Impact of entomological interventions on malaria vector bionomics in low transmission settings in Zambia

Abstract

Entomological interventions for malaria control are being scaled up in the context of the integrated vector management strategy in Zambia. This paper reports the continuous entomological monitoring of the operational impact of indoor residual insecticide spraying (IRS) and distribution of about 6 million insecticide-impregnated bed-nets (ITN) over two peak malaria transmission seasons. Mosquitoes were captured daily using exit window traps at monitoring sentinel sites and analyzed for species identification, densities, and sporozoite rates to assess the efficacy of the vector control tools. All the three major malaria vectors; Anopheles gambiae senso stricto (s.s.), Anopheles arabiensis andAnopheles funestus were collected and identified. The intervention effect of IRS and ITNs was more pronounced on A. gambiae s.s. and A. funestus than A. arabiensis (c2 = 0.003, df = 1, P = 0.956), indicating that A. gambiae s.s. and A. funestus are amenable to control by IRS and ITNs. None of these vectors tested positive for Plasmodium falciparumsporozoites, thus, signifying their lack of transmission potential. This study demonstrates that entomological monitoring and evaluation is an indispensable underpinning for rational insecticide based malaria vector control. It provides compelling evidence for the need to integrate entomological parameters into routine surveillance systems, and also strongly substantiates the deployment of the integrated vector management strategy. Key words: Zambia, malaria, impact, indoor residual spraying, insecticide treated nets, transmission.