High frequency of recombination-driven allelic diversity and temporal variation of Plasmodium falciparum msp1 in Tanzania.

A major mechanism for the generation allelic diversity in the Plasmodium falciparum msp1 gene is meiotic recombination in the Anopheles mosquito. The frequency of recombination events is dependent on the intensity of transmission. Herein we investigate the frequency of recombination-driven allelic diversity and temporal variation of msp1 in Rufiji, eastern coastal Tanzania, where malaria transmission is intense. We identified 5' recombinant types, 3' sequence types, and msp1 haplotypes (unique associations of 5' recombinant types and 3' sequence types) to measure the extent and temporal variation of msp1 allelic diversity. The results show that msp1 haplotype diversity is higher in Tanzania as compared with areas with lower transmission rates. The frequencies of individual polymorphic regions/sites remained stable during the study period. However, the frequency distribution of msp1 haplotypes varied between 1993 and 1998. These results suggest that frequent recombination events between msp1 alleles intermittently generate novel alleles in high transmission areas.