Origins
- See History of known cases and spread for early cases of HIV / AIDS
HIV is thought to have originated in non-human primates in sub-Saharan Africa and was transferred to humans late in the 19th or early in the 20th century.[175][176][177] The first paper recognizing a pattern of opportunistic infections characteristic of AIDS was published in 1981.[178]
Both HIV-1 and HIV-2 are believed to have originated in West-Central Africa and to have jumped species (a process known as zoonosis) from non-human primates to humans. 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).[179][180] The closest relative of HIV-2 is SIV(smm), a virus of the sooty mangabey (Cercocebus atys atys), an Old World monkey living in litoral West Africa (from southern Senegal to western Ivory Coast.[21] 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.[181]
There is evidence that humans who participate in bushmeat activities, either as hunters or as bushmeat vendors, commonly acquire SIV.[182] However, only a few of these infections were able to cause epidemics in humans, and all did so in the late 19th—early 20th century. To explain why HIV became epidemic only by that time, there are several theories, each invoking specific driving factors that may have promoted SIV adaptation to humans, or initial spread: social changes following colonialism,[183] rapid transmission of SIV through unsafe or unsterile injections (that is, injections in which the needle is reused without being sterilised),[184] colonial abuses and unsafe smallpox vaccinations or injections,[185] or prostitution and the concomitant high frequency of genital ulcer diseases (such as syphilis) in nascent colonial cities[186][187]
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