2003;87:103-9.

203. Garcia HH, Gonzalez AE, Gilman RH, Moulton LH, Verastegui M, Rodriguez S, et al. Combined human and porcine mass chemotherapy for the control of T. solium. Am J Trop Med Hyg 2006 May;74(5):850-5.

204. International Task Force for Disease Eradication. Summary of the Fourth Meeting of the ITFDE (II). Carter Center . 2003. Ref Type: Online SourceAvailable: http://www.cartercenter.org/documents/1367.pdf

205. Sarti E, Schantz PM, Avila G, Ambrosio J, Medina-Santillan R, Flisser A. Mass treatment against human taeniasis for the control of cysticercosis: a population-based intervention study. Trans R Soc Trop Med Hyg 2000 Jan;94(1):85-9.

206. Wu W, Qian X, Huang Y, Hong Q. A review of the control of Clonorchiasis sinensis and Taenia solium taeniasis/cysticercosis in China. Parasitol Res 2012 Nov;111(5):1879-84.

207. Sarti E, Flisser A, Schantz PM, Gleizer M, Loya M, Plancarte A, et al. Development and evaluation of a health education intervention against Taenia solium in a rural community in Mexico. Am J Trop Med Hyg 1997 Feb;56(2):127-32.

208. Ngowi HA, Carabin H, Kassuku AA, Mlozi MR, Mlangwa JE, Willingham AL, III. A health-education intervention trial to reduce porcine cysticercosis in Mbulu District, Tanzania. Prev Vet Med 2008 Jun 15;85(1-2):52-67.

Bibliography

135

209. Kyvsgaard NC, Johansen MV, Carabin H. Simulating transmission and control of Taenia solium infections using a Reed-Frost stochastic model. Int J Parasitol 2007 Apr;37(5):547-58.

210. Molyneux DH, Hopkins DR, Zagaria N. Disease eradication, elimination and control: the need for accurate and consistent usage. Trends Parasitol 2004 Aug;20(8):347-51.

211. Van K, I, Vansteenkiste W, Claes M, Geerts S, Brandt J. Improved detection of circulating antigen in cattle infected with Taenia saginata metacestodes. Vet Parasitol 1998 Apr 30;76(4):269-74.

212. Hall A, Latham MC, Crompton DW, Stephenson LS. Taenia saginata (Cestoda) in western Kenya: the reliability of faecal examinations in diagnosis. Parasitology 1981 Aug;83(Pt 1):91-101.

213. R: A language and environment for statistical computing [computer program]. Version 2.15.1. Vienna, Austria: The R Foundation for Statistical Computing; 2012.

214. Nguekam JP, Zoli AP, Zogo PO, Kamga AC, Speybroeck N, Dorny P, et al. A seroepidemiological study of human cysticercosis in West Cameroon. Trop Med Int Health 2003 Feb;8(2):144-9.

215. Thomas LF. Epidemiology of Taenia solium Cysticercosis in western Kenya. Scotland, Edinburgh: The University of Edinburgh; 2014.

216. Carabin H, Millogo A, Praet N, Hounton S, Tarnagda Z, Ganaba R, et al. Seroprevalence to the antigens of Taenia solium cysticercosis among residents of three villages in Burkina Faso: a cross-sectional study. PLoS Negl Trop Dis 2009;3(11):e555.

217. Secka A, Grimm F, Marcotty T, Geysen D, Niang AM, Ngale V, et al. Old focus of cysticercosis in a senegalese village revisited after half a century. Acta Trop 2011 Aug;119(2-3):199-202.

218. Nitiema P, Carabin H, Hounton S, Praet N, Cowan LD, Ganaba R, et al. Prevalence case-control study of epilepsy in three Burkina Faso villages. Acta Neurol Scand 2012 Oct;126(4):270-8.

219. Mwanjali G, Kihamia C, Kakoko DV, Lekule F, Ngowi H, Johansen MV, et al. Prevalence and risk factors associated with human Taenia solium infections in Mbozi district, Mbeya region, Tanzania. PLoS Negl Trop Dis 2013 Mar;7(3):e2102.

220. Diaz F, Garcia HH, Gilman RH, Gonzales AE, Castro M, Tsang VC, et al. Epidemiology of taeniasis and cysticercosis in a Peruvian village. The Cysticercosis Working Group in Peru. Am J Epidemiol 1992 Apr 15;135(8):875-82.

221. Sarti E, Schantz PM, Plancarte A, Wilson M, Gutierrez OI, Aguilera J, et al. Epidemiological investigation of Taenia solium taeniasis and cysticercosis in a rural village of Michoacan state, Mexico. Trans R Soc Trop Med Hyg 1994 Jan;88(1):49-52.

222. Sanchez AL, Medina MT, Ljungstrom I. Prevalence of taeniasis and cysticercosis in a population of urban residence in Honduras. Acta Trop 1998 May;69(2):141-9.

223. Garcia HH, Araoz R, Gilman RH, Valdez J, Gonzalez AE, Gavidia C, et al. Increased prevalence of cysticercosis and taeniasis among professional fried pork vendors and the general population of a village in the Peruvian highlands. Cysticercosis Working Group in Peru. Am J Trop Med Hyg 1998 Dec;59(6):902-5.

Bibliography

136

224. Sanchez AL, Lindback J, Schantz PM, Sone M, Sakai H, Medina MT, et al. A population-based, case-control study of Taenia solium taeniasis and cysticercosis. Ann Trop Med Parasitol 1999 Apr;93(3):247-58.

225. Agudelo FP, Palacio LG. [Prevalence of Taenia solium antibodies in humans and in pigs in an endemic area of Colombia]. Rev Neurol 2003 Apr 16;36(8):706-9.

226. Moro PL, Lopera L, Bonifacio N, Gilman RH, Silva B, Verastegui M, et al. Taenia solium infection in a rural community in the Peruvian Andes. Ann Trop Med Parasitol 2003 Jun;97(4):373-9.

227. Montano SM, Villaran MV, Ylquimiche L, Figueroa JJ, Rodriguez S, Bautista CT, et al. Neurocysticercosis: association between seizures, serology, and brain CT in rural Peru. Neurology 2005 Jul 26;65(2):229-33.

228. Agudelo-Florez P, Restrepo BN, Palacio LG. [Knowledge and practices concerning taeniasis-cysticercosis in Colombian pig-breeders]. Rev Salud Publica (Bogota ) 2009 Mar;11(2):191-9.

229. Jayaraman T, Prabhakaran V, Babu P, Raghava MV, Rajshekhar V, Dorny P, et al. Relative seroprevalence of cysticercus antigens and antibodies and antibodies to Taenia ova in a population sample in south India suggests immunity against neurocysticercosis. Trans R Soc Trop Med Hyg 2011 Mar;105(3):153-9.

230. Theis JH, Goldsmith RS, Flisser A, Koss J, Chioino C, Plancarte A, et al. Detection by immunoblot assay of antibodies to Taenia solium cysticerci in sera from residents of rural communities and from epileptic patients in Bali, Indonesia. Southeast Asian J Trop Med Public Health 1994 Sep;25(3):464-8.

231. Raghava MV, Prabhakaran V, Jayaraman T, Muliyil J, Oommen A, Dorny P, et al. Detecting spatial clusters of Taenia solium infections in a rural block in South India. Trans R Soc Trop Med Hyg 2010 Sep;104(9):601-12.

232. Martinez-Hernandez F, Jimenez-Gonzalez DE, Chenillo P, Alonso-Fernandez C, Maravilla P, Flisser A. Geographical widespread of two lineages of Taenia solium due to human migrations: can population genetic analysis strengthen this hypothesis? Infect Genet Evol 2009 Dec;9(6):1108-14.

233. Singh G. Neurocysticercosos in South-Central America and the Indian subcontinent. A comparative evaluation. Arq Neuropsiquiatr 1997 Sep;55(3A):349-56.

234. Chavarria A, Roger B, Fragoso G, Tapia G, Fleury A, Dumas M, et al. TH2 profile in asymptomatic Taenia solium human neurocysticercosis. Microbes Infect 2003 Oct;5(12):1109-15.

235. Sarti-Gutierrez EJ, Schantz PM, Lara-Aguilera R, Gomez DH, Flisser A. Taenia solium taeniasis and cysticercosis in a Mexican village. Trop Med Parasitol 1988 Sep;39(3):194-8.

236. Lawson JR, Gemmell MA. The potential role of blowflies in the transmission of taeniid tapeworm eggs. Parasitology 1985 Aug;91 ( Pt 1):129-43.

237. Lawson JR, Gemmell MA. Transmission of taeniid tapeworm eggs via blowflies to intermediate hosts. Parasitology 1990 Feb;100 Pt 1:143-6.

Bibliography

137

238. Meza-Lucas A, Carmona-Miranda L, Garcia-Jeronimo RC, Torrero-Miranda A, Gonzalez-Hidalgo G, Lopez-Castellanos G, et al. Short report: limited and short-lasting humoral response in Taenia solium: seropositive households compared with patients with neurocysticercosis. Am J Trop Med Hyg 2003 Aug;69(2):223-7.

239. Foyaca-Sibat H, Cowan LD, Carabin H, Targonska I, Anwary MA, Serrano-Ocana G, et al. Accuracy of serological testing for the diagnosis of prevalent neurocysticercosis in outpatients with epilepsy, Eastern Cape Province, South Africa. PLoS Negl Trop Dis 2009;3(12):e562.

240. Mwape KE, Blocher J, Wiefek J, Schmidt K, Dorny P, Praet N, et al. Prevalence of Neurocysticercosis in People with Epilepsy in the Eastern Province of Zambia. PLoS Negl Trop Dis 2015 Aug;9(8):e0003972.

241. World Health Organization (WHO). Epilepsy Fact Sheet. WHO, editor. WHO . 2015. Geneva, Switzerland, WHO. 28-5-2015. Ref Type: Online SourceAvailable: http://www.who.int/mediacentre/factsheets/fs999/en/

242. Keilbach NM, de Aluja AS, Sarti-Gutierrez E. A programme to control taeniasis-cysticercosis (T. solium): experiences in a Mexican village. Acta Leiden 1989;57(2):181-9.

243. Flores MG, Castillo A. Esfera Pública N.4: Una mirada desde la sociedad civil a la gobernanza del Sistema Nacional de Salud. Grupo Faro, editor. [4]. 2012. Quito Ecuador, Grupo Faro. Esfera Pública. Ref Type: Serial (Book,Monograph)Available: http://www.grupofaro.org/sites/default/files/archivos/publicaciones/2012/2012-05-07/ep-gobernanzasalud-4.pdf

244. Ministerio de Salud Pública del Ecuador (MSP). Enfermedades y eventos de notificación obligatoria. Ministerio de Salud Pública del Ecuador (MSP) . 2009. Ministerio de Salud Pública del Ecuador (MSP). Ref Type: Online SourceAvailable: http://www.msp.gob.ec

245. Hueston WD, Walker KD. Macroepidemiological contributions to quantitative risk assessment. Rev Sci Tech 1993 Dec;12(4):1197-201.

246. Sistema Integrado de Indicadores Sociales del Ecuador (SIISE). Indicadores sociales del Ecuador 2008. Sistema Integrado de Indicadores Sociales del Ecuador . 2008. Ref Type: Online SourceAvailable: http://www.siise.gob.ec/

247. Yanez A. La salud desde la mirada de los derechos humanos. Quito-Ecuador: Grupo FARO; 2013.

248. World Health Organization (WHO). International Classification of Diseases (ICD). 2014. Ref Type: Online SourceAvailable: http://www.who.int/classifications/icd/en/

249. Instituto Nacional de Meteorología e hidrología (INHAMI). Mapa de precipitación media multianual (1965-1999). 2015. Ref Type: Online SourceAvailable: http://www.serviciometeorologico.gob.ec/biblioteca/

250. Kulldorff M. A spatial scan statistic. Communications in Statistics - Theory and Methods 1997;26(6):1481-96.

251. Patil GP, Taillie C. Geographic and Network Surveillance via Scan Statistics for Critical Area Detection. Statistical Science 2003;14(4):457-65.

Bibliography

138

252. Hu MC, Pavlicova M, Nunes EV. Zero-inflated and hurdle models of count data with extra zeros: examples from an HIV-risk reduction intervention trial. Am J Drug Alcohol Abuse 2011 Sep;37(5):367-75.

253. Raftery A. Bayesian Model Selection in Social Research. Sociological Methodology 1995;25:111-63.

254. Zuur A, Savaliev A, Ieno EN. Zero Inflated Models and Generalized Linear Mixed Models with R. 1st ed. Highland Statistics Limited; 2012.

255. Political Science Computational Laboratory (Pscl package) [computer program]. R environment: CRAN; 2015.

256. Support functions and dataset for Venable and Ripley's MASS [computer program]. R environment: 2015.

257. Hoeting J, Madigan D, Raftery A, Volinsky C. Bayesian model averaging: A tutorial. Statistical Science 1999;14(4):382-417.

258. Bayesian Model Averaging package in R (BMA) [computer program]. r topics: R package distributed through CRAN; 2010.

259. Ver Hoef JM, Boveng PL. Quasi-Poisson vs. negative binomial regression: how should we model overdispersed count data? Ecology 2007 Nov;88(11):2766-72.

260. Idro R, Marsh K, John CC, Newton CR. Cerebral Malaria; Mechanisms Of Brain Injury And Strategies For Improved Neuro-Cognitive Outcome. Pediatr Res 2010 Oct;68(4):267-74.

261. Pawlowski Z, Allan J, Sarti E. Control of Taenia solium taeniasis/cysticercosis: from research towards implementation. Int J Parasitol 2005 Oct;35(11-12):1221-32.

262. Sander JW. Infectious agents and epilepsy. In: Knobler S, O'Connor S, Lemon SM, Najafi M, editors. Institute of Medicine (US) Forum on Microbial Threats.Washington (DC): National Academies Press (US); 2004.

263. Yemadje LP, Houinato D, Quet F, Druet-Cabanac M, Preux PM. Understanding the differences in prevalence of epilepsy in tropical regions. Epilepsia 2011 Aug;52(8):1376-81.

264. Vaid N, Fekadu S, Alemu S, Dessie A, Wabe G, Phillips DI, et al. Epilepsy, poverty and early under-nutrition in rural Ethiopia. Seizure 2012 Nov;21(9):734-9.

265. Organization of American States (OAS). Criterios y Acciones para el cumplimiento de las metas del milenio en agua y saneamiento. OAS, editor. OAS . 2010. Washington D.C. United States of America, OAS. 28-5-2015. Ref Type: Online SourceAvailable: http://www.oas.org/dsd/MinisterialMeeting/CRITERIOS%20Y%20ACCIONES%20EN%20PRO%20CUMPLIMIENTO%20ODM%20AGUA%20Y%20SANEAMIENTO.pdf

266. Nash TE, Del Brutto OH, Butman JA, Corona T, Delgado-Escueta A, Duron RM, et al. Calcific neurocysticercosis and epileptogenesis. Neurology 2004 Jun 8;62(11):1934-8.

267. Cruz ME, Cruz I, Preux PM, Schantz P, Dumas M. Headache and cysticercosis in Ecuador, South America. Headache 1995 Feb;35(2):93-7.

268. OIE. World Animal Health Information Database 2005. 2005. Ref Type: Online SourceAvailable: http://www.oie.int/wahid-prod/public.php?page=home

Bibliography

139

269. Agrocalidad. Programa Nacional Sanitario Porcino. Agrocalidad, editor. 2010. Agrocalidad. Ref Type: Serial (Book,Monograph)Available: http://www.agrocalidad.gob.ec

270. Placencia M, Shorvon SD, Paredes V, Bimos C, Sander JW, Suarez J, et al. Epileptic seizures in an Andean region of Ecuador. Incidence and prevalence and regional variation. Brain 1992 Jun;115 ( Pt 3):771-82.

271. Instituto Nacional de Estadísticas y Censos (INEC). Censo poblacional y vivienda del Ecuador 2010. Instituto Nacional de Estadísticas y Censos . 2010. Ecuador, Ecuador en Cifras, Instituto Nacional de Estadísticas y Censos. Ref Type: Online SourceAvailable: http://www.ecuadorencifras.gob.ec/censo-de-poblacion-y-vivienda/

272. Pal DK, Carpio A, Sander JW. Neurocysticercosis and epilepsy in developing countries. J Neurol Neurosurg Psychiatry 2000 Feb;68(2):137-43.

273. Huisa BN, Menacho LA, Rodriguez S, Bustos JA, Gilman RH, Tsang VC, et al. Taeniasis and cysticercosis in housemaids working in affluent neighborhoods in Lima, Peru. Am J Trop Med Hyg 2005 Sep;73(3):496-500.

274. Assana E, Amadou F, Thys E, Lightowlers MW, Zoli AP, Dorny P, et al. Pig-farming systems and porcine cysticercosis in the north of Cameroon. J Helminthol 2010 Dec;84(4):441-6.

275. Ngoungou EB, Preux PM. Cerebral malaria and epilepsy. Epilepsia 2008 Aug;49 Suppl 6:19-24.

276. Medina MT, Rosas E, Rubio-Donnadieu F, Sotelo J. Neurocysticercosis as the main cause of late-onset epilepsy in Mexico. Arch Intern Med 1990 Feb;150(2):325-7.

277. Ministerio de Salud Pública del Ecuador (MSP). Datos esenciales de salud: Una miradad a la década 2000-2010. Quito-Ecuador: Ministerio de Salud Pública; 2012.

278. Benitez-Ortiz. Los Cerdos Locales en los Sistemas Tradicionales de Producción. Roma: FAO; 2001.

279. Berkvens D, Speybroeck N, Praet N, Adel A, Lesaffre E. Estimating disease prevalence in a Bayesian framework using probabilistic constraints. Epidemiology 2006 Mar;17(2):145-53.

280. Ihaka R, and Gentleman R. R: A language for data analysis and graphics. Journal of Computational and Graphical Statistics 5[3], 299-314. 1996. Ref Type: Magazine Article

281. Lunn DJ, Thomas A, Best N, Spiegelhalter D. WinBUGS - A Bayesian modelling framework: Concepts, structure, and extensibility Statistics and Computing. Statistics and Computing 10[4], 325-337. 10-10-2000. Kluwer Academic Publishers. Ref Type: Magazine Article

282. Rosenstock S, Jorgensen T, Andersen L, Bonnevie O. Seroconversion and seroreversion in IgG antibodies to Helicobacter pylori: a serology based prospective cohort study. J Epidemiol Community Health 2000 Jun;54(6):444-50.

283. Villaran MV, Montano SM, Gonzalvez G, Moyano LM, Chero JC, Rodriguez S, et al. Epilepsy and neurocysticercosis: an incidence study in a Peruvian rural population. Neuroepidemiology 2009;33(1):25-31.

Bibliography

140

284. Dohoo I, Martin W, Stryhn H. Measures of Disease Frequency. In: McPike M, editor. Veterinary Epidemiologic Research. 1st ed. Charlottetown, Prince Edward Island, Canada: AVC Inc.; 2003. p. 65-84.

285. Epitools: Epidemiology Tools [computer program]. Version R package version 0.5-6 2010.

286. Speybroeck N, Lindsey P, Billiouw M, Madder M, Lindsey J, Berkvens D. Modelling diapause termination of Rhipicephalus appendiculatus using statistical tools to detect sudden behavioural changes and time dependencies. Environ Ecol Stat 2006;13(1):69-87.

287. Ngowi HA, Kassuku AA, Maeda GE, Boa ME, Carabin H, Willingham AL, III. Risk factors for the prevalence of porcine cysticercosis in Mbulu District, Tanzania. Vet Parasitol 2004 Apr 15;120(4):275-83.

288. Pouedet MS, Zoli AP, Nguekam, Vondou L, Assana E, Speybroeck N, et al. Epidemiological survey of swine cysticercosis in two rural communities of West-Cameroon. Vet Parasitol 2002 May 30;106(1):45-54.

289. Blocher J, Schmutzhard E, Wilkins PP, Gupton PN, Schaffert M, Auer H, et al. A cross-sectional study of people with epilepsy and neurocysticercosis in Tanzania: clinical characteristics and diagnostic approaches. PLoS Negl Trop Dis 2011 Jun;5(6):e1185.

290. Braae UC, Saarnak CF, Mukaratirwa S, Devleesschauwer B, Magnussen P, Johansen MV. Taenia solium taeniosis/cysticercosis and the co-distribution with schistosomiasis in Africa. Parasit Vectors 2015;8:323.

291. Murray CJ, Lopez AD. Global mortality, disability, and the contribution of risk factors: Global Burden of Disease Study. Lancet 1997 May 17;349(9063):1436-42.

292. Sousa-Figueiredo JC, Stanton MC, Katokele S, Arinaitwe M, Adriko M, Balfour L, et al. Mapping of Schistosomiasis and Soil-Transmitted Helminths in Namibia: The First Large-Scale Protocol to Formally Include Rapid Diagnostic Tests. PLoS Negl Trop Dis 2015 Jul;9(7):e0003831.

293. Gonzales I, Miranda JJ, Rodriguez S, Vargas V, Cjuno A, Smeeth L, et al. Seizures, cysticercosis and rural-to-urban migration: the PERU MIGRANT study. Trop Med Int Health 2015 Apr;20(4):546-52.

294. Pawlowski ZS. Control of neurocysticercosis by routine medical and veterinary services. Trans R Soc Trop Med Hyg 2008 Mar;102(3):228-32.

295. World Health Organization (WHO), FAO, OIE, ILRI. Assembling a framework for intensified control of taeniasis and neurocysticercosis caused by Taenia solium: report of an informal consultation. Switzerland: WHO; 2014.

296. International Task Force for Disease Eradication. Summary of the Twenty first Meeting of the ITFDE (II). Carter Center . 2013. Carter Center. Ref Type: Online SourceAvailable: http://www.cartercenter.org/resources/pdfs/news/health_publications/itfde/ITFDE-summary-071013.pdf

297. Garcia-Garcia ML, Torres M, Correa D, Flisser A, Sosa-Lechuga A, Velasco O, et al. Prevalence and risk of cysticercosis and taeniasis in an urban population of soldiers and their relatives. Am J Trop Med Hyg 1999 Sep;61(3):386-9.

Bibliography

141

298. Joshi DD, Poudyal PM, Jimba M, Mishra PN, Neave LA, Maharjan M. Controlling Taenia solium in Nepal using the PRECEDE-PROCEED model. Southeast Asian J Trop Med Public Health 2001;32 Suppl 2:94-7.

299. O'Neal SE, Moyano LM, Ayvar V, Rodriguez S, Gavidia C, Wilkins PP, et al. Ring-screening to control endemic transmission of Taenia solium. PLoS Negl Trop Dis 2014 Sep;8(9):e3125.

300. Fleury A, Morales J, Bobes RJ, Dumas M, Yanez O, Pina J, et al. An epidemiological study of familial neurocysticercosis in an endemic Mexican community. Trans R Soc Trop Med Hyg 2006 Jun;100(6):551-8.

301. Braae UC, Devleesschauwer B, Gabriël S, Dorny P, Speybroeck N, Magnussen P, et al. CystiSim – an agent-based model for Taenia solium transmission and control. 1st Cystinet International Conference taeniosis And Cysticercosis: A One Health Challenge - Belgrade 2015: University of Belgrade Institute for Medical Research; 2015.

302. World Health Organization (WHO). WHO declares Ecuador free of onchocerciasis (river blindness). WHO . 2014. Ref Type: Online SourceAvailable: http://www.who.int/neglected_diseases/ecuador_free_from_onchocerciasis/en/

303. OIE. List of FMD free Member Countries. OIE, editor. OIE . 2015. Ref Type: Online SourceAvailable: http://www.oie.int/en/animal-health-in-the-world/official-disease-status/fmd/list-of-fmd-free-members/

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