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School-based deworming and community-wide
transmission of soil transmitted helminths
Déirdre HollingsworthUniversity of Warwick
Liverpool School of Tropical Medicine
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Soil-transmitted helminths• Burden of disease (WHO estimates)
– Up to 1.2 billion people infected with one or more of the soil-transmitted helminths
– 135,000 deaths per year
• Disabling effects– Anaemia– Stunted growth– Impaired cognitive development
• Want to maximise impact of drug donations in London Declaration:– 400m albendazole, GlaxoSmithKlein– 200m mebendazole, Johnson &
Johnson Despommier D et al. Parasitic Diseases. 2001
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Key questions for control of soil-transmitted infections by
chemotherapy1. What should be the target of control programmes?2. Is elimination in a defined area possible by
chemotherapy alone?3. What are the best indicators for assessing the impact
of control?4. What level of infection across a community should
trigger mass chemotherapy to minimise morbidity?5. For a given transmission level, how often should
mass or targeted chemotherapy be administered to sustain infection prevalence and intensity below defined levels?
Anderson, Hollingsworth et al Lancet (2012)
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Key questions for control of soil-transmitted infections by
chemotherapy1. What should be the target of control programmes?2. Is elimination in a defined area possible by
chemotherapy alone?3. What are the best indicators for assessing the impact
of control?4. What level of infection across a community should
trigger mass chemotherapy to minimise morbidity?5. For a given transmission level, how often should
mass or targeted chemotherapy be administered to sustain infection prevalence and intensity below defined levels?
Anderson, Hollingsworth et al Lancet (2012)
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Key questions for control of soil-transmitted infections by
chemotherapy1. What should be the target of control programmes?2. Is elimination in a defined area possible by
chemotherapy alone?3. What are the best indicators for assessing the impact
of control?4. What level of infection across a community should
trigger mass chemotherapy to minimise morbidity?5. For a given transmission level, how often should
mass or targeted chemotherapy be administered to sustain infection prevalence and intensity below defined levels?
Anderson, Hollingsworth et al Lancet (2012)
![Page 6: School-based deworming and community-wide transmission of soil transmitted helminths](https://reader035.vdocuments.us/reader035/viewer/2022062517/56812d9b550346895d92b9ce/html5/thumbnails/6.jpg)
Key questions for control of soil-transmitted infections by
chemotherapy1. What should be the target of control programmes?2. Is elimination in a defined area possible by
chemotherapy alone?3. What are the best indicators for assessing the impact
of control?4. What level of infection across a community should
trigger mass chemotherapy to minimise morbidity?5. For a given transmission level, how often should
mass or targeted chemotherapy be administered to sustain infection prevalence and intensity below defined levels?
Anderson, Hollingsworth et al Lancet (2012)
![Page 7: School-based deworming and community-wide transmission of soil transmitted helminths](https://reader035.vdocuments.us/reader035/viewer/2022062517/56812d9b550346895d92b9ce/html5/thumbnails/7.jpg)
Key questions for control of soil-transmitted infections by
chemotherapy1. What should be the target of control programmes?2. Is elimination in a defined area possible by
chemotherapy alone?3. What are the best indicators for assessing the impact
of control?4. What level of infection across a community should
trigger mass chemotherapy to minimise morbidity?5. For a given transmission level, how often should
mass or targeted chemotherapy be administered to sustain infection prevalence and intensity below defined levels?
Anderson, Hollingsworth et al Lancet (2012)
![Page 8: School-based deworming and community-wide transmission of soil transmitted helminths](https://reader035.vdocuments.us/reader035/viewer/2022062517/56812d9b550346895d92b9ce/html5/thumbnails/8.jpg)
Key questions for control of soil-transmitted infections by
chemotherapy6. As the prevalence and intensity fall after repeated
rounds of treatment, can the interval between treatments increase, and by how much?
7. How is the interval between treatments affected by the species mix in the community?
8. How do the demography of the population and the starting geographical distribution of infection affect the structure of optimum treatment programmes when resources are finite?
9. In terms of cost-effectiveness, is it best to target school children, those predisposed to heavy infection, or the entire community?
10.How might repeated mass treatment affect the evolution of drug resistance and how can this risk be minimised?
Anderson, Hollingsworth et al Lancet (2012)
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Key questions for control of soil-transmitted infections by
chemotherapy6. As the prevalence and intensity fall after repeated
rounds of treatment, can the interval between treatments increase, and by how much?
7. How is the interval between treatments affected by the species mix in the community?
8. How do the demography of the population and the starting geographical distribution of infection affect the structure of optimum treatment programmes when resources are finite?
9. In terms of cost-effectiveness, is it best to target school children, those predisposed to heavy infection, or the entire community?
10.How might repeated mass treatment affect the evolution of drug resistance and how can this risk be minimised?
Anderson, Hollingsworth et al Lancet (2012)
![Page 10: School-based deworming and community-wide transmission of soil transmitted helminths](https://reader035.vdocuments.us/reader035/viewer/2022062517/56812d9b550346895d92b9ce/html5/thumbnails/10.jpg)
Key questions for control of soil-transmitted infections by
chemotherapy6. As the prevalence and intensity fall after repeated
rounds of treatment, can the interval between treatments increase, and by how much?
7. How is the interval between treatments affected by the species mix in the community?
8. How do the demography of the population and the starting geographical distribution of infection affect the structure of optimum treatment programmes when resources are finite?
9. In terms of cost-effectiveness, is it best to target school children, those predisposed to heavy infection, or the entire community?
10.How might repeated mass treatment affect the evolution of drug resistance and how can this risk be minimised?
Anderson, Hollingsworth et al Lancet (2012)
![Page 11: School-based deworming and community-wide transmission of soil transmitted helminths](https://reader035.vdocuments.us/reader035/viewer/2022062517/56812d9b550346895d92b9ce/html5/thumbnails/11.jpg)
Key questions for control of soil-transmitted infections by
chemotherapy6. As the prevalence and intensity fall after repeated
rounds of treatment, can the interval between treatments increase, and by how much?
7. How is the interval between treatments affected by the species mix in the community?
8. How do the demography of the population and the starting geographical distribution of infection affect the structure of optimum treatment programmes when resources are finite?
9. In terms of cost-effectiveness, is it best to target school children, those predisposed to heavy infection, or the entire community?
10.How might repeated mass treatment affect the evolution of drug resistance and how can this risk be minimised?
Anderson, Hollingsworth et al Lancet (2012)
![Page 12: School-based deworming and community-wide transmission of soil transmitted helminths](https://reader035.vdocuments.us/reader035/viewer/2022062517/56812d9b550346895d92b9ce/html5/thumbnails/12.jpg)
Key questions for control of soil-transmitted infections by
chemotherapy6. As the prevalence and intensity fall after repeated
rounds of treatment, can the interval between treatments increase, and by how much?
7. How is the interval between treatments affected by the species mix in the community?
8. How do the demography of the population and the starting geographical distribution of infection affect the structure of optimum treatment programmes when resources are finite?
9. In terms of cost-effectiveness, is it best to target school children, those predisposed to heavy infection, or the entire community?
10.How might repeated mass treatment affect the evolution of drug resistance and how can this risk be minimised?
Anderson, Hollingsworth et al Lancet (2012)
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Why school-based deworming?
• Burden of disease in children• Existing infrastructure for delivery
– Integration with other school health programmes
• What is the impact on transmission?
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Empirical studiesReference Main
targetCountry Drug Interv
alRounds
Age group targeted (yrs)
Impact on untreated
Asaolu et al (1991) Parasitology
Ascaris, Trichuris, Hookworm
Nigeria levamisole
3 mths
4 (1yr)
2-15 Intensity, Ascaris only
Thein-Hliang et al (1990) WHO Bulletin
Ascaris Myanmar levamisole
6 mths
2-4 (1-2yr)
1-191-145-19
Intensity and prevalence
Thein-Hliang et al (1991) Trans RSTMH
Ascaris Myanmar levamisole
3 mths
4 (1 yr)
<152--12
Intensity and prevalence
Bundy et al (1990) Trans RSTMH
TrichurisAscaris
Monserrat
albendazole
4 mths
2, 4 (8, 16 mths)
2-15 Intensity and prevalence
We need a framework for thinking about the impact of treating only 5-14 year olds
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How many worms are exposed to treatment?
• Demography– What proportion of population are
school-aged?
• Behaviour– What proportion of children attend
school?
• Epidemiology– What is the load of worms in children?
Anderson, Truscott, Pullan, Brooker, Hollingsworth PLoS NTDs (2013) in press
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School attendance• Enrolment varies by country, by age and by
region• Attendance at deworming days may be higher
than ordinary school days.
Som
alia
Centr
al ..
.
Djibouti
Benin
Nig
eri
a
Burk
ina..
.
Kenya
Yem
en
Angola
Bangla
...
Uganda
Moza
m..
.
Nepal
Egypt
Unit
ed .
..
Leso
tho
Myanm
ar
Zim
b..
.
Suri
nam
e
Peru
Alg
eri
a
Kaza
kh..
.040
80
Primary urban Primary rural Secondary attendance
Perc
en
tag
e o
f ch
ild
ren
Source: UNICEF
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How many worms are exposed to treatment?
• Demography– What proportion of population are
school-aged?
• Behaviour– What proportion of children attend
school?
• Epidemiology– What is the load of worms in children?
Anderson, Truscott, Pullan, Brooker, Hollingsworth PLoS NTDs (2013) in press
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Round worm• High worm
burdens in children
Anderson et al PLoS NTDs (2013) in press
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Round worm• High worm
burdens in children
Anderson et al PLoS NTDs (2013) in press
18%
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Round worm• High worm
burdens in children
49% worms in 5-14yr olds
Anderson et al PLoS NTDs (2013) in press
18%
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Hookworm• Lower
burden in children
Anderson et al PLoS NTDs (2013) in press
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Hookworm• Lower
burden in children
Anderson et al PLoS NTDs (2013) in press
31%
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Hookworm• Lower
burden in children
16% egg output in 5-14yr olds
Anderson et al PLoS NTDs (2013) in press
31%
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Impact on transmission
• % of worms or output in school-age children is a crude calculation of likely impact
• Impact on transmission depends on– Extent transmission from children to
adults and younger children – Vice versa
• Investigate scenarios using mathematical models
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Anderson et al PLoS NTDs (2013) in press
Two separate groups contributing equally to same infected pool• Treated group (30%)
see much larger effect• Untreated group very
little impact
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Anderson et al PLoS NTDs (2013) in press
Children over-contribute to transmission• Starting intensity in
untreated group is lower
• Larger impact on this group of treating the children
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Prog
ram
me
impa
ctDrug efficacy
~80-90%
% of parasites treated
Impact on transmission
More studies needed
?
School Enrolment~20-90%
% parasites in school children
~10-50%
Demography X Parasites
A. lumbricoides
Demography
X Parasites
Hookw
orm
Anderson et al PLoS NTDs (2013) in press
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How to address this question
• Monitoring impact of school-based treatment on whole communities – Whole age-profiles before and after
treatment
• Detailed studies of the dynamics of ‘bounce-back’ in adults and children – Robust parameter estimation– Trials of different treatment strategies
• Genetic studies – Identifying transmission networks
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Responding to programmatic need
Control strategies• Mapping, monitoring &
evaluation• Frequency of &
targeting of treatment• Programme design
Research• Mapping, sampling• Epidemiology of
transmission and control
• Diagnostic design and evaluation
Programme designSampling frameworks
New tools
Research questionsField data
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Acknowledgements
• Imperial College London– Professor Sir Roy Anderson– Dr James Truscott– Helminth researchers
• London School of Hygiene and Tropical Medicine– Professor Simon Brooker– Dr Rachel Pullan
• Funders– Bill and Melinda Gates Foundation– Partnership for Child Development– Imperial College Junior Research Fellowship