Study: Deadly Malaria Strain Came From Chimps

A deadly form of malaria has something in common with HIV. Both appear to have jumped to humans from chimpanzees, according to a study in the Proceedings of the National Academy of Sciences.

The study promises to clear up a lot of confusion about the origin of malignant malaria, which kills more than 1 million people each year.

A chimpanzee in Cameroon's Mfou National Park. i i

According to researchers, parasites found in the blood of this chimpanzee and others in Cameroon's Mfou National Park are the ancestors of those that cause a deadly form of malaria in humans. Researchers say this discovery shows that malaria jumped from chimpanzees to humans, much the way that HIV originated. Matthew LeBreton/Global Viral Forecasting Initiative hide caption

itoggle caption Matthew LeBreton/Global Viral Forecasting Initiative
A chimpanzee in Cameroon's Mfou National Park.

According to researchers, parasites found in the blood of this chimpanzee and others in Cameroon's Mfou National Park are the ancestors of those that cause a deadly form of malaria in humans. Researchers say this discovery shows that malaria jumped from chimpanzees to humans, much the way that HIV originated.

Matthew LeBreton/Global Viral Forecasting Initiative

Genetic analyses from the early 1990s suggested that it might have come from birds.

"Everybody was a little skeptical of that result," says Daniel Hartl, Higgins Professor of Biology at Harvard University. "But that's the way the data were pointing at the time."

One of the skeptics was Francisco Ayala of the University of California, Irvine, an author of the new paper.

Ayala has spent the past 15 years trying to trace the origin of the parasite responsible for malignant malaria. "It's a very, very nasty disease," he says.

Ayala thought it was more likely that the human parasite Plasmodium falciparum had come from chimps than birds. So he had a graduate student search for parasites in chimps that were genetically similar.

The effort turned up a parasite that was a much better match than those found in birds. It was a chimp parasite called Plasmodium reichenowi.

In Search Of A Common Ancestor

Then Ayala's team set out to learn whether the reichenowi parasite had infected a common ancestor of humans and chimps millions of years ago, or made the jump to humans more recently.

Chimpanzees in Cameroon's Mfou National Park. i i

A group of chimpanzees in Mfou National Park, Cameroon. For the study, researchers analyzed the blood and tissue samples of nearly 100 chimps from Cameroon and Ivory Coast. Nathan Wolfe/Global Viral Forecasting Initiative hide caption

itoggle caption Nathan Wolfe/Global Viral Forecasting Initiative
Chimpanzees in Cameroon's Mfou National Park.

A group of chimpanzees in Mfou National Park, Cameroon. For the study, researchers analyzed the blood and tissue samples of nearly 100 chimps from Cameroon and Ivory Coast.

Nathan Wolfe/Global Viral Forecasting Initiative

The team did this by analyzing the genes of malaria parasites from both chimps and humans. They focused on regions of DNA that Ayala calls "timekeepers" because mutations tend to accumulate at a known rate.

The regions act as a sort of genetic clock. The longer a parasite has been around, the more mutations it acquires.

Ayala's team found that the chimp parasite, Plasmodium reichenowi, had a lot more mutations than the human parasite, Plasmodium falciparum.

That meant the chimp parasite was an ancestor of the human version and that "at some point there was a transmission from a chimp to a human," Ayala says.

A Major Revision Of Malaria's History

Hartl says the finding offers a major revision of malaria's history.

"It suggests that there was a single transfer from chimps to humans, and that it surely occurred well within the last, let's say, 100,000 years," he says.

The transfer may even have happened within the past 10,000 years, scientists say.

That's when nomadic people in Africa began to settle down and cultivate the land. This created denser populations and lots of standing water — conditions that make it easy for mosquitoes to transmit parasites from one person to the next.

Hartl says the events suggested by Ayala's study make sense to him. "This brings the human malaria picture into consonance with what we know about other monkey and primate malarias," he says

It also means this form of malaria has a history much more like that of HIV.

Scientists say that knowing the origin of malignant malaria should make it easier to come up with better medicines, or a vaccine.

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