RELATIONSHIPS BETWEEN PLASMODIUM-FALCIPARUM TRANSMISSION BY VECTOR POPULATIONS AND THE INCIDENCE OF SEVERE DISEASE AT 9 SITES ON THE KENYANCOAST

The transmission of Plasmodium falciparum was studied in relation to t he incidence of severe malaria infections at nine sites in the Kilifi District in Kenya. Intensive mosquito sampling during a one-year perio d yielded Anopheles gambiae s.l., An. funestus, An. coustani, An. squa mosus, An. nili, and An. pharoensis. Anopheles gambiae s.l. was the pr edominant vector, comprising 98.4% of the total anophelines collected. Overall, 3.5% of 2,868 An. gambiae s.l. collected indoors and 0.8% of 261 collected outdoors contained P. falciparum sporozoites. Transmiss ion was detected during 10 months, with peak periods from June to Augu st and December to January. In eight of the nine sites, entomologic in oculation rates (EIRs) averaged only four infective bites per year (ra nge 0-18); an annual EIR of 60 was measured for the site with the high est intensity of transmission. The incidence of severe malaria infecti ons, ranging from 8.6 to 38.1 per 1,000 children (0-4 years), was not associated with EIRs. At these sites on the coast of Kenya, a high inc idence of severe disease occurs under conditions of very low levels of transmission by vector populations. With respect to conventional appr oaches for vector control in Africa, decreases in transmission, even t o levels barely detectable by standard approaches, may not yield corre sponding long-term reductions in the incidence of severe disease.