Apparently the HIV problem started with hunters of wild chimpanzees in southern Cameroon in 1930s. They hunted chimpanzees infected with a simian version of the virus called SIV and contracted the disease from them.

"How many different transmission events occurred between that initial hunter and this virus making it to Kinshasa, I don't know. It could have been one, it could have been 10, it could have been 100," said Dr. Beatrice Hahn of the University of Alabama at Birmingham. "Eventually, it ended up in an urban area, and that's where it really got going."

Kinshasa is a town in the nearby country of Congo where the first documented case of HIV infection happened in 1959.

This discovery ends a decade long quest for the origin of HIV. Scientists have previously suspected that HIV could have appeared from apes because SIV found in captive apes genetically resembles HIV. The team of researchers, including experts from the universities of Nottingham, Montpellier and Alabama, has now found that wild chimpanzees in south-east Cameroon have a form of SIV that is very closely related to HIV.

"It is likely that the jump between chimps and humans occurred in south-east Cameroon - and that virus then spread across the world," said Paul Sharp, professor of genetics at the University of Nottingham. "When you consider that HIV probably originated more than 75 years ago, it is most unlikely that there are any viruses out there that will prove to be more closely related to the human virus."

This discovery has more than just a historic relevance - it offers new avenues for a potential vaccine. Although the chimps are infected with SIV they don't manifest the symptoms of AIDS. Why is that? No one knows so far.

"We're 25 years into this pandemic," Hahn said. "We don't have a cure. We don't have a vaccine. But we know where it came from." Yusef Azad, policy director of the National Aids Trust also said: "This research is interesting as all discoveries which relate to the history and origins of HIV could be of value to the vital work being carried out by scientists in developing a HIV vaccine."

Image: SIV