Recent independent evolution of msp1 polymorphism in Plasmodium vivax and related simian malaria parasites

The Plasmodium MSP-1 is a promising malaria vaccine candidate. However, the highly polymorphic nature of the MSP-1 gene (msp1) presents a potential obstacle for effective vaccine development. To investigate the evolutionary history of msp1 polymorphism in P. vivax, we construct phylogenetic trees of msp1 from P. vivax and related monkey malaria parasite species. All P. vivax msp1 alleles cluster in the P. vivax lineage and are not distributed among other species. Similarly, all P. cynomolgi msp1 alleles cluster in the P. cynomolgi lineage. This suggests that, in contrast to presumed ancient origin of P. falciparum msp1 polymorphism, the origin of P. vivax msp1 polymorphism is relatively recent. We observed positive selection in the P. vivax lineage but not in P. cynomolgi. Also, positive selection acts on different regions of msp1 in P. vivax and P. falciparum. This study shows that the evolutionary history of msp1 differs greatly among parasite lineages.