Malaria in the Pare area of Tanganyika

Abstract

A sequel to an earlier paper describes the effects, during 3 years, on the vector mosquitoes and on the human malaria of the spraying of huts with the residual insecticide Dieldrin. Typical A. funestus completely disappeared and there were great reductions in the numbers of A. gambiae found alive in huts. The population of A. gambiae was also reduced, except in places where there were opportunities for extensive feeding on cattle. There were no changes in the host choices of A. gambiae. In many dissections for sporozoites the only infected mosquitoes found were from inadequately sprayed places. The action of Dieldrin was studied. Although it caused some irritation and its lethal action was slow, Dieldrin, in the dosages used, was found to cause a high mortality amongst A. gambiae coming into contact with sprayed surfaces, and this effect was very persistent. No change in susceptibility to Dieldrin occurred in A. gambiae, but this was found in other arthropods. There was a considerable fall in all human malaria indices, but evidence from several sources suggested that a low degree of malaria transmission continued throughout. Possible reasons for this are discussed, with the causes of persistent parasites in older children.