Insecticide susceptibility status of malaria vectors, Anopheles culicifacies, Anopheles fluviatilis and Anopheles minimus in the tribal districts of Jharkhand state of India

Abstract

Background and objectives: Insecticide resistance in malaria vectors has been a major challenge to vector control programs and updated information to the commonly used insecticides is essential for planning appropriate vector control measures. Anopheles culicifacies and An. fluviatilis are the two main vectors prevalent in Jharkhand state of India and role of An. minimus is contemplated in the transmission of malaria in this state. All the districts in the state are predominantly inhabited by the tribal population and are endemic for malaria. A study was undertaken in 12 districts of Jharkhand state to determine the insecticide susceptibility status of the 3 prevalent primary vector species, An. culicifacies, An. fluviatilis, and An. minimus. Methods: Wild-caught adult female An. culicifacies, An. fluviatilis, and An. minimus, mosquitoes were collected from stratified ecotypes from different localities of 12 tribal districts of Jharkhand state during 2018 and 2019. Susceptibility tube tests were conducted following the WHO method using test kits. Mosquitoes were exposed to WHO impregnated papers with the prescribed discriminatory dosages of DDT - 4%, malathion - 5%, deltamethrin - 0.05%, permethrin - 0.75%, cyfluthrin - 0.15% and lambda cyhalothrin - 0.05%. Results: Results indicated that An. culicifacies has developed multiple insecticide resistance in all the 12 districts of Jharkhand state. An. fluviatilis was reported resistant for the first time to DDT in all the districts but was susceptible to malathion, deltamethrin, and permethrin whereas in one district it showed possible resistance to malathion. An. minimus was studied in Noamundi CHC of West Singhbhum district, showed possible resistance against DDT but was susceptible to malathion, deltamethrin, and permethrin. Interpretation & conclusion: The development of multiple insecticide resistance in An. culicifacies including to pyrethroids, has been a concern for malaria control programmes for effective vector management but a report of resistance to DDT for the first time in An. fluviatlis in all the districts in the state is alarming, An. minimus was found in possible resistance category to DDT in one district and both the species were reported susceptible to malathion, deltamethrin, and permethrin. The result of the present study indicates a need for regular monitoring to assess the insecticide susceptibility to formulate effective vector control measures and resistance management.