A UC Irvine scientist is part of a team that helped track down the evolutionary origin of one of the world’s most notorious killers: malaria.

The parasite that causes malignant malaria jumped from chimpanzees to humans as recently as 5,000 years ago, and the transfer might have been accomplished by a single mosquito, according to a study being published this week.

The study, which involved sampling of chimpanzee blood in equatorial Africa, says the transfer likely took place between 2 million and 5,000 years ago — far more recently than 5 million years ago, the time previously considered likely by scientists.

The discovery could help in developing a vaccine for malaria, which kills about 1.5 million people worldwide each year, and could also improve scientific understanding of other diseases transferred from animals to humans including HIV, sars, and the avian and swine flu.

“It’s probable a mutation in the parasite made it effective against us,” said UC Irvine evolutionary biologist Francisco Ayala, who co-authored the study. “That occurred fairly recently, probably not much earlier than a few thousand years ago.”

Malignant malaria in humans comes from a type of parasite, Plasmodium falciparum, which accounts for 85 percent of all infections.

Chimpanzees carry a close relative of the parasite, Plasmodium reichenowi. But the assumption among scientists was that those two parasite strains separated about 5 million years ago.

To investigate the timeline, scientists took blood samples from wild chimps living in sanctuaries in Camaroon and Ivory Coast. Then they analyzed the genes of the malarial parasite strains they found.

One of the chimpanzee strains was shown to be an ancestor to all the strains that affect humans around the planet.

That means the transfer could have involved a bite from a single mosquito; multiple transfers also are possible, but less likely, Ayala said.

And while there is no way to be sure exactly when that took place within the likely timeframe of 2 million to 5,000-years-ago, Ayala was also involved in an earlier study showing that malignant malaria began spreading rapidly through the tropics with the advent of agriculture about 5,000 years ago.

“It began in agricultural Africa at the end of the Neolithic,” Ayala said. Forest burning and the spread of civilization helped mosquitoes to breed, enhancing the spread of the malaria parasite, he said.

There were likely two key mutations involved, he said: one that affected the ability of the parasites to enter human blood cells, and a second in the parasite itself.

The study with lead author Stephen Rich, a professor at the University of Massachusetts Amherst who was once Ayala’s graduate student,  was to be published this week online in the Proceedings of the National Academy of Sciences.

(Photo of Francisco Ayala courtesy UC Irvine.)

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