Insecticide resistance intensity and efficacy of synergists with pyrethroids in Anopheles gambiae s.l. (Diptera: Culicidae) from Southern Togo

Abstract

Background: This study was designed to provide insecticide resistance data for decision making in terms of resistance management plans in Togo. Methods: The susceptibility status of Anopheles gambiae s.l. (Diptera: Culicidae) to insecticides used in public health was assessed using the WHO tube test protocol. Pyrethroid resistance intensity bioassays were performed following the CDC bottle test protocol. The activity of detoxification enzymes was tested using the synergists PBO, DEF, and EA. Species-specific identification of An. gambiae s.l. and kdr mutation genotyping were performed using PCR techniques. Results: Local populations of An. gambiae s.l. showed full susceptibility (i.e., mortality rates (MR) = 100%) to pirimiphos methyl at Lomé, Kovié, Anié, and Kpèlè Toutou. At Baguida, mortality was 90%, indicating possible resistance to pirimiphos methyl. Resistance was recorded to DDT (MR: 2-20.5%), bendiocarb (MR: 15-62.5%), and propoxur (MR: 19.25-51.75%) at all sites. A high intensity of pyrethroid resistance was recorded and the detoxification enzymes contributing to resistance were oxidases, esterases, and glutathione-s-transferases based on the synergist tests. An. gambiae s.s. and An. coluzzii were the main species identified. High kdr L1014F and low kdr L1014S allele frequencies were detected at all localities. Conclusion: This study suggests the need to reinforce current insecticide-based malaria control interventions (IRS and LLINs) with complementary tools.