Scientists Find Missing AIDS Link

Monkeys may have spread HIV-like virus to chimps

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THURSDAY, June 12, 2003 (HealthDayNews) -- Researchers say they've discovered evidence that an early form of AIDS infected two monkey species before moving on to chimpanzees and then to humans. The findings boost theories suggesting that the virus has a history of jumping from species to species and may have moved into man through the simple act of hunting.

The report comes as the SARS and monkeypox outbreaks attract attention to the transmission of disease between animals and people. "People don't like the idea that this can happen because it's a very scary thought. You can't control it," said study co-author Dr. Beatrice H. Hahn, a professor of medicine at the University of Alabama at Birmingham.

Scientists suspect that chimpanzees transmitted AIDS to humans because their strain of SIV, or simian immunodeficiency virus, is very similar to HIV-1, the most common strain of the AIDS virus in humans. "What we don't know is how this transmission occurred," Hahn said.

HIV is, of course, a devastating epidemic in humans. But while SIV infects chimpanzees and monkeys, it doesn't appear to hurt them. "The hypothesis is that these species have had their infections for a long, long time. They have simply learned to adapt," Hahn said.

Some experts suspect that humans became infected by eating chimpanzees, while others have blamed manmade factors, like the polio vaccine, for making people more susceptible.

Hahn is a member of a team of international researchers who have spent nearly a decade investigating HIV and its precursors in apes. In the new study, they examined genetic links between SIV in chimpanzees and in two kinds of monkeys -- red-capped mangabeys and greater spot-nosed monkeys. (Chimpanzees are apes, not monkeys.)

Mangabeys are already well-known to AIDS researchers because they appear to have transmitted the virus that became HIV-2 to humans. (HIV-2 is milder than the more common HIV-1 and found mainly in West Africa.)

According to the researchers, the genetic analysis suggests that strains of SIV in the monkeys appear to have combined in the chimpanzees to create a new strain. The theory makes sense, they say, because chimpanzees hunt the monkeys, and the disease is spread through blood.

It's not clear when the disease jumped from the monkeys to chimpanzees, but it was probably tens of thousands of years ago, Hahn said.

If SIV can jump from monkey to chimpanzee through hunting, it adds support to the theory that the disease could have spread from chimpanzees to humans naturally instead of due to an unusual factor like human vaccination, she said. The monkeys and chimpanzees "weren't vaccinated, I can tell you that," she said.

While the study findings don't appear to have any immediate relevance for efforts to fight AIDS in people, an expert said it's vital to understand how the disease evolved, especially considering that monkeys and chimpanzees aren't sickened by it.

"We will never been rid of HIV. It will be in our population forever. It's not like smallpox that can be eliminated," said Dr. Shawn P. O'Neil, assistant professor of pathology at the New England Primate Research Center. "We have to control its transmission and figure out how to control it so it doesn't kill us. It's important to learn how these other species have lived with this virus."

On the other hand, the study findings suggest the possibility that more deadly diseases could move from monkeys and chimpanzees to humans through hunting, said Murray Gardner, professor emeritus of pathology at the University of California at Davis and an expert in AIDS-like disease in monkeys. "Will it happen again? Let's hope not, but this raises the potential."

More information

Learn more about the origins of AIDS from Avert.org. The Centers for Disease Control and Prevention has information about HIV-2, the AIDS strain that may have come from monkeys.

SOURCES: Beatrice H. Hahn, M.D., professor of medicine, University of Alabama, Birmingham; Shawn P. O'Neill, Ph.D., D.V.M., assistant professor of pathology, New England Regional Primate Research Center, Southborough, Mass.; Murray Gardner, M.D., professor emeritus of pathology, University of California, Davis. June 13, 2003 Science
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