A virus identical to HIV is endemic among wild gorillas in Africa and its source of transmission was probably through chimpanzees, according to researchers on Wednesday.
Statistics have shown that around 40 million people worldwide are living with HIV/AIDS.
Although monkeys in Africa infected with simian immunodeficiency virus (SIV) are said to be the source of two of the three strains of the virus in humans the source of the third has been unknown, until now.
Martine Peeters, a virologist at the University of Montpellier in France said, 'It is the first time that someone has done a survey among wild gorillas to see whether they were infected with an SIV.'
She added, 'We showed they were infected and moreover they are infected with a virus that is closely related to HIV-1 and a particular variant O.'
Humans are believed to have become infected with HIV when they slaughtered infected chimpanzees for food. Around 25 million people have died of HIV/AIDS since the virus was identified a quarter of a century ago.
Three strains or groups of HIV - M, N and O have been identified. Group M is the most common strain and has spread around the globe. Strain N is linked to few cases in Cameroon and group O represents about one percent of HIV/AIDS cases in Cameroon and surrounding countries.
'It is only there that we find it,' Peeters explained, referring to the O strain.
She and her colleagues have collected and analyzed hundreds of droppings from wild gorillas and chimpanzees living in remote forest areas in Cameroon. The animals are hunted for food and medicines even today.
An analysis of the samples showed the gorillas were infected with a strain of SIV related to the O group. The infected gorillas lived nearly 400 kilometers (250 miles) apart so the scientists believe it is likely SIV infection is endemic in the animals.
Peeters, who reported the findings in the journal Nature, said, 'We have discovered it in gorillas but we think the primary reservoir are still chimpanzees. We think chimpanzees transmitted it to gorillas but we don't know who transmitted it to humans - the gorilla or the chimp.'
How the gorillas became infected in the first place is still a mystery because gorillas are vegetarians and encounters with chimpanzees are thought to be rare.
Knowing the origin of the HIV and its crossing of species is important in the understanding of what happens to the virus when it jumps species. Although there is no known cure or vaccine for HIV/AIDS drugs can help to control the replication of the virus in the body.