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.
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 ITN to distribute, the National Malaria Control Programme (NMCP) of Niger and its partners, conducted insecticide resistance monitoring in selected sites across the country. Methods The susceptibility of Anopheles gambiae sensu lato (s.l.) to chlorfenapyr and pyrethroid insecticides was investigated in a total of sixteen sites in 2019 and 2020, using 2–5-day-old adults reared from wild collected larvae per site. 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-L1014F and L1014S) and acetylcholinesterase (ace-1 G119S) mutations were further characterized using polymerase chain reaction (PCR). Results High resistance intensity to all pyrethroids tested was observed in all sites except for alpha-cypermethrin in Gaya and Tessaoua and permethrin in Gaya in 2019 recording moderate resistance intensity. Similarly, Balleyara, Keita and Tillabery yielded moderate resistance intensity for alpha-cypermethrin and deltamethrin, and Niamey V low resistance intensity against deltamethrin and permethrin in 2020. Pre-exposure to PBO substantially increased susceptibility with average increases in mortality between 0 and 70% for tested pyrethroids. Susceptibility to chlorfenapyr (100 µg/bottle) was recorded in all sites except in Tessaoua and Magaria where susceptibility was recorded at the dose of 200 µg/bottle. Anopheles coluzzii was the predominant malaria vector species in most of the sites followed by An. gambiae sensu stricto (s.s.) and Anopheles arabiensis. The kdr-L1014S allele, investigated for the first time, was detected in the country. Both kdr-L1014F (frequencies [0.46–0.81]) and L1014S (frequencies [0.41–0.87]) were present in all sites while the ace-1 G119S was between 0.08 and 0.20. Conclusion The data collected will guide the NMCP in making evidence-based decisions to better adapt vector control strategies and insecticide resistance management in Niger, starting with mass distribution of new generation ITNs such as interceptor G2 and PBO ITNs.
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