Assessing complex member composition and insecticide resistance status of <i>Anopheles gambiae s.l.</i> in three coastal health districts of Côte d’Ivoire

Abstract

Abstract Although malaria is endemic in Coastal Côte d’Ivoire, updated data on the resistance profile of the main vector, Anopheles gambiae sensu lato ( s.l .), are still lacking, thus compromising decision-making for an effective vector control intervention. This study investigated the complex members and the insecticide resistance in the Anopheles gambiae s.l. populations in coastal Côte d’Ivoire. Between 2018 and 2020, bioassays were conducted on female An. gambiae s.l. mosquitoes in three coastal health districts (Aboisso, Jacqueville and San Pedro) of Côte d’Ivoire. Pyrethroids deltamethrin, permethrin and alphacypermethrin (1X, 5X and 10X), clothianidin and synergist piperonyl butoxide (PBO) combined with pyrethroid 1X were tested using WHO tube bioassays. Chlorfenapyr was evaluated using CDC bottle bioassays. An. gambiae complex members and Vgsc 995F, Vgsc 995S and Ace-1 280S mutations were identified using polymerase chain reaction (PCR) technique. Overall, Anopheles. gambiae s.l. populations were primarily composed of Anopheles coluzzii (88.24%, n = 312), followed by Anopheles gambiae sensu stricto ( s.s. ) (7.56%) and hybrids (4.17%). These populations displayed strong resistance to pyrethroids at standard diagnostic doses, with mortality remaining below 98% even at 10X doses, except for alphacypermethrin in Aboisso. Pre-exposure to PBO significantly increased mortality but did not fully restore susceptibility, except for alphacypermethrin in Jacqueville. Clothianidin restored full susceptibility in Jacqueville and San Pedro, while chlorfenapyr restored susceptibility in Aboisso at 100 µg ai/bottle and all three districts at 200 μg ai/bottle. Vgsc 995F mutation dominated, with frequencies varying from 71.2% to 79.3%. Vgsc 995S had low, and showed frequencies ranging from 2.3% to 5.7%. Ace-1 280S prevalence varied between 4.2% and 42.9%. Coastal Côte d’Ivoire’s An. gambiae s.l. populations were mainly composed of Anopheles coluzzii and showed high resistance to pyrethroids. Clothianidin, chlorfenapyr, and PBO with pyrethroids increased mortality, indicating their potential use as an alternative for malaria vector control.