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HIV Ancestor Much Older Than Previously Thought

September 17, 2010

The immunodeficiency condition found in monkeys that was the ancestor of the HIV virus is far older than first believed, according to a new study by researchers from the University of Arizona and Tulane University. The study is published in Friday’s edition of the journal Science.

“The simian immunodeficiency virus, or SIV, is at least 32,000 to 75,000 years old, and likely much older, according to a genetic analysis of unique SIV strains found in monkeys on Bioko Island, a former peninsula that separated from mainland Africa after the Ice Age more than 10,000 years ago,” a statement from the University of Arizona said.

Previously, DNA sequencing has estimated that SIV was only a few hundred years old.

“The study results have implications for HIV. SIV, unlike HIV, does not cause AIDS in most of its primate hosts. If it took thousands of years for SIV to evolve into a primarily non-lethal state, it would likely take a very long time for HIV to naturally follow the same trajectory,” according to the press release.

The research, which was led by Tulane National Primate Research Center virologist Preston Marx and University of Arizona evolutionary biologist Michael Worobey, tested “DNA samples from monkey populations that had been isolated for thousands of years,” according to a separate Tulane press release.

They found that four SIV strains taken from moneys on Bioko Island “were highly genetically divergent” from similar samples gathered from sites on the African mainland, and that they were able to use computer modeling to show that the mutation rate was “much slower than previously thought.”

“It’s like finding a fossilized piece of virus evolution,” Worobey said in a statement. “We now have this little island that is revealing clues about SIV, and it says, ‘It’s old.’ Now we know that humans were almost certainly exposed to SIV for a long time, probably hundreds of thousands of years.”

If that was the case, why did it take until the 20th Century for HIV to develop?

“Something happened in the 20th century to change this relatively benign monkey virus into something that was much more potent and could start the epidemic. We don’t know what that flashpoint was, but there had to be one,” said Marx.

Image Caption: Island-specific strains of the simian immunodeficiency virus (SIV), which infects monkeys such as the Bioko Drill, revealed the virus has been around thousands of years longer than previously thought. Credit: Preston Marx, Tulane University

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