[1][2] All known subgroups of HIV-1 and HIV-2 are thought to have entered humans as distinct cross-species transmissions of Simian immunodeficiency virus (SIV) from primates.
[4] SIVcpz itself emerged in chimpanzees as the result of a recombination of two separate lineages of SIV known to infect red-capped mangabey, and Cercopithecus species.
[3][5] HIV-1 group M (responsible for the global pandemic) is estimated to have emerged in humans around 1920 near Kinshasa, then part of the Belgian Congo.
[9] The isolated strain was found to be most closely related to modern genome sequences of HIV-1 (M) subgroup D. Possible cases of AIDS from this period include: Researchers begin to note the spread of Pneumocystis pneumonia and concurrent Cytomegalovirus infections, considered novel to the European continent, and both AIDS related conditions.
[8] Robert Rayford, a 16-year-old boy who died in 1969, is considered to be the first recorded case of AIDS in the United States.
[18] Arvid Darre Noe (an anagram of his birth name Arne Vidar Røed) was a Norwegian sailor and truck driver who was probably infected in Cameroon some time between 1962 and 1965, and died on 24 April 1976.