The virus in monkeys that led to HIV in humans is far older than previously believed, says a new study. It had been thought that simian immunodeficiency virus (SIV) was only a few hundred years old, but a team of American and African scientists say SIV has been around for at least 32,000 years and perhaps as long as one million years, Bloomberg news reported. The researchers identified four strains of SIV in monkeys on Bioko Island, which has been separated from mainland Africa for more than 10,000 years. The island strains of SIV are very different than those on the mainland. Using computer models to determine the rate of DNA change, the scientists concluded that SIV is at least 32,000 years old and likely much older, Bloomberg reported. This means that monkeys have had a long time to adapt to SIV, which explains why it doesn't make them ill. But it raises questions about why HIV only emerged in the 20th century. Humans have long hunted monkeys and would have regularly been exposed to SIV. "Something happened in the 20th century to change this relatively benign monkey virus into something that was much more potent and could start the (HIV) epidemic," study leader Preston Marx, of Tulane University in New Orleans, said in a statement. "We dont know what that flashpoint was but there had to be one."
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