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

Abstract

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.

Leishmaniasis in Sri Lanka: spatial distribution and seasonal variations from 2009 to 2016

“…Poverty plays a major role in facilitating poor sanitary and housing conditions which contribute to enhancing peridomestic sand fly breeding and resting sites [31]. More than 80% of houses in the rural sector in Sri Lanka still use firewood for cooking while only one third of urban households use wood [17].…”

Characterisation of cutaneous leishmaniasis in Matara district, southern Sri Lanka: evidence for case clustering

“…Poverty that prevail in these regions may play a major role in facilitating sub-standard housing with un-plastered brick walls and poor domestic sanitary conditions that increase peri-domestic sand fly propagation and resting sites, as well as their contact with humans. 25,29 Absence or low usage of protective measures against insect bites such as bed nets, with or without impregnation with insecticides was identified as a risk factor for disease acquisition. However, the regular bed nets (without insecticide impregnation) are known to be ineffective in preventing sand fly bites, due to the fact that sand flies can easily penetrate these nets due to their large pore sizes.…”

“…[25][26][27] However, a study conducted in the Southern part of the country 10 years later provided clues as to the higher prevalence of disease in ages between 11 and 40 years, with house-hold clustering and poor housing conditions as risk factors. 11,25,28 The vector habits in the two areas are believed to be different, [29][30][31][32] which might explain the different epidemiological patterns observed in the two locations within Sri Lanka. Another limiting factor apparent in the past studies was the primary dependence on passive methods for case detection, where only the patients who were referred to a local hospital were studied, 11,28,33 which may understate disease prevalence, fail to represent geographical boundaries and may not illustrate an unbiased picture of the risk factors involved.…”

Leishmaniasis in Sri Lanka: The need for effective targeting of island-specific issues through strategic implementation of global management plans for disease detection and control

“…34,35 Sandflies of the genus Sergentomyia were recently also identified as potential vectors of leishmaniasis in CL-endemic areas of the island. 36 Eleven species from the genus Sergentomyia have been recorded to date, 37 which provided a challenge to identify accurately a number of sibling species and vector sibling counterparts. Subsequently, implementation of DNA barcoding using cytochrome C oxidase subunit 1 was able to delineate Sri Lankan sandfly species.…”