An increasing role of pyrethroid-resistant Anopheles funestus in malaria transmission in the Lake Zone, Tanzania

<jats:title>Abstract</jats:title><jats:p><jats:italic>Anopheles funestus</jats:italic> is playing an increasing role in malaria transmission in parts of sub-Saharan Africa, where <jats:italic>An. gambiae</jats:italic> s.s. has been effectively controlled by long-lasting insecticidal nets. We investigated vector population bionomics, insecticide resistance and malaria transmission dynamics in 86 study clusters in North-West Tanzania. <jats:italic>An. funestus</jats:italic> s.l. represented 94.5% (4740/5016) of all vectors and was responsible for the majority of malaria transmission (96.5%), with a sporozoite rate of 3.4% and average monthly entomological inoculation rate (EIR) of 4.57 per house. Micro-geographical heterogeneity in species composition, abundance and transmission was observed across the study district in relation to key ecological differences between northern and southern clusters, with significantly higher densities, proportions and EIR of <jats:italic>An. funestus</jats:italic> s.l. collected from the South. <jats:italic>An. gambiae</jats:italic> s.l. (5.5%) density, principally <jats:italic>An. arabiensis</jats:italic> (81.1%) and <jats:italic>An. gambiae</jats:italic> s.s. (18.9%), was much lower and closely correlated with seasonal rainfall. Both <jats:italic>An. funestus</jats:italic> s.l. and <jats:italic>An. gambiae</jats:italic> s.l. were similarly resistant to alpha-cypermethrin and permethrin. Overexpression of <jats:italic>CYP9K1, CYP6P3, CYP6P4</jats:italic> and <jats:italic>CYP6M2</jats:italic> and high L1014S-<jats:italic>kdr</jats:italic> mutation frequency were detected in <jats:italic>An. gambiae</jats:italic> s.s. populations. Study findings highlight the urgent need for novel vector control tools to tackle persistent malaria transmission in the Lake Region of Tanzania.</jats:p>