Susceptibility to DDT and pyrethroids, and detection of knockdown resistance mutation in Anopheles gambiae sensu lato in Southern Togo

Abstract

Insecticides play an important role in malaria control programmes especially in Sub-Saharan Africa. However, the development of resistance by vectors to most commonly used public health insecticides has become a very crucial problem. DDT (Dichlorodiphenyltrichloroethane) was used worldwide to control malaria vectors and pyrethroids have been used in many vector control projects due to their known efficiency and lower toxicity to humans and non-target organisms. In West Africa, resistance to pyrethroid in the major malaria vector, Anopheles gambiae, had been reported in several countries. The last publication on this phenomenon in Togo was done in Togo in 2005. An update on the susceptibility of the malaria vector and characterization of its resistance mechanism becomes therefore crucial. Newly emerged female mosquitoes of two to five days old were selected and exposed to DDT 4%, Permethrin 1% and Deltamethrin 0.05%, the WHO diagnostic doses. These adult mosquitoes were from larvae of Anopheles gambiae sensu lato collected from rural and urban settings and reared in an insectary. A susceptible laboratory strain of An. gambiae sensu stricto was used as reference. Species identification was made using the morphological characteristics, PCR (polymerase chain reaction), and HhaI (Haemophilus haemoliticus) restriction digest. Knockdown resistance mutation screening was conducted on both living and dead mosquitoes. An. gambiae sensu stricto was the only sibling species of the complex present in Kovié and Lomé. The molecular M form was predominant in the two localities (almost 100%). High resistance level was observed in Lomé 1.19%, 56.45% and 41.17%; and in Kovié 0.91%, 55.55% and 67% mortality respectively to DDT 4%, Deltamethrin 0.05% and Permethrin 1% with a very high knockdown time (TKD50). Up to 70% of resistant individuals have been obtained in the two localities. It is important to inspect these localities through routine tests in order to decide on possible alternative strategies to be used. This study showed that An. gambiae is highly resistant to both DDT and pyrethroids in Lomé and Kovié, with the presence of kdr allele.

Keyword: Anopheles gambiae s.s, DDT, pyrethroids, kdr, Southern Togo