Malaria transmission and rice cultivation in Lagdo, northern Cameroon

Cross-sectional entomological surveys were carried out during the 2006 dry and rainy seasons in Lagdo, Cameroon to measure the impact of rice cultivation on malaria transmission and to monitor vector susceptibility to insecticides. Adult anopheline mosquitoes were captured on human volunteers and by pyrethrum spray collections. A total of 4740 mosquitoes was collected during the study. Anopheles arabiensis was the major species and the main malaria vector in all study sites, followed by A. funestus. Malaria transmission was high in the non-irrigated zone of Mayo Mbocki, whereas in the irrigated area of Gounougou it was below detection level during the dry season and high during the rainy season. Insecticide susceptibility tests performed on A. gambiae s.l. populations detected resistance to lambdacyhalothrin and to a lower extent to deltamethrin. All survivors were A. arabiensis. None of the surviving mosquitoes carried the kdr mutation, suggesting an alternative resistance mechanism.