Page last updated at 23:15 GMT, Monday, 3 August 2009 00:15 UK

'Proof' malaria began in chimps

Image courtesy of Nathan Wolfe, Global Viral Forecasting Initiative.
A chimp from the Mfou National Park in Cameroon

Scientists say they have genetic proof malaria spread by mosquitoes jumped species from chimpanzees to humans.

By looking at blood samples, a US team discovered all world strains of the human malaria parasite falciparum stem from a malaria parasite in chimps.

They tell Proceedings of the National Academy of Sciences how the species shift probably happened 10,000 years ago when humans turned to agriculture.

Man's encroachment upon the natural forest habitat of chimps is blamed.

It brought the two species into close contact and the deforestation created pools of stagnant water and other conditions favourable for mosquito breeding.

"Today, human encroachment into the last forest habitats has further extended, leading to a higher risk of transfer of new pathogens, including new malaria parasites," the researchers warn.

Species jump

Previously, malaria's origin in humans had been unclear.

But this latest work suggests malaria, like HIV, has jumped species from one of our closest relatives.

Although chimps were known to harbour a parasite - Plasmodium reichenowi - that is closely related to the most common of the human malaria parasites, Plasmodium falciparum, many scientists had assumed that the two had co-existed separately.

Four strains infect humans, falciparum being the most common
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But blood tests on 94 wild and captive chimpanzees in Cameroon and the Ivory Coast suggest falciparum evolved from reichenowi.

Francisco Ayala, of the University of California, Irvine, and colleagues found eight new strains of reichenowi that had striking similarities to falciparum and were genetic precursors to the human disease.

The leap could have happened as early as two to three million years ago, but most likely to our Neolithic ancestors as recently as 10,000 years ago.

The scientists hope their discovery will help others looking for new drugs and vaccines to stop human malaria.

Professor Brian Greenwood, a malaria expert at the London School of Hygiene and Tropical Medicine, said: "This is interesting work.

"There has been dispute about how long falciparum has been around for and as genetic techniques get better we can get a more accurate idea."

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