Efficacy of Mosquito Shield, a transfluthrin spatial emanator against wild, free-flying pyrethroid-resistant Anopheles gambiae s.l.; an experimental hut evaluation in Benin, West Africa

BackgroundSpatial emanators disrupt mosquito behaviour by inducing movement away from chemical stimuli and interfering with host detection and feeding. These tools were recently endorsed by the World Health Organization (WHO) for malaria control, based largely on clinical evidence from East Africa. Mosquito ShieldTM is a passive, transfluthrin-based emanator designed to provide month-long protection in enclosed or semi-enclosed spaces. This study evaluated its entomological efficacy under experimental hut conditions in Benin, West Africa to generate evidence in support of WHO prequalification. MethodsAn experimental hut trial was conducted against wild free-flying pyrethroid-resistant Anopheles gambiae s.l. at the Cove field station in southern Benin over two 32-day product life cycles of Mosquito ShieldTM. Sixteen West African-style experimental huts were assigned to Mosquito ShieldTM or a placebo control. Efficacy was measured using human landing catches (HLC) and mosquito aspirations following standard hut testing methods. Primary endpoints included protective efficacy against mosquito landing (HLC) and personal protection against blood-feeding (mosquito aspiration). Secondary endpoints included deterrence, exophily, mortality, and blood-feeding inhibition. WHO susceptibility bioassays were conducted on the local An gambiae s.l. population to investigate susceptibility to public health insecticides during the trial. ResultsWHO susceptibility bioassays confirmed high levels of resistance to pyrethroids, including transfluthrin, in the local Anopheles gambiae s.l. population. A total of 5,682 An. gambiae s.l. and 6,158 Mansonia africana were collected through HLCs, and 1,436 An. gambiae s.l. by mosquito aspirations. Mosquito ShieldTM significantly reduced mosquito landing, providing 43.0% protective efficacy (95% CI: 24.0-57.0; p < 0.001) against An. gambiae s.l. and 38.0% protective efficacy (95% CI: 12.0-57.0; p = 0.008) against Mansonia africana. Mosquito aspiration data showed 48.5% deterrence, 29.9% blood-feeding inhibition, and 64% personal protection (95% CI: 21.9-81.8; p < 0.001) against An. gambiae s.l. No mosquito mortality was observed in the control huts, whereas mortality of An. gambiae s.l. reached 49.0% in HLC collections and 22.7% in aspiration collections. Mosquito ShieldTM also induced >96% mortality in Mansonia africana, demonstrating both lethal and behavioural effects against both vector species. ConclusionsMosquito ShieldTM significantly reduced mosquito entry, landing, blood-feeding, and survival of pyrethroid-resistant An. gambiae s.l. under semi-field experimental hut conditions in West Africa, with additional effects against Mansonia africana. These results support its WHO prequalification and highlight its potential as a complementary vector control tool to strengthen malaria prevention and provide additional benefits for integrated control of other vector-borne diseases.