Monitoring Insecticide Resistance among Malaria Vectors in Coastal Kenya

Abstract

Long Lasting Insecticidal Nets (LLINs) and Indoor Residual Spraying (IRS) are effective measures of malaria vector control. Pyrethroid insecticides are recommended for use in LLINs and IRS due to their low mammalian toxicity and fast action. Currently pyrethroid resistance has been reported in western and eastern Africa, therefore monitoring of resistance is important in all malaria endemic countries. The overall goal of this study was to monitor resistance levels in malaria vectors along the Kenyan coast. Susceptibility of malaria vectors to pyrethroids and use of LLINs was determined in Kilifi, Malindi and Taveta districts of Coastal Kenya. Three sentinel sites from each district were selected and mosquitoes were sampled from each sentinel site in the three districts. The collected Anopheles mosquitoes were reared to adults in the insectary. Two to five days old An. gambiae mosquitoes were assessed for resistance levels to Deltamethrin (0.05%), Lambdacyhalothrin (0.05%), Oichlorodiphenlytrichloroethane (DOT 4%), Bendiocarb (0.1 %) and Fenitrothion (0.1 %). Knockdown time (KOT) was recorded up to 60 minutes and maintained for 24hrs post-exposure on 10 % sucrose solution, after which mortality was recorded. Furthermore, in each sentinel site, a questionnaire on use of LLINs and other antimosquito tools was evaluated. The susceptibility test showed that mosquito mortality after 24 hrs for deltarnethrin was 97%, 93.5%, and 100% in Malindi, Kilifi and Taveta, respectively, while for Lambdacyhalothrin mosquito mortality was recorded at 97% (Malindi), 95.67% (Kilifi), and 97.5% (Taveta). In addition, the study found that use of LLINs was below 80%. This study revealed development of resistance to deltamethrin and Lambdacyhalothrin in An. gambiae s.l. in Kilifi, Malindi and Taveta. It is therefore strongly recommended that the impact of this development on malaria control efforts be closely monitored before this problem becomes widespread in the East African Region.