Reduced performance of community bednets against pyrethroid-resistant Anopheles funestus and Anopheles gambiae, major malaria vectors in Cameroon

Abstract

Background: Long-lasting insecticidal nets are a vital tool in the fight against malaria vectors. However, their efficacy in the field can be impacted by several factors including patterns of usage, net age, resistance, and the delayed mortality effect that could influence malaria transmission. Here, we investigated the effectiveness of various brands of LLINs from markets and households in Cameroon, on pyrethroid-resistant mosquitoes and assessed their post-exposure effect.Methods: After quality control on susceptible lab strain, immediate and delayed mortality effects of LLINs (bought and collected from households in Elende in 2019) exposure were evaluated using standard WHO cone tests on Anopheles gambiae and Anopheles funestus populations collected from the Centre region of Cameroon. Alive female mosquitoes were genotyped for various resistance markers at different time-points post-exposure to evaluate the impact of insecticide resistance on the efficacy of bednets.Results and conclusion: High mortality rates were obtained with the laboratory susceptible strain when exposed to all pyrethroid-only brands of purchased nets (Olyset®Net, Super Net, PermaNet®2, Yorkool®, Royal Sentry®) (68.66 ± 8.35% to 93.33 ± 2.90%). However, low mortality was observed against wild An. funestus mosquitoes (0±0% to 28±6.7%) indicating a reduced performance of these nets against field mosquitoes. In addition, bednets collected from households showed reduced efficacy on the laboratory strain (19%- 66% mortality) and displayed a significant loss of efficacy against the local wild strains (mortality 0 ± 0% to 4 ± 2.6% for An. gambiae s.l. and 0 ± 0% to 8 ± 3.2% for An. funestus). However, compared to the unexposed group, mosquitoes exposed to bed nets showed a significantly reduced longevity indicating that the efficacy of these nets is not completely lost. CYP6P9a-RR and L119F-GSTe2 resistant mosquitoes had greater longevity after exposure to the Olyset net compared to their susceptible counterparts pointing the impact of resistance on bed nets efficacy and delay mortality. These findings present evidence of the actual impact of resistance on the quality and efficacy of LLINs in use in the community but also on the level of resistance of local vector populations to these nets highlighting the need to use new generation nets not relying only on pyrethroids.

Characterizing pyrethroid resistance and mechanisms in Anopheles gambiae (s.s.) and Anopheles arabiensis from 11 districts in Uganda

“…Various non-pyrethroid insecticides have been deployed, including bendiocarb (a carbamate), pirimiphos-methyl (an organophosphate) and clothianidin (a neonicotinoid), all with differing modes of action found to be suitable alternatives to pyrethroids ( Akogbéto et al., 2010 ; Agossa et al., 2014 ; Fongnikin et al., 2020 ). However, the substantial benefits of LLINs and IRS are threatened by widespread insecticide resistance in Uganda ( Mawejje et al., 2013 ; Mulamba et al., 2014 ; Okia et al., 2018 ; Tchouakui et al., 2021 ), and elsewhere ( Ochomo et al., 2013 , 2014 ; Yipmo et al., 2022 ).…”