Scientists Pursue Origins of HIV

http://www.wired.com/news/medtech/0,1286,59227,00.html 

Researchers have identified another piece in the puzzle of how HIV emerged from the wilderness to spawn one of the most devastating epidemics humanity has ever known.

The same researchers who in 1999 traced the disease in humans to chimpanzees in west central Africa have now discovered how the chimps got the disease in the first place. They report their results in Friday's issue of Science. 

The researchers found that chimps acquired the disease from eating one of their favorite prey: monkeys. The primate version of HIV, called SIV (simian immunodeficiency virus), emerged in chimps apparently through a commingling of two monkey viruses from the red-capped mangabey and the greater spot-nosed monkey.

"This is similar to the means by which humans probably first became infected, by butchering chimpanzees for bushmeat,'" said Paul M. Sharp, one of the researchers involved in the study, and a professor at the Institute of Genetics at the University of Nottingham in the United Kingdom.

Chimps are 98 percent genetically the same as humans, and they don't get sick from SIV. This is an especially important clue for developing an HIV vaccine, the researchers said. Understanding what prevents chimps from getting sick would help scientists duplicate resistance to AIDS symptoms in humans.

Chimps likely picked up viruses from both types of monkeys, and eventually a hybrid formed, the researchers said. That probably happened tens of thousands of years ago, which may have given chimps an opportunity to evolve resistance to an AIDS-like disease.

Later, the new virus was transmitted to humans and became HIV-1. (Researchers have traced HIV-2, another version of the human virus, to the sooty mangabey).

Worldwide, 16,000 people become infected with HIV -- the virus that causes AIDS -- every day, according to the Joint United Nations Programme on HIV/AIDS, or UNAIDS. About half the 38.6 million adults with HIV or AIDS worldwide are women, and 3.2 million are children younger than the age of 15.

In the United States, 900,000 people have HIV and 40,000 new infections appear annually, according to NAIAD, the National Institute of Allergy and Infectious Diseases. More than half those infected are people of color, and half of all new cases are people under 25.

The new study further debunks a theory that HIV may have emerged from the polio vaccine, Sharp said. The Science study shows that the virus likely developed through natural processes rather than as an accident of medicine.

"Don't get me started!" Sharp said in an e-mail response to questions about the polio vaccine hypothesis. "That 'theory' is already essentially dead in the minds of all but a few individuals -- who lack expertise in the relevant areas."

That theory suggests the polio vaccine was created using chimpanzee cells infected with a virus that became HIV. But it places the chimps in eastern Africa in the late 1950s. Sharp's research, however, has found that HIV-1 was derived from SIV in chimpanzees from west central Africa around 1930.

"So, wrong chimps, wrong time," he said.

Other groups have studied samples of the old oral polio vaccines, Sharp said, finding no sign of SIV. They did find DNA from macaques (but not from chimps), and it was no secret the vaccine developers used macaque kidney cells.

The new study means researchers should focus more on studying the natural SIV infection in wild chimpanzees, Sharp said.

"For example, it would be interesting to learn whether they have picked up SIVs from any other monkey species," Sharp said. "Because of the similarity between chimpanzees and humans, any virus that successfully adapts to spreading among chimpanzees would be a candidate for a further jump to humans: a potential HIV-3."

Beatrice Hahn, a professor of medicine at the University of Alabama at Birmingham and co- author of the new study, said that while a mysterious HIV-3 is not likely to be infecting people now, it's something researchers should keep an eye out for, and try to prevent.

"The question is, because of practices currently ongoing, are we creating more opportunities for cross-species transfer of these and other infections?" Hahn asked. "We just had SARS and yesterday we had monkey pox."