What can be learned from the residual efficacy of three formulations of insecticides (pirimiphos-methyl, clothianidin and deltamethrin mixture, and clothianidin alone) in large-scale in community trial in North Benin, West Africa?

Abstract

Background In Alibori and Donga, two departments of high malaria incidence of Northern Benin, pirimiphos-methyl, mixture deltamethrin + clothianidin, as well as clothianidin were used at large scale for IRS. The present study aimed to assess the residual efficacy of these products. Methods Immatures of Anopheles gambiae sensu lato (s.l.) collected in the communes of Kandi and Gogounou (Department of Alibori), Djougou and Copargo (Department of Donga) were reared until adulthood. Females aged 2–5 days were used for susceptibility tube tests following the WHO protocol. The tests were conducted with deltamethrin (0.05%), bendiocarb (0.1%), pirimiphos-methyl (0.25%) and clothianidin (2% weight per volume). For cone tests performed on cement and mud walls, the An. gambiae Kisumu susceptible strain was used. After the quality control of the IRS performed 1-week post-campaign, the evaluation of the residual activity of the different tested insecticides/mixture of insecticides was conducted on a monthly basis. Results Over the three study years, deltamethrin resistance was observed in all the communes. With bendiocarb, resistance or possible resistance was observed. In 2019 and 2020, full susceptibility to pirimiphos-methyl was observed, while possible resistance to the same product was detected in 2021 in Djougou, Gogounou and Kandi. With clothianidin, full susceptibility was observed 4–6 days post-exposure. The residual activity lasted 4–5 months for pirimiphos-methyl, and 8–10 months for clothianidin and the mixture deltamethrin + clothianidin. A slightly better efficacy of the different tested products was observed on cement walls compared to the mud walls. Conclusion Overall, An. gambiae s.l. was fully susceptible to clothianidin, while resistance/possible resistance was observed the other tested insecticides. In addition, clothianidin-based insecticides showed a better residual activity compared to pirimiphos-methyl, showing thus their ability to provide an improved and prolonged control of pyrethroid resistant vectors.

Dramatic resurgence of malaria after 7 years of intensive vector control interventions in Eastern Uganda

“…(19) Subsequent studies of field populations of common Anopheles species from Kenya, Benin, and Cote d’Ivoire also reported high mortality rates following exposure to clothianidin. (20, 21, 22, 23) It should be noted that clothianidin is slower acting than other commonly used insecticide classes, requiring a longer holding period to fully assess post-exposure mortality. (18, 24, 25) Despite these encouraging reports, some recent data have suggested the existence of reduced susceptibility to clothianidin among African vectors, as reported in this study.…”

Long-Lasting Insecticide-Treated Nets Combined or Not with Indoor Residual Spraying May Not Be Sufficient to Eliminate Malaria: A Case-Control Study, Benin, West Africa

“…In Cobly, the first edition of IRS was implemented in 2011 using the insecticide bendiocarb [22]. In 2014, pirimiphos-methyl 300 CS (PM 300 CS) insecticide was used for IRS exhibiting and its residual activity lasted 4-5 months on both mud and cement walls [22][23][24]. PM 300 CS induced more than 80% mortality in susceptible "Kisumu" Anopheles gambiae after 24 h, 48 h, and 72 h of exposure [24].…”

“…In 2014, pirimiphos-methyl 300 CS (PM 300 CS) insecticide was used for IRS exhibiting and its residual activity lasted 4-5 months on both mud and cement walls [22][23][24]. PM 300 CS induced more than 80% mortality in susceptible "Kisumu" Anopheles gambiae after 24 h, 48 h, and 72 h of exposure [24]. Other aspects of the methodology used for implementing IRS in Benin is described elsewhere [22][23][24].…”

“…PM 300 CS induced more than 80% mortality in susceptible "Kisumu" Anopheles gambiae after 24 h, 48 h, and 72 h of exposure [24]. Other aspects of the methodology used for implementing IRS in Benin is described elsewhere [22][23][24].…”