AIDS came from gorillas as well as chimpanzees, new research suggests.
Two of the four known groups of viruses that cause the disease have been traced back to the great apes that share about 98 per cent of their DNA with humans.
It had been known simian immunodeficiency virus (SIV) – the monkey equivalent of HIV – had jumped from chimpanzees into humans, but now it seems gorillas in Cameroon also played a vital role.
Scientists say understanding the disease’s origins will help predict the future risk of an outbreak.
The connection was uncovered after researchers analysed faecal samples collected in remote forests.
They found HIV-1 groups known as ‘O’ and ‘P’ originated in western lowland gorillas.
HIV-1 – the virus that causes AIDS – has jumped species to infect humans on at least four separate occasions.
The other lineages, ‘M’ and ‘N’, are known to have started in geographically distinct chimpanzee communities in southern Cameroon.
Group ‘M’ gave rise to the AIDS pandemic – infecting over 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.
But ‘O’ – although not as widespread and prevalent as ‘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 SIV strains – the pre-cursors of HIV.