Multiple insecticide resistance target sites in adult field strains of An. gambiae (s.l.) from southeastern Senegal

Background: High coverage of long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) are the cornerstones of vector control strategy in Senegal where insecticide resistance by the target vectors species is a great of concern. This study explores insecticide susceptibility profile and target-site mutations mechanisms within the Anopheles gambiae complex in southeastern Senegal.

Methods: Larvae of Anopheles spp. were collected in two sites from southeastern Senegal Kedougou and Wassadou/Badi in October and November 2014, and reared until adult emergence. Wild F₀ adult mosquitoes were morphologically identified to species. Susceptibility of 3-5-day-old An. gambiae (s.l.) samples to 11 insecticides belonging to the four insecticide classes was assessed using the WHO insecticide susceptibility bioassays. Tested samples were identified using molecular techniques and insecticide resistance target-site mutations (kdr, ace-1 and rdl) were determined.

Results: A total of 3742 An. gambiae (s.l.) were exposed to insecticides (2439 from Kedougou and 1303 from Wassadou-Badi). Tests with pyrethroid insecticides and DDT showed high level of resistance in both Kedougou and Wassadou/Badi. Resistance to pirimiphos-methyl and malathion was not detected while resistance to bendoicarb and fenitrothion was confirmed in Kedougou. Of the 745 specimens of An. gambiae (s.l.) genotyped, An. gambiae (s.s.) (71.6%) was the predominant species, followed by An. arabiensis (21.7%), An. coluzzii (6.3%) and hybrids (An. gambiae (s.s.)/An. coluzzii; 0.4%). All target site mutations investigated (Vgsc-1014F, Vgsc-1014S, Ace-1 and Rdl) were found at different frequencies in the species of the Anopheles gambiae complex. Vgsc-1014F mutation was more frequent in An. gambiae (s.s.) and An. coluzzii than An. arabiensis. Vgsc-1014S was present in An. gambiae (s.l.) populations in Wassadou but not in Kedougou. Ace-1 and rdl mutations were more frequent in An. gambiae (s.s.) in comparison to An. arabiensis and An. coluzzii.

Conclusions: Resistance to all the four insecticide classes tested was detected in southeastern Senegal as well as all target site mutations investigated were found. Data will be used by the national Malaria Control Programme.