Pyrethroids and DDT tolerance of Anopheles gambiae s.l. from Sengerema District, an area of intensive pesticide usage in north-western Tanzania
2017
Objective
To assess the susceptibility status of malaria vectors to pyrethroids and dichlorodiphenyltrichloroethane (DDT), characterize the mechanisms underlying resistance, and to evaluate the role of agro-chemical use in resistance selection among malaria vectors in Sengerema agro ecosystem zone, Tanzania.
Methods
Mosquito larvae were collected from farms and reared to obtain adults. The susceptibility status of An. gambiae s.l. was assessed using WHO bioassay tests to permethrin, deltamethrin, lambdacyhalothrin, etofenprox, cyfluthrin, and DDT. Resistant specimens were screened for knockdown resistance gene (kdr), followed by sequencing both Western and Eastern African variants. A gas chromatography mass spectrophotometer (GC-MS) was used to determine pesticide residues in soil and sediments from mosquitoes’ breeding habitats.
Results
Anopheles gambiae s.l. was resistant to all the insecticides tested. The population of Anopheles gambiae s.l was composed of Anopheles arabiensis by 91%. The East African kdr (L1014S) allele was found in 13 of 305 specimens that survived insecticides exposure, with an allele frequency from 0.9% to 50%. DDTs residues were found in soils at a concentration up to 9.90 ng/g (dry weight).
Conclusion
The observed high resistance levels of An. gambiae s.l., the detection of kdr mutations and pesticide residues in mosquito breeding habitats demonstrate vector resistance mediated by pesticide usage. An integrated intervention through collaboration of agricultural, livestock and vector control units is vital.
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