Bio-efficacy of Olyset^® Plus, PermaNet^® 3.0 and Interceptor^® G2 on pyrethroid-resistant populations of Anopheles gambiae s.l. prior to the June 2023 net distribution campaign in Benin, West Africa

Background: This study investigates the effectiveness of new-generation mosquito nets, like Olyset^® Plus and PermaNet^® 3.0, and dual-action nets such as Interceptor^® G2, against pyrethroid-resistant Anopheles gambiae mosquitoes following the 2023 mass distribution of long-lasting insecticidal nets in Benin.

Methods: We tested wild mosquito populations from six communes in Benin against various pyrethroid (permethrin 0.75%, alphacypermethrin 0.05%, and deltamethrin 0.05%) using WHO tube tests. Additionally, we exposed mosquitoes to chlorfenapyr 100 µg/ml using the CDC bottle bioassay method. A subset of mosquitoes underwent biochemical and PCR tests to check the overexpression of metabolic enzymes and the Kdr L1014F mutation. We evaluated the effectiveness of Olyset^® Plus, PermaNet^® 3.0, and Interceptor^® G2 nets using cone and tunnel tests on both laboratory and field populations of An. gambiae.

Results: Overall, the highest mortality rate was 60% with pyrethroid and 98 to100% with chlorfenapyr. In cone tests, all three types of nets induced mortality rates above 80% in the susceptible laboratory strain of An. gambiae. Notably, Olyset^® Plus showed the highest mortality rates for pyrethroid-resistant mosquitoes in cone tests, ranging from 81.03% (95% CI: 68.59-90.13) in Djougou to 96.08% (95% CI: 86.54-99.52) in Akpro-Missérété. PermaNet^® 3.0 had variable rates, from 42.5% (95% CI: 27.04-59.11) in Djougou to 58.54% (95% CI: 42.11-73.68) in Porto-Novo. However, revealed good results for Interceptor^® G2, with 94% (95% CI: 87.40-97.77) mortality and 89.09% blood sampling inhibition in local populations of An. gambiae. In comparison, Interceptor^® had lower rates of 17% (95% CI: 10.23-25.82) and 60%, respectively.

Conclusion: These results suggest that tunnel tests are effective for evaluating dual-active ingredient nets. Additionally, Interceptor^® G2 and PBO nets like Olyset^® Plus could be considered as alternatives against pyrethroid-resistant mosquitoes.