article · Infectious Diseases of Poverty
Growing resistance to pyrethroid insecticides threatens malaria prevention strategies reliant on standard bed nets. This study evaluated the performance of dual-active ingredient and synergist bed nets against pyrethroid-resistant malaria vectors from multiple sites in Cameroon. Testing included laboratory assays and experimental hut trials assessing both unwashed nets and nets washed twenty times. The chlorfenapyr-based Interceptor G2 net demonstrated the highest efficacy against wild pyrethroid-resistant Anopheles funestus, achieving 87.8 percent mortality when unwashed and 55.6 percent mortality after twenty washes. In contrast, standard pyrethroid-only nets caused only 18.2 percent mortality. Interceptor G2, Permanet 3.0, and Royal Guard all provided substantially higher blood-feeding inhibition than the standard net. Furthermore, mosquitoes carrying the pyrethroid resistance marker kdrw remained susceptible to Interceptor G2. These semi-field findings support deploying chlorfenapyr-treated nets in Cameroon, subject to broader multi-location validation.
Malaria control relies heavily on insecticide-treated bed nets, but widespread mosquito resistance to conventional pyrethroids diminishes their protective value. Demonstrating that next-generation bed nets containing chlorfenapyr retain high killing and bite-prevention capacity against resistant vector populations provides crucial guidance for public health programmes. It offers an effective path forward for maintaining vector control and reducing malaria transmission where traditional nets are failing.
The findings directly inform vector control procurement and deployment strategies for public health authorities, international donors, and bed net manufacturers. Interceptor G2 is already a manufactured commercial product tested here in semi-field conditions. While the technology is applied and tested for targeted operational uptake, the evidence indicates that further validation across additional locations and vector species is required before advancing to large-scale implementation.
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Abstract Background The increasing reports of resistance to pyrethroid insecticides associated with reduced efficacy of pyrethroid-only interventions highlight the urgency of introducing new non-pyrethroid-only control tools. Here, we investigated the performance of piperonyl-butoxide (PBO)-pyrethroid [Permanet 3.0 (P3.0)] and dual active ingredients (AI) nets [Interceptor G2 (IG2): containing pyrethroids and chlorfenapyr and Royal Guard (RG): containing pyrethroids and pyriproxyfen] compared to pyrethroid-only net Royal Sentry (RS) against pyrethroid-resistant malaria vectors in Cameroon. Methods The efficacy of these tools was firstly evaluated on Anopheles gambiae s.l. and Anopheles funestus s.l. from Gounougou, Mibellon, Mangoum, Nkolondom, and Elende using cone/tunnel assays. In addition, experimental hut trials (EHT) were performed to evaluate the performance of unwashed and 20 times washed nets in semi-field conditions. Furthermore, pyrethroid-resistant markers were genotyped in dead vs alive, blood-fed vs unfed mosquitoes after exposure to the nets to evaluate the impact of these markers on net performance. The XLSTAT software was used to calculate the various entomological outcomes and the Chi-square test was used to compare the efficacy of various nets. The odds ratio and Fisher exact test were then used to establish the statistical significance of any association between insecticide resistance markers and bed net efficacy . Results Interceptor G2 was the most effective net against wild pyrethroid-resistant An. funestus followed by Permanet 3.0. In EHT, this net induced up to 87.8% mortality [95% confidence interval ( CI ): 83.5–92.1%) and 55.6% (95% CI : 48.5–62.7%) after 20 washes whilst unwashed pyrethroid-only net (Royal Sentry) killed just 18.2% (95% CI : 13.4–22.9%) of host-seeking An. funestus . The unwashed Permanet 3.0 killed up to 53.8% (95% CI : 44.3–63.4%) of field-resistant mosquitoes and 47.2% (95% CI : 37.7–56.7%) when washed 20 times, and the Royal Guard 13.2% (95% CI : 9.0–17.3%) for unwashed net and 8.5% (95% CI : 5.7–11.4%) for the 20 washed net. Interceptor G2, Permanet 3.0, and Royal Guard provided better personal protection (blood-feeding inhibition 66.2%, 77.8%, and 92.8%, respectively) compared to pyrethroid-only net Royal Sentry (8.4%). Interestingly, a negative association was found between kdrw and the chlorfenapyr-based net Interceptor G2 ( χ 2 = 138; P < 0.0001) with homozygote-resistant mosquitoes predominantly found in the dead ones. Conclusions The high mortality recorded with Interceptor G2 against pyrethroid-resistant malaria vectors in this study provides first semi-field evidence of high efficacy against these major malaria vectors in Cameroon encouraging the implementation of this novel net for malaria control in the country. However, the performance of this net should be established in other locations and on other major malaria vectors before implementation at a large scale. Graphical Abstract
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DOI: 10.1186/s40249-023-01132-w
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