Efficacy and durability (insecticidal and physical) of next generation insecticide-treated nets against pyrethroid resistant malaria vectors in Tanzania: A multi-faceted study

Vector control interventions, particularly the scale-up of pyrethroid-treated bed nets (ITNs), have significantly reduced malaria transmission in sub-Saharan Africa over the past two decades. However, pyrethroid resistance threatens ITN effectiveness, especially as nets degradeover time. This thesis evaluates the bio-efficacy and durability of three new dual-active ingredient (A.I.) ITNs (Interceptor G2, Royal Guard, and Olyset Plus) compared to standard Interceptor nets. A cluster-randomized controlled trial (cRCT) was conducted in Misungwi, Tanzania, in January 2019, distributing 40,000 nets of each type. Over 36 months, 3,072 ITNs of each type were monitored at 6–12 month intervals to assess survivorship and fabric integrity. Results showed a median functional survival of less than three years, with Olyset Plus having the shortest lifespan of 0.9 years. Bio-efficacy studies at Kilimanjaro Christian Medical University College (KCMUCo) and the National Institute for Medical Research (NIMR) showed all ITNs met WHO bio-efficacy criteria, influenced mainly by blood-feeding inhibition rather than mortality. Against a resistant strain of An. gambiae s.s., new dual A.I. ITNs showed higher mortality than the reference net (Interceptor), with this advantage lasting 24 months. Fertility effects of pyriproxyfen in Royal Guard were observed up to six months in laboratory assays. In experimental hut trials (EHTs), Royal Guard and Interceptor G2 demonstrated superior efficacy for entomological outcomes for one year, while Olyset Plus showed benefits only when new. In the cRCT, Royal Guard and Olyset Plus showed similar trends, while Interceptor G2 provided consistent protection for three years. This study underscores the value of dual A.I. ITNs in community settings, emphasizing the need for continuous monitoring and research to develop longer-lasting ITNs and enhance malaria control in sub-Saharan Africa