14 DAY TRIAL // At the end of 2005, 38.6 million people were reported living with HIV and the virus has killed since its discovery 25 million people.
The disease was first discovered among gay community in California in 1981, but the virus was conclusively detected in 1984. Based on a "molecular clock" (the rate at which a virus mutates), scientists think that the virus jumped from ape to man in the 1920s or 30s, probably through a bite or by a hunter who touched infected corpses and took the virus through a cut.
In the last 20 years, chimpanzees were pointed as the virus source. Now, a team from the Institut de Recherche pour le D?veloppement in Montpellier, France, has uncovered a connection between HIV and gorillas, after analyzing 536 chimps and gorillas fecal samples from remote Cameroonian forests. The scientists were searching for traces of the simian immunodeficiency virus (SIV) among chimpanzees and tested the feces for antibodies to HIV-1, the primary driver of the human epidemic. As expected, 40 of the 323 chimp samples had antibodies, but - surprisingly - six gorilla samples were positive, and the team found an AIDS-like virus, named SIVgor, from three individuals.
The same team made earlier this year the most persuasive study pointing out chimpanzees as the source of the human HIV. They are thought to have initially spread SIV to humans, where this virus mutated into HIV, a form adapted to the human host.
During the previous study, the scientists isolated an AIDS-like virus, baptized SIVcpz, from chimps. Several of the SIVcpz strains closely resembled the human HIVs types. Genetic analysis of SIVgor showed that it resembles HIV-1 strains (known as "group O") which are rare and found among humans in central West Africa and have not been previously found in chimps. "We were not expecting to find that kind of virus," says Martin Peeters, one of the researchers. "It's making the puzzle more complicated than it was before."
Gorillas appear to be widely infected with this virus, as the fecal samples came from populations that live nearly 400 kilometers (250 miles) apart. There are two gorilla species: western gorilla (Gorilla gorilla) and eastern gorilla ( Gorilla beringei).
The infected populations are of western gorilla, but by now it is unknown if the eastern species is also infected. "Gorillas are hunted for food and medicinal use, and it is possible that these practices may have been responsible for the HIV-1 group O zoonosis [animal-borne pathogen]," wrote the French team. SIV-infected gorillas "could pose an ongoing risk to humans."
It seems that humans infected with SIVgor by hunting gorillas, or maybe a related SIVcpz from group O could still be found in chimpanzees. As phylogenetic analyses point to chimpanzees as the original source of SIVgor, many point toward them to have infected gorillas, as well as humans with SIVgor. "To my knowledge, no aggressive interactions have ever been witnessed [between the two species]," says primatologist Caroline Tutin who studied great apes in Gabon for 15 years.
The finding "is definitely an interesting twist," says Nathan Wolfe, an epidemiologist at Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland. "Just when we thought things were nice and neatly wrapped up with [the origin] story, there's a surprise."