Their closest simian relatives are SIVcpz in chimpanzees (Pan troglodytes troglodytes) from West central Africa and SIVsm in sooty mangabeys (Cercocebus atys) from West Africa (39, 40, 48), respectively. Genetic characterization of new West African simian immunodeficiency virus SIVsm: geographic clustering of household-derived SIV strains with human immunodeficiency virus type 2 subtypes and genetically diverse viruses from a single feral sooty mangabey troop.
Phylogenetic studies of primate lentiviruses provide evidence that some SIV lineages have co-evolved with their hosts, but on the other hand they show also multiple examples of cross-species transmission from simians to humans and between different simian species (44, 86). Figure 1: Genomic organization of the primate lentiviruses. In HIV-1 and SIVcpz the env and nef gene do not overlap, but in SIVgsn, mon, and mus env and nef genes overlap. PCR followed by sequence and phylogenetic analysis is therefore necessary to confirm SIV infection. Today, SIV infection was confirmed by partial or full-length genome sequencing in 27 species. All major SIV lineages known to date were discovered because their primate hosts had antibodies that cross-reacted with HIV-1 or HIV-2 antigens (10, 11, 15, 19, 22, 26, 33, 30, 41, 45, 72, 74, 95).