Entomological risk factors for severe malaria in a peri-urban area of The Gambia

Abstract

A study was undertaken of possible entomological risk factors for severe malaria in a peri-urban area of The Gambia. Households of children who had experienced a severe or a mild attack of malaria and of matched controls were visited and their characteristics recorded. Mosquitoes were then collected in the bedrooms of study subjects using both insecticide spray catches and light traps. Mud-walled buildings and bedrooms without ceilings were found more frequently in the households of children who had experienced malaria than in those of controls. Only one difference, which may have arisen by chance, was found between the households of severe and of mild malaria cases; animals were recorded significantly more frequently in the compounds of the severe cases. Mosquito catches reported on two occasions 2 weeks apart showed good reproducibility, indicating that measurements made at the time that a child presented with malaria were likely to reflect those that would have been present at the time that the child was infected. Anopheles gambiae s.l. was found on average more frequently in the bedrooms of children who had experienced malaria than in those of the controls but no difference was found in mosquito numbers between bedrooms of severe or mild cases of malaria. The human blood index and sporozoite rate were similar in mosquitoes caught in households of malaria cases and in those of controls. No evidence was found to support the hypothesis that the level of exposure to malaria-infected mosquitoes is a risk factor for the development of severe malaria.