Cutaneous leishmaniasis vector control perspectives using lambdacyhalothrinresidual house spraying in El Ingenio, Miranda State, Venezuela

Abstract

An indoor vector control trial was carried out between December 1996 and February 1997, with the aimof reducing the population densities of Lutzomyia ovallesi, the proven vector of cutaneous leishmaniasis (CL) in El Ingenio, Miranda State, Venezuela. Houses were matched according to their structure (‘ bahareque’ [mud and straw], concrete, and wood) and randomly assigned to a control group ( n = 19) or a treated group ( n = 20) that was sprayed with 25 mg/m 2 of lambdacyhalothrin. This dose was selected on the basis of a laboratory susceptibility test of Lu. ovallesi to pyrethroids. Sandfly abundance was measured using CDC light traps 7–79 d post-intervention, by which time the sandfly population in control houses had declined to very low levels, at what was the end of the transmission season. Catches of total females, fed females, and males were significantly lower in sprayed than in control houses immediately after treatment. Catches of total females and males in sprayed houses recovered, reaching the level of control houses after 7 and 11 weeks, respectively. Bioassays following WHO protocols using contact cones on a sandfly laboratory colony showed a short residual effect of the insecticide explaining these results. In contrast, there was no tendency for catches of fed females in the sprayed houses to recover during the course of the trial. Previous studies of adult population dynamics showed a short season of high abundance. Combined with these results, we believe that 2 indoor sprayings with lambdacyhalothrin, the first at the beginning of November and the second at the beginning of January, would considerably reduce the Lu. ovallesi population, and control CL transmission in this and other foci where this sandfly is considered to be the main vector.