MALARIA - EVEN MORE CHRONIC IN NATURE THAN PREVIOUSLY THOUGHT - EVIDENCE FOR SUBPATENT PARASITEMIA DETECTABLE BY THE POLYMERASE CHAIN-REACTION

In high endemicity areas, malaria is a chronic disease: examination of blood films reveals that up to half of the population, particularly c hildren, harbour parasites at any one given time. The parasitological status of the remainder was addressed using the polymerase chain react ion, a technique 100 to 1000 times more sensitive than microscopy, on a series of samples from Dielmo, a holoendemic area of Senegal. Two-th irds of the microscopically negative individuals were found to harbour subpatent levels of Plasmodium falciparum, suggesting that more than 90% of the exposed population at any one time, i.e. in a cross-section al survey, are chronically infected. This also means that the range of parasite loads harboured by humans with various degrees of exposure i s remarkably large, probably reflecting a large range of effectiveness of the defence mechanisms against malaria parasites, none of which is fully efficient.