Modelling the impact of adopting new-generation insecticide-treated nets on malaria transmission and insecticide resistance

BackgroundThe widespread insecticide resistance increasingly threatens malaria elimination, prompting a reassessment of vector control strategies. As Tanzania transitions from standard pyrethroid-only insecticide-treated nets (ITNs) to new-generation nets, evaluating the impact of this shift on malaria transmission and resistance is critical. MethodsUsing the agent-based malaria model, EMOD, we assessed the impact of three ITN types, standard pyrethroid-only nets, pyrethroid-PBO nets (Olyset(R) Plus/PermaNet(R) 3.0), and the dual active, Interceptor(R) G2 nets (IG2) on malaria transmission and the evolution of insecticide resistance. We also evaluated different sequences for introducing the new-generation nets, and the impact of combining ITNs with indoor residual spraying (IRS). The model was calibrated using incidence and prevalence data from two regions in northwestern Tanzania, incorporating seasonality, insecticide resistance, and behaviors of dominant vectors Anopheles funestus (highly anthropophilic, endophilic) and Anopheles arabiensis (more opportunistic readily biting non-human hosts outdoors). ResultsChanging from standard pyrethroid-only ITNs to pyrethroid-PBO and thereafter to IG2 ITNs reduced homozygous-resistant An. funestus and An. arabiensis by 62.2% and 92.8%, respectively, and reduced incidence and prevalence by 94% and 75.2% respectively, under conditions where the probability of mosquito pyrethroid resistance was 0.75. Deploying IRS before the peak malaria transmission season in mid-May, in the second year following pyrethroid-PBO ITNs distribution, and repeating this every three years, reduced malaria incidence and prevalence by 76.4% and 52%, respectively. ConclusionIn contrast to continuous use of standard pyrethroid-only ITNs, which sustains resistance selection, transitioning to new-generation ITNs, with or without periodic IRS, can disrupt the evolutionary trajectory of pyrethroid resistance, reduce malaria burden, and strengthen progress toward elimination.