picked up and analyzed wild chimp droppings said on
Thursday they had shown how HIV originated in wild apes in
Cameroon and then spread in humans across Africa and
eventually the world.
published in the journal Science, supports other
studies that suggest people somehow caught the deadly human
immunodeficiency virus from chimpanzees, perhaps by killing
and eating them.
"It says that the
chimpanzee group that gave rise to HIV...this chimp
community resides in Cameroon," said Beatrice Hahn of the
University of Alabama, who led the study. "But that
doesn't mean the epidemic originated there, because it
didn't," Hahn, who has been studying the genetic
origin of HIV for years, said in a telephone interview.
"We actually know
where the epidemic took off. The epidemic took off in
Kinshasa, in Brazzaville." Kinshasa is in the Democratic
Republic of Congo, formerly Zaire, and faces
Brazzaville, in Congo, across the Congo River.
traced HIV to a man who gave a blood sample in 1959 in
Kinshasa, then called Leopoldville. Later analysis found
In people, HIV
leads to AIDS, but chimps have a version called simian
immune deficiency virus that causes them no harm. Humans are
the only animals naturally susceptible to HIV.
AIDS was only
identified 25 years ago. HIV now infects 40 million people
around the world and has killed 25 million. Spread via
blood, sexual contact, and from mother to child during
birth or breast-feeding, HIV has no cure and there is
no vaccine, although drug cocktails can help control
And like so many
new infections, HIV appears to have been passed to
humans from animals they slaughtered.
SIV has been
found in captive chimps, but Hahn wanted to show it could be
found in the wild too. Her international team got the
cooperation of the government in Cameroon, and they
hired skilled trackers. "The chimps in that area are
hunted. It's certainly impossible to see them. It is
hard to track them and find these materials," she said.
But the trackers
managed to collect 599 samples of droppings. Hahn's lab
found DNA, identified each individual chimp, and then found
evidence of the virus.
"We went to 10
field sites, and we found evidence of infection in
five. We were able to identify a total of 16 infected
chimps, and we were able to get viral sequences from
all of them," Hahn said.
Up to 35% of the
apes in some communities were infected. Not only that,
they could find different varieties, called clades, of the
virus. "We found some of the clades were really,
really very closely related to the human virus, and
others were not," she said.
by a river were infected with different clades, Hahn
said. And a river may have carried the virus into the human
"So how do you
get from southern Cameroon to the Democratic Republic
of Congo?" Hahn asked. "Some human must have done so. There
is a river that goes from that southeastern corner of
Cameroon down to the Congo River."
hardwood traders used the Sangha River in the 1930s, when
the original human-to-human transmission is believed
to have happened. Hahn's study suggests the virus
passed from chimpanzees to people more than once.
"We don't really
know how these transmissions occurred," Hahn said. "We
know that you don't get it from petting a chimp or from a
toilet seat, just like you can't get HIV from a toilet seat.
It requires exposure to infected blood and infected
body fluids. So if you get bitten by an angry chimp
while you are hunting it, that could do it."
Hahn's study only
applies to the HIV group M, which is the main strain of
the virus responsible for the AIDS pandemic.
"It is quite
possible that still other [chimpanzee SIV] lineages
exist that could pose risks for human infection and prove
problematic for HIV diagnostics and vaccines," her
team wrote. (Reuters)