Two of the four known groups of human AIDS viruses (HIV-1 groups O and P) originated in western lowland gorillas, according researchers who conducted a comprehensive survey of simian immunodeficiency virus (SIV) infection in African gorillas.

HIV-1, the virus that causes AIDS, has jumped species to infect humans on at least four separate occasions, generating four HIV-1 lineages -- groups M, N, O, and P. Previous research from this team found that groups M and N originated in geographically distinct chimpanzee communities in southern Cameroon, but the origins of groups O and P remained uncertain.

The four cross-species transmissions have had very different outcomes in humans. Group M gave rise to the AIDS pandemic, infecting more than 40 million people worldwide by spreading across Africa and throughout the rest of the world. Groups N and P, at the other extreme, have only been found in a few individuals from Cameroon. However, group O, although not as widespread and prevalent as group M, has nonetheless infected about 100,000 people in west central Africa.

The team screened fecal samples from western lowland gorillas, eastern lowland gorillas, and mountain gorillas in Cameroon, Gabon, the Democratic Republic of Congo, and Uganda for evidence of SIVgor infection. They identified four field sites in southern Cameroon where western lowland gorillas harbor SIVgor.

"Viral sequencing revealed a high degree of genetic diversity among the different gorilla samples," explains co-author Beatrice Hahn, MD, a professor of Medicine and Microbiology at University of Pennsylvania School of Medicine. "Two of the gorilla virus lineages were particularly closely related to HIV-1 groups O and P. This told us that these two groups originated in western lowland gorillas." 

"Understanding emerging disease origins is critical to gauge future human infection risks," adds Martine Peeters from the University of Montpellier. "From this study and others that our team has conducted in the past it has become clear that both chimpanzees and gorillas harbor viruses that are capable of crossing the species barrier to humans and have the potential to cause major disease outbreaks." 

Published in Proceedings of the National Academy of Sciences.  Funded in part by grants from the National Institutes of Health (NIH R37 AI50529, R01 AI 058715, P30 AI 045008, R37 AI 066998, R01 AI064001, AI 089246).