The Origins of HIV-1 and the Emergence of Lentiviral Disease in Primates

Each Ientivirus has a rather narrow host range.²² Infrequent interspecies transmissions give rise to new viruses and diseases. This potential is best illustrated by the origins of HIV-1 and HIV-2 in separate transmissions of ancestral nonhuman primate lentiviruses to humans.²³,²⁴ HIV-1 and HIV-2 each seem to have arisen several times.^24-26 The three distinct genetic groups of HIV-1 (M, N, and O) resulted from independent cross-species transmission events.²⁷ The best estimates from maximum­likelihood phylogenetic methods place the last common ancestor of the M (“main”) group before 1940.25,²⁶ Severe pathology (AIDS) was also observed when simian lentiviruses, which do not cause evident disease in their Old World host species, infected Asian macaques in captivity.²⁸ Similarly, FIV infects many large feline species throughout the world, but only domestic cats develop clearly recognizable disease, which is severe and closely mimics human AIDS clinically and virologically.²⁹,3⁰