An international team of scientists has traced the origin of Plasmodium vivax
, the second-worst malaria parasite of humans, to Africa, according to a study published this week in Nature Communications
. Until recently, the closest genetic relatives of human P. vivax
were found only in Asian macaques, leading researchers to believe that P. vivax
originated in Asia.
The study, led by researchers from the Perelman School of Medicine at the University of Pennsylvania, found that wild-living apes in central Africa are widely infected with parasites that, genetically, are nearly identical to human P. vivax
This finding overturns the dogma that P. vivax
originated in Asia, despite being most prevalent in humans there now, and also solves other vexing questions about P. vivax
infection: how a mutation conferring resistance to P. vivax
occurs at high frequency in the very region where this parasite seems absent and how travelers returning from regions where almost all humans lack the receptor for P. vivax
can be infected with this parasite.
Of Ape and Human Parasites
Members of the labs of Beatrice Hahn, MD, and George Shaw, MD, PhD, both professors of Medicine and Microbiology at Penn, in collaboration with Paul Sharp, PhD, an evolutionary biologist from the University of Edinburgh, and Martine Peeters, PhD, a microbiologist from the Institut de Recherche pour le Développement and the University of Montpellier, tested over 5,000 ape fecal samples from dozens of field stations and sanctuaries in Africa for P. vivax
DNA. They found P. vivax
-like sequences in chimpanzees, in western and eastern gorillas, but not in bonobos. Ape P. vivax
was highly prevalent in wild communities, exhibiting infection rates consistent with stable transmission of the parasite within the wild apes.
Ape P. vivax
infects both gorillas and chimpanzees, unlike the ape precursor of P. falciparum
, the deadliest human malaria parasite, which only infects gorillas. The origin of P. falciparum
in gorillas was discovered several years ago by the same international group of investigators. The team continued its widespread screen of malaria parasite DNA in wild-living primates, and noted that P. vivax
was also endemic in gorillas and chimpanzees in central Africa.
To examine the evolutionary relationships between ape and human parasites, the team generated parasite DNA sequences from wild and sanctuary apes, as well as from a global sampling of human P. vivax
infections. They constructed a family tree of the sequences and found that ape and human parasites were very closely related. But ape parasites were more diverse than the human parasites and did not group according to their host species. In contrast, the human parasites formed a single lineage that fell within the branches of ape parasite sequences.