Source -
http://en.wikipedia.org/wiki/Origin_of_AIDS
Most HIV researchers agree that HIV evolved from the closely related
Simian Immunodeficiency Virus (SIV), and that HIV 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.
[edit] HIV-1 spread from chimpanzees
[edit] Where
Because HIV-1 is closely related to a strain of the simian immunodeficiency virus that infects the
chimpanzee subspecies
Pan troglodytes troglodytes (SIVcpz), scientists generally accept
[4][5] that the virus originated in populations of wild chimpanzees in West-Central Africa.
[6] Exactly where this occurred—in the southeastern rain forests of
Cameroon (modern
East Province) near the
Sanaga River, or further south near
Kinshasa in the
Democratic Republic of the Congo—has been a matter of scientific discussion.
[7][6][8]
[edit] When
Using HIV-1 sequences preserved in human biological samples along with estimates of viral mutation rates, scientists calculate that the jump from chimpanzee to human probably happened during the late 19th or early 20th century, a time of rapid urbanisation and colonisation in equatorial Africa. Exactly when the
zoonosis occurred is not known. Some estimates suggest that HIV-1 (group M) entered the human population in the early 20th century, probably between 1915 and 1941.
[9][10] A study published in 2008, analyzing viral sequences recovered from a recently-discovered 1960 biopsy along with previously-known sequences, suggested a common ancestor between 1884 and 1924.
[11][12]
Genetic recombination had earlier been thought to "seriously confound" such phylogenetic analysis, but later "work has suggested that recombination is not likely to systematically bias [results]", although recombination is "expected to increase variance".
[2] The results of the study supported the later work and indicated that HIV evolves "fairly reliably".
[11][13]
[edit] How
According to the 'Hunter Theory', the "simplest and most plausible explanation for the cross-species transmission",
[4] the virus was transmitted from a chimpanzee to a human when a
bushmeat hunter was bitten or cut while hunting or butchering an animal. The resulting exposure of the hunter to blood or other bodily fluids of the chimpanzee could have resulted in infection.
[14]
[edit] Method of spread
Zoonosis (transfer of a pathogen from non-human animals to humans) and subsequent spread of the pathogen between humans, requires the following conditions:
- a human population;
- a nearby population of a host animal;
- an infectious pathogen in the host animal that can spread from animal to human;
- interaction between the species to transmit enough of the pathogen to humans to establish a human foothold, which could have taken millions of individual exposures;
- ability of the pathogen to spread from human to human (perhaps acquired by mutation);
- some method allowing the pathogen to disperse widely, preventing the infection from "burning out" by either killing off its human hosts or provoking immunity in a local population of humans.
Such requirements existed for
smallpox and for the 20th century
Spanish flu at
Fort Riley,
Kansas, where the animal reservoir seems to have been two species,
chickens and
pigs.[
citation needed]
Conditions introduced by colonisation may have been conducive to the spread of the virus. The hardships of forced labour could have suppressed the immune system of the initial hunter, allowing the virus to infect and take hold in a new host. Rapid urbanisation brought infected people into close contact with others, and colonial commerce provided opportunities for further geographical spread.
[12] Vaccination campaigns against illnesses such as
sleeping sickness may have sped the initial spread of HIV-1 when immunisation needles were re-used.
[15] Other technological and social disruptions, especially those that affected the food supply and the hunting of
bushmeat, may also have promoted the cross-over from chimpanzees and the spread amongst humans.
[16]
SIV in non-human primates tends to cause a non-fatal disease. 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
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.
[17]
. I see parakeet is talking about the african monkey theory, but its full of leaks as it doesnt seem to take into account that at the same time it was spreading in africa it was also spreading in new york and san fran. we all know that parakeet holds to the notion that there are no conspriacies for anything on earth. A notion that is also extreme in one way. The spread of knowledge requires an open mind unless you believe that the masses are created to be sheep for the rich and powerful.
