Malaria in the pare area of Tanzania III The course of malaria transmission since the suspension of an experimental programme of residual insecticide spraying

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Abstract
Malarious communities in South Pare, in northern Tanzania, were protected during a 3-year experimental program of residual insecticide spraying which ended early in 1959. On the conclusion of the spraying program a treatment organization was set up to soften the clinical impact of the inevitable resurgence of malaria. The results obtained by this organization are reviewed. Although much of the area was very malarious in former times, the resumption of intense malaria transmission there was delayed. This delay is attributed largely to changes brought about in the original vector mosquito populations, which originated during the residual spraying campaign but persisted beyond the interval during which the mosquitoes were exposed to the direct activity of the residual insecticide. The once important local vector, Anopheles funestus, failed to re-establish itself completely in the area by mid-1966; it seems probable that the Seuth Pare A. gambiae underwent selection during the residual spraying campaign, resulting in the ascendancy of a relatively exophilic population of the species which lingered for several years after selection pressure was lifted. The increased use of antimalarial drugs for the treatment of fever also restrained any overall increase in malaria parasite rates. This report covers a period of 7 years since the final round of residual insecticide spraying. As the epidemiological situation in South Pare is not yet stable, further regular surveys should be conducted.