RELATION BETWEEN SEVERE MALARIA MORBIDITY IN CHILDREN AND LEVEL OF PLASMODIUM-FALCIPARUM TRANSMISSION IN AFRICA

Background Malaria remains a major cause of mortality and morbidity in Africa; Many approaches to malaria control involve reducing the chanc es of infection but little is known of the relations between parasite exposure and the development of effective clinical immunity so the lon gterm effect of suck approaches to control on the pattern and frequenc y of malaria cannot be predicted. Methods We have prospectively record ed paediatric admissions with severe malaria over three to five years from five discrete communities in The Gambia and Kenya, Demographic an alysis of the communities exposed to disease risk allowed the estimati on of age-specific rates for severe malaria. Within each community the exposure to Plasmodium falciparum infection was determined through re peated parasitological and serological surveys among children and infa nts,We used acute respiratory-tract infections (ARI) as a comparison. Findings 3556 malaria admissions were recorded for the five sites. Mar ked differences were observed in age, clinical spectrum and rates of s evere malaria between the five sites, Paradoxically, the risks of seve re disease in childhood were lowest among populations with the highest transmission intensities, and the highest disease risks were observed among populations exposed to low-to-moderate intensities of transmiss ion. For severe malaria, for example, admission rates (per 1000 per ye ar) for children up to their 10th birthday were estimated as 3.9, 25.8 , 25.9, 16.7 and 18.0 in the five communities; the forces of infection estimated for those communities (new infections per infant per month) were 0.001, 0.034, 0.050, 0.093, and 0.176, respectively. Similar tre nds were noted for cerebral malaria and for severe malaria anaemia but not for ARI. Mean age of disease decreased with increasing transmissi on intensity. Interpretation We propose that a critical determinant of life-time disease risk is the ability to develop clinical immunity ea rly in life during a period when other protective mechanisms may opera te. In highly endemic areas measures which reduce parasite transmissio n,and thus immunity, may lead to a change in both the clinical spectru m of severe disease and the overall burden of severe malaria morbidity .