BackgroundBecause domestic dogs are reservoir hosts for visceral leishmaniasis (VL) in Brazil, one of the approaches used to reduce human disease incidence is to cull infected dogs. However, the results of controlled intervention trials based on serological screening of dogs and killing of seropositive animals are equivocal. A prophylactic vaccine to protect dogs from being infectious to the sand fly vector could be an effective strategy to provide sustained control. Here, we investigated whether a currently licensed commercial subunit rA2 protein–saponin vaccine (Leish-tec®) had an additional effect to dog culling on reducing the canine infectious populations.Methodology/Principal findingsThis prospective study was conducted in an L. infantum highly endemic area of southeast Brazil. At the onset of the intervention, all of the eligible dogs received through subcutaneous route a three-dose vaccine course at 21-day intervals and a booster on month 12. For the purpose of comparison, newly recruited healthy dogs were included as the exposed control group. To ascertain vaccine-induced protection, dogs were screened on clinical and serological criteria every 6 months for a 2-year follow-up period. Antibody-based tests and histopathological examination of post-mortem tissue specimens from euthanized animals were used as a marker of infection. The standardized vaccine regime, apart from being safe, was immunogenic as immunized animals responded with a pronounced production of anti-A2-specific IgG antibodies. It should be noted the mean seroconversion time for infection obtained among immunized exposed dogs (~ 18 months), which was twice as high as that for unvaccinated ones (~ 9 months). After two transmission cycles completed, the cumulative incidence of infection did differ significantly (P = 0.016) between the vaccinated (27%) and unvaccinated (42%) dogs. However, the expected efficacy for the vaccine in inducing clinical protection was not evident since 43% of vaccine recipients developed disease over time. Our estimates also indicated that immunoprophylaxis by Leish-tec® vaccine in addition to dog culling might not have an impact on bringing down the incidence of canine infection with L. infantum in areas of high transmission rates.Conclusions/SignificanceLeish-tec® as a prophylactic vaccine showed promise but needs to be further optimized to be effective in dogs under field conditions, and thereby positively impacts human incidence.

Aim The aim of this study was to test the hypothesis that the dispersal of sylvatic triatomines to anthropic habitats is stimulated by degradation of their natural habitat.Location State of Espírito Santo, south-eastern Brazil.Methods We georeferenced records of domiciliary captures of sylvatic triatomines (1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005) obtained from the database of the entomological surveillance programme of the Brazilian National Health Foundation. We partitioned the study area into 543 equal hexagons and attributed information on the presence/absence of triatomines and climatic, topographic and biological variables to each. Using generalized additive models (GAMs), we defined the determinant variables for triatomine presence/absence and demarcated the potential areas in which they might occur. We then subjected the hexagons with a high probability of triatomine presence to a second analysis, adding information on the number of domiciliary captures of triatomines and landscape indices that measured quantitative and spatial patterns of forest fragments. We used GAMs to determine the indices that influenced the number of domiciliary captures of triatomines. ResultsThe presence of triatomines was characterized by a strong positive correlation with variability of terrain slope. This variable was used to demarcate the areas where triatomines were likely to occur. Landscape indices associated with the number of domiciliary captures of triatomines were the number of patches, the fractal dimension index, the total core area and the clumpiness index. Main conclusionsOur results do not support the hypothesis that domiciliary invasion by sylvatic triatomines is stimulated by environmental degradation. Instead, the results suggest that less degraded areas maintain larger populations of triatomines and consequently present higher indices of dispersal and domiciliary invasion. Particular landscape patterns and dispositions of human dwellings, however, may enhance the probability of triatomines being attracted to the artificial light of dwellings. Initiation of flight and consequent dispersal is a naturally occurring process that allows triatomines to find and colonize areas that favour the survival of their offspring.

Cutaneous leishmaniasis (CL) is caused by a protozoan of the genus Leishmania and is transmitted by sand flies. The state of Espírito Santo (ES), an endemic area in southeast Brazil, has shown a considerably high prevalence in recent decades. Environmental niche modelling (ENM) is a useful tool for predicting potential disease risk. In this study, ENM was applied to sand fly species and CL cases in ES to identify the principal vector and risk areas of the disease. Sand flies were collected in 466 rural localities between 1997 and 2013 using active and passive capture. Insects were identified to the species level, and the localities were georeferenced. Twenty-one bioclimatic variables were selected from WorldClim. Maxent was used to construct models projecting the potential distribution for five Lutzomyia species and CL cases. ENMTools was used to overlap the species and the CL case models. The Kruskal–Wallis test was performed, adopting a 5% significance level. Approximately 250,000 specimens were captured, belonging to 43 species. The area under the curve (AUC) was considered acceptable for all models. The slope was considered relevant to the construction of the models for all the species identified. The overlay test identified Lutzomyia intermedia as the main vector of CL in southeast Brazil. ENM tools enable an analysis of the association among environmental variables, vector distributions and CL cases, which can be used to support epidemiologic and entomological vigilance actions to control the expansion of CL in vulnerable areas.

Espécimes adultos de Triatoma vitticeps são capturados freqüentemente por moradores em áreas rurais do Estado do Espírito Santo, Brasil. Com o objetivo de determinar o índice de infecção natural desta espécie, examinamos os dejetos de 116 espécimes silvestres, capturados em 27 municípios do estado, após repasto sanguíneo em ave e dejeção espontânea. Destes, 100 (86,2%) estavam infectados por flagelados morfologicamente semelhantes a Trypanosoma cruzi. Detectamos índices de infecção natural de Tritoma vitticeps superiores ao de estudos anteriores. A baixa incidência da doença de Chagas no estado se deve provavelmente a dejeção tardia deste vetor visto que trabalhos sobre especificidade alimentar demonstraram presença marcante de Tritoma vitticeps no intradomicilio e contato freqüente com o homem. O elevado índice de infecção natural observado reforça a necessidade de se manter a vigilância entomológica sobre este triatomíneo.

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