Countrywide insecticide resistance monitoring and first report of the presence of knock down resistance east in Niger, West Africa

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Abstract Background Mass distribution of insecticide treated nets (ITNs) is the principal malaria vector control strategy adopted by Niger. To better inform on the most appropriate ITNs to distribute, the Niger National Malaria Control Programme (NMCP), with the support of the U.S. President’s Malaria Initiative and its partners, conducted insecticide resistance monitoring in sixteen sites selected across the country. Methods The susceptibility of Anopheles gambiae sensu lato (s.l.) to chlorfenapyr and pyrethroid insecticides was investigated in nine sites in 2019 and fifteen sites in 2020, including eightfrom the previous year. The susceptibility status, pyrethroid resistance intensity at 5 and 10 times the diagnostic concentrations, and piperonyl butoxide (PBO) synergism with diagnostic concentrations of deltamethrin, permethrin and alpha-cypermethrin were assessed using WHO bioassays. Two doses (100 and 200 µg/bottle) of chlorfenapyr were tested using the CDC bottle assay method. Species composition and allele frequencies for knock-down resistance (kdr-west and kdr-east) and acetylcholinesterase (ace-1) mutations were further characterized using polymerase chain reaction (PCR). Results High resistance to all pyrethroids tested was observed in all sixteen sites during both years. Pre-exposure to PBO substantially increased susceptibility with average increases in mortality from 30 to 70% for deltamethrin, 0 to 60% for permethrin, and 5 to 70% for alpha-cypermethrin. Susceptibility to chlorfenapyr (100 ug/bottle) was recorded in all sites except in Tessaoua and Magaria where susceptibility was recorded at the dose of 200 ug/bottle. The kdr-e allele, investigated for the first time, was detected in the country. Both kdr-w and kdr-e were present in all 15 sites surveyed in 2020, at frequencies between 0.46–0.81 and 0.41–0.87, respectively. An. coluzzii was the predominant malaria vector species in the 16 sites surveyed for insecticide susceptibility followed by An. gambiae s.s. and An. arabiensis. Conclusion The data collected showed high resistance to pyrethroids with the involvement of various resistance mechanisms, which will guide the NMCP in making evidence-based decisions to better adapt vector control strategies and insecticide resistance management in Niger, starting with the introduction of new generation ITNs such as interceptor G2 and PBO ITNs for mass distribution campaigns, by targeting sites where the vector population showed susceptibility to chlorfenapyr or increased mortality using PBO synergism.

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