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http://apnews.myway.com/article/20060525/D8HR3QEO0.html
(Associated Press)

HIV's Ancestry Traced to Wild Chimps

May 25, 7:26 PM (ET)

By LAURAN NEERGAARD

WASHINGTON (AP) - Twenty-five years after the first AIDS cases
emerged, scientists have confirmed that the HIV virus plaguing humans
really did originate in wild chimpanzees, in a corner of Cameroon.

Solving the mystery of HIV's ancestry was dirty work. Scientists
employed trackers to plunge through dense jungle and collect the fresh
feces of wild apes - more than 1,300 samples in all.

Before that, it took seven years of research just to develop the
testing methods to genetically trace the primate version of the virus
in living wild chimps without hurting the endangered species.

Until now, "no one was able to look. No one had the tools," said Dr.
Beatrice Hahn of the University of Alabama at Birmingham. She led the
team of international researchers that reported the success in
Friday's edition of the journal Science.

"We're 25 years into this pandemic," Hahn said. "We don't have a cure.
We don't have a vaccine. But we know where it came from. At least we
can make a check mark on one of those."

Scientists long have known that nonhuman primates carry their own
version of the AIDS virus, called SIV or simian immunodeficiency
virus. But with one exception, it had been found only in captive
chimpanzees, particularly a subspecies that in the wild populates
mostly West Africa.

It was not known how prevalent the virus was in chimps in the wild, or
how genetically or geographically diverse it was, complicating efforts
to pin down the jump from animal to man.

Hahn's team tested chimp feces for SIV antibodies, finding them in a
subspecies called Pan troglodytes troglodytes in southern Cameroon.

Chimps tend to form geographically distinct communities. By
genetically analyzing the feces, researchers could trace individual
infected chimps. The team found some chimp communities with infection
rates as high as 35 percent, while others had no infection at all.

Every single infected chimp had a common base genetic pattern that
indicated a common ancestor, Hahn said.

There are three types of HIV-1, the strain of the human virus
responsible for most of the worldwide epidemic. Genetic analysis let
Hahn identify chimp communities near Cameroon's Sanaga River whose
viral strains are most closely related to the most common of those
HIV-1 subtypes.

"The genetic similarity was striking," Hahn said.

The first human known to be infected with HIV was a man from Kinshasa
in the nearby country of Congo who had his blood stored in 1959 as
part of a medical study, decades before scientists knew the AIDS virus
existed.

Presumably, someone in rural Cameroon was bitten by a chimp or was cut
while butchering one and became infected with the ape virus. That
person passed it to someone else.

The Sanaga River long has been a commercial waterway, for transporting
hardwood, ivory and other items to more urban areas. Eventually,
someone infected made it to Kinshasa.

"How many different transmission events occurred between that initial
hunter and this virus making it to Kinshasa, I don't know. It could
have been one, it could have been 10, it could have been 100," Hahn
said. "Eventually, it ended up in an urban area, and that's where it
really got going."

Somewhere in all that spread, the virus became more deadly to people
than it is to chimps, who seldom are bothered much by SIV.

The research seems to settle any question of HIV's origin, said Dr.
Anthony Fauci, the National Institutes of Health's AIDS chief.

When tracing a virus' evolution, "it's important to get as close to
the source as you can," he said. "It's of historic interest."