LOW-LEVEL PLASMODIUM-FALCIPARUM TRANSMISSION AND THE INCIDENCE OF SEVERE MALARIA INFECTIONS ON THE KENYAN COAST

The transmission of Plasmodium falciparum was studied in relation to t he incidence of severe malaria infections at Sokoke and Kilifi town, K ilifi District, Kenya. Intensive mosquito sampling during a one-year p eriod yielded Anopheles gambiae s.l., An. funestus, and An. coustani. Anopheles gambiae s.l. was the predominant vector, comprising 87.9% an d 97.9% of the total anophelines collected in Sokoke and Kilifi town, respectively. The proportion of An. gambiae s.l. with P. falciparum sp orozoite infections was 4.1% (20 of 491) in Sokoke and 2.2% (3 of 138) in Kilifi town; no infections were detected in An. funestus or in An. coustani. Entomologic inoculation rates indicated that residents were exposed to only 8.0 infective bites per year in Sokoke and 1.5 in Kil ifi town. Transmission was detected during only six months in Sokoke a nd three months in Kilifi town despite low-level, year-round vector ac tivity. The yearly incidence of severe P. falciparum infections in chi ldren, 1-4 years of age was 24.1 per 1,000 in Sokoke and 4.2 per 1,000 in Kilifi town. Monthly patterns of transmission corresponded closely with the incidence of severe-infections. At these sites on the coast of Kenya, the spatial and temporal incidence of severe malaria infecti ons is associated with low-level P. falciparum transmission by vector populations.