A virus that is killing chimpanzees in the wild may be an intermediate stage in the evolution of the deadly human strain.
Scientists believe they have found a "missing link" in the evolution of the virus that causes Aids. It bridges the gap between an infection that does no harm to most non-human primates and one that kills millions of people.
The suspected link is a virus that is killing chimpanzees in the wild at a disturbingly high rate, according to a study in tomorrow's issue of the journal Nature. Chimpanzees are the first primate shown to get sick in the wild in significant numbers from a virus related to HIV. They are also humans' closest relative among primates.
The discovery of the disease killing chimps may help doctors to come up with better treatments or a workable vaccine for humans, experts said.
The primate version of the virus that causes AIDS is called simian immunodeficiency virus (SIV), but most apes and monkeys that are infected with it show no symptoms of illness. "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 in Birmingham.
The nine-year study of chimps in their natural habitat at Gombe National Park in Tanzania found chimps infected with SIV had a death rate 10 to 16 times as high as uninfected chimps. And postmortems of infected chimps showed unusually low T cell counts that are just like the levels found in humans with AIDS, said Hahn.
And when scientists looked at the strain infecting the chimps, they found that it was a close relative of the virus that first infected humans.
"From an evolutionary and epidemiological point of view, these data can be regarded as a 'missing link' in the history of the HIV pandemic," said Aids researcher Dr Daniel Douek of the National Institute of Allergy and Infectious Diseases, who was not involved in the Nature study.
Monkeys and apes other than chimps seem to have an evolutionary adaptation, probably at the level of their cell receptors, that allows them to survive the virus, Douek said. The infection in chimps is more recent so they haven't adapted.
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