EPIDEMIOLOGICAL DATA CONCERNING ONE YEAR OF A MALARIA SURVEILLANCE PILOT PROJECT IN SOUTHERN RHODESIA.

Few factual data have been published on the problem of disappearing malaria due to Plasmodium falciparum in Africa. In Southern Rhodesia a surveillance project has been under way since January 1961. The author describes malaria surveillance procedures, methods, organization and costs for the year 1962-63 and presents data relevant to a sparsely populated part of rural Africa where a surveillance visitor can cover a population of only some 3500 by monthly house-to-house visits. Through such visits, and through special surveys, an annual blood examination rate of 25% was achieved in the area at fairly low cost.It was found in the area studied, where 98% of infections are due to P. falciparum, that even Africans who have previously attained a high level of immunity will produce typical fever and associated malaria symptoms on reinfection after several years. Methods of case detection have proved adequately sensitive, despite the problem of asymptomatic carriers and despite the difficulty of obtaining true medical histories. Evidence is produced that much residual low-level transmission occurs indoors, although Anopheles gambiae are found in low density in human dwellings. Drug dosages and preventive treatment are described in detail; to reduce the number of asymptomatic carriers, single-dose presumptive treatment is advocated, at least in the last year of the attack phase. Many of the findings presented will be applicable to other African countries where malaria has been reduced to a low incidence.