Impact of replacing indoor residual spraying with next-generation PBO-based insecticide-treated nets on malaria transmission drivers in pyrethroid-resistant settings of Burkina Faso

Increasing insecticide resistance among malaria vectors threatens the effectiveness of conventional malaria control interventions in Burkina Faso. Following reduced susceptibility of Anopheles gambiae s.l. populations to pyrethroids and organophosphates, the National Malaria Control Programme replaced indoor residual spraying (IRS) with next-generation piperonyl butoxide insecticide-treated nets (PBO-ITNs) in several high-transmission districts. This study assessed the entomological impact of this transition in Kampti and Solenzo from 2021 to 2023. A longitudinal entomological survey was conducted during three consecutive malaria transmission seasons in two pyrethroid-resistant districts of Burkina Faso. Three intervention phases were evaluated: IRS combined with standard insecticide-treated nets (ITNs) in 2021, IRS withdrawal with PBO-ITN deployment in 2022, and PBO-ITNs alone in 2023. Adult mosquitoes were collected monthly using human landing catches and pyrethrum spray catches. Mosquitoes were morphologically identified, with molecular identification performed by PCR. Plasmodium falciparum sporozoite infection was detected using ELISA. Human biting rates (HBR), indoor resting densities (IRD), sporozoite rates (SR), and entomological inoculation rates (EIR) were compared across years and collection settings. A total of 15,533 mosquitoes were collected, of which Anopheles gambiae s.l. represented 95.5%. Marked temporal and spatial reductions in malaria transmission indicators were observed following IRS withdrawal and PBO-ITN deployment. Human biting rates, indoor resting densities, and EIR progressively declined over the study period, particularly in Solenzo. In Kampti, cumulative outdoor EIR decreased from 87 infective bites/person/year in 2021 to 17 infective bites/person/year in 2023. In Solenzo, no infected mosquitoes were detected after 2021. Logistic regression analysis revealed significantly lower odds of mosquito infection during the transition phase in 2022 and under PBO-ITN-only conditions in 2023 compared with the IRS-active period. The replacement of IRS with PBO-ITNs was associated with substantial reductions in vector density, human exposure to bites, and malaria transmission intensity in both study districts. Despite widespread pyrethroid resistance, PBO-ITNs maintained strong entomological effectiveness, particularly in Solenzo where transmission was interrupted after 2021. These findings highlight the operational potential of PBO-ITNs as a sustainable alternative to IRS in high-transmission settings of Burkina Faso.