High efficacy of chlorfenapyr-based net Interceptor® G2 against pyrethroid-resistant malaria vectors from Cameroon

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 (χ2 = 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

Substrate promiscuity of key resistance P450s confers clothianidin resistance whilst increasing chlorfenapyr potency in malaria vectors

“…The low mortality response obtained with the pyrethroid-only net could be associated to pyrethroid resistance driven by CYP6P9a/b as previously reported in this strain 27,28 and the An funestus from Malawi 43 . The greater e cacy of the CFP-based net observed in this study as previously reported in Benin, Tanzania, and Cameroon 24,44,45 should be therefore attributed to the potential bioactivation of chlorfenapyr by P450s in pyrethroid-resistant mosquitoes. Interceptor® G2 could be therefore an e cient replacement for pyrethroid-only ITNs for the reduction of malaria transmission malaria vectors as observed in Benin and Tanzania 19,46 .…”

“…These insecticide chemistries have been presented as good alternatives as they have different mechanism of actions and unique targets 17,18 . Interceptor G2 net treated with alpha-cypermethrin and chlorfenapyr is one example of a long-lasting dual insecticide mixture net that has shown great promise at controlling pyrethroid-resistant malaria vectors in randomised cluster control trials conducted in Benin and Tanzania [19][20][21] and several experimental hut trials across the continent [21][22][23][24] . The new insecticide formulation combining the neonicotinoid, clothianidin (CLTD) and the pyrethroid deltamethrin (8:1 w/w) under the brand name Fludora Fusion® developed by Bayer (Bayer CropScience, Monheim, Germany) for indoor residual spraying (IRS) as a tool for insecticide resistance management (IRM) has also demonstrated its high e cacy against various malaria vectors, including pyrethroid-resistant populations 17,18 .…”

A descriptive review of next-generation insecticide-treated bed nets for malaria control

“…and An. funestus showed no increased mortality compared to pITNs (Tchouakui et al, 2023). The only other published RG study recorded that mid-low mortality levels are induced with An.…”

“…funestus, and An. gambiae s.s./s.l (Corbel et al, 2010;Koudou et al, 2011;Pennetier et al, 2013;Awolola et al, 2014;Ketoh et al, 2018;Oumbouke et al, 2019;Pwalia et al, 2019;Tchakounte et al, 2019;Ibrahim et al, 2020;Menze et al, 2020;Barreaux et al, 2022;Menze et al, 2022;Tchouakui et al, 2023). To confirm that the success of PBO is through direct inhibition of P450s, studies provided evidence of P450-mediated resistance through several indicators: mortality in bioassays with a preexposure to PBO; P450 activity assays; and higher frequencies of P450 allelic markers (Awolola et al, 2014;Ketoh et al, 2018;Menze et al, 2022).…”

“…gambiae s.l. in Cote d'Ivoire, Burkina Faso, Benin, and Cameroon (Bayili et al, 2017;Camara et al, 2018;Syme et al, 2023b;Syme et al, 2023a;Tchouakui et al, 2023). Differences were evident between net manufacturers, with IG2 outperforming PBO and other CFP nets (PermaNet 3.0, DuraNet Plus, and PermaNet Dual) in Cameroon and Benin (Syme et al, 2023b;Syme et al, 2023a;Tchouakui et al, 2023), whilst in Cote d'Ivoire and Benin, the use of PermaNet 3.0 and PermaNet Dual resulted in higher mortality than RG and Olyset Plus (Ngufor et al, 2022;Tchouakui et al, 2023).…”