Evidence supporting deployment of next generation insecticide treated nets in Burkina Faso: bioassays with either chlorfenapyr or piperonyl butoxide increase mortality of pyrethroid-resistant Anopheles gambiae

Abstract

Background Pyrethroid resistance poses a major threat to the efficacy of insecticide-treated nets (ITNs) in Burkina Faso and throughout sub-Saharan Africa, particularly where resistance is present at high intensity. For such areas, there are alternative ITNs available, including the synergist piperonyl butoxide (PBO)-based ITNs and dual active ingredient ITNs such as Interceptor G2 (treated with chlorfenapyr and alpha-cypermethrin). Before deploying alternative ITNs on a large scale it is crucial to characterize the resistance profiles of primary malaria vector species for evidence-based decision making. Methods Larvae from the predominant vector, Anopheles gambiae sensu lato (s.l.) were collected from 15 sites located throughout Burkina Faso and reared to adults for bioassays to assess insecticide resistance status. Resistance intensity assays were conducted using WHO tube tests to determine the level of resistance to pyrethroids commonly used on ITNs at 1×, 5 × and 10 × times the diagnostic dose. WHO tube tests were also used for PBO synergist bioassays with deltamethrin and permethrin. Bottle bioassays were conducted to determine susceptibility to chlorfenapyr at a dose of 100 µg/bottle. Results WHO tube tests revealed high intensity resistance in An. gambiae s.l. to deltamethrin and alpha-cypermethrin in all sites tested. Resistance intensity to permethrin was either moderate or high in 13 sites. PBO pre-exposure followed by deltamethrin restored full susceptibility in one site and partially restored susceptibility in all but one of the remaining sites (often reaching mortality greater than 80%). PBO pre-exposure followed by permethrin partially restored susceptibility in 12 sites. There was no significant increase in permethrin mortality after PBO pre-exposure in Kampti, Karangasso-Vigué or Mangodara; while in Seguenega, Orodara and Bobo-Dioulasso there was a significant increase in mortality, but rates remained below 50%. Susceptibility to chlorfenapyr was confirmed in 14 sites. Conclusion High pyrethroid resistance intensity in An. gambiae s.l. is widespread across Burkina Faso and may be a predictor of reduced pyrethroid ITN effectiveness. PBO + deltamethrin ITNs would likely provide greater control than pyrethroid nets. However, since susceptibility in bioassays was not restored in most sites following pre-exposure to PBO, Interceptor G2 may be a better long-term solution as susceptibility was recorded to chlorfenapyr in nearly all sites. This study provides evidence supporting the introduction of both Interceptor G2 nets and PBO nets, which were distributed in Burkina Faso in 2019 as part of a mass campaign.

Natural plant diet impacts phenotypic expression of pyrethroid resistance in Anopheles mosquitoes

“…This means that the mosquitoes were highly resistant according to the WHO criteria, i.e., a mortality less than 90% at the discriminating concentration of 0.05% (1×) and less than 98% at the 10 × dose 2 . These results con rm the high insecticide resistance status of this mosquito population 54 .…”

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

“…The use of LLINs that contain PBO can be encouraged for resistance management based on our results. Hien et al [9] showed that PBO partially restored the susceptibility of An. gambiae s.l.…”

“…Resistance has already been reported in various West African countries including Benin, Burkina Faso, Mali [3][4][5] and particularly in Togo [6,7]. Recent studies showed that the use of synergists and combination of insecticide formulations can increase the susceptibility of malaria vectors in areas with high pyrethroid resistance [8,9]. To support the sustainability of control strategies, it is essential to consider that resistance management should be systematically integrated into any vector control policy [2].…”

Essential oils of plants and their combinations as an alternative adulticides against Anopheles gambiae (Diptera: Culicidae) populations

“…Today, a limiting factor in the development of these strategies were the absence of alternative classes of insecticides for LLINs. However, in recent years, several studies have shown that the use of piperonyl butoxide (PBO) as a synergist restores susceptibility to deltamethrin or permethrin in several regions of the country 9 , 10 .…”