AIDS-like disease is found in chimps

CHICAGO — Scientists think they have found a "missing link" in the evolution of the virus that causes AIDS. It bridges the gap between the infection that does no harm to most monkeys and the one that kills millions of people.

A team of scientists studying the wild-chimpanzee population in Tanzania's Gombe National Park discovered chimps falling ill and dying of an AIDS-like disease, a finding that researchers hope could lead to new insights into the disease and to a vaccine.

The study's results are being published in the new edition of the British research journal Nature. The article reveals that Gombe chimps infected by certain strains of SIV (simian immunodeficiency virus) can contract an AIDS-like disease. Infected Gombe chimps died 10 to 16 times more frequently during the study than uninfected chimps.

The results of the nine-year study overturn previous evidence that suggested chimpanzees were immune to AIDS and that SIV infections in them were harmless. Researchers already knew some wild-chimpanzee populations had individuals infected with SIV from eating infected monkeys.

Chimpanzees are the first primate besides humans shown to get sick in the wild in significant numbers from a virus related to HIV. Chimps are also humans' closest relative among primates.

The discovery of the disease killing chimps may help doctors come up with better treatments or a workable vaccine for humans, experts said.

Most apes and monkeys that have SIV show no symptoms or illness. So "if we could figure out why the monkeys don't get sick, perhaps we could apply that to people," said study lead author Beatrice Hahn, a professor of medicine at the University of Alabama, Birmingham.

Necropsies of infected chimps showed unusually low counts of T-cell white blood proteins that are just like the levels found in humans with AIDS, Hahn said in a phone interview.

A strain of SIV at some point mutated into HIV (human immunodeficiency virus) in wild chimps in Cameroon in West Africa, where it jumped into the human population when infected chimp meat was eaten by humans.

Over several years of surveillance, the study showed that 10 to 20 percent of the Gombe chimps were SIV-infected.

The knowledge that some SIV strains can cause AIDS-like disease in chimps is a unique opportunity, AIDS researchers said, to study how the two closely related viruses become disease-causing agents in two closely related species: chimps and humans. Being able to compare and contrast the two viruses, they said, should speed development of more effective AIDS therapies and vaccines.

"It is a pretty momentous study," Danny Douek, chief of the human immunology section of the National Institutes of Health (NIH) vaccine-research center in Bethesda, Md., wrote in an e-mail. He was not involved in the Nature study.

"From an evolutionary and epidemiological point of view, these data can be regarded as a 'missing link' in the history of the HIV pandemic," he added.

Monkeys and apes — except for chimps — seem to survive the virus because of some kind of evolutionary adaptation, probably on the cell receptors, Douek wrote. The infection of chimps is more recent so they haven't adapted, he wrote.

Hahn said chimps and people probably caught the virus the same way, by eating infected monkeys. And they both spread it the same way, through sexual activity.

The animals in the study are the same wild chimpanzees that have been followed continuously by scientists since famed primatologist Jane Goodall began watching them in 1960, a key factor in the new study's revelations because the animals were used to seeing human scientific observers in their African forest home, making it easier to track them.