NO INFLUENCE OF AGE ON INFECTION COMPLEXITY AND ALLELIC DISTRIBUTION IN PLASMODIUM-FALCIPARUM INFECTIONS IN NDIOP, A SENEGALESE VILLAGE WITH SEASONAL, MESOENDEMIC MALARIA

We have shown previously that in Dielmo, a Senegalese village with int ense perennial Plasmodium falciparum transmission, the infection compl exity and the distribution of some allelic types harbored by asymptoma tic carriers was age-dependent. We report here an investigation of the se parameters in Ndiop, a village located 5 km from Dielmo, where mala ria is mesoendemic and seasonal, and where immunity is acquired at a v ery low rate, as indicated by the lifelong distribution of P. falcipar um clinical attacks. Blood was collected from 143 and 125 inhabitants, including 122 individuals sampled in both surveys, during two cross-s ectional surveys at one-month intervals during the 1994 transmission s eason. Plasmodium falciparum parasites were genotyped for three polymo rphic single copy genes. Genetic diversity was very large, with 17, 43 , and nine distinct alleles detected for the merozoite surface protein -1 (MSP-1), MSP-2, and glutamate-rich protein loci, respectively. Thes e figures, similar to those previously observed in Dielmo, indicate th at the parasite genetic diversity is not directly related to the inocu lation rate, at least in the range of transmission intensity studied h ere. The complexity of the asymptomatic infections (average number of distinct genotypes per isolate) was more than two-fold lower in Ndiop than in Dielmo and importantly, did not decrease with age. Likewise, t he allele distribution was not influenced by age, contrasting with the observations made in Dielmo. This indicates that the number of parasi te types per isolate and the influence of age on complexity and allele distribution depend on the level of endemicity, consistent with the i nterpretation that they reflect acquired antiparasite immunity.