The human immunodeficiency virus (HIV), originated from non-human primates in Sub-Saharan Africa and was transferred to humans during the late 19th or early 20th century.
Types of HIV
HIV-1 and HIV-2. HIV-1 is more virulent, is more easily transmitted and is the cause of the vast majority of HIV infections globally.[1] The pandemic strain of HIV-1 is closely related to a virus found in the chimpanzees of the subspecies Pan troglodytes troglodytes, which lives in the forests of the Central African nations of Cameroon, Equatorial Guinea, Gabon, Republic of Congo (or Congo-Brazzaville), and Central African Republic. HIV-2 is less transmittable and is largely confined to West Africa, along with its closest relative, a virus of the sooty mangabey (Cercocebus atys atys), an Old World monkey inhabiting southern Senegal, Guinea-Bissau, Guinea, Sierra Leone, Liberia, and western Ivory Coast.
Transmission of HIV from non-humans to humans
Most HIV researchers agree that HIV evolved at some point from the closely related Simian immunodeficiency virus (SIV), and that SIV or HIV (post mutation) was transferred from non-human primates to humans in the recent past (as a type of zoonosis). Research in this area is conducted using molecular phylogenetics, comparing viral genomic sequences to determine relatedness.
HIV-1 from chimpanzees and gorillas to humans
Scientists generally accept that the known strains (or groups) of HIV-1 are most closely related to the simian immunodeficiency viruses (SIVs) endemic in wild ape populations of West Central African forests. Particularly, each of the known HIV-1 strains is either closely related to the SIV that infects the chimpanzee subspecies Pan troglodytes troglodytes (SIVcpz), or to the SIV that infects Western lowland gorillas (Gorilla gorilla gorilla), called SIVgor.
The pandemic HIV-1 strain (group M or Main) and a very rare strain only found in a few Cameroonian people (group N) are clearly derived from SIVcpz strains endemic in Pan troglodytes troglodytes chimpanzee populations living in Cameroon.[3] Another very rare HIV-1 strain (group P) is clearly derived from SIVgor strains of Cameroon.[6] Finally, the primate ancestor of HIV-1 group O, a strain infecting tens of thousands of people mostly from Cameroon but also from neighboring countries, is still uncertain, but there is evidence that it is either SIVcpz or SIVgor.
The pandemic HIV-1 group M is most closely related to the SIVcpz collected from the southeastern rain forests of Cameroon (modern East Province) near the Sangha River.[3] Thus, this region is presumably where the virus was first transmitted from chimpanzees to humans. However, reviews of the epidemiological evidence of early HIV-1 infection in stored blood samples, and of old cases of AIDS in Central Africa have led many scientists to believe that HIV-1 group M early human center was probably not in Cameroon, but rather farther south in the Democratic Republic of the Congo, more probably in its capital city, Kinshasa.
It was how ever proposed by Beatrice Hahn, Paul Sharp, and colleagues that "[the epidemic emergence of HIV] most likely reflects changes in population structure and behaviour in Africa during the 20th century and perhaps medical interventions that provided the opportunity for rapid human-to-human spread of the virus". After the Scramble for Africa started in the 1880s, European colonial powers established cities, towns, and other colonial stations.
A largely masculine labor force was hastily recruited to work in fluvial and sea ports, railways, other infrastructures, and in plantations. This disrupted traditional tribal values, and favored sexual promiscuity. In the nascent cities women felt relatively liberated from rural tribal rules and many remained unmarried or divorced during long periods,this being very rare in African traditional societies. This was accompanied by unprecedented increase in people's movements.
Iatrogenic theories propose that medical interventions were responsible for HIV origins. By proposing factors that only appeared in Central and West Africa after the late 19th century, they seek to explain why all HIV groups also started after that.
The theories centered on the role of parenteral risks, such as unsterile injections, transfusions, or smallpox vaccinations are accepted as plausible by most scientists of the field.
In most non-human primate species, natural SIV infection does not cause a fatal disease (but see below). Comparison of the gene sequence of SIV with HIV should therefore give us information about the factors necessary to cause disease in humans. The factors that determine the virulence of HIV as compared to most SIVs are only now being elucidated. Non-human SIVs contain a nef gene that down-regulates CD3, CD4, and MHC class I expression; most non-human SIVs therefore do not induce immunodeficiency; the HIV-1 nef gene however has lost its ability to down-regulate CD3, which results in the immune activation and apoptosis that is characteristic of chronic HIV infection.
In addition, a long term survey of chimpanzees naturally infected with SIVcpz in Gombe, Tanzania, found that, contrary to the previous paradigm, chimpanzees with SIVcpz infection do experience an increased mortality, and also suffer from a Human AIDS-like illness.[41] SIV pathogenicity in wild animals could exist in other chimpanzee subspecies and other primate species as well, and stay unrecognized by lack of relevant long term studies.
History of spread of HIV and AIDS
HIV-1 strains are thought to have arrived in the United States from Haiti in the late 1960s or early '70s. HIV-1 is believed to have arrived in Haiti from central Africa, possibly through professional contacts with the Democratic Republic of the Congo. The current consensus is that HIV was introduced to Haiti by an unknown individual or individuals who contracted it while working in the Democratic Republic of the Congo circa 1966, or from another person who worked there during that time. A mini-epidemic followed, and, circa 1969, yet another unknown individual brought HIV from Haiti to the United States. The vast majority of cases of AIDS outside sub-Saharan Africa can be traced back to that single patient[51] (although numerous unrelated incidents of AIDS among Haitian immigrants to the U.S. were recorded in the early 1980s, and, as evidenced by the case of Robert Rayford, isolated incidents of this infection may have been occurring as early as 1966.) The virus eventually entered male gay communities in large United States cities, where a combination of sexual promiscuity (with individuals reportedly averaging over 11 unprotected sexual partners per year and relatively high transmission rates associated with anal intercourse allowed it spread explosively enough to finally be noticed.
Because of the long incubation period of HIV (up to a decade or longer) before symptoms of AIDS appear, and because of the initially low incidence, HIV was not noticed at first. By the time the first reported cases of AIDS were found in large United States cities, the prevalence of HIV infection in some communities had passed 5%Worldwide, HIV infection has spread from urban to rural areas, and has appeared in regions such as China and India.
A Canadian airline steward named Gaëtan Dugas was referred to as "Patient 0" in an early AIDS study by Dr. William Darrow of the Centers for Disease Control. Because of this, many people had considered Dugas to be responsible for bringing HIV to North America. This is not accurate, however, as HIV had spread long before Dugas began his career. This rumor may have started with Randy Shilts' 1987 book And the Band Played On (and the 1993 movie based on it, in which Dugas is referred to as AIDS' Patient Zero), but neither the book nor the movie state that he had been the first to bring the virus to North America. He was called "Patient Zero" because at least 40 of the 248 people known to be infected by HIV in 1983 had had sex with him, or with someone who had sexual intercourse with him .
The AIDS epidemic officially began on June 5, 1981, when the U.S. Centers for Disease Control and Prevention in its Morbidity and Mortality Weekly Report newsletter reported unusual clusters of Pneumocystis pneumonia (PCP) caused by a form of Pneumocystis carinii (now recognized as a distinct species Pneumocystis jirovecii) in five homosexual men in Los Angeles.
Over the next 18 months, more PCP clusters were discovered among otherwise healthy men in cities throughout the country, along with other opportunistic diseases (such as Kaposi's sarcoma and persistent, generalized lymphadenopathy), common in immunosuppressed patients.
In June 1982, a report of a group of cases amongst gay men in Southern California suggested that a sexually transmitted infectious agent might be the etiological agent, and the syndrome was initially termed "GRID", or gay-related immune deficiency.
Health authorities soon realized that nearly half of the people identified with the syndrome were not homosexual men. The same opportunistic infections were also reported among hemophiliacs, heterosexual intravenous drug users, and Haitian immigrants—leading some researchers to call it the "4H" disease.
By August 1982, the disease was being referred to by its new CDC and was later changed to Acquired Immune Deficiency Syndrome (AIDS). AIDS was first seen in Nigeria in 1986.
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