In 1999, a strain of SIV (called SIVcpz) was found in a chimpanzee that was almost identical to HIV in humans. The researchers who discovered this connection concluded that it proved chimpanzees were the source of HIV-1, and that the virus had at some point crossed species from chimps to humans.

 

Old world monkeys are naturally infected with more than 40 different lentiviruses, termed simian immunodeficiency viruses (SIVs) with a suffix to denote their primate species of origin (e.g.SIV smm from sooty mangabeys).

 

Several of these SIVs have croseed the species barrier to great apes and humans, generating new pathogens. Known examples of cross-species trasmissions, as well as the resulting viruses, are highlighted in red.