Streamlined durability monitoring of DuraNet® Plus and Interceptor® G2 insecticide-treated nets in Northern Region, Cameroon: assessment results in two sites from 2022 to 2025

Abstract

Abstract Background Insecticide-treated nets (ITNs) are a critical vector control and malaria prevention tool. Routine monitoring of ITN physical and chemical durability is key to assessing their performance under real-world conditions. A streamlined ITN durability monitoring methodology, focusing on bioeffectiveness, was deployed in Northern Region, Cameroon from 2022 to 2025. Assessment objectives were to measure the insecticidal efficacy of pyrethroid (pyr) + piperonyl butoxide (PBO) DuraNet Plus (DNP) and pry + chlorfenapyr (CFP) Interceptor G2 (IG2) ITNs, monitor physical integrity and estimate attrition. Methods This was a prospective assessment using repeat cross-sectional cluster surveys of ITNs randomly sampled from a primary sampling frame after annual assessment timepoints. Two study districts, Lagdo and Pitoa, were selected for their proximity and similarities in climate, demographics and malaria burden. Questionnaires captured information on ITN use in households from which ITNs were sampled. Sampled ITNs underwent physical hole inspection, as well as bioassay and chemical residue analyses. Primary outcomes of interest were pyr-resistant mosquito mortality (measured as 24-hour mortality for DNP ITNs and 72-hour mortality for IG2 ITNs) and mean chemical content. ITN attrition was also assessed, as were potential associations between ITN use factors and chemical content retention. Results Pry-resistant strain mortality was just 5% at endline for DNP ITNs, corresponding with an 82% decrease in PBO content compared to the manufacturer’s target dose. Endline IG2 pyr-resistant strain 72-hour mortality was 55%, corresponding with a 79% decrease in CFP content compared to the manufacturer’s target dose. Ever washing an ITN (p = 0.046), use of bleach (p = 0.009) and net physical integrity (p = 0.004) were significantly associated with reductions in mean chemical content in IG2 ITNs. All cause attrition was estimated at 51% for DNP ITNs and 32% for IG2 ITNs at endline. Conclusion These are the first published SDM results. IG2 ITNs in Lagdo outperformed DNP ITNs in Pitoa on measures of pyr-resistant strain mortality and chemical residue loss. Durability monitoring or post-market ITN surveillance data from other sites is necessary to identify trends in DNP performance under real-world conditions.