Molecular characteristics of Plasmodium falciparum infections in man

Plasmodium falciparum diversity has been analysed in two Senegalese village s with different transmission conditions and distinct kinetics of immunity acquisition. A very large allelic polymorphism was observed in both village s, with a similar number of alleles but quite distinct allelic frequencies, indicating a substantial micro-geographical heterogeneity of malaria paras ite populations. In addition, the molecular characteristics of the infectio ns differed in both villages. As in most endemic areas, many infected subje cts carry multiple parasite clones. In Dielmo, the number of distinct clone s hosted decreases at the age of acquisition of an efficient immunity. Ther e was no influence of age on the number of clones hosted in Ndiop where adu lts experience clinical attacks. This indicates that complexity reflects ac quired immunity. The precise longitudinal follow-up of parasitaemia, clinical signs and para site genetic characteristics showed a rapid turn over of parasite populatio ns in the peripheral blood during the transmission season, suggesting that immunity does not prevent infection but restricts multiplication of numerou s genotypes at the erythrocytic stage. Clinical malaria occurs after a rapi d, apparently unrestricted growth of recently inoculated parasites. The suc cessive clinical attacks experienced by children are associated with genoty pes different for each attack and different from those that the child carri ed during preceding asymptomatic phases. These data indicate that parasite diversity contributes to the pathology of infection and that control of par asite density, which is at least in part strain-specific, is an essential e lement of protection against malaria clinical attacks. (C) 1999 Elsevier, P aris.