Insecticide resistance intensity in Anopheles gambiae s.l. populations from Nioro and Ndoffane health districts, Senegal

Abstract Background Malaria remains a major public health concern in sub-Saharan Africa. In Senegal, the increasing resistance of Anopheles gambiae sensu lato ( s.l. ) to main public health insecticides threatens the effectiveness of long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS). This study aimed to assess insecticide resistance intensity and to determine the distribution of kdr and Ace - 1 resistance mutations in wild An. gambiae s.l. populations from Nioro and Ndoffane districts (Kaolack region). Methods Anopheles larvae were collected between September and November 2018 and reared under insectary conditions. Adult females were subjected to World Health Organization (WHO) susceptibility assays using five insecticides: three pyrethroids, one carbamate and one organophosphate. Resistance intensity assays were conducted at 5 × and 10 × diagnostic concentrations. Species within the An. gambiae complex and the East-kdr (1014S) , West-kdr (1014F) and Ace-1 (G119S) were identified using Polymerase Chain Reaction (PCR) technique. Results A total of 1830 females An. gambiae s.l. were tested . Widespread resistance to pyrethroids and organophosphates was observed in both districts, while in Ndoffane complete susceptibility to bendiocarb was recorded and in Nioro resistance was observed. Anopheles arabiensis was the predominant species (> 90%), followed by An. gambiae s.s. and An. coluzzii . The frequencies of East-kdr and West-kdr mutations were higher in Ndoffane (40.4% and 30.8%) than in Nioro (10.6% and 13.1%). The Ace-1 (G119S) mutation was detected exclusively in the heterozygous state across all the study populations. Conclusions The studied vectors exhibit multiple insecticide resistance mechanisms, likely driven by combined selection pressures from agricultural and public health insecticide use. Strengthening entomological surveillance and implementing integrated resistance management strategies are essential to preserve the effectiveness of malaria vector control interventions in Senegal.