Origins

Left to right: the
African green monkey source of
SIV, the
sooty mangabey source of
HIV-2 and the
chimpanzee source of
HIV-1
Both HIV-1 and HIV-2 are believed to have originated in non-human
primates in West-central Africa and were
transferred to humans in the early 20th century.
[11]HIV-1 appears to have originated in southern
Cameroon through the evolution of SIV(cpz), a
simian immunodeficiency virus (SIV) that infects wild
chimpanzees(HIV-1 descends from the SIVcpz endemic in the chimpanzee subspecies
Pan troglodytes troglodytes).
[211][212] The closest relative of HIV-2 is SIV(smm), a virus of the
sooty mangabey (
Cercocebus atys atys), an Old World monkey living in coastal West Africa (from southern
Senegal to western
Côte d'Ivoire).
[77] New World monkeys such as the
owl monkey are resistant to
HIV-1 infection, possibly because of a genomic
fusion of two viral resistance genes.
[213] HIV-1 is thought to have jumped the species barrier on at least three separate occasions, giving rise to the three groups of the virus, M, N, and O.
[214]
There is evidence that humans who participate in
bushmeat activities, either as hunters or as bushmeat vendors, commonly acquire SIV.
[215] However, SIV is a weak virus which is typically suppressed by the human immune system within weeks of infection. It is thought that several transmissions of the virus from individual to individual in quick succession are necessary to allow it enough time to mutate into HIV.
[216] Furthermore, due to its relatively low person-to-person transmission rate, SIV can only spread throughout the population in the presence of one or more high-risk transmission channels, which are thought to have been absent in Africa before the 20th century.
Specific proposed high-risk transmission channels, allowing the virus to adapt to humans and spread throughout the society, depend on the proposed timing of the animal-to-human crossing. Genetic studies of the virus suggest that the most recent common ancestor of the HIV-1 M group dates back to circa 1910.
[217] Proponents of this dating link the HIV epidemic with the emergence of
colonialism and growth of large colonial African cities, leading to social changes, including a higher degree of sexual promiscuity, the spread of
prostitution, and the accompanying high frequency of
genital ulcer diseases (such as
syphilis) in nascent colonial cities.
[218] While transmission rates of HIV during vaginal intercourse are low under regular circumstances, they are increased many fold if one of the partners suffers from a
sexually transmitted infectioncausing genital ulcers. Early 1900s colonial cities were notable due to their high prevalence of prostitution and genital ulcers, to the degree that, as of 1928, as many as 45% of female residents of eastern
Kinshasawere thought to have been prostitutes, and, as of 1933, around 15% of all residents of the same city had
syphilis.
[218]
An alternative view holds that unsafe medical practices in Africa after World War II, such as unsterile reuse of single use syringes during mass vaccination, antibiotic and anti-malaria treatment campaigns, were the initial vector that allowed the virus to adapt to humans and spread.
[216][219][220]
The earliest well documented case of HIV in a human dates back to 1959 in
the Congo.
[221] The virus may have been present in the United States as early as 1966,
[222] but the vast majority of infections occurring outside sub-Saharan Africa (including the U.S.) can be traced back to a single unknown individual who became infected with HIV in
Haiti and then brought the infection to the United States some time around 1969.
[223] The epidemic then rapidly spread among high-risk groups (initially, sexually promiscuous men who have sex with men). By 1978, the prevalence of HIV-1 among homosexual male residents of
New Yorkand
San Francisco was estimated at 5%, suggesting that several thousand individuals in the country had been infected.
It was spread by a white guy get it right