Malaria and urbanization in central Africa: the example of Brazzaville. Part III: Relationships between urbanization and the intensity of malaria transmission.

The authors present a map of malaria transmission intensity in Brazzaville from which they analyse the impact of urbanization on anopheline density and transmission of malaria. Whereas at first each new human settlement promotes the introduction or the proliferation of A. gambiae, the major vector of malaria in Central Africa, urban growth later proves to be unfavourable to this vector. Apart from the canalization of surface water and improvement in sanitation, it is the increase in population density which seems, by its direct or indirect consequences in urban areas, to determine the decrease in malaria transmission intensity. By favouring the absorption of the last remaining open spaces and by the accompanying domestic pollution, urbanization tends to eliminate an increasing number of A. gambiae breeding places; by limiting the dispersion of anopheles from breeding sites, it tends to focus malaria transmission and by thinning out the subsisting anopheline population among a denser human population, it tends to reduce the degree of exposure of each person.