Malaria appears to have jumped to humans from gorillas, and the parasite may have spread globally from a single gorilla to a single human, researchers reported on September 22. DNA from the droppings of nearly 3,000 apes - gorillas, chimpanzees and bonobos - shows the strain of malaria parasite most common in humans is virtually identical to one of many strains that infects gorillas.
It is far more distant than strains affecting chimps and their close cousins, the bonobos, Beatrice Hahn of the University of Alabama at Birmingham and colleagues reported.
Hahn and colleagues used ape droppings collected to study the origins of the AIDS virus for their study, published in the journal Nature.
"We had them all nicely organised, genetically characterised in our freezer," Hahn said in a telephone interview.
Hahn's team tested genetic material from the human immunodeficiency virus for their AIDS studies and took a similar approach for the latest work, looking for DNA from malaria parasites, including the Plasmodium falciparum parasite that causes most human cases.
"Wild apes, in particular the common chimps and the western gorillas, are naturally infected with at least eight or nine different Plasmodium species," Hahn said.
For years chimps were the chief suspects. But Hahn's data shows that gorillas, and only gorillas, are infected by a Plasmodium species virtually identical on the genetic level to the type that infects humans.
"Now, how many mosquitoes were biting however many humans or gorillas I do not know," Hahn said. "But the end result is, based on sequence analysis of 105 human Plasmodium parasites, it looks like there was a single transmission."
In other words, the parasite only had to infect one person or a small group of people before quickly taking hold and spreading to much of the world.
Malaria, which kills an estimated 800,000 people a year according to the World Health Organisation, is spread when a mosquito feeds on an infected person and carries the parasite to another human. There is no cure and no vaccine, although drugs can control the infection and help prevent the spread.
The findings could eventually have implications for efforts to get rid of malaria, said Dr Larry Slutsker, who heads the malaria program at the U.S. Centers for Disease Control and Prevention.
"If we were trying to eradicate, meaning we were trying to rid the planet of every last parasite and there was a reservoir in western gorillas, that would have implications for eradication. I don't think we are there, obviously," he said.
Gorillas, or the areas where they live, would likely have to be included in any such program so the parasite could not once again move into people.
Slutsker said the parasite may not necessarily have spread to people from apes via a mosquito. It can also be spread by direct blood transfer - perhaps while a gorilla was being butchered for food. Many experts believe this is how HIV first spread to humans.
What the researchers cannot say is when this happened. HIV mutates - evolves - quickly and these changes can be used as what is known as a molecular clock to date changes. Malaria parasites change much more slowly, Edward Holmes of Pennsylvania State University wrote in a commentary on the Nature study.
Many human diseases come from animals, including influenza, plague and West Nile virus.
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