The origin of HIV has been a mystery since 1984, when researchers first conclusively showed that it causes AIDS. Over the past 20 years, evidence has accumulated that points to Africa and a similar virus in chimpanzees. Many scientists suspect that the chimp virus jumped into humans who hunt and butcher these great apes. Now a group led by virologist Martine Peeters of the Institut de Recherche pour le Développement in Montpellier, France, has found that gorillas may have played a supporting role in the origin of the AIDS epidemic.
As Peeters and co-workers report in tomorrow's issue of Nature, they uncovered a connection to gorillas after analyzing fecal samples collected in remote Cameroonian forests. The researchers collected nearly 600 specimens of feces from both chimpanzees and gorillas and then tested them for antibodies to HIV-1, the primary driver of the human epidemic. To their surprise, six gorilla samples tested positive, and they extracted an AIDS-like virus--which they dubbed SIVgor--from three individuals.
Earlier this year, Peeters co-authored a landmark study that, more persuasively than ever before, singled out chimpanzees as the source of the human AIDS epidemic (Science, 28 July, p. 523). That study similarly analyzed fecal samples and isolated an AIDS-like virus, called SIVcpz, from 16 chimpanzees. Several of these SIVcpz isolates closely resembled the family of HIVs that most commonly infect humans. SIVgor, however, resembles a group of HIV-1 viruses--known as "group O"--that is rare in humans and has not been previously linked to chimps. "We were not expecting to find that kind of virus," says Peeters. "It's making the puzzle more complicated than it was before."
The Peeters group suggests that humans may have become infected by SIVgor by hunting gorillas, or that an SIVcpz from group O may still be found in chimpanzees. As for how gorillas became infected, phylogenetic analyses suggest that chimpanzees were the original "reservoir" of SIVgor. So could chimps have given the virus to gorillas? Primatologist Caroline Tutin, who studied great apes in Gabon for 15 years until recently retiring from fieldwork, is skeptical. "To my knowledge, no aggressive interactions have ever been witnessed [between the two species]," says Tutin.
The finding of an HIV-related virus in gorillas "is definitely an interesting twist," says Nathan Wolfe, an epidemiologist at Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland, who also has searched for new AIDS-like viruses in Cameroon. "Just when we thought things were nice and neatly wrapped up with [the origin] story, there's a surprise."