Tracing the evolution of a human malarial parasite

A study unravels the evolutionary history of the human malarial parasite Plasmodium vivax. Every year, more than 8 million people are infected with the malarial parasite P. vivax, mostly in Southeast Asia and South America. Human P. vivax has failed to gain a foothold in Africa due to the high prevalence of a protective mutation in red blood cells that renders people resistant. However, the discovery of related parasites in wild-living African apes suggests that P. vivax may have originated in Africa. Beatrice Hahn and colleagues compared genome sequences of P. vivax isolated from the blood of six chimpanzees and one gorilla from Cameroon, Gabon, and Côte d'Ivoire with the genomes of P. vivax strains from Asia, South America, and Oceania; previous analyses of ape P. vivax were restricted to a few gene fragments amplified from ape fecal samples. Ape and human parasite genomes were nearly identical, differing in around 2% of coding DNA sequences, but ape parasites were around 10-fold more genetically diverse than human parasites and exhibited different patterns of genetic polymorphism. Ape parasites retain intact sequences of three genes implicated in parasite binding to red blood cells, whereas those genes have been decommissioned in human parasites. However, the encoded ape parasite proteins did not preferentially bind to ape over human red blood cells in lab assays. Together, the findings suggest a scenario in which P. vivax passed through an evolutionary bottleneck: The ancestral strain may have infected both apes and humans in Africa, hitchhiked out of the continent with humans, and, as the subsequent spread of the protective mutation all but eliminated the human parasite in Africa, rapidly expanded elsewhere. The findings illuminate the evolution of P. vivax and indicate that African apes harbor a cache of Plasmodium that merits monitoring in malaria eradication efforts, according to the authors.

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Article #18-10053: "Evolutionary history of human Plasmodium vivax revealed by genome-wide analyses of related ape parasites," by Dorothy Loy et al.

MEDIA CONTACT: Beatrice Hahn, University of Pennsylvania, Philadelphia, PA; tel: 215-746-8515, 205-427-3571; e-mail: <bhahn@pennmedicine.upenn.edu>; Paul Sharp, University of Edinburgh, UNITED KINGDOM; tel: +44-131-651-3684; e-mail: paul.sharp@ed.ac.uk