Sean Markey
for National Geographic News
November 9, 2006
A form of HIV has been found in wild gorillas in western central Africa. This is the first time the AIDS-causing virus has been detected in primates other than chimps and humans.
It is also the "first time someone has looked at HIV infection in wild living gorillas," said Martine Peeters, a virologist at the French government's Institut de Recherche Pour le Développement and at the University of Montpellier, France.
"We found they were infected—and to our surprise are infected with a virus which is closely related to the one we find in chimpanzees and also in humans."
Simian immunodeficiency virus (SIV) was detected in gorilla populations more than 250 miles (400 kilometers) apart, suggesting that SIV may be common and widespread in the lowland gorilla subspecies.
Peeters is the lead author of a study published today in the journal Nature. She says chimpanzees may have transmitted the virus to gorillas.
Reservoir Species
The gorilla virus is closely related to HIV-1 group O, one of three HIV groups known to infect humans.
A different viral strain, HIV-1 group M, is responsible for the current global HIV/AIDS pandemic. Some 40 million people are currently infected, and an estimated 25 million have died of AIDS.
The team of international scientists used antibody tests and RNA analysis on hundreds of chimp and gorilla fecal samples collected in the remote forests of Cameroon (Cameroon map, facts, and music). RNA, or ribonucleic acid, helps control chemical activities in cells.
Researchers did not survey the mountain gorilla subspecies, which lives in East Africa.
Earlier this year the same team reported that the chimpanzees in southeast Cameroon were the primary reservoir of the HIV-1 group M virus.
At the time, the researchers also suggested the chimps were the reservoir for a second, less common HIV-1 strain known as group N. Group N is currently responsible for only about ten human HIV cases in Cameroon. The HIV-1 group O virus, though, is responsible for about one percent of current human HIV cases in Cameroon. Until the latest study, group O had not been found in nonhuman primates.
Peeters says it is still too early to say whether western lowland gorillas are a reservoir species or merely a carrier of the virus.
But she believes chimpanzees could have infected gorillas with the group O virus in the distant past.
More than 30 primate species are known to carry SIV viruses, the study authors note.
But—unlike HIV-positive humans—chimps, gorillas, and other primates that carry SIV do not appear to suffer illness.
Peeters says a goal now "is to find out how [HIV] moved—when, how, and which animal transmitted it to humans."
Such findings could better explain the processes that drive some viruses to leap from animals to humans and cause global disease pandemics, while other outbreaks remain restricted to small populations, Peeters says.
"What we would like to know now is, [is] this virus circulating in chimpanzees and gorillas? How [have these] been transmitted from one species to another? What happens amongst humans when there is cross-species transmission?"
Biologist Eddie Holmes studies virus evolution at Pennsylvania State University in University Park.
Holmes described the new study as "extraordinary."
"I guess I ruled out gorillas as a carrier of HIV," he said, adding that "it is amazing to learn that there is a new primate carrier of HIV."
He thinks the findings are also significant because they further illuminate the diversity of the HIV virus in natural populations and the processes by which these viruses jump species.
"If you look at the rise of HIV, there's been a jump from chimpanzees to humans," Holmes said. He attributes the transfer of HIV to logging and to trading wild animal meat, both activities that bring humans into close contact with ape and monkey flesh.
Holmes says growing human interaction with wild species—as a result of changing land use, deforestation, global travel, war, famine, and the expansion of cities—will provide more opportunities for new viruses to emerge.
