Complexity of Plasmodium falciparum infections is consistent over time andprotects against clinical disease in Tanzanian children

The complexity of Plasmodium falciparum populations in 21 children was stud ied in repetitive samples over 4 years in an area of Tanzania where the org anism is holoendemic, Genotyping was done by a polymerase chain reaction me thod that targets three highly polymorphic regions of the merozoite surface protein (MSP) 1 block 2, MSP 2, and the glutamine-rich protein. Eight chil dren were repeatedly parasitemic, 5 had scanty parasitemias, and 8 were con sistently nonparasitemic, Varying numbers of genotypes were detected in the parasitemic children, but the multiplicity of infection was significantly constant within each child. The children with frequent parasitemias experie nced fewer clinical episodes during the study period than those without par asitemias, There was also a tendency for children with more complex infecti ons to experience fewer episodes. The children had consistent parasitologic profiles over the 4 years. Although few subjects were studied and the resu lts will require confirmation, the results suggest that asymptomatic (espec ially polyclonal) II falciparum infection protects against clinical disease from new infections.