Certain types of HIV appear to have originated in West African gorillas, and were likely transmitted to humans through bush meat hunting, Reuters reports. Previous research has identified chimpanzees in southern Cameroon as the source of HIV-1 group M, which has infected 40 million people around the world, as well as group N, which has only been identified in 20 people.

Publishing their findings in the Proceedings of the National Academy of Sciences, researchers looked for evidence of SIVgor, the gorilla version of HIV, by examining feces from gorillas throughout Central Africa, including 2,611 western lowland gorillas, 103 eastern lowland gorillas, and 218 mountain gorillas in Cameroon, Gabon, the Democratic Republic of the Congo and Uganda.

Their genetic analyses traced the roots of groups O and P to western lowland gorillas in southern Cameroon. Group O is the second most common in humans behind group M, having infected about 100,000 people in Cameroon, Gabon, Nigeria and other adjacent nations. Just two people have been identified as carrying HIV-1 group P.

The researchers estimated that group O made the interspecies jump at the beginning of the 20th century and group P somewhat later on in the century.

To read the Reuters story, click here.

To read the study abstract, click here.