Susceptibility of Anopheles gambiae from Côte d’Ivoire to insecticides used on insecticide-treated nets: evaluating the additional entomological impact of piperonyl butoxide and chlorfenapyr

• Published in: Malaria Journal
• Main Authors: Bernard L. Kouassi, Constant Edi, Emmanuel Tia, Lucien Y. Konan, Maurice A. Akré, Alphonsine A. Koffi, Allassane F. Ouattara, Antoine Mea Tanoh, Pascal Zinzindohoue, Blaise Kouadio, McKenzie Andre, Seth R. Irish, Jennifer Armistead, Dereje Dengela, Ndombour G. Cissé, Cecilia Flatley, Joseph Chabi
• Format: Article in Journal/Newspaper
• Language: English
• Published: BMC 2020
• Subjects: Insecticide resistance; Pyrethroids; Piperonyl butoxide; Chlorfenapyr; Anopheles gambiae; Vector control; Arctic medicine. Tropical medicine; RC955-962; Infectious and parasitic diseases; RC109-216; Arctic
• Online Access: https://doi.org/10.1186/s12936-020-03523-y; https://doaj.org/article/21fe09c94d204c3f8edea3b57c76236d

Abstract Background Pyrethroid-treated mosquito nets are currently the mainstay of vector control in Côte d’Ivoire. However, resistance to pyrethroids has been reported across the country, limiting options for insecticide resistance management due to the paucity of alternative insecticides. Two types of insecticide-treated nets (ITNs), ITNs with pyrethroids and the synergist piperonyl butoxide (PBO), and Interceptor®G2 nets, a net treated with a combination of chlorfenapyr and alpha-cypermethrin, are believed to help in the control of pyrethroid-resistant mosquitoes. Methods The susceptibility of Anopheles gambiae sensu lato (s.l.) to pyrethroid insecticides with and without pre-exposure to PBO as well as to chlorfenapyr was investigated in fifteen sites across the country. Susceptibility tests were conducted on 2- to 4-day old adult female An. gambiae s.l. reared from larval collections. The resistance status, intensity, and effects of PBO on mortality after exposure to different concentrations of deltamethrin, permethrin and alpha-cypermethrin were determined using WHO susceptibility test kits. In the absence of a WHO-recommended standard protocol for chlorfenapyr, two interim doses (100 and 200 µg/bottle) were used to test the susceptibility of mosquitoes using the CDC bottle assay method. Results Pre-exposure to PBO did not result in full restoration of susceptibility to any of the three pyrethroids for the An. gambiae s.l. populations from any of the sites surveyed. However, PBO pre-exposure did increase mortality for all three pyrethroids, particularly deltamethrin (from 4.4 to 48.9%). Anopheles gambiae s.l. from only one site (Bettie) were susceptible to chlorfenapyr at the dose of 100 µg active ingredient (a.i.)/bottle. At the dose of 200 µg (a.i.)/bottle, susceptibility was only recorded in 10 of the 15 sites. Conclusion Low mosquito mortality was found for pyrethroids alone, and while PBO increased mortality, it did not restore full susceptibility. The vector was not fully susceptible to chlorfenapyr ...