The Origin of Malaria

Recent studies have shown that Plasmodium falciparum, A parasite that causes malaria in humans made the jump from Apes to humans several million years ago (Plasmodium reichenowi is the ancestor of P.falciparum). Plasmodium falciparum is the deadliest of the five known strains of malaria parasites, causing several hundred million cases each year, of which around a million are fatal. The chimp carries its own type of malaria parasite, Plasmodium reichenowi, and it was thought that P. falciparum was simply one of P. reichenowi's many strains.

This assumption was indirectly strengthened by findings that the AIDS virus probably came to humans from chimps, which have a similar immunodeficiency microbe. The first case may have occurred in central-western Africa around a century ago, possibly involving an individual who ate or handled infected bushmeat (I don't believe this). But a new look at the origins of malaria, published in the British science journal Nature, says that the Plasmodium parasite crossed from another of our great-ape cousins, the gorilla, and adapted to humans.

Weimin Liu research.

To Weimin Liu from the University of Alabama, something wasn’t quite right. People seemed to have settled on a chimpanzee conclusion without thoroughly testing for Plasmodium in other apes. Fortunately, Liu’s team was well placed to fill in those blanks. For their research, they had already amassed a massive collection of ape faeces: an unenviable collection of 1,827 samples from chimps, 805 from gorillas and 107 from bonobos. Virtually all of these samples came from wild apes with little human contact; only 28 came from a habituated group of gorillas.

Liu scoured all of these samples for Plasmodium DNA, sequenced what he could find, and built a family tree that charted the evolutionary relationships between them. His results were very clear. For a start, Plasmodium parasites don’t infect either eastern gorillas or bonobos, but they do infect chimpanzees and western gorillas. That narrows down the source of human malaria to these two apes.

Liu also found that all of the samples of P. falciparum taken from humans were most closely related to a single lineage of gorilla parasites. P.reichenowi is an exclusively chimp parasite, belonging to a different branch of the Plasmodium family tree. The answer was clear: P.falciparum did not evolve from P.reichenowi and it didn’t come from chimpanzees. Instead, it jumped into humans from western gorillas.

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