Barra de Guaratiba is a coastal area of the city of Rio de Janeiro where American visceral leishmaniasis (AVL) is endemic. Although control measures including killing of dogs and use of insecticides have been applied at this locality, the canine seroprevalence remains at 25% and during 1995 and 1997 eight autochthonous human cases were notified. In order to evaluate factors related to the increase of the risk for Leishmania (Leishmania) chagasi infection in dogs we have screened 365 dogs by anti-Leishmania immunofluorescent antibody test (IFAT) and captured sandflies in the domestic and peridomestic environment. Some variables related to the infection were assessed by uni- and multivariate analysis. The distance of the residence from the forest border, its altitude and the presence of the opossum Didelphis marsupialis in the backyard, were found predictor factors for L. (L.) chagasi infection in dogs in Barra de Guaratiba. The presence of Lutzomyia longipalpis in the peridomestic environment indicates the possibility of appearence of new human cases. Our data also suggest the presence of a sylvatic enzootic cycle at this locality.

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In Barra de Guaratiba, an endemic area for American visceral leishmaniasis (AVL) in Rio de Janeiro, Brazil, control campaigns were unable to reduce canine infection rates. This difficulty prompted an in-depth study of dogs as a reservoir for Leishmania chagasi in the peri-urban environment through clinical and serological follow-up using the immunofluorescence and Western blot techniques. Recognition of 29 kDa and 32 kDa peptides by sera from dogs with proven L. chagasi infection was observed. Furthermore, only sera from symptomatic dogs recognized the 68.5 kDa antigen, so the latter should be considered a parameter for culling dogs from endemic areas. The WB technique proved to be more sensitive than IFA, since the 29 and 32 kDa peptide fractions were even recognized by sera from AVL seronegative dogs up to 8 months before IFA seroconversion. Proximity to wooded areas was an important risk factor for L. chagasi infection in dogs, possibly due to the presence of wild reservoirs.

BackgroundThe opossum Didelphis have been considered as natural hosts of Leishmania parasites in the New World, suggesting an important role in the epidemiology of Visceral Leishmaniasis (VL). Among six extant species that belong to the genus Didelphis, only two (D. marsupialis and D. albiventris), have been mentioned as natural hosts of Leishmania infantum in Brazil and Colombia. In the present paper, it is reported for the first time, the observation of intracellular parasites (amastigotes) in tissues of Didelphis aurita naturally infected with Leishmania infantum in Brazil. We also discuss some aspects associated to the relationship between L. infantum and the geographical distribution of some species of the genus Didelphis.MethodsThe opossums studied were caught by wire traps (Tomahawk) in Barra de Guaratiba, a peri-urban area in Rio de Janeiro. The opossums were killed with an overdose of Thiopental sodium.At necropsy, macroscopic alterations were examined and samples from liver, spleen, lymph nodes, ear, abdominal skin, scent glands and bone marrow were collected for parasitological and molecular diagnoses.ResultsForty-eight opossums were captured in an AVL endemic region, 30 being caught in a mangrove area and eighteen animals in a forest area near to some residential-yards. Among the thirty opossums trapped in the mangrove area, all of them were negative by both imprint and sera samples assayed on Dipstick Tests, that is a test based on a combination of protein-A colloidal gold conjugate and rk39 Leishmania antigen to detect anti-Leishmania antibody in serum or plasma. At the macroscopic examination one out of eighteen opossums, caught close to the forest, presented alterations compatible with spleen hypertrophy and three were positive by Dipstick Tests (16.6%) and presented amastigotes in the spleen and in one of them, the parasites were also observed in a submandibular lymph node. Leishmania infantum infections were confirmed through dot blot hybridization using a L. infantum-specific biotinylated probe.ConclusionsIn the present paper we present the first report of amastigotes in the tissues of Didelphis aurita (Mammalia: Marsupialia) naturally infected with Leishmania infantum. We also attempt to claim the particular role of some opossum species as hosts of Leishmania infantum, contributing at least in part on the description of potential sylvatic reservoirs.

Marsupials have been the subjects of studies of both experimental and natural infections with different species of Leishmania in the Americas as well as Australia. Over a century has passed since the first description of a mammal being infected with Leishmania and since then several reviews have been published on the systematics of the parasites as well as their hosts. Consequently, an update of this information is needed in order to assure correct identification of the species involved in each case. A comprehensive review was undertaken and included most of the records of marsupials being infected with Leishmania sp. Emphasis was placed on parasitological, eco epidemiological and taxonomic information of both the parasites and mammalian hosts. The clinical profiles of the infections varied from severe, which principally occurred in experimentally infected animals, to asymptomatic, which was typical of natural infections. Marsupials must be considered one of the most important groups of mammalian hosts of Leishmania sp. Important factors, such as their ancient origin, wide geographical distribution and susceptibility to infections by different species of Leishmania, but with considerable resistance to the disease, could indicate that didelphids play a key role in the evolution of Leishmania in the New World.