Editing HIV (section)

===Origins===
Both HIV-1 and HIV-2 are believed to have originated in non-human [[primate]]s in West-central Africa, and are believed to have transferred to humans (a process known as [[zoonosis]]) in the early 20th century.<ref name=Orgin2011>{{cite journal | vauthors = Sharp PM, Hahn BH | title = Origins of HIV and the AIDS Pandemic | journal = Cold Spring Harbor Perspectives in Medicine | volume = 1 | issue = 1 | pages = a006841 | year = 2011 | pmid = 22229120 | pmc = 3234451 | doi = 10.1101/cshperspect.a006841 }}</ref><ref name=Faria2014>{{cite journal | vauthors = Faria NR, Rambaut A, Suchard MA, Baele G, Bedford T, Ward MJ, Tatem AJ, Sousa JD, Arinaminpathy N, Pépin J, Posada D, Peeters M, Pybus OG, Lemey P | title = The early spread and epidemic ignition of HIV-1 in human populations | journal = Science | volume = 346 | issue = 6205 | pages = 56–61 | year = 2014 | pmid = 25278604| pmc = 4254776| doi = 10.1126/science.1256739 | bibcode = 2014Sci...346...56F }}</ref>

HIV-1 appears to have originated in southern [[Cameroon]] through the evolution of SIVcpz, a [[simian immunodeficiency virus]] (SIV) that infects wild [[common chimpanzee|chimpanzee]]s (HIV-1 descends from the SIVcpz endemic in the chimpanzee subspecies ''[[Central chimpanzee|Pan troglodytes troglodytes]]'').<ref name="pmid9989410">{{cite journal | vauthors = Gao F, Bailes E, Robertson DL, Chen Y, Rodenburg CM, Michael SF, Cummins LB, Arthur LO, Peeters M, Shaw GM, Sharp PM, Hahn BH | title = Origin of HIV-1 in the chimpanzee Pan troglodytes troglodytes | journal = Nature | volume = 397 | issue = 6718 | pages = 436–41 | year = 1999 | pmid = 9989410 | doi = 10.1038/17130 | bibcode = 1999Natur.397..436G | s2cid = 4432185 | doi-access = free }}</ref><ref name=Keele>{{cite journal | vauthors = Keele BF, Van Heuverswyn F, Li Y, Bailes E, Takehisa J, Santiago ML, Bibollet-Ruche F, Chen Y, Wain LV, Liegeois F, Loul S, Ngole EM, Bienvenue Y, Delaporte E, Brookfield JF, Sharp PM, Shaw GM, Peeters M, Hahn BH | title = Chimpanzee reservoirs of pandemic and nonpandemic HIV-1 | journal = Science | volume = 313 | issue = 5786 | pages = 523–6 | year = 2006 | pmid = 16728595 | pmc = 2442710 | doi = 10.1126/science.1126531 | bibcode = 2006Sci...313..523K }}</ref> The closest relative of HIV-2 is SIVsmm, a virus of the [[sooty mangabey]] (''Cercocebus atys atys''), an [[Old World monkey]] living in littoral West Africa (from southern [[Senegal]] to western [[Ivory Coast|Côte d'Ivoire]]).<ref name=Reeves /> [[New World monkey]]s such as the [[Night monkey|owl monkey]] are resistant to HIV-1 infection, possibly because of a [[fusion gene|genomic fusion]] of two viral resistance genes.<ref name=Goodier>{{cite journal | vauthors = Goodier JL, Kazazian HH | title = Retrotransposons revisited: the restraint and rehabilitation of parasites | journal = Cell | volume = 135 | issue = 1 | pages = 23–35 | year = 2008 | pmid = 18854152 | doi = 10.1016/j.cell.2008.09.022 | s2cid = 3093360 | doi-access = free }}</ref>

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.<ref name="Sharp2001">{{cite journal | vauthors = Sharp PM, Bailes E, Chaudhuri RR, Rodenburg CM, Santiago MO, Hahn BH | title = The origins of acquired immune deficiency syndrome viruses: where and when? | journal = Philosophical Transactions of the Royal Society B | volume = 356 | issue = 1410 | pages = 867–76 | year = 2001 | pmid = 11405934 | pmc = 1088480 | doi = 10.1098/rstb.2001.0863 }}</ref>

[[File:SIV primates.jpg|left|upright=1.8|thumb|Left to right: the [[African green monkey]] source of [[Simian immunodeficiency virus|SIV]], the [[sooty mangabey]] source of [[HIV-2]], and the chimpanzee source of [[HIV-1]]]]
There is evidence that humans who participate in [[bushmeat]] activities, either as hunters or as bushmeat vendors, commonly acquire SIV.<ref name=Kalish2005>{{cite journal | vauthors = Kalish ML, Wolfe ND, Ndongmo CB, McNicholl J, Robbins KE, Aidoo M, Fonjungo PN, Alemnji G, Zeh C, Djoko CF, Mpoudi-Ngole E, Burke DS, Folks TM | title = Central African hunters exposed to simian immunodeficiency virus | journal = Emerging Infectious Diseases | volume = 11 | issue = 12 | pages = 1928–30 | year = 2005 | pmid = 16485481 | pmc = 3367631 | doi = 10.3201/eid1112.050394 }}</ref> However, SIV is a weak virus, and it 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.<ref name=Marx2001>{{cite journal | vauthors = Marx PA, Alcabes PG, Drucker E | title = Serial human passage of simian immunodeficiency virus by unsterile injections and the emergence of epidemic human immunodeficiency virus in Africa | journal = Philosophical Transactions of the Royal Society B | volume = 356 | issue = 1410 | pages = 911–20 | year = 2001 | pmid = 11405938 | pmc = 1088484 | doi = 10.1098/rstb.2001.0867 }}</ref> Furthermore, due to its relatively low person-to-person transmission rate, it 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 prior to 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}}.<ref name=Worobey2008>{{cite journal | vauthors = Worobey M, Gemmel M, Teuwen DE, Haselkorn T, Kunstman K, Bunce M, Muyembe JJ, Kabongo JM, Kalengayi RM, Van Marck E, Gilbert MT, Wolinsky SM | title = Direct evidence of extensive diversity of HIV-1 in Kinshasa by 1960 | journal = Nature | volume = 455 | issue = 7213 | pages = 661–4 | year = 2008 | pmid = 18833279 | pmc = 3682493 | doi = 10.1038/nature07390 | bibcode = 2008Natur.455..661W }}</ref> 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 different patterns of sexual contact (especially multiple, concurrent partnerships), the spread of [[prostitution]], and the concomitant high frequency of [[genital ulcer]] diseases (such as [[syphilis]]) in nascent colonial cities.<ref name=Sousa2010>{{cite journal | vauthors = de Sousa JD, Müller V, Lemey P, Vandamme AM | title = High GUD incidence in the early 20th century created a particularly permissive time window for the origin and initial spread of epidemic HIV strains | journal = PLOS ONE | volume = 5 | issue = 4 | pages = e9936 | year = 2010 | pmid = 20376191 | pmc = 2848574 | doi = 10.1371/journal.pone.0009936 | veditors = Martin DP | bibcode = 2010PLoSO...5.9936S | doi-access = free }}</ref> While transmission rates of HIV during vaginal intercourse are typically low, they are increased manyfold if one of the partners has a [[Sexually transmitted disease|sexually transmitted infection]] resulting in genital ulcers. Early 1900s colonial cities were notable for their high prevalence of prostitution and genital ulcers to the degree that as of 1928 as many as 45% of female residents of eastern [[Kinshasa|Leopoldville (currently Kinshasa)]] were thought to have been prostitutes and as of 1933 around 15% of all residents of the same city were infected by one of the forms of [[syphilis]].<ref name=Sousa2010 />

The earliest, well-documented case of HIV in a human dates back to 1959 in the [[Belgian Congo]].<ref name=Zhu>{{cite journal | vauthors = Zhu T, Korber BT, Nahmias AJ, Hooper E, Sharp PM, Ho DD | title = An African HIV-1 Sequence from 1959 and Implications for the Origin of the epidemic | journal = Nature | volume = 391 | issue = 6667 | pages = 594–7 | year = 1998 | pmid = 9468138 | doi = 10.1038/35400 | bibcode = 1998Natur.391..594Z | s2cid = 4416837 | doi-access = free }}</ref> The virus may have been present in the United States as early as the mid- to late 1960s, as a sixteen-year-old male named [[Robert Rayford]] presented with symptoms in 1966 and died in 1969.<ref>{{cite news| vauthors = Kolata G |title=Boy's 1969 death suggests AIDS invaded U.S. several times|work=[[The New York Times]] |date=October 28, 1987 |url=https://query.nytimes.com/gst/fullpage.html?res=9B0DEFD6173AF93BA15753C1A961948260 |access-date=February 11, 2009}}</ref>

An alternative and likely complementary hypothesis points to the widespread use of unsafe medical practices in Africa during years following World War II, such as unsterile reuse of single-use syringes during mass vaccination, antibiotic, and anti-malaria treatment campaigns.<ref name=Marx2001 /><ref name="Chitnis2000">{{cite journal | vauthors = Chitnis A, Rawls D, Moore J | title = Origin of HIV type 1 in colonial French Equatorial Africa? | journal = AIDS Research and Human Retroviruses | volume = 16 | issue = 1 | pages = 5–8 | date = January 2000 | pmid = 10628811 | doi = 10.1089/088922200309548 | s2cid = 17783758 }}</ref><ref name="McNeil">{{cite news|first=Donald Jr. |last=McNeil|author-link=Donald McNeil, Jr|date=September 16, 2010|title=Precursor to H.I.V. was in monkeys for millennia|work=[[The New York Times]]|url=https://www.nytimes.com/2010/09/17/health/17aids.html |archive-url=https://ghostarchive.org/archive/20220103/https://www.nytimes.com/2010/09/17/health/17aids.html |archive-date=2022-01-03 |url-access=subscription |url-status=live|access-date=September 17, 2010|quote=Dr. Marx believes that the crucial event was the introduction into Africa of millions of inexpensive, mass-produced syringes in the 1950s. ... suspect that the growth of colonial cities is to blame. Before 1910, no Central African town had more than 10,000 people. But urban migration rose, increasing sexual contacts and leading to red-light districts.}}{{cbignore}}</ref> Research on the timing of most recent common ancestor for HIV-1 groups M and O, as well as on HIV-2 groups A and B, indicates that SIV has given rise to transmissible HIV lineages throughout the twentieth century.<ref name=":0">{{cite journal | vauthors = Wertheim JO, Worobey M | title = Dating the age of the SIV lineages that gave rise to HIV-1 and HIV-2 | journal = PLOS Computational Biology | volume = 5 | issue = 5 | pages = e1000377 | date = May 2009 | pmid = 19412344 | pmc = 2669881 | doi = 10.1371/journal.pcbi.1000377 | bibcode = 2009PLSCB...5E0377W | doi-access = free }}</ref> The dispersed timing of these transmissions to humans implies that no single external factor is needed to explain the cross-species transmission of HIV. This observation is consistent with both of the two prevailing views of the origin of the HIV epidemics, namely SIV transmission to humans during the slaughter or butchering of infected primates, and the colonial expansion of sub-Saharan African cities.<ref name=":0" />