Efficacy and Usage of Insecticide-Treated Nets in Areas of High Insecticide Resistance: A Comparative Study in Central Cameroon

Background Insecticide-Treated Nets (ITNs) remain the primary tool recommended by the World Health Organization (WHO) for effectively reducing vector density and interrupting malaria transmission by preventing vector-human contact. In this study, we evaluated the insecticidal effectiveness and usage patterns of three brands of ITNs in the Emana and Minkama health areas of central Cameroon. Methods Phenotypic resistance to permethrin, deltamethrin, α-cypermethrin, pirimiphos-methyl, and bendiocarb was assessed using WHO susceptibility tests on adult Anopheles gambiae s.l. from F ₁ progenies. The study evaluated three ITN types: Olyset® Net, MAG-Net® LN and PermaNet® 3.0, and examined the physical integrity of 300 nets through visual inspection and measurements. Cone bioassays tested insecticidal efficacy against field populations and a susceptible reference strain. Surveys collected data on ITN ownership, usage, acceptance, and maintenance. Additionally, species composition and kdr mutation frequencies were determined from subsamples to investigate resistance mechanisms and correlate them with ITN effectiveness. Results Anopheles gambiae s.l. populations at both sites showed resistance to permethrin, deltamethrin, and α-cypermethrin, but remained susceptible to bendiocarb. In Emana, high susceptibility to pirimiphos-methyl was observed (98.25%). Pre-exposure to PBO significantly increased mortality rates for pyrethroids, rising from 6–25% to over 97%, indicating metabolic resistance mechanisms. In Minkama, PBO increased mortality from 8% to 58% for α-cypermethrin, 37% to 99% for permethrin, and 80% to 100% for deltamethrin. Among tested ITNs, PermaNet® 3.0 was most effective, achieving 99% mortality in Emana and 99.4% in Minkama, though overall ITN efficacy varied (25–99% in Emana; 30-99.5% in Minkama), compared to 80–100% in a susceptible strain. Only 52.9% of surveyed individuals reported using the 99 ITNs evaluated. Species analysis showed that An. gambiae was predominant (57.6% in Emana, 52.8% in Minkama), alongside An. coluzzii (26.6% in Emana, 33.4% in Minkama). The L1014F kdr mutation frequency ranged from 0.08 to 0.45 in Emana and 0.18 to 0.62 in Minkama, indicating widespread pyrethroid resistance. Conclusion Integrating combination nets into a comprehensive malaria control strategy, alongside efforts to improve ITN access, is vital for managing transmission amid insecticide resistance. Future success depends on coordinated interventions tailored to local ecological conditions and vector resistance profiles.