Simian Immunodeficiency Virus/SIVsm
The sooty mangabey (SM) (Cercocebus atys) is the natural host of a simian immunodeficiency virus, termed SIVsm, which gave rise to human immunodeficiency virus type 2 (HIV-2).  SIV causes chronic infection in sooty mangabeys but does not cause AIDS in this species. When SIV is transmitted from an infected mangabey to a rhesus macaque, the macaque develops Simian AIDS (SAIDS).  Sooty mangabeys, all known strains of SIV, and all known strains of HIV-2 are endemic to west Africa from Senegal to the Ivory coast, the epicentre of the HIV-2 epidemic. In this region, sooty mangabeys are kept as pets and hunted as food. The resulting close contact between humans and mangabeys allows for the transmission of infections between these animals and humans. 
SIV jumped from mangabey to humans on seven separate occasions to establish seven distinct, lineages. These lineages are called clades, subtypes, or groups in the scientific literature. These groups are designated A through G. Groups A and B are the only clades of HV-2 that are epidemic in humans. SIV is endemic to more than thirty African primate species. Numerous nonhuman primate lentiviruses have been discovered. 
The genomes of six major strains of SIV have been fully sequenced.