Allelic diversity in the merozoite surface protein-1 and epidemiology of multiple-clone Plasmodium falciparum infections in Northern Tanzania

Allelic diversity in the merozoite surface protein-1 (MSP-1) of Plasmodium falciparum, a major malaria vaccine candidate, was examined in clinical iso lates from holoendemic northern Tanzania. The variable blocks 2, 4a, 4b, 6, and 10 of the MSP-1 gene were typed by allelic type-specific polymerase ch ain reaction. Twenty-four possible MSP-1 gene types were defined as unique combinations of allelic types detected in each variable block. Thirteen gen e types were identified, and 187 P. falciparum populations were fully typed among 79 isolates. In contrast with recent findings in Vietnam, we were un able to detect nonrandom associations between allelic types in the typed va riable blocks. Most patients (60%) harbored more than 1 genetically distinc t parasite population (average: 2.37 populations per isolate) and, in 1 pat ient, 6 different versions of this single-copy gene were found. Statistical analysis suggests that parasites carrying different MSP-1 gene types are n ot independently distributed in the host population. The epidemiological co nsequences of these findings are discussed.