Efficacy of Interceptor G2, Royal Guard and PermaNet 3.0 against pyrethroid- resistant Anopheles gambiae s.l. from Za-Kpota, Southern Benin: an experimental hut trial

Abstract

Background Widespread use of insecticide-treated nets (ITNs) has made a major contribution to the dramatic decline in malaria cases and deaths seen across Africa in the 21st century. Unfortunately, this control strategy is threatened by the rapid spread of resistance to pyrethroid insecticides in malaria vectors. Dual-active-ingredient insecticidal nets are available to mitigate the impact of pyrethroid resistance and data is needed on the efficacy of these different nets against local mosquito populations to make evidence based decisions regarding product selection in specific use settings. Methods Two experimental Hut Trials were performed in Za-Kpota Southern Benin in 2021 to evaluate the performance of Interceptor G2 (BASF), Royal Guard (DCT) and PermaNet 3.0, (Vestergaard) compared to untreated or standard pyrethroid ITNs, against free-flying wild Anopheles gambiae mosquitoes. Both unwashed nets and those that had been in use for up to 2 years were assessed. Mosquitoes collected in the hut were followed up after exposure to assess the sublethal effects of treatments on certain life-history traits. Results The predominant species in the study site was Anopheles. gambiae s.s. Both Anopheles coluzzii and Anopheles gambiae s.s. were resistant to pyrethroids (deltamethrin susceptibility was restored by PBO pre-exposure). In experimental hut trials Royal Guard induced the highest blood-feeding inhibition (OR = 0.05; CI = 0.01–0.6; p < 0.001) relative to PermaNet 2.0. Interceptor G2 induced the highest 72 hour mortality rate (OR = 5.9; CI = 2.7–12.6; p < 0.001) compared to PermaNet 2.0. The highest risk of death in An. gambiae s.l. was observed with Interceptor G2 (HR = 6.5; CI = 5.7–7.6; p < 0.001) and PermaNet 3.0 (HR = 4.4; CI = 3.4–5.7; p < 0.001) compared to Untreated net. Lower mortality was recorded with Interceptor G2 aged compared to new Interceptor G2. Oviposition rates were low in mosquitoes collected from huts containing ITNs compared to untreated controls. No mosquitoes oviposited from huts with Royal Guad nets. Conclusion All of the dual active ingredient nets showed superior reductions in the survival of pyrethroid resistant An. gambiae s.s. compared to standard pyrethroid only ITNs.