A study on phlebotomine sandflies (Diptera: Phlebotomidae) in Dickwella, southern Sri Lanka, an endemic focus for cutaneous leishmaniasis

Cutaneous leishmaniasis (CL) has become an important health problem in Sri Lanka. Dickwella Divisional Secretariat Division (DSD) located in southern Sri Lanka has been identified as a highly endemic focus for CL. However, to date, the potential sandfly vectors of the Leishmania parasite causing CL have not been elucidated in this focus. This study aimed to determine the species composition and population dynamics of sandflies prevalent at three sampling stations representing different ecological conditions in two high-risk areas in Dickwella DSD, over a period of 27 consecutive weeks. Resting sandflies (i.e. indoor collection) were collected from the lavatories of human households using Castro aspirators at weekly intervals. In addition, cattle-baited traps were deployed at bi-weekly intervals to capture foraging sandflies (outdoor collection). Sergentomyia zeylanica Annandale was found to be the only sandfly species and hence was considered as the potential vector of the Leishmania parasite that causes CL. As a whole, 84 and 96% of the sampling occasions were positive for resting and foraging sandflies, respectively. Seventy-six per cent of the lavatories sampled contained sandflies regardless of the sampling station. Altogether, 34,481 sandflies were captured from lavatories, whereas 691 were collected in cattle-baited traps. The ecological habitat, which comprised dense vegetation and a stagnant water body, seemed to be highly productive for this sandfly species. However, dryness and heavy rains negatively affected its population density. The sex ratio of the sandflies was male-biased at 1:2 (females:males). The findings of this study suggested that the management strategies of S. zeylanica could be targeted on lavatories especially after moderate rains.