The microepidemiology of malaria and its importance to malaria control.

Recent studies in West Africa and in Papua New Guinea have shown that the prevalence of malaria can vary widely between neighbouring villages and within different parts of the same village. Both genetic and environmental factors are likely to contribute to these variations. Clustering in households of genetically determined red cell abnormalities, and possibly of immune response genes, may contribute to differences in the prevalence of malaria within a village. Environmental factors probably play the major part in explaining differences between villages. The position of a village in relation to mosquito breeding sites, the design of houses and the level at which anti-mosquito measures are used will all influence the degree to which its inhabitants are exposed to infection. Attitudes to the treatment of a case of malaria may also contribute to local variations in the prevalence of malaria. Malaria parasitaemia and splenomegaly will be less frequent in a community where effective treatment is given immediately at home, or sought promptly from a primary health care worker, than in a neighbouring community where there is a much greater reliance on traditional medicines. Recognition of local variations in the prevalence of malaria is important because identification of the factors responsible for a low prevalence in one village but a high one in a neighbouring community may indicate a possible control measure. Local variations in the epidemiology of malaria must also be taken into account when any kind of malaria intervention trial is planned.