WASHINGTON (AP) - Scientists may have found a "missing link" in the evolution of the virus that causes AIDS.
According to a study in the journal Nature, the link is a virus that is killing chimpanzees in the wild at a disturbingly high rate.
Chimps are the first primate besides man that have been shown to get sick in the wild in significant numbers from a virus related to HIV. And the discovery of the disease that's killing them might help doctors come up with a workable vaccine for humans.
The monkey version of HIV causes no symptoms or illness in most apes and monkeys that have it.
But studies of the chimps that died from the infection found that they were killed by a particular strain that was the closest relative possible to the virus that first infected humans.