Leishmania and sand flies:: proximity to woodland as a risk factor for infection in a rural focus of visceral leishmaniasis in west central Venezuela

To relate entomological, epidemiological and geographical data to understand the transmission dynamics of visceral leishmaniasis (VL) in a closed focus in western Venezuela. Spatial and temporal patterns of Lutzomyia pseudolongipalpis, the most prevalent phlebotomine sand fly species (99.7%), were studied in El Brasilar, Curarigua, Lara State, Venezuela, a small rural community of 20 dwellings and 118 inhabitants. The sand fly population was monitored using Centers for Disease Control light traps monthly throughout 1 year in the domestic and sylvatic habitats and for 3 months in all inhabited houses. Temporal variation followed the yearly bimodal pattern of precipitation with the highest population densities in April and December. Infection with flagellates suggestive of Leishmania spp. was detected in 0.01% of 10 026 dissected females of L. pseudolongipalpis, which proved to be highly endophilic. Prevalence of Leishmania infection in people, as measured by the leishmanin skin test, was correlated with distance of the houses from the woodland and with sand fly abundance. A logistic regression model showed that for people who live in the village, the proximity to the woodland (linear) should be considered a risk factor for Leishmania infection (binary) (z = -2.02, P = 0.04, OR = 0.98, 95% CI = 0.97-0.99). This was consistent with the association between the proportion of VL infection and the log of sand fly abundance, which was negatively correlated with distance from the woodland. We discuss strategies that might be useful in controlling VL transmission in this endemic focus.