The Presence of Leishmania infantum DNA in Sand Flies Reflects Their Proximity to Human and Canine Visceral Leishmaniasis

Visceral leishmaniasis (VL) is a vector-borne disease caused by Leishmania infantum infections in Brazil, and Lutzomyia longipalpis is its main vector. It is not well understood how L. infantum circulates between three hosts of public health importance: dogs, humans, and sand flies. The focus of this study was to determine the detection rate of L. infantum DNA in sand flies and evaluate the relative contribution of the three hosts as sand fly blood sources. Insects were collected using light traps in households with recent history of human VL, close neighbors of VL cases, and households with no recent history of human VL. DNA was extracted from single sand fly guts and L. infantum DNA, and sources of blood were identified by quantitative polymerase chain reaction (qPCR) using specific cytochrome B. Among 248 female sand flies captured, qPCR detected L. infantum DNA in 56% of them. Sand flies captured in households with recent history of human VL or VL endemic neighbors were, respectively, 3.73 (95% CI: 1.64-8.48; P = 4.92e-04) or 6.38 (95% CI: 3.37-12.09; P = 4.62e-10) times more likely to carry L. infantum DNA compared with sand flies captured in houses with no history of VL. Dog blood was most common, but multiple blood sources were detected in individual flies. Our findings reaffirm the role of dogs as L. infantum reservoirs in northeast Brazil. These findings highlight the importance of topical insecticides as measures to prevent canine L. infantum infection and limit the risk of human infection.