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.

No abstract

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.

Visceral leishmaniasis is a vector-borne disease highly influenced by eco-epidemiological factors. Geographical information systems (GIS) have proved to be a suitable approach for the analysis of environmental components that affect the spatial distribution of diseases. Exploiting this methodology, a model was developed for the mapping of the distribution and incidence of canine leishmaniasis in an endemic area of Brazil. Local variations were observed with respect to infection incidence and distribution of serological titers, i.e. high titers were noted close to areas with preserved vegetation, while low titers were more frequent in areas where people kept chickens. Based on these results, we conclude that the environment plays an important role in generating relatively protected areas within larger endemic regions, but that it can also contribute to the creation of hotspots with clusters of comparatively high serological titers indicating a high level of transmission compared with neighbouring areas.

We performed a serological, clinical, and parasitological follow-up of a dog population in an endemic area of American Visceral Leishmaniasis estimated by indirect immunofluorescent assay (IFA) and western blot (WB). After twelve months, the results obtained from IFA demonstrated that 50% were seropositive and two serological profiles were observed: the first one ranging from 1/40 to 1/80 and the second ≥1/160. By WB, it was observed that the same percentage and sera from positive dogs presented the recognition of the peptides of 29 and 32 kDa up to 8 months before IFA serum conversion. Among the positive dogs, all the sera from symptomatic ones with tissue parasitism recognized the peptide of 68.5 kDa. Our results suggest the need of modifications in the control measures regarding the elimination of the dogs. They also corroborate the high sensitivity and specificity of western blot in the diagnosis of canine leishmaniasis, suggesting the possibility of its association with IFA.

Neutrophils are the most numerous leukocyte in mammals and normally they are the first phagocyte observed in recently damaged or infected tissues. They play a key role in the innate immune responses to Leishmania and several other microorganisms, nonetheless an exacerbated neutrophils activity can generate a harmful response to the host, therefore its turnover rate is very important to maintain the homeostasis and averts the host tissue damage. Both apoptosis followed by phagocytosis by mononuclear phagocytes (eferocytosis) and reverse transmigration have been considered the main processes for the clearance of neutrophils from injured or infected tissues. However, the interaction with Leishmania and other microbes, as well as molecules produced by arthropod vectors such as sandflies saliva can modify the behavior of neutrophils, causing immediate lysis to prolong their life. In fact, as a result of a long course of coevolution, several microorganisms have developed skills to avoid neutrophil effector mechanisms and take advantage of neutrophil clearance pathways to promote their spread in the host's body. Leishmania, Chlamydia pneumoniae and Yersinia pestis for example use the efferocytic Trojan horse process for their dissemination and immune protection, in a different way vaccinia Ankara virus and Toxoplasma gondii exploit the neutrophil reverse transmigration for the same reason. Here we present an overview of some characteristics of neutrophils and their different destinations after interaction with several microorganisms, with an emphasis on Leishmania species. It was also suggested the probable role of neutrophils reverse transmigration as another possible route for the spreading of Leishmania in the visceral leishmaniasis.