73 leishmaniases

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Infectious Diseases of the Dog and Cat, 3rd Edition

CHAPTER 73 Leishmaniases

The leishmaniases are a group of infectious diseases that affect people and domestic and wild animals worldwide and

are caused by members of the genusLeishmania. The infection is transmitted by sandflies of the genusPhlebotomus

in the Old World andLutzomyiain the New World. Visceral leishmaniasis, the most severe disease form, is a

frequent cause of clinical illness in dogs in some regions but is less common in cats. Reservoir hosts vary within

different geographic areas and can include domestic or wild animals. Infected domestic dogs serve as reservoirs of

the disease for people in several areas where leishmaniasis is endemic. Dogs are reservoirs forLeishmania infantum

infection in an area that stretches from Portugal to China. They are also reservoirs of infection for foxes and

opossums in an area ofLeishmania chagasi (infantum)that extends from southern Mexico to South America. Canine

leishmaniasis is also sometimes found in nonendemic countries because of international tourists and immigrants who

bring infected pets or because of dog importation. Dogs can be asymptomatic carriers of leishmaniases that are

infectious to sandflies, and infection may go unnoticed for a long time. In this chapter, a global coverage of

leishmaniasis will be presented, followed by two recognized geographic forms of emerging disease in animals in the

New World.

LEISHMANIASIS

Gad Baneth

Etiology

Leishmaniasis is caused by diphasic protozoans of the genusLeishmaniain the class Kinetoplasta and family

Trypanosomatidae. About 30 different leishmanial species are found in various parts of the Old World and New

World (Fig. 73-1). Of these, about 20 are responsible for a wide spectrum of clinical illnesses in people.15

Most

Leishmaniaspp. that infect people are zoonotic, and only a few are strictly anthroponotic(i.e., transmitted

directly from person to person via sandflies). Leishmaniasis is endemic in 88 countries66 in the Old World

and 22 in the New World. Approximately 12 million people are infected with leishmaniasis, and some 350million people are at risk of acquiring the disease, with a yearly incidence of 1 to 1.5 million new cases of

cutaneous disease and 500,000 new cases of the potentially fatal visceral form.55,56

Dogs are frequently

involved in sylvan and urban cycles of zoonoticLeishmaniaspp. that cause disease in people in many parts of

the world.217

Based on seroprevalence studies from Spain, France, Italy, and Portugal, it has been estimated

that 2.5 million dogs in these countries are infected with visceral leishmaniasis.142

The number of infected dogs

in South America is also estimated to be in the millions, with high infection rates being reported in some areas

of Brazil.

The genusLeishmaniais divided into the subgeneraLeishmaniaand Vianniabased on the differences in

sandfly development. Many species are recognized within these subgenera. Classification is primarily based on

DNA sequence comparisons, electrophoresis migration patterns of isoenzymes (zymodemes), and reactivity to

monoclonal antibodies and to membrane-shed antigens.

The diseases caused by the variousLeishmaniaspp. in people are divided into three forms according to their

clinical manifestations (Table 73-1): cutaneous leishmaniasis (CL), mucocutaneous leishmaniasis (MCL), and

visceral leishmaniasis (VL). Some species cause more than one form of the disease.

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Canine leishmaniasis is often classified as VL because it is associated with some of theLeishmaniaspp. that

cause VL in people; however, dogs usually have visceral and cutaneous involvement.L. chagasi, the VL agent

in South America, is considered to be synonymous withL. infantumbased on various genetic analyses.135

The

low genetic variability ofL. chagasiis consistent with recent importation to the New World, and it is thought

that it was introduced by infected dogs from Europe that arrived with settlers.

Epidemiology

The natural cycle ofLeishmaniainfection involves a sandfly vector and a vertebrate host in which different

forms of the parasite are found. Hematophagous female sandflies harborLeishmaniapromastigotes in their guts

and transmit the parasite during a blood meal to wild or domestic animals and people, where the amastigote

form develops. Phlebotomine sandflies of the genusPhlebotomusin the Old World andLutzomyiain the New

World are the natural vectors of leishmaniasis. Sandflies are small insects with a body length seldom exceeding

3 mm.105

The biting activity of sandflies is crepuscular and nocturnal. In the Mediterranean region and Asia,

sandflies are primarily active in the warm monthsfrom spring to late fall. In Latin America, some sandflies

are active throughout the year. They do not move long distances, and studies have shown that they are seldom

dispersed more than 1 km from their breeding sites. Many species of sandfly exist, but only some of them act as

disease vectors. Different vector species may be found in distinct geographic regions and ecologic niches. Some

sandfly species exclusively transmit only oneLeishmaniaspecies, whereas others are vectors for more than one

species. The vectorial capacity of different sandfly species appears to be related to the ability of promastigotes

to specifically bind to receptors in the sandfly gut. When they do not bind to the sandfly gut, the parasites that

initially replicated in the gut lumen are excreted with the sandfly feces and presumably do not reach the critical

mass needed to infect a host during a second blood meal. Organisms of the Vianniasubgenus ofLeishmania

braziliensisreplicate in the hindgut, in contrast to the midgut replication characteristic of all otherLeishmania

species.

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Fig 73-1 Distribution of cutaneous and mucocutaneous (A)and visceral (B)

leishmaniasis. (Data modified from World Health Organization. 1984.

The leishmaniases. The WHO Expert Committee. WHO Technical ReportSeries No. 701. Geneva, WHO; map courtesy University of Georgia,

Athens, Ga.)



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In vertebrate hosts,Leishmaniais found in macrophages in its nonflagellate form, the amastigote. Amastigotes

are ovoid or round, 2.5 to 5 m long and 1.5 to 2 m wide. In addition to a basophilic-staining nucleus, a

rod-shape, darker staining kinetoplast is visible with Wright's or Giemsa stain (Fig. 73-2). Amastigotes multiply

by binary fission, rupture out of the macrophage, and infect new cells. Sandflies can ingest the amastigotes

when they become engorged with blood from an infected host. In the sandfly, amastigotes are freed from their

host cells, undergo a series of morphologic alterations, transform into the extracellular flagellated promastigote

form, and replicate in the sandfly gut (Fig. 73-3). Promastigotes are injected with saliva into the skin of a

vertebrate host when the female feeds again. After inoculation into the host, the promastigotes lose their flagella

and transform back into amastigotes (Fig. 73-4).

Table 73-1 Leishmanial Species and Types of Diseases

CLINICAL DISEASE OLD WORLD NEW WORLD

Visceral L. donovani L. chagasia

L. infantuma,b

(L. infantum)a

L. tropicac

Cutaneous L. aethiopica L. mexicanab

L. major L. amazonensis

L. infantum L. venezuelensisb

L. tropica L. (Viannia) braziliensisb,d

L. panamensisd

L. peruvianad

L. guyanensis

L. lainsoni

L. naiffi

L. shawi

Mucocutaneous L. braziliensis

L. guyanensis

L. panamensis

a Main causative agents of canine visceral leishmaniasis.

b Reported to infect domestic cats.

c Rare cause of canine leishmaniasis.

d Causative agents of American tegumentary leishmaniasis in dogs in South or Central America.

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Fig 73-2 L. infantumamastigotes in canine macrophage from popliteal lymph

node aspirate (May-Grunwald-Giemsa stain, 500).

Domestic dogs (Canis familiaris) are considered the main VL reservoirs for people in the Mediterranean basin,

Middle East, and South America, whereL. infantum (L. chagasi)is the causative agent of infection. In regions

with a high infection rate among dogs, the incidence of clinical VL in the general human population is

generally low217

; however, human exposure rates (as determined by the prevalence of specific antibodies or

positive leishmanin skin test results), which indicate past exposure toLeishmaniaorganisms, may be

high.2,4,141,216

In the Indian subcontinent and East Africa, whereLeishmania donovaniis the agent of VL,

people are the reservoir hosts, and animals do not appear to play a significant role in the anthroponotic

epidemiology of infection. The main reservoir hosts forLeishmaniaspp. causing CL and MCL in people are

rodents and other wild animal species. Domestic cats are rarely hosts.

Fig 73-3 Leishmaniapromastigotes grown in culture. Note round nuclei and

rod-shape kinetoplast (May-Grunwald-Giemsa stain, 1000).



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Canine VL caused byL. infantumis an important cause of zoonotic disease in many endemic countries and

areas, including Spain, Portugal, southern France, Italy, Malta, Greece, Turkey, Israel, Egypt, Tunisia, Algeria,

Morocco, Iraq, Iran, the former Asian republics of the Union of the Soviet Socialist Republics, Pakistan, and

some parts of China.18,131,137,170,208Recent information indicates that VL may occur also in a part of southern

Germany.112

Reports have been made of sporadic cases of canine leishmaniasis caused by importation or

transport of infected dogs to countries where sandfly transmission of VL does not occur, such as Holland,

England, and Sweden.206

Similarly, dogs are a reservoir ofL. infantum (L. chagasi)infection for people in

South America.41

Because many dogs in endemic areas harbor asymptomatic infections, infection rates are

often estimated not only by the presence of clinical signs compatible with the disease, but also by serologic

methods, the presence of parasite DNA in the tissues or blood, or both as determined by the polymerase chain

reaction (PCR). Canine infection rates as shown by PCR and serology in highly endemic foci such as the

Balearic Islands of Spain,199

the Marseille area in France,26

and Greece118

approach 70% to 80%. This is a

much higher prevalence of infection than that associated with symptomatic disease or determined by serology

alone. It is thought that most or all dogs in these areas are infected during their lives. Some dogs succumb to the

infection, others harbor the pathogen and are resistant to the development of clinical disease, and some dogs areable to eliminate the pathogen before developing clinical disease. In other areas, infection is not as highly

prevalent, possibly because of less favorable environmental conditions for transmission and vectors.142,221

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Fig 73-4 The life cycle of L. infantum. A, Uninfected sandfly feeds on an

infected host and (B)ingests infected macrophages in host tissues. C,

The organisms are released from the infected macrophages into thesandfly gut and (D)transform into motile promastigotes which

replicate in the sandfly gut. E, The promastigotes are regurgitated

during feeding of the infected sandfly. The infected sandfly transmits

the infection to the new host during feeding. (Courtesy University of

Georgia, Athens, Ga.)



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Canine infection occurs mostly in rural areas or the outskirts of towns; however, urbanization of canine and

human infection has been reported and poses a threat to the well-being of large dogs and humans.49,142

L.

infantuminfection has been reported in wild canids such as foxes (Vulpes vulpes)and jackals (Canis aureus)in

Europe and the Middle East and in crab-eating foxes (Cerdocyon thous)in South America.*These wild canine

species may demonstrate signs of disease or be asymptomatic. Infected crab-eating foxes were found to have

low rates of transmission to the sandflyLutzomyia longipalpisand were therefore not considered important as

reservoirs of VL in Brazil.45

The particular role of wild canids in the epidemiology and spread of sylvaticL.

infantuminfection to domestic dogs (Canis familiaris) and people is not well understood and should be

separately investigated in every ecosystem where this disease is found. AlthoughL. infantumis naturally

transmitted through the bites of sandflies, vertical in utero transmission from a dam to its offspring has been

documented in a few reports.58

Rhipicephalus sanguineushas been shown to acquireLeishmaniaorganism in

their guts after feeding on infected dogs40a

; however, its competence as a vector has not been confirmed.

Leishmania tropicaoccurs in the Old World and is a rare cause of infection in dogs.L. tropicais an important

agent of CL in people in some parts of the Middle East and Africa. It also caused VL in American soldiers

returning from the Persian Gulf after the 1991 Operation Desert Storm124

and in patients from India.179

It has

been sporadically found in dogs with CL from Tunisia and Morocco54

and from another dog from Morocco

with VL and no dermal abnormalities.92

However,L. tropicainfection is rare compared with the common

canineL. infantuminfection.

* References 1, 18, 43, 47, 97, 125, 190.

Pathogenesis

As the sandfly bites,Leishmaniapromastigotes are transferred with the sandfly saliva into the vertebrate host's

skin. The promastigotes are then phagocytized by macrophages and multiply as amastigotes within

phagolysosomes that separate them from the host cell defense mechanisms. When the macrophage ruptures,

freed amastigotes penetrate additional host cells and disseminate from the local bite site. They travel throughout

the host's body but primarily to the hemolymphatic system organs and remote dermal areas to create a

generalized infection.

As mentioned previously, not every dog naturally or experimentally infected withLeishmaniadevelops

disease.107,162

The immune responses mounted by dogs at the time of infection and thereafter appear to be the

most important factor in determining whether they develop a generalized infection and whether and when the

infection will progress from a asymptomatic state into symptomatic disease. Infection initially has no apparent

symptoms but later might progress into a symptomatic disease unless the replication of amastigotes is halted by

immune mechanisms. Dogs that are able to resist an infection by either resolving it and eliminating the parasite

or restricting the infection and remaining consistently asymptomatic are clinically resistant. Animals that are

predisposed to developing an infection and symptomatic disease are considered susceptible. The innate, or

nonspecific, immune response is the first line of defense encountered byLeishmaniaparasites when entering

the susceptible host. One of several suggested mechanisms by whichLeishmaniaparasites depress the innate

host immune defenses involves the ability of amastigotes to survive and replicate within macrophage

phagolysosomes by producing compounds such as lypophosphoglycans that inhibit phagosome maturation.180

Specific immune responses play a major role in susceptibility to infection. An experimental model of cutaneous

leishmaniasis in mice infected withLeishmania majorhas shown that a susceptible mouse strain, which

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typically develops a T-helper (Th) type 2 (Th2) cellular response, succumbed to infection. This Th2 response

resulted in secretion of specific cytokines such as interleukin-4 (IL)-4 and interleukin-10 (IL)-10 and production

of a significant antibody response. Other mouse strains that respond with a different set of cytokines, including

interferon-(IFN-) and interleukin-12 (IL)-12, typical of a Th1 response are resistant to infection.93,187

IFN-

secreted from T cells activates macrophages for the elimination of parasites. This general concept derived from

the experimental CL model of a Th-cell dichotomyin which one type of Th-cell response produces resistance

or cure and a second type produces susceptibility and disease exacerbationhas been applied to infections with

other pathogens in many hosts. However, whether this concept applies to VL is unclear. In experimental murine

VL, both types of responses develop,103,140

and it is the balance of the Th1/Th2 responses that is considered to

be important in controlling parasite replication, disease progression, or a cure. The balance between the two

types of cellular immune responses also appears to be important in natural canine and human VL.

Protective immunity to leishmaniasis in dogs is mediated by T cells.162

Resistance to experimental infection

withL. infantumin dogs is associated with proliferation of peripheral blood lymphocytes, which produce IL-2,

tumor necrosis factor, and IFN-with parasite antigen-specific stimulation. In addition,L. infantuminfected

macrophages are lysed in a histocompatibility complex-restricted manner by CD8+ cytotoxic T cells, CD4+

cytotoxic T cells, or both. These processes are suppressed in symptomatic dogs, in which T-cell proliferation

with leishmanial antigen and antigen-specific IFN-production are depressed and a marked IgG response to the

parasite ensues.51,133,162,163

A strong delayed-type hypersensitivity response with the leishmanin intradermal

skin test indicative of a cell-mediated response toLeishmaniainfection is found in infection-resistant dogs that

have been exposed to the parasite and is absent in highly symptomatic dogs.162,197,198

In addition, intracellular

killing of the parasite by neutrophils and monocytes is impaired.34

During the infection, dogs become

increasingly immunosuppressed and develop lower CD4+ lymphocyte counts and experience a decrease in the

CD4+/CD8+ ratio.32,143

This finding is commonly associated with retroviral diseases, such as the human

immunodeficiency virus (HIV) in people and feline immunodeficiency virus (FIV) in cats, and is proportional

to the degree of susceptibility to opportunistic pathogens. Moreover, it has been demonstrated that the

infectiousness of dogs with leishmaniasis to sandflies increases proportionally with the decrease in CD4+

counts.

91

Susceptibility and resistance to canine VL appear to have a genetic basis. The prevalence of overt VL among

Ibizan hounds in the Balearic Islands is lower than among other breeds, and it has been shown that this breed

mounts a predominantly cellular immune response againstL. infantum.198

A study on the polymorphism of the

canine NRAMP1 gene, which encodes an iron transporter protein involved in the control of intraphagosomal

replication of parasites and macrophage activation, has implied that susceptible dogs have mutations in this

gene.7A DLA class II DLA-DRB1 genotype, which is a dog major histocompatibility complex class II allele,

has been linked to the risk of being infected in an endemic area in Brazil.169

Canine VL is usually a chronic disease, and clinical signs of disease may develop 3 months to 7 years after

infection. T-lymphocyte regions in the lymphoid organs become depleted, and antibody-producing B-cell

regions proliferate. The proliferation of B lymphocytes, plasma cells, histiocytes, and macrophages results in

generalized lymphadenomegaly, splenomegaly, and consistent hyperglobulinemia. The immunoglobulin

response is usually massive; however, it is not a protective response and can eventually be detrimental.

Autoantibodies that may be associated with the development of pathologic phenomena such as

immune-mediated thrombocytopenia and anemia are also frequently produced. Another potential hazard of

impaired T-cell regulation with exuberant B-cell activity is the generation of large amounts of circulating

immune complexes (CICs).121

CIC deposition in the walls of blood vessels may cause vasculitis, polyarthritis,

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uveitis, and glomerulonephritis. In dogs, CIC deposition in the kidneys eventually results in renal failure, which

is the main cause of death of dogs with leishmaniasis. Systemic vasculitis may lead to local ischemia that

causes visceral and cutaneous necrosis and, although rare, to nervous system involvement.77,168

CICs may also

include cryoglobulins. These proteins may precipitate in the blood vessels of the extremities when exposed to

cold and cause ischemic necrosis.192

Canine leishmaniasis is most often associated with various skin lesions, which are generalized rather than local

becauseL. infantumdisseminates all over the body.167

It may also be detected in healthy-looking skin and not

necessarily in dermal lesions.196

The more rare form of generalized nodular lesions (the nodular form of

leishmaniasis) probably indicates that a dog mounted a less effective immune response than that associated with

generalized alopecia.72

Although rare, skin lesions could be restricted to a few ulcerations or nodules.

Dogs with leishmaniasis may show signs of a hemorrhagic diathesisprimarily epistaxis. Histopathology of the

nasal mucosa of 10 dogs with CL, three of which had a history of epistaxis, revealed that all 10 dogs had

ulcerative and inflammatory lesions that could be involved with bleeding.102

Other than nasal ulcers, possible

causes include paraglobulinemia, which may interfere with fibrin polymerization and which in association withuremia may inhibit thrombocyte function. In addition, thrombocytopenia may develop as a result of CIC,

autoantibodies, splenic pooling, or bone marrow suppression. Anemia usually develops as a sequel to the

decreased erythropoiesis of chronic disease or to chronic renal failure but may be aggravated by blood loss, an

immune-based destruction of erythrocytes, or both.

Clinical Findings

Dogs

Canine VL is a chronic systemic disease. The signs of disease are highly variable and often begin with slight

but progressive dullness and insidious exercise intolerance. The clinical findings in canine leishmaniasis are

presented in Table 73-2.

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Table 73-2 Clinical Findings in 80 Dogs with Leishmaniasis191

FINDINGS PERCENTAGE OF DOGSCLINICAL AND HISTORICAL

FINDINGS

Decreased endurance 67.5

Weight loss 64

Somnolence 60

Increased fluid intake 40

Anorexia 32.5

Diarrhea 30

Vomiting 26

Polyphagia 15

Epistaxis 15

Melena 12.5

Sneezing 10

Coughing 6

Fainting 6PHYSICAL EXAMINATION

ABNORMALITIES

Lymphadenomegaly 90

Skin involvement 89

Cachexia 47.5

Abnormal locomotion 37.5

Hyperthermia 36

Conjunctivitis 32.5

Palpable spleen 32.5

Abnormal nails 20

Rhinitis 10

Keratitis 7.5

Pneumonia 2.5

Icterus 2.5

Uveitis 1.3

Panophthalmitis 1.3

Fig 73-5 Canine leishmaniasis showing exfoliative dermatitis and scaling on

face.



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The prevalence of cutaneous lesions in dogs with symptomatic leishmaniasis ranges between 56% to

90%.40,109,191

Dermatologic abnormalities may occur in the apparent absence of other obvious signs of

disease, but any animal with dermal manifestations of leishmaniasis should be presumed to have visceral

involvement, because the parasites disseminate throughout the body before generalized skin lesions develop.

Dermatologic abnormalities vary in character and extent but are rarely pruritic. Most dogs develop a

progressive and symmetric alopecia with exfoliative dermatitis and desquamation, usually commencing on

the head and extending to the rest of the body (Fig. 73-5). In addition, some animals develop ulcerations on

the nose and the pinna (Fig. 73-6) or chapping of the muzzle or the footpads. Less frequently,

mucocutaneous ulcers (Fig. 73-7), cutaneous nodules, mucosal nodules, or pustular eruptions

develop.78,109,111,71a

Lymphadenomegaly of multiple superficial lymph nodes frequently develops in canine

VL119b

with lymph nodes enlarging 2 to 6 times their normal size and occasionally mimicking clinical

findings of lymphosarcoma. Splenomegaly is also frequently detected by abdominal palpation.

Fig 73-6 Canine leishmaniasis showing scaling on pinna and face.

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Fig 73-7 Mucocutaneous ulceration in a dog with leishmaniasis.

Approximately 20% to 40% of the dogs diagnosed with VL have ocular lesions, including

keratoconjunctivitis and lymphoplasmacytic or granulomatous uveitis (Fig. 73-8).40,80,160,191

In some cases,

ocular abnormalities are the only clinical signs.160

Abnormally long or brittle nails (onychogryphosis), a

rather specific finding, develop in a small proportion of the patients. Epistaxis is another clinical sign that

may be develop in conjunction with other typical abnormalities or as the only presenting sign in canine VL(Fig. 73-9).

102

Fig 73-8 Ocular lesions in leishmaniasis showing junctivitis in a dog with

uveitis.



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Fig 73-9 Epistaxis in St. Bernard with leishmaniasis and no dermal lesions.

Fig 73-10 Dog with characteristic features of leishmaniasis. Note cachexia,

muscle atrophy, and excessive scaling.

Weight loss and muscle atrophy are the most common signs of visceral involvement (Fig. 73-10). Some dogs

lose weight despite having a ravenous appetite. A serious worsening of condition is often associated with

ensuing renal failure. Progressive renal failure may be accompanied by anorexia, mental depression,

polyuria, polydipsia, and vomiting. Transient diarrhea may occur. Renal failure may be the sole apparent

abnormality in dogs with VL; dogs with this condition in endemic areas should be tested for leishmaniasis.

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In cases of overt disease, decreased physical activity is obvious and related to somnolence, decreased

endurance, and locomotion disturbances. Locomotion disturbances may be caused by neuralgia, polyarthritis,

polymyositis, footpad clefts, interdigital ulcers, osteoarticular and osteolytic lesions, or proliferative

periostitis.5,28,200bBody rectal temperature may fluctuate but is usually normal or subfebrile.

Immunosuppression may promote the occurrence of concomitant infections, hence the clinical picture may

be complicated by conditions such as demodicosis, pyoderma, gastrointestinal disease, and pneumonia.

Combined infections withEhrlichia,Babesia,Hepatozoon, Trypanosoma, andDirofilariaare quite common

whenLeishmaniainfection occurs in regions where these organisms are also endemic. Other less common

manifestations may include pericardial tamponade,75

masticatory myositis,210

pancreatitis,36

meninigitis,215

chronic colitis,67

pemphigus,83

and polyarthritis.201

Thrombosis has also occurred as a result of the nephrotic

syndrome caused by glomerulonephritis.72,74

Signs caused by disseminated intravascular coagulation or its

complications may occur.76

Cats

Feline leishmaniasis is rare. Symptomatic leishmaniasis in domestic cats have included infection withL.

infantum,154,165,180a

Leishmania mexicana,20,46

Leishmania venezuelensis,29,30

L. (Viannia) braziliensis,186

and unspecified species.96

Sporadic cases of feline leishmaniasis in southern Europe caused byL. infantumhave been described. The

cats had cutaneous ulcerative or nodular lesions essentially similar to those found in dogs (Fig.

73-11).96,165,178a,160a

One cat had visceral involvement that included hepatosplenomegaly, icterus,

lymphoplasmocytic gastroenteritis with abundantLeishmaniaparasites, and membranous

glomerulonephritis.96

A second cat from whichL. infantumMON-1 zymodeme was cultured had

disseminated crusty cutaneous lesions and amastigotes in the bone marrow.154

Another cat with disseminated

disease had uveitis as a predominant finding.119a

Infected cats were seropositive forLeishmaniaantigen by

various serologic methods.96,154,165

Infection was reported in cats with feline leukemia virus and FIV165

and

also from cats with no retroviral disease.154

Serologic or PCR surveys of cat populations in canine

leishmaniasis-endemic regions in southern Europe indicate that feline infection might be more widespread

than indicated by clinical manifestations.

Fig 73-11 Cutaneous ulcer in cat with leishmaniasis. (Courtesy Maria Grazia

Pennisi, University of Messina, Messina, Italy.)

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Reports of feline leishmaniasis in the New World have primarily discussed cutaneous infections with species

that cause CL in people. Pinnal nodules caused byL. mexicanawere diagnosed in a cat from southern

Texas.46

Thirty months after radical pinnectomy was performed, the cat developed similar pinnal lesions that

progressed to more diffuse lesions on the muzzle and in the nasal mucosa. No visceral organ involvement

was found on necropsy.20

Nodular lesions on the nose and ears have been observed in cats with CL in aL.

venezuelensisendemic region of Venezuela.29

Infection with a dermatotrophicLeishmania (Viannia)species

in a cat from Brazil was detected in a proliferative interdigital lesion on the cat's posterior paw.159

In other

instances,L. (V.) braziliensiswas isolated from cutaneous lesions from two cats in Brazil.186,200a

Experimental studies showed that cats were susceptible to a generally self-limiting infection with a human

isolate of this organism.190a

L. chagasiDNA sequences were amplified from a lesion on a cat's nose; the cat

was from a previously nonendemic area in Brazil.181

Diagnosis

Clinical Laboratory Findings

A summary of the clinicopathologic findings from three large case series studies on canine

leishmaniasis40,110,191

is shown in Table 73-3. The most consistent serum biochemistry findings in dogs with

clinical VL are serum hyperproteinemia with hyperglobulinemia and hypoalbuminemia resulting in a

decreased albumin/globulin ratio. Marked hyperglobulinemia in dogs fromLeishmania-endemic regions with

no apparent cause or in dogs that have traveled to such areas should be investigated for VL. Mild increases

of liver enzyme activities are frequent; however, grossly elevated liver enzyme activities, severe azotemia, or

both are found in only a minority of dogs with VL. Proteinuria and some pathologic renal symptoms develop

in most dogs with this disease, and subsequent renal failure caused by immune-complex glomerulonephritis

eventually develops in dogs with progressive pathologic renal symptoms. The urinary protein/creatinine ratio

and enzymuria have been proposed as tests for assessing renal damage in affected animals.

156,157

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Table 73-3 Clinicopathologic Abnormalities in Dogs with Visceral

Leishmaniasis40,110,191

ABNORMALITY PERCENTAGE OF DOGS

Hyperproteinemia 63.372.840,110

Hyperglobulinemia 7610040,191

Hypoalbuminemia 689440,191

Decreased albumin/globulin ratio 7640

Azotemia 164540,191

Increased serum alkaline phosphatase activity165140,191

Increased alanine aminotrasferase activity 166140,191

Proteinuria 71.585110,191

Anemia 6073.4110,191

Leukocytosis 2440

Leukopenia 22191

Thromobocytopenia 29.35040,191

Positive for antinuclear antibody 315340,191

Positive Coombs' test 218440,191

Mild to moderate nonregenrative anemia is frequently found. More rarely, regenerative hemolytic anemia

caused by immune-mediated mechanisms is detected. Thrombocytopenia, mild leukocytosis, or leukopenia

are inconsistent findings. However, lymphopenia is frequently reported in dogs with VL. Test results for

antinuclear antibodies can be positive in dogs withL. infantuminfections, especially if co-pathogenic

infections are present.195

Parasites are rarely detected in peripheral blood.71b

Definitive diagnosis of leishmaniasis can be confirmed by microscopic demonstration of parasites in

cytologic preparations or histopathologic specimens, serology, culture of the organism in appropriate

medium, or detection of parasite DNA using molecular methods.

Serologic Testing

Various serologic methods have been used to detect serum anti-Leishmaniaantibodies. Methods have

included indirect fluorescent antibody testing, the enzyme-linked immunosorbent assay (ELISA), direct

agglutination assays, and Western blotting.*A purified recombinant antigen for ELISA, rK39, has been used

for detection of VL in people and dogs.176,182,152a

In general, these methods have good sensitivities and

specificities for the diagnosis of clinical VL. In naturally infected dogs, antibodies are present usually long

before clinical signs of disease appear. Asymptomatically infected dogs that are slowly developing overt

disease are often seropositive. However, a low positive titer result may be detected in animals that have been

exposed but have not developed disease or in dogs that are persistent asymptomatic carriers. In an animal

with compatible disease signs, a positive titer result strongly supports the preliminary diagnosis. Antibodies

are very rarely undetectable in dogs with clinical signs of leishmaniasis. However, serology is thought to

underestimate the true prevalence of asymptomatic infection in canine populations in endemic regions.118,199

In cases with inconclusive serologic results, additional detection methods are advised.100

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Decreasing titer results have been used to monitor therapy,13,66,213

but titer results may decrease with the

reduction in parasitic burden and not necessarily with total parasite elimination. Therefore results are often

not consistent with parasitic cure, and relapses can occur frequently despite an initial lowering in antibody

titer results. Serologic cross-reactivity with other pathogens is a problem in regions where Trypanosomaspp.

are found, particularly in South and North America, where Trypanosoma cruziis a pathogen of domestic

canines and wild carnivores.90

* References 71, 94, 126, 152, 184, 211, 214.

Organism Identification by Microscopy and Culture

Definitive diagnosis is usually based on cytologic or his-tologic identification of amastigoteseither

contained in macrophages or freein routinely stained smears from lymph nodes, splenic aspirates, skin

touch impressions, or bone marrow. The specificity of these methods is virtually 100%, but depending on the

time spent searching for parasites, the maximum sensitivity is 80% in dogs with clinical signs of the disease

and lower in asymptomatic seropositive dogs. Cytologic studies may reveal few or no demonstrable parasites

in dogs with overt clinical signs of disease. Identification of amastigotes in formalin-fixed,

paraffin-embedded sections of canine skin or visceral tissues may be facilitated by immunohistochemical

methods such as immunoperoxidase staining.33,68

The diagnosis may also be established by the culture of

parasites from tissues in Novy-MacNeal-Nicolle medium or Schneider'sDrosophilamedium or by the

inoculation of hamsters.

Polymerase Chain Reaction

PCR demonstration of leishmanial DNA in tissues of infected animals is sensitive. It is routinely used for

diagnostic purposes, epidemiologic studies, and screening for human and canine blood donors.13,134

Several

protocols with different target gene sequences have been used in laboratories. The small-subunit rRNA gene,

the internal transcribed spacer of the ribosomal operon, and high-copy sequences of kinetoplast DNA(kDNA) are frequently used as PCR targets.

113PCR can be performed on DNA extracted from tissues,

blood, or even histopathologic specimens.99,178

Noninvasive conjunctival PCR has recently been shown to

be accurate in the direct diagnosis of canine infection.202

Pathologic Findings

Severely affected patients with chronic symptomatic disease are usually cachectic. The organs primarily

affected are the skin and hemolymphatic organs. Generalized enlargement of lymph nodes and splenomegaly

are usually present. Hepatomegaly may be present but is less common. Small, light-colored focal nodular

granulomas may develop in various organs, including the skin and the kidneys. Mucosal ulcerations in the

stomach, intestine, and colon are occasionally observed. Petechiae and ecchymotic bleeding in mucosal and

serosal membranes develop in some cases. Osteolytic or proliferative periosteal lesions may be found in various

parts of the skeleton.5

Histopathology reveals granulomatous perifolliculitis and perivascular dermatitis. Multifocal or diffuse

plasmacytic infiltration of the skin, spleen, lymph nodes, liver, kidneys, bone marrow, intestine, and

conjunctiva may be observed, with an occasional or large numbers of amastigotes in macrophages. Renal

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lesions include glomerulonephritis, interstitial nephritis, and occasionally amyloidosis.147,222

Amyloidosis may

also be present in the liver and other organs. Nervous system involvement withLeishmaniaorganisms in

choroid plexus inflammatory cells has been reported.149

Therapy

Dogs

Canine leishmaniasis in dogs is more resistant to therapy than human leishmaniasis, and only rarely are

Leishmaniaorganisms completely eliminated with available drugs.19

Relapses necessitating retreatment are

the rule rather than the exception, although some dogs may eventually become cured of the clinical disease

(Table 73-4).

For decades, pentavalent antimonials (Sb5+

) have been the primary drug for treatment of canine and human

VL. They selectively inhibit the protozoal enzymes required for glycolytic and fatty acid oxidation. Two Sb5+

-containing agents have been administered to dogs: meglumine antimoniate (trade name Glucantime; Merial,

Lyon, France) and sodium stibogluconate (trade name Pentostam; Wellcome Foundation Ltd, United

Kingdom; see Drug Formulary, Appendix 8). Both agents must be injected daily and may cause serious

adverse effects. Meglumine antimoniate appears to cause milder side effects, but it is not licensed for use in

some countries, including the United States. Sodium stibogluconate is currently involved in an

investigational new drug protocol for human physicians through the Centers for Disease Control and

Prevention (CDC) in the United States. The development ofL. infantumstrains that are resistant to Sb5+

has

been reported in France, Spain, and Italy and is a major veterinary and public health concern.37,38,86,116

Dosage regimens for Sb5+

vary widely. Sb5+

is quickly excreted in the urine. Only a small part is reduced to

the toxic Sb3+

, which may accumulate in the body. However, normal doses of the drug rarely cause signs of

toxicity unless administered daily for longer than 2 months or administered to a patient with renal, cardiac,

or hepatic failure. Antimonials may be injected intramuscularly (IM), subcutaneously (SC), or intravenously

(IV). IM injections in the thigh have resulted in severe lameness as a result of muscle fibrosis. Possible local

complications of SC administration are less serious but include local inflammation. IV injections may cause

thrombophlebitis and hence thrombosis. Results of pharmacokinetic studies of Sb5+

compounds in dogs are

controversial,205,209

but the clinical effect and parasitologic clearance is the same when 100 mg/kg of

meglumine antimoniate is given IV once daily or SC divided into two daily doses.193

Table 73-4 Antimicrobial Therapy for Canine Leishmaniasis

DRUGa

DOSE (MG/KG)b ROUTE INTERVAL (HOURS) DURATION

c(WEEKS)

Meglumine

antimoniate

(Glucuantime)

100 IV, SC 24 34

Sodium

stibogluconated

(Pentostam)

3050 IV, SC 24 34

Allopurinole 20 PO 1224 Indefinitely

IV,Intravenous;SC, subcutaneous; PO,by mouth.

693

694

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a For additional information on use of these drugs, see Drug Formulary, Appendix 8.

b Dose per administration at specified interval.

c All long-term survivors must be treated on multiple occasions because of relapses.

d Available in the United States for treatment of human infections by special request from the

Centers for Disease Control and Prevention, Atlanta, Ga.

e Some studies suggest that combined therapy with allopurinol and antimony compounds is the

most effective for treatingL. infantuminfections.

An alternative to Sb5+

injection in dogs is therapy with allopurinol39,110

(see Drug Formulary, Appendix 8).

Allopurinol is a hypoxanthine compound that is metabolized byLeishmaniaspp. to produce an analogue of

inosine. The analogue is incorporated into leishmanial RNA, causing faulty protein translation and inhibition

of parasite multiplication. This drug is less expensive than Sb5+

compounds, can be administered orally, has

few adverse effects, and is readily available, even in the United States and other countries. Use of allopurinol

causes hyperxanthinuria, which may incidentally produce urolithiasis. It is used with increasing frequency by

veterinarians, often in combination with Sb5+

.8,52,66,82,207

Dosage schedules vary widely, and the optimaldose has not been defined. Clinical remission is frequently obtained by treating with allopurinol alone. A

dose of 20 mg/kg once daily often results in remarkable clinical improvement within 4 weeks and reduction

of parasites to undetectable numbers. However, relapses consistently occur once therapy has been

discontinued. Even after conscientious administration of the drug for 6 months, complete recovery is rare.119

Relapses develop more insidiously and are often less serious than with meglumine; however, deterioration of

kidney function may commence during allopurinol therapy despite resolution of dermal lesions and general

improvement in the clinical condition. This progression is likely caused by continuation of immune complex

deposition. When Sb5+

is used as the initial drug for treatment, allopurinol may be used in combination.158b

At the end of combined treatment, allopurinol is commonly recommended for long-term maintenance

therapy or even indefinitely for dogs diagnosed with symptomatic leishmaniasis. In a study from Holland,

dogs treated with 20 mg/kg per day of allopurinol had a 78% chance of survival for more than 4 years (if

they did not have severe renal failure when therapy was started).194

Amphotericin B (AMB), a polyene macrolide primarily used as an antifungal drug, also has activity against

some protozoa. It acts by binding to ergosterol and altering the cell membrane permeability. AMB has a

profound toxic effect on the canine kidney by causing renal vasoconstriction and reduction of the glomerular

filtration rate and possibly by acting directly on renal epithelial cells. It can be administered to dogs with

leishmaniasis in a highly nephrotoxic free form, lipid emulsion, or liposomal formulation that reduces its

toxic effects and directs the drug to being taken up by macrophages and accumulating in visceral organs.

Liposomal AMB is effective in the treatment of people and has largely replaced therapy of human patients

with antimonials in Italy and other European countries.86

However, a study on the use of liposomal AMB in

dogs failed to show that treated dogs had long-term clinical improvements with elimination of the

infection.150

The use of AMB in a lipid emulsion of soybean oil administered IV to dogs pretreated with

saline and mannitol has had higher clinical cure success rates and more negative posttreatment parasitologic

tests in some animals. This therapy is associated primarily with transient side effects of anorexia and

vomiting and requires careful monitoring of renal parameters.42,115

Additional drugs that are not recommended as first-line therapy for canine VL because of the adverse effects

associated with treatment include pentamidine and aminosidine.166,175

Pentamidine, an aromatic diamidine

used also for pneumocystosis, babesiosis, and trypanomiasis, is injected IM in dogs and can cause severe



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irritation at the site of injection, hypotension, tachycardia, and vomiting. Aminosidine sulphate is an

aminoglycoside antibiotic that is toxic at doses that are clinically effective againstLeishmania. Other drugs

that are being investigated for the treatment of canine leishmaniasis include alkylphosphocholine derivatives

related to the drug miltefosine, which is used for treating some forms of human VL,199a

and metronidazole.

In a trial comparing the efficacy of conventional treatment with meglumine antimoniate and allopurinol

against use of metronidazole and spiramycin, treated dogs showed some clinical improvement without a

parasitologic cure, similar to control dogs.160a

If dogs are seriously ill, and especially if they are in severe renal failure, it may be necessary to restore fluid

and acid-base balances before antileishmanial drugs are administered. Because of its lower toxicity,

allopurinol is preferred to a Sb5+

compound in these cases. The prognosis of canine leishmaniasis depends on

the severity of injury to the dog's systems at the time of diagnosis and the dog's individual response and rate

of deterioration. In dogs that have not reached a progressive state of renal failure, treatment frequently

significantly improves dermal and visceral signs of the disease. Immune responses were monitored in dogs

before and after treatment and have indicated that in some cases, parasite-specific cell mediated immunity

that is absent before therapy is regained after drug administration but may deteriorate again during a clinical

relapse.53,143,175

Cats

Almost no published information is available on drug therapy for feline leishmaniasis. One cat in Spain with

primarily cutaneous lesions was treated with 5 mg/kg of meglumine antimoniate SC combined with 10

mg/kg ketoconazole orally. A 4-week course of combined therapy was repeated three times, with 10 days

without therapy between each course, and resulted in the resolution of the cutaneous lesions.96

Topical

treatment of cutaneousL. mexicanainfection in a cat with clotrimazole and subsequently with paromomycin

did not improve the dermal lesions.20

Control and Prevention

Efforts to control leishmaniasis in the canine populations in endemic countries are controversial and generally

have not been considered to be successful.14,44,59,158

Killing symptomatic and seropositive dogs is obviously

unacceptable to the owners, but it is also ineffective because nonsymptomatic dogs, occasionally seronegative

dogs, and possibly wild canids are sources of parasite transmission. Furthermore, available methods for testing

do not identify all infected dogs, and a population of young susceptible puppies can replace the culled

animals.145

Spraying for sandfly vectors and eradicating their presumptive breeding places has limited

effectiveness in preventing spread of the disease. No prophylactic drug has yet been shown to be effective

against infection, and medical treatment of infected dogs with antileishmanial drugs is ineffective in eliminating

the parasite.

Sandfly vectors of VL are primarily active outside houses, therefore selective spraying inside houses is

ineffective. However, spraying inside and around kennels could reduce the risk of infection. Measures to

protect the individual dog include keeping the animal indoors as much as possible from 1 hour before sunset to

1 hour after dawn during the vector season and installation of fine-mesh screens to keep sandflies out of

kennels. Topical insecticides for protecting dogs against sandfly bites include solutions, spot-on tubes, sprays,

and collars. A spray containing permethrin and pyroproxyfene (trade name Duowin; Virbac, Fort Worth, Tex.,

694

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www.virbacorp.com) is recommended every 3 weeks for adult dogs and every 2 weeks for puppies.139

A

spot-on containing imidacloprid and permethrin (K9 Advantix, Bayer, Leverkusen, Germany) is

recommended for dogs every 4 weeks for repelling sandflies. Deltamethrin-impregnated collars (trade name

Scalibor; Intervet, Boxmeer, Netherlands; www.intervet.com) have been shown to protect dogs for about 8

months from more than 90% of bites fromPhlebotomus perniciosus, the primary vector ofL. infantumin

France, andLutzomyia longipalpis, a major South American vector.50,106

A controlled study on the effect of

using collars on dogs in a focus of VL in Iran indicated that the seroconversion rate after 1 year in dogs and

children in intervention villages was significantly lower than in control villages.136

Topical insecticide

protection appears to be valuable for dogs in endemic regions during transmission seasons and for dogs

traveling to these areas. Use of collars on client-owned infected dogs treated medically and living in infected

areas is warranted.

Vaccination of dogs against VL could be a major preventative measure. Trials with several types of candidate

vaccines forLeishmaniain animal models have been carried out during the past 4 decades. These included the

assessment of attenuated or killed whole parasites, purified parasite fractions, recombinant antigens, live

bacteria expressingLeishmaniaantigens, DNA vaccines, and the use of numerous adjuvants.31,31a,85

A canine

vaccine is now commercially available in Brazil, and another vaccine brand is likely to be marketed in Europe

in the near future.

Public Health Considerations

VL is a serious human disease that may be fatal if untreated. Malnutrition appears to be a predisposing factor

for the progression of infection.11,17

Traditionally, VL primarily affected young children and infants, but now it

is also often a complication in adults infected with HIV or those receiving cytostatic or immunosuppressive

drugs.88,101,177,218

Transmission ofL. infantumfrom dogs or wild canids to people via sandflies is considered to be the primary

route of infection involved in zoonotic VL. Asymptomatically infected dogs have been shown to be infectious

to sandflies, and symptomatic dogs may be infectious shortly after treatment with antileishmanial drugs.8

Ownership of an infected dog does not appear to be a major risk factor for human infections in Europe, where

the ratio of clinically affected people to dogs is usually low. However, a study from Iran indicated that dog

ownership is a significant risk factor for childhood seropositivity.137

The link between dog and human

infections probably differs from one region and life style to another and could depend on multiple factors

including human nutrition, time spent outdoors, the density of dogs, and the behavior of sandfly vectors.

Transmission by direct contact between dogs and people is speculated to be rare, if it occurs at all, and although

it has not been well documented, it cannot be ruled out. Transmission ofL. infantumthrough blood products has

been reported in dogs that received blood transfusions from infected canine donors and in people.153

Studies in

Spain of humans who use IV drugs and share needles have indicated that the infection was transmitted through

the needles.48

Therefore direct contact with contaminated hypodermic needles or with open wounds or exudates

from dogs with leishmaniasis should be avoided.

Infected pets may remain disease carriers despite treatment. In areas where sandfly vectors are found, this poses

a problem to owners, veterinarians, and local public health and environmental agencies who are concerned with

the risk to people and animals. Before deciding on the fate of an infected pet, owners should be consulted and

educated about the disease, its zoonotic nature, the prognosis for their dog, what should be expected from

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therapy, and safety precautions that should be taken. A clear, official policy based on relevant research and a

calculated estimation of the risk to the community is desirable.

CANINE AND FELINE AMERICAN TEGUMENTARY LEISHMANIASIS

Gad Baneth

Cutaneous (tegumentary) leishmaniasis is caused byL. (V.) braziliensis,L. (V.) peruviana, or related species and

affects dogs and people in South America. Infection in dogs has been reported from Brazil, Argentina, Bolivia,

Peru, Ecuador, Colombia, Venezuela, and Panama.123,173

Sporadic infection of cats has also been

reported.159,186,59a,200a

Outbreaks of American tegumentary leishmaniasis have been associated with deforestation

of jungle areas.155

The clinical signs of disease in dogs include chronic ulcerative lesions on the ears or other areas of the skin,

mucocutanous erosive lesions, and lymphadenomegaly.129,155,164

Ulceration sometimes involves the nasal or

auricular cartilage.

129

Hematogenous dissemination of parasites in dogs is likely, and the presence of parasiteDNA has been demonstrated by PCR of the blood and bone marrow from symptomatically and asymptomatically

infected dogs.174

Cats have developed cutaneous nodular lesions on their skin. Diagnosis can be confirmed by

microscopic detection of parasites in lesions, in culture, by specific serologic tests, or by PCR. The number of

parasites found in canine dermal lesions is usually low. Infected dogs respond to antimonial therapy; however,

they remain infected after therapy and commonly have clinical relapses.164

Numerous wild animals including

opossums and rodents have been reported to be infected with the agents of tegumentary leishmanaisis. Although it

is involved in this disease, the dog does not appear to be a significant reservoir host of infection for people.173

CANINE VISCERAL LEISHMANIASIS IN NORTH AMERICA

Edward B. Breitschwerdt

Peter Schantz

Endemic VL is an emerging disease in dogs in North America. Although human and canine VL are well

established in parts of Asia, Africa, southern Europe, Central America, and South America, VL has been

infrequently reported in people and domestic animals in the United States and Canada.

Etiology

Before 2000, most cases of canine VL in the United States and Canada were associated with a history of

international travel.98,119,183,219

However, between 1980 and 2001, four reports of canine VL were made in

which the dogs had no history of foreign travel. These reports included an American foxhound from a kennel in

Oklahoma, an English foxhound maintained in a closed research colony at The Ohio State University, a pet

basenji from Texas, and a pet toy poodle from Maryland.9,62,189,204

The infected dogs in these reports had not

traveled outside of the United States, and neither a source of infection nor an insect vector was ever identified.

Two additional outbreaks of VL in foxhounds were recognized by one of the authors in kennels in Michigan in

1989 and Alabama in 1994. Since that time, several laboratories have identified serologic, molecular, or

culture-based evidence ofL. infantuminfection in numerous foxhounds that are indigenous to the United States

(Fig. 73-12).60

Retrospectively, it now appears that canine VL was established as an autochthonous disease in

695

696

73.2

73.3

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American foxhounds in North America, at least after 1979.9Investigation of a disease outbreak among

foxhounds in an index kennel located in Duchess County, New York, ultimately led to the discovery that

infection withL. infantumwas well established in foxhounds throughout much of North America. The initial

outbreak investigation involved a cooperative effort among the College of Veterinary Medicine at North

Carolina State University, the Division of Parasitic Diseases in the National Center for Infectious Diseases of

the CDC (Atlanta, Ga.), the Walter Reed Army Institute of Research (Washington, DC), the New York State

Department of Agriculture and Markets and Department of Health, local veterinarians, and the kennel owners

and staff.81

At the time VL was diagnosed in the four index cases, 46 (41%) of 112 dogs in the New York

foxhound kennel were infected. Infection was diagnosed by a positiveLeishmaniaculture result, PCR

amplification ofLeishmaniaDNA, identification of amastigotes by cytology or histopathology, or seroreactivity

(all titers equal to or greater than 1:64) toLeishmaniaantigens. This suggested a high rate of exposure or

infection withLeishmaniaspecies within the kennel population, particularly because serologic testing tends to

underestimate the prevalence and incidence ofLeishmaniainfections in endemic regions. After infection, dogs

or people can remain subclinically infected for months to years before the onset of disease manifestations.

Fig 73-12 Seroprevalence of leishmaniasis in dog kennels. Numbers tested are

shown, and number with positive results are in parentheses. Solid

dots indicate states where organism has been isolated from affected

dogs. (Data courtesy Zandra Duprey, Centers for Disease Control and

Prevention, Atlanta, Ga.; map courtesy, University of Georgia, Athens,

Ga.)

Subsequent to the New York kennel investigation, the CDC screened more than 10,000 foxhounds and found

seropositive foxhounds in 69 kennels in 21 states and 2 Canadian provinces.

185

Now that this disease hasbecome endemic in the United States, it is possible that leishmaniasis will be recognized more often in dog

breeds other than American foxhounds. In addition, autochthonous human cases may be diagnosed in the

United States in the future.



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Epidemiology

In endemic regions, Phlebotomine sandflies (genusLutzomyiain the New World) are the primary insect vectors

for transmission ofLeishmaniaspp.70,173

In addition to dogs and humans, cats, horses, coyotes, foxes, and

rodents can be infected withLeishmaniaspp. However, dogs are considered the primaryL. infantumreservoir

in endemic countries in southern Europe (France, Italy, Spain, and Malta). Based on isoenzyme electrophoresis,

many of the North American isolates obtained from 40 foxhounds, including the isolate obtained from a

foxhound in Oklahoma in 1980, areL. infantumMON-1, which is the predominantLeishmaniazymodeme

found in southern Europe.9,81,89

In endemic regions the protozoal life cycle begins when the infective form

the promastigoteis injected into the skin of the vertebrate host by the sandfly (see Fig. 73-4).104

After

entering the host, the promastigote is transformed into the nonflagellated formthe amastigote. Amastigote

multiplication in macrophages occurs by binary fission either locally in the cutaneous or mucocutaneous forms

or systemically throughout the reticuloendothelial system in the visceral form. Vectors ingest amastigotes while

obtaining a blood meal from the infected host. If ingested by an unsuitable vector, the amastigotes are either

destroyed or passed out in the feces. If the vector is suitable, ingested amastigotes transform into promastigotesand attach to the midgut epithelium of the sandfly. Promastigotes then detach and move cranially to the foregut,

where some attach and others remain free for subsequent transmission through a bite, which completes the

transmission cycle. In certain regions, additional epidemiologic complexity is created by the ability of certain

sandflies to serve as hosts to multipleLeishmaniaspp.

Fourteen species ofLutzomyiasandflies have been recorded in North America, and only three (Lutzomyia

shannoni, Lutzomyia diabolica, andLutzomyia vexator)have been suspected as vectors forLeishmania

spp.104,117,220

Because of the lack of human leishmaniasis in the United States, protozoal research laboratories

have only recently evaluated indigenous sandfly species for their ability to transmitL. donovani. The most

prevalent sandfly in the southeastern United States (all Atlantic coastal states south of Pennsylvania and west to

Louisiana) isL. shannoni. Previous studies have demonstrated thatL. shannonidevelop a very heavy

parasitemia when feeding on dogs infected withL. infantum; however, the vector competence ofL. shannoni

for transmission ofL. infantumhas not been established. In the previously mentioned New York kennel, asignificant correlation was found between a positiveLeishmaniastatus andEhrlichia canisseroreactivity (p=

0.03).81

Although not thought to occur in nature,L. infantumhas been experimentally transmitted by

Rhipicephalus sanguineus, a known vector forE. canis.138

Foxhounds with a positiveLeishmaniastatus were 5

times more likely to have traveled to the southeastern United States or to have been older than 18 months of

age. These factors tend to support the presence of a competent insect vector, potentially in the southeastern

United States. No evidence supports vector transmission in the northeastern United States; adjacent foxhound

kennels and beagles and basset hounds housed on the same premises during the summer months had no

serologic evidence of exposure toL. infantum. 81 Serologic screening of pet dogs, coyotes, and foxes from the

United States has not resulted in the detection ofL. infantumantibodies.81

The mode ofL. infantum

transmission among foxhounds in North America has not yet been determined.

Foxhound kennels are geographically distributed throughout much of the United States. Because of thesubstantial number of foxhounds with serologic evidence of exposure toLeishmaniaspecies, dog-to-dog

transmission via direct contact, exposure to blood products from an infected dog, or possibly during parturition

or breeding may explain the high prevalence of leishmaniasis in this breed. Historic evidence from nonendemic

countries supports dog-to-dog transmission by direct contact (referred to as mechanical transfer) and perinatal

transmission.127,194

Leishmaniasis can also be transmitted from dog to dog by blood transfusions.153

In these

696

697

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instances, macrophages containing amastigotes serve as the source of infection. The Penn Animal Blood Bank

at the Veterinary Hospital of the University of Pennsylvania has documented transmission ofL. infantumfrom

foxhound donors to canine patients.153

Because of the highL. infantumseroprevalence, the use of foxhounds as

blood donors in North America may not be advisable, particularly because serologic testing may not detect

chronically infected dogs.

Clinical Findings

Clinical manifestations in foxhounds included chronic wasting, conjunctivitis, anterior uveitis, retinitis, facial

alopecia, severe muscle atrophy, lymphadenopathy, polyarthritis, and protein-losing nephropathy, which may

be accompanied by renal failure.81,153

These are the same abnormalities associated with canine VL in endemic

regions. Despite chronic infection, hematologic and biochemical abnormalities may be mild or absent. When

present, anemia, thrombocytopenia, lymphocytosis, hypoalbuminemia, hyperglobulinemia, hyperamylasemia,

and azotemia are the most frequently detected laboratory abnormalities. In addition to foxhounds, other breeds

of dogs with unexplained wasting disease, especially if accompanied by hypergammaglobulinemia, bilateral

facial alopecia similar to the pattern observed for demodectic mange, or unexplained glomerulonephritis and

protein-losing glomerulonephropathy, should be tested for exposure toL. infantum. In pet dogs, owners have

reported behavioral changes, including an increase in aggressive tendencies, as the first indication of

leishmaniasis.

Diagnosis

VL can be diagnosed by cytologic or histopathologic identification of organisms, isolation of amastigotes,

detection of serum antibodies, or PCR amplification of leishmanial DNA. Antibody titers of greater than 1:16

are considered indicative ofLeishmaniaexposure.185

However, serologic cross-reactivity betweenLeishmania

spp. and T. cruzican occur, a factor that should be considered, particularly in kennel or hunting dogs. Although

T. cruziis enzootic among wild animals throughout much of North America, reports of infections in domestic

dogs have generally been limited to Texas, Louisiana Oklahoma, and Virginia (see Chapter 72).21,22,79

The

extent to which infection with T. cruzicontributes to the high level of seroreactivity toLeishmaniaspecies

antigens in North American foxhounds remains unclear. Western immunoblotting or the use of a T. cruzi

specific ELISA test (developed for humans) may help differentiate between exposure toL. infantumand to T.

cruzi. Although presumably infrequent, dogs can be infected withLeishmaniaspecies without developing a

detectable antibody response. In foxhounds, this is particularly true when a dog is chronically infected but has

not developed clinical disease manifestations. As an alternative to serologic testing, PCR can be used to

confirm the diagnosis. Of the seroreactive foxhounds from the New York kennel, infection in 65% (26 out of

40) was confirmed by PCR detection ofLeishmaniaspecies DNA in peripheral blood anticoagulated by

ethylenediaminetetraacetic acid (EDTA).81

Peripheral blood was selected as the diagnostic sample for PCR

because of convenience; however, the sensitivity of PCR to confirmLeishmaniainfection in seropositive dogs

or to detect subclinical infection can be enhanced by examination of lymph node or bone marrow aspirates

rather than blood.13,171

For diagnostic assistance with leishmaniasis, serum (for antibody determination) or

EDTA blood (for PCR) samples can be submitted to the Vector-Borne Diseases Diagnostic Laboratory, North

Carolina State University, Raleigh, N.C. (Contact the laboratory for appropriate submission forms before

submitting specimens; see Appendix 5for specific contact information for this laboratory.)

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Therapy

For details regarding treatment of sick dogs, refer to the previous generalLeishmaniasissection in this chapter.

No treatment protocol has been proved to cure VL in dogs.65

Despite clinical improvement or a clinical cure

(i.e., a healthy appearance after treatment), relapses are common, and chemotherapeutic elimination ofL.

infantumhas not been achieved with any drug tested. However, continuous chemotherapy with allopurinol most

likely decreases the parasitemia to a level that has little risk of direct or sandfly transmission (see Table

73-4).39,52

Therefore this approach could be used for the medical management of pet or kennel dogs in the

United States; however, periodic (every 6 months to 1 year) serologic screening of uninfected dogs in the

kennel or household is recommended. In nonendemic regions, euthanasia has been promoted to prevent

leishmaniasis from becoming established. Some foxhound kennels have adopted a test-and-elimination

approach in an effort to remove infected dogs from the environment.

Public Health Considerations

Because of sandfly exposure in endemic regions, the incidence of leishmaniasis in people is about 2 million

cases per year (1.5 million cases of the cutaneous form and 500,000 cases of the visceral form).217

If untreated,

leishmaniasis is generally fatal. Disease manifestations in people can be quite nonspecific in immunocompetent

individuals; however, children and severely immunocompromised people are most likely to develop serious

disease manifestations.L. infantumwas detected by PCR and culture in asymptomatic carriers who were blood

donors in France.67

Numerous pet dogs belonging to military personnel and other individuals fromLeishmania-endemic regions are

being transported to the United States.151

Although potentially chronically infected, these dogs can remain

healthy for months to years after being introduced or reintroduced to United States. If sandflies in North

America are able to transmit VL from infected to susceptible dogs, then vector transmission of this serious

human pathogen from infected dogs to humans is possible. An autochthonous human case of VL from the

United States has not been reported, and no data supports vector transmission among dogs in North America.

Suggested Readings*

* See the CD-ROM for a complete list of references.

7. Altet, L, Francino, O, Solano-Gallego, L, et al.: Mapping and sequencing of the canine NRAMP1 gene

and identification of mutations in leishmaniasis-susceptible dogs.Infect Immun. 70, 2002, 27632771.

19. Baneth, G, Shaw, SE: Chemotherapy of canine leishmaniosis. Vet Parasitol. 106, 2002, 315324.

40. Ciaramella, P, Oliva, G, De Luna, R, et al.: A retrospective clinical study of canine leishmaniasis in 150

dogs naturally infected withL. infantum. Vet Rec. 141, 1997, 539543.

91. Guarga, JL, Moreno, J, Lucientes, J, et al.: Canine leishmaniasis transmission: higher infectivity

amongst naturally infected dogs to sand flies is associated with lower proportions of T helper cells.Res Vet

Sci. 69, 2000, 249253.

103. Kaye, PM, Curry, AJ, Blackwell, JM: Differential production of Th1- and Th2-derived cytokines does

not determine the genetically controlled or vaccine-induced rate of cure in murine visceral leishmaniasis.J

Immunol. 146, 1991, 27632770.

697

698

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118. Leontidas, LS, Saridomichelakis, MN, Billinis, C, et al.: A cross-sectional study ofLeishmaniaspp.

infection in clinically healthy dogs with polymerase chain reaction and serology in Greece. Vet Parasitol.

109, 2002, 1927.

140. Miralles, GD, Stoeckle, MY, McDermott, DF, et al.: Th1 and Th2 cell-associated cytokines inexperimental visceral leishmaniasis.Infect Immun. 62, 1994, 10581063.

143. Moreno, J, Nieto, J, Chamizo, C, et al.: The immune response and PMBC subsets in canine visceral

leishmaniasis before, and after, chemotherapy. Vet Immunol Immunopathol. 71, 1999, 181195.

173. Reithinger, R, Davies, CR: Is the domestic dog (Canis familiaris) a reservoir host of American

cutaneous leishmaniasis? A critical review of the current evidence.Am J Trop Med Hyg. 61, 1999, 530541.

199. Solano-Gallego, L, Morel, P, Arboix, M, et al.: Prevalence ofLeishmania infantuminfection in dogs

living in an area of canine leishmaniasis endemicity using PCR on several tissues and serology.J Clin

Microbiol. 39, 2001, 560563.

Uncited references

44. Courtenay, O, Quinell, RJ, Garcez, LM, et al.: Infectiousness in a cohort of Brazilian dogs: why culling

fails to control visceral leishmaniasis in areas of high transmission.J Infect Dis. 186, 2002, 13141320.

85. Gradoni, L: An update on antileishmanial vaccine candidates and prospects for a canineLeishmania

vaccine. Vet Parasitol. 100, 2001, 87103.

136. Mazloumi Gavgani, AS, Hodjati, MH, Mohite, H, et al.: Effect of insecticide-impregnated dog collars

on incidence of zoonotic visceral leishmaniasis in Iranian children: a matched-cluster randomized trial.

Lancet. 360, 2002, 374379.

184a. Schantz, P, Steurer, FJ, Duprey, ZH, et al.: Autochthonous visceral leishmaniasis in dogs in North

America.J Am Vet Med Assoc. 226, 2005, 13161322.

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