The frequency of American visceral leishmaniasis affecting humans on Margarita Island, Venezuela, has increased in recent years, and infected dogs appear to constitute the principal source of infection. ELISA tests with Leishmania donovani promastigotes and rK39 antigen from L. chagasi in serum from 541 dogs were positive in 33.1% and 21.6% of the samples, respectively. A second blood sample taken from 50 animals after 8-10 months revealed an increase from 24% to 40% of ELISA positivity to both antigens, suggesting high susceptibility and transmission in the canine population. Among 42 serologically positive dogs, 33% of which showed clinical signs of disease, 79% were positive in polymerase chain reactions using primers specific for the L. donovani complex. Control measures including epidemiological hypersurveillance, the humane sacrifice of infected dogs, and rapid diagnosis and treatment of human cases have been initiated.

Human and canine VL are unevenly distributed in Venezuela. The distribution may reflect such factors as differences among the states in human population density, vector density, and the presence or absence of other trypanosomatidae. Particularly high infection rates in very young children as well as in domestic dogs occur in semiurban communities of Nueva Esparta, where other human-infecting trypanosomatidae have not been reported. Control measures related to limiting canine infection might contribute to disease control where VL infections are frequent. Reducing VL mortality requires increased awareness among medical professionals of the possibility of VL in the differential diagnosis of hepato-splenic syndromes, particularly in children.

Abstract. An endemic focus of American visceral leishmaniasis (AVL) in eastern Venezuela has been evaluated in terms of patients (n ϭ 48), immunologic reactivity to Leishmania in household contacts (n ϭ 187) and neighborhood controls (n ϭ 170), detection of Leishmania (L. donovani complex) in dogs and wild animals by the polymerase chain reaction (PCR) and characteristics of the sandfly population. The male:female ratio of patients was 1.18:1; 89.6% were Յ12 years old. Serologic reactivity was significantly higher in household contacts than in controls (P ϭ 0.0008), as was the size of leishmanin reactions in contacts Յ10 years of age (P ϭ 0.0141). Leishmania donovani complex-specific PCRs were positive in dogs, an opossum (Didelphis marsupialis), and a black rat (Rattus rattus). Lutzomyia longipalpis and Lu. evansi, both implicated in the transmission of AVL, were identified among the 386 sand flies examined. These observations provide the bases for an active control program as well as further studies of reservoirs and vector-host relationships in this area.American visceral leishmaniasis (AVL) is caused by protozoa of the Leishmania donovani complex and is endemic throughout much of Central and South America. The causative agent in the Americas is considered to be L. chagasi sensu lato. Investigations in Brazil have shown that infection by L. chagasi is characterized by a spectrum of responses, including asymptomatic subclinical infections; relatively prolonged mild infection that may progress to classical AVL or heal spontaneously and severe classical visceral leishmaniasis.

American cutaneous leishmaniasis (ACL) presents a spectrum of clinical and immunological manifestations. Since the nature of the cellular response appears to play a fundamental role in determining the characteristics of the immunoglobulin isotype of specific antibody responses, we have compared the relative levels of specific antibodies of the four IgG isotypes against Leishmania in sera from patients with different clinical manifestations of ACL. Using a specific antibody capture assay, significant levels of antibodies of the IgG1, 2 and 3 isotypes were detected in localized cutaneous leishmaniasis (LCL); the average level of IgG4 antibodies was low and they were not detected in 10/20 sera. Sera from muco-cutaneous leishmaniasis (MCL) gave a comparatively strong IgG1 response. Sera from diffuse cutaneous leishmaniasis (DCL), the rare form characterized by antigen-specific anergy of cell-mediated immunity, showed highly significant levels of IgG4 antibodies compared to antibody levels of this isotype in the other groups; IgG1 and IgG2 levels were also elevated. Based on other studies of the relationship between the IgG isotype response and cell-mediated immunity, these results confirm a Th1-like CD4+ T cell response in LCL and MCL and a significant Th2-like response in DCL.

Sixty-five patients were diagnosed with visceral leishmaniasis (VL) on