MEDICINE UPDATE: DIAGNOSTICS AND TREATMENTS


ynx, and genitalia; and they can occur concurrently or 1 to 5 years after resolution of cutaneous lesions. These lesions will not heal spontaneously. Visceral leishmaniasis, otherwise known as “kala azar,” is a chronic, insidious disease that may be preceded by cutaneous lesions. Visceral leishmaniasis is usu- ally associated with species of the Leishmania don- ovani complex (L donovani, L infantum, Leishmania chagasi) and L tropica. Clinical signs include fe- ver, weight loss, anemia, anorexia, cough, diarrhea, and darkening of the skin. Splenomegaly, hepato- megaly, lymphadenopathy, thrombocytopenia, and leukopenia may all be present as the parasite in- vades the reticuloendothelial system. Visceral dis- ease is fatal unless treated, and treated patients will remain carriers and can recrudesce if immuno- suppressed.


Canine


Dogs are the most commonly affected domestic spe- cies, with 63% to 80% seropositivity in endemic ar- eas in which they are thought to be the primary reservoir for L infantum and maintain the disease in domestic cycles.10 In endemic areas, all breeds of dogs are affected. Dogs, like humans, can develop cutaneous or visceral disease. Cutaneous lesions can present as nonpruritic exfoliative dermatitis, nodules, ulcers, and long, brittle nails. Visceral disease results in lethargy, weight loss, anorexia, anemia, splenomegaly, epistaxis, hematuria, me- lena, chronic renal failure, and death. Ocular le- sions have also been reported and include conjunctivitis, keratitis, and uveitis. The majority of cases of canine leishmaniasis in the United States have historically involved international travel. However, there have been reports of isolated cases and outbreaks, primarily in foxhounds. In 2000, a New York kennel reported four foxhounds with L in- fantum visceral leishmaniasis without a history of travel. This led to widespread testing, and by 2005, 60 kennels in 22 states and two Canadian provinces were found to have seropositive Foxhounds. Cur- rent studies of Foxhound kennels show a 9.8% sero- prevalence; however, in high-risk kennels, the percentage of quantitative polymerase chain reac- tion (qPCR)-positive dogs is 44.8%.10


4. Diagnosis


Microscopic evaluation of an impression smear or biopsy of the border surrounding the cutaneous le- sion is often the preliminary means of diagnosis. There will be a marked inflammatory response, and numerous intracellular protozoa will be seen within macrophages and occasionally extracellu- larly. These 1- to 4-m intracellular organisms have an eccentrically placed, basophilic, round nu- cleus and a rod-shaped kinetoplast oriented perpen- dicular to the long axis of the oval nucleus (Fig. 2). This morphology is indicative of the amasitogote form of Leishmania. Electron microscopy will al- low more detailed examination of the intracellular


258 2013  Vol. 59  AAEP PROCEEDINGS


Fig. 2. Fine-needle aspirate of an ulcerated mass from a horse with cutaneous leishmaniasis exhibiting an intracellular amasti- gote (arrow). Photo courtesy of Dr. Mark Dunbar.


amastigotes. Immunohistochemistry can be used to confirm the diagnosis of leishmaniasis and has been performed successfully in the horse.5,14,17 Culture and qPCR can be performed by the Cen-


ters for Disease Control and Prevention or by vari- ous university research labs. Isoenzyme analysis of cultured parasites has been the conventional ap- proach for species identification. However, PCR and sequence analysis can identify the organism to the species level more rapidly and with greater sen- sitivity, depending on the targeted region.18 It is worth noting in the context of equine leishmaniasis that PCR methods used to detect Old World leish- maniasis have been reported to fail to detect L sia- mensis.1,5,6 Amplification of a 350–base pair internal transcriber spacer 1 (ITS1) fragment has been successful in identifying this organism.1,5 Sequence analysis of the ITS1 amplification prod- ucts classifies L siamensis as neither Old World nor New World.5 Serologic testing in humans and canines is the primary diagnostic test used for surveillance of vis- ceral infections but is less reliable for cutaneous disease. Indirect fluorescent antibody (IFA) testing can be performed by the Centers for Disease Control. Unfortunately, it may cross-react with antibodies to Trypanosoma cruzi. One horse with L braziliensis was positive for anti-Leishmania antibodies on IFAT11; however, IFAT in one horse in Germany with confirmed L infantum cutaneous lesions on PCR failed to yield a positive result.14 Cutaneous lesions in peo- ple may also result in no detectable level of serum antibodies; however, skin testing for delayed type hy- persensitivity may be positive in human cutaneous disease. Delayed type hypersensitivity reaction skin testing has been performed in the horse11 but is not standardized. Anti–Linfantum antibodies have been


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