"None of the wicked will understand, but those who are wise will understand."
Daniel 12:10

4. Finally, in Central Africa, humans have been exposed for centuries to SIVs and the epidemic has apparently only emerged in the second half of the last century, which suggests the intervention of some favoring factor(s) in the emergence of HIV. These factors might be represented by the deforestation, increase of urbanization and travel in the 20th century. Also it was postulated that the main factor behind the emergence of HIV in human population might be represented by an increase of the use of injections with unsterile needles and syringes. This factor might significantly promote viral adaptation through serial passages or favor adaptation by other mechanisms such as recombination.

One should note that most of the SIVs reported so far have not been grown in vitro, thus, the statement that with very few exceptions all SIVs infect human PBMCs might not be true. In fact, most of the cercopithecine SIVs do not grow in human PBMCs. 

These arguments indicate that viral cross-species transmission is in itself not the only requirement for the generation of epidemics, and that the origin of HIV should not be confused with the origins ofAIDS.

Other factors must be required for HIV adaptation and epidemic spread in the new human host. All these aspects being considered, AIDS is not a zoonosis in the strict definition, but a human infectious disease of simian origin, similar to hepatitis B and HTLV infections.

In conclusion, the study of SIV has identified only the simian origin of HIV. Questions still remain: which factor(s) has driven the cross-species transmission, virus adaptation and how can new cross-species transmissions be avoided?"