Chimp virus tied directly to human AIDS in Africa

By Lawrence K. Altman The New York Times
FRIDAY, MAY 26, 2006

NEW YORK By studying chimpanzee droppings in remote African jungles, scientists have found direct evidence of a missing link between a chimpanzee virus and the one that causes human AIDS, they reported. 

Scientists have long suspected that chimpanzees are the source of the human AIDS pandemic because at least one subspecies carries a simian immune deficiency virus closely related to HIV, the human virus that causes AIDS. 

But because the simian virus, known as SIVcpz, was identified in chimpanzees in captivity, researchers could not be sure that the same simian virus existed among these apes in the wild. 

It does, according to a report released Thursday by a team of U.S., European and Cameroon scientists in the journal Science. They found it by testing hundreds of chimpanzee droppings collected in Cameroon. 

The genetic and immunologic tests were developed in stages over the last seven years to help trace the evolution of HIV and solve the mysterious origins of AIDS, said Dr. Beatrice Hahn, a virologist at the University of Alabama in Birmingham. Hahn headed the team that conducted the study, which combined genetics and epidemiology. 

The new findings, she said in a telephone interview, do not explain the entire chain of events that led from the first human HIV infection to the infection of 65 million people around the world. 

But, Hahn reported, her team's findings show "for the first time a clear picture of the origin of HIV-1 and the seeds of the AIDS pandemic." HIV-1 is the virus that causes the vast majority of AIDS cases in the world. 

Studies estimate that the human AIDS virus jumped species between 50 and 75 years ago. But no one knows who the first infected person was or how that person acquired HIV. 

The earliest documented HIV infection was in 1959 in an unidentified man in Kinshasa, then in the Belgian Congo. The man participated anonymously in a genetic study conducted by Dr. Arno Motulsky of the University of Washington in Seattle. 

Hahn said her team theorized that HIV was first transmitted locally somewhere in west central Africa. Because the subspecies of chimpanzees, Pan troglodytes troglodytes - in which the simian virus had been found in captivity - lives in the wild in Cameroon, Gabon and Republic of Congo, the first infection could have been in any of those areas. 

If the transmission occurred in southern Cameroon, where the new chimpanzee studies were conducted, an infected person or persons could have carried the virus traveling by river to Kinshasa. From there, it could have spread further and eventually around the world, according to her hypothesis. 

Hahn's team asked hunters, members of expeditions and workers sent by local health officials to collect fecal samples from the forest floor. 

The trekkers collected 599 fecal samples in 10 forest sites throughout the southern part of Cameroon. 

Hahn then tested for antibodies that detect SIVcpz. She found evidence of infection with that virus in five of the 10 field sites. The team found that there was widespread but uneven infection with the simian virus.

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