Molecular and biochemical characterization of a sand fly population from Sri Lanka: evidence for insecticide resistance due to altered esterases and insensitive acetylcholinesterase

Abstract

With an increasing incidence of cutaneous leishmaniasis in Sri Lanka, particularly in northern provinces, insecticide-mediated vector control is under consideration. Optimizing such a strategy requires the characterization of sand fly populations in target areas with regard to species composition and extant resistance, among other parameters. Sand flies were collected by human bait and cattle-baited net traps on Delft Island, used as an illegal transit location by many refugees returning to the north of Sri Lanka from southern India where leishmaniasis is endemic. For species identification, genomic DNA was extracted and a fragment of the ribosomal 18S gene amplified. The sequence from all flies analysed matched that of Phlebotomus argentipes Annandale & Brunetti, the primary vector in India and the most likely vector in Sri Lanka. Independent morphological analysis also identified P. argentipes. To establish the current susceptibility status of vector species, data were obtained at the biochemical level, from which potential cross-resistance to alternative insecticides can be predicted. The Delft Island collection was assayed for the activities of four enzyme systems involved in insecticide resistance (acetylcholinesterase, non-specific carboxylesterases, glutathione-S-transferases and cytochrome p450 monooxygenases), establishing baselines against which subsequent collections can be evaluated. There was preliminary evidence for elevated esterases and altered acetylcholinesterase in this population, the first report of these resistance mechanisms in sand flies to our knowledge, which probably arose from the malathion-based spraying regimes of the Anti-Malarial Campaign.

Leishmaniasis in Sri Lanka: a decade old story

“…27 Sand fly behaviour has also been studied in the 1970's, 1990's and in 2005. 23,24,25,26 Both zoophilic and anthropophilic behaviour patterns have been identified in these studies.…”

“…Sand fly research in Sri Lanka has a long history and the presence of sand flies has been reported since as early as the 1940's. 22,23,24 More recent information on Phlebotomine sand flies in Sri Lanka is available since 2005 25 where small numbers of Sergentomyia ceylanica were also identified. 26 Disregarding the negligible percentages of this species, P. argentipes could be the putative local vector of leishmaniasis in this country.…”

Resistencia metabólica a insecticidas organofosforados en Anopheles aquasalis Curry 1932, municipio Libertador, estado Sucre, Venezuela

“…No obstante, Surendran et al (23) reportaron, en poblaciones de Phlebotomus argentipus de Egipto, que solamente en unos pocos individuos se detectó aumento de la actividad de GST y alteración de la AChe. Esto puede representar resistencia seleccionada por el rociamiento con malatión.…”

Prevalence of Sand Flies andLeishmania donovaniInfection in a Natural Population of FemalePhlebotomus argentipesin Bihar State, India

“…AJ244359.1) (Surendran et al 2005). The sequence of Leishmania-specific PCR products were aligned and compared with the 18S rRNA sequence of L. donovani (GenBank accession no.…”

“…An initial denaturation of 15 min at 95°C, followed by PCR amplification for 35 cycles of denaturation (95°C for 30 sec), annealing (57°C for 30 sec), and polymerization (72°C for 40 sec), with final extension of 10 min at 72°C. To discriminate P. argentipes from other species, the amplified PCR product was subjected to restriction digestion using a Hae III restriction enzyme (recognition site GGCC; New England Bio Labs, Hitchin, Herts, U.K.) in the supplied reaction buffer supplemented with 1 mg/mL -1 BSA at 37°C for 2 h. The whole reaction was electrophoresed on a 1.5% (w/v) agarose gel and stained with ethidium bromide (Surendran et al 2005).…”