Unresolved direction of host transfer of Plasmodium vivax v. P. simium and P. malariae v. P. brasilianum.

The evolutionary history of two human malaria parasites, Plasmodium vivax and Plasmodium malariae, remains unresolved. The near genetic identity between human P. vivax and P. malariae, and primate P. simium and P. brasilianum, respectively, suggests that recent host transfers occurred, but questions remain, such as whether the transfer was from humans to New World monkeys or vice versa, and when the transfers occurred. Here, we investigate the phylogenies, haplotype networks, positive selection and genetic diversity among these parasite species by means of four genes. Human P. vivax and primate P. simium recently derived one from the other; at least two host transfers have occurred. Human P. malariae and primate P. brasilianum also have recently derived one from the other by lateral host transfer. The direction of the host transfer cannot be decided in either one of the two pairs of species, owing to the scarcity of available strains from the primate parasites.