Simian Immuno Deficiency Virus?

Question

Human Immunodeficiency Virus originated in the chimpanzee's of cameroon as S.I.V., But how did it pass on to humans as H.I.V.?

Answer 1

HIV originated in primates as far as is known. Possible ways for this virus to have originally infected humans include the hunting and eating of the original primate species; a bite would be another possible route. From this point, the virus ultimately spread to the rest of the world.

If a cross species jump is indeed the origin of HIV then the following conditions would most likely be required:
a large human population,
a large nearby population of a host animal,
a pathogen that eventually mutates to spread from animal to human,
interaction between the species to transmit enough of it to humans to establish a human foothold, which may take millions of individual exposures,
a mutation of same pathogen that can spread from human to human,
some method that allows the pathogen to disperse widely so it does not "burn out" in a local population of humans.

Such requirements existed in the remote past with smallpox, and also with the 20th century Spanish Flu.

Two species of HIV infect humans: HIV-1 and HIV-2. HIV-1 is more virulent and more easily transmitted. HIV-1 is the source of the majority of HIV infections throughout the world, while HIV-2 is less easily transmitted and is largely confined to West Africa.

Both species of the virus (HIV-1 and HIV-2) are believed to have originated in West-Central Africa and jumped species (zoonosis) from primates to humans. HIV-1 evolved from a Simian Immunodeficiency Virus (SIVcpz) found in the chimpanzee subspecies Pan troglodytes troglodytes. DNA sequencing indicates that HIV-1 (group M) entered the human population in the early 20th century, probably sometime between 1915 and 1941. HIV-2 crossed species from a different strain of SIV, this one found in sooty mangabeys (an Old World monkey) of Guinea-Bissau.