Members of the Anopheles gambiae complex are important malaria vectors in Tanzania. This study investigated the distribution of An. gambiae complex and their insecticide resistance profile relative to their ecological differences in Tanzania.
Wild anopheles mosquitoes were collected by indoor-resting catch from 12 districts located across various ecological zones of Tanzania. These were morphologically identified and An. gambiae tested for resistance to deltamethrin, lambdacyhalothrin, permethrin and DDT using standard WHO methods. Molecular diagnostics were used to genotype mosquitoes and detecting resistance mechanisms.
A total of 7,596 mosquitoes were morphologically identified as An. gambiae s.l. of which, 2,536 were identified to their species level. Out of these, 65.5% and 34.5% were An. arabiensis and An. gambiae s.s respectively. Both species occurred in sympatry in 30.8% of the sites; while An. arabiensis occurred alone in 69.2%. Overall An. arabiensis predominated and was distributed widely across all ecological zones. The species complex was resistance to three pyrethroids tested. The distribution of resistance was however not homogenous. Resistance to DDT was also recorded in one site. Presence of kdr-L1014S and kdr-L1014F were recorded in some parts of the country occurring in both species with varying allelic frequencies. Members of Cytochrome-P450; CYP6P3, CYP6M2, CYP6Z1 and CYP6Z3 were significantly overexpressed in An. gambiae s.s resistant to DDT.
This study demonstrates predominance and wide distribution of An. arabiensis. It also shows the occurrence of pyrethroid resistance to main malaria vectors in Tanzania which need to be managed.