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Malarial whodunit: the plot thickens

gorillaz.jpgPosted on behalf of Joseph Milton

When it comes to the ongoing question of which of our primate relatives first spread the malaria parasite, Plasmodium falciparum, to humans, the verdict may have just become a little less murky.

Through the years the identity parade of likely suspects has included chimps, gorillas and, most recently, a monkey — the spot-nosed guenon (Cercopithecus nictitans).

Back in July I wrote about P. falciparum’s possible origins in guenons. I reported a Proceedings of the National Academy of Sciences paper by Franck Prugnolle from the Institut de Recherche pour le Développement, France, and his colleagues that identified a single guenon, born wild but kept as a pet, that was infected with a strain of P. falciparum similar to those found in gorillas. The authors concluded that monkeys could have been responsible for the spread of the malaria parasite to humans.

The paper flew in the face of an earlier Nature study that implicated gorillas, and evolutionary biologist Paul Sharp of the University of Edinburgh, UK, who worked on the gorilla study, contacted me recently to highlight his team’s somewhat scathing response to the suggestion that P. falciparum is just as likely to come from guenons as gorillas.


In a letter to PNAS, Sharp and his colleagues point to the fact that the parasite was found in a single captive guenon, whereas their study recorded a high incidence of infection by three Plasmodium species, one of which is very closely related to human P. falciparum, in 11 gorilla populations separated by distances of up to 750 kilometres. This suggests that gorillas are a natural reservoir for malarial parasites, while no such evidence exists to suggest the same in guenons, says Sharp.

In addition, evolutionary trees of malarial parasites created by Sharp’s team show that human P. falciparum DNA sequences nest within gorilla-derived sequences, and the sequence from Prugnolle’s infected guenon simply suggests the monkey caught malaria from a gorilla, Sharp says.

Although these parasitic species appear to be highly host-specific in the wild, adds Sharp, captive chimps and bonobos have become infected with human strains in the past, so the idea that a pet guenon picked up the infection from a gorilla is certainly not beyond the realm of possibility.

It would seem that when it comes to apportioning the blame for the spread of malaria to humans, gorillas are firmly back in the dock.

Image of gorilla courtesy of Corey Leopold via Flickr under Creative Commons.

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