Site-specific bio-efficacy of Interceptor G2 and Royal Guard against highly pyrethroid- 1 resistant Anopheles gambiae s.l. in experimental hut in southwestern Burkina Faso

Insecticide-treated nets (ITNs) lowered malaria cases and deaths by 68% in endemic regions by 2015, but rising resistance has slowed progress. Burkina Faso faces high resistance levels challenging vector control. This study assessed the effectiveness of Interceptor G2 (IG2) and Royal Guard (RG) ITNs against highly resistant (< 10% mortality rate to alpha-cypermethrin 0.05%) Anopheles gambiae s.l. in Experimental Hut Trials in Tannounyan region, Burkina Faso. Among 22,234 collected mosquitoes collected over three years, 66.6% were An. gambiae s.l. with Anopheles coluzzii and An. gambiae s.s., dominant in Tengrela and Tiefora respectively. Unwashed IG2 ITNs induced the highest mosquito mortality rates, 57% and 34% as 72-hour mortality in Tiefora and Tengrela respectively; mortality rates were higher for An. gambiae than An. coluzzii and significantly higher in both sites compared to standard ITNs. Net washing or aging reduced the efficacy of both IG2 and RG. Only unwashed RG nets reduced blood feeding success compared to standard ITNs. Follow up on the sublethal effects of the different arms showed, RG ITNs drastically reduced Anopheles gambiae s.l. offspring number compared to other nets. Results suggest, dual-ingredient nets' impact varies with local vector ecology, underscoring the need for targeted strategies of deployment and monitoring.