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Wild chimps harbour AIDS virus


Researchers used chimp poop to confirm the origin of HIV (Image: Mike Wilson)

The closest viral relative to HIV has been traced, for the first time, to wild chimpanzees, confirming the theory that these creatures are the original source of AIDS.

A team led by Dr Beatrice Hahn of the University of Alabama at Birmingham report their study of wild chimpanzees from southern Cameroon, in today's issue the journal Science.

"It says that the chimpanzee group that gave rise to HIV ... this chimp community resides in Cameroon," says Hahn, who has been studying the genetic origin of HIV for years.

In people, HIV leads to AIDS but chimps have a version called simian immune deficiency virus (SIV) that causes them no harm.

To date 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 to locate the elusive chimps.

"It is hard to track them," says Hahn.

But the trackers managed to collect 599 samples of droppings from the chimpanzee subspecies Pan troglodytes troglodytes.

Hahn's lab found viral DNA and evidence of the virus itself in the droppings and estimated the prevalence of SIV infection in the associated chimp populations.

"We went to 10 field sites and we found evidence of infection in five," Hahn says.

"We were able to identify a total of 16 infected chimps and we were able to get viral sequences from all of them."

Widespread infection

Up to 35% of the apes in some communities were infected with SIV and different varieties or "clades" of the virus were found.

"We found some of the clades were really, really very closely related to the human virus and others were not," says Hahn.

She says chimps separated by a river were infected with different clades,

And a river may have carried the virus into the human population.

Cameroon not the origin of the epidemic

While SIV has been found in Cameroon the epidemic is known to have originated elsewhere.

"The epidemic took off in Kinshasa, in Brazzaville," says Hahn.

Kinshasa is in the Democratic Republic of Congo, formerly Zaire, and faces Brazzaville, in Congo, across the Congo River.

Studies have traced HIV to a man who gave a blood sample in 1959 in Kinshasa, then called Leopoldville.

"So how do you get from southern Cameroon to the Democratic Republic of Congo?" Hahn asks.

"Some human must have done so. There is a river that goes from that southeastern corner of Cameroon down to the Congo river."

Ivory and hardwood traders used the Sangha River in the 1930s, when the original human-to-human transmission is believed to have happened.

Transmission still a mystery

Hahn's study suggests the virus passed from chimpanzees to people more than once.

"We don't really know how these transmissions occurred," Hahn says.

"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," she says.

"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 and team'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," Hahn and team say.

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, there is no vaccine against HIV although drug cocktails can help control it.

Tags: health, biology, ecology, cloning-and-dna