Different malaria control activities in an area of Liberia--effects on malariometric parameters.

The epidemiology of malaria was studied in a West African mining town (Yekepa) and three surrounding zones defined as Close, Middle and Far areas. Malariometric parameters were investigated in children two to nine years of age at the end of the rainy season. In Yekepa, vector control measures and intense suppression of malaria with drugs had created an almost hypoendemic situation with a spleen rate of 11%. In Close area, vector control was applied to some extent and malaria drugs were frequently used for treatment; the spleen rate was 40%. In Middle area, a mobile clinic provided sporadic malaria treatment to small children, but the clinic did not reach out to Far area. The spleen rates were 95 and 99%, respectively. Three species of Plasmodium were found in all areas. The prevalences in Far area were P. falciparum 82%, P. malariae 39% and P. ovale 9%. The crude parasite rates increased from 13% in Yekepa to 92% in Far area, whereas haematocrit levels decreased from 37.6 to 35.2, respectively. Plasmodium falciparum seropositivity, as measured by indirect immunofluorescence, was 74% in Yekepa and 99% in Middle and Far areas. Total IgG concentrations ranged from 18 g1(-1) in Yekepa to 33 g1(-1) in Far area. Three main anopheline species were found in the zones outside Yekepa. Their relative frequencies in Far area were Anopheles funestus 45%, A. hancocki 37%, and A. gambiae 18%. The local inoculation rates gradually increased outwards from Yekepa from less than 0.01 to 0.17 inoculations per man and night at the beginning of the dry season.(ABSTRACT TRUNCATED AT 250 WORDS)