From the time that HIV infections came to the notice of the medical community, scientists have been attempting to trace its origins.
An electron microscope scan of a HUV-1 virion budding from a cultured lymphocyte
If the above process was occurring in your body, you would be in for a lot of problems.
The latest research conclusions are that the first cases occurred around the year 1920, in the African city of Kinshasa, now captital of the Democratic Republic of Congo.
Scientists have been able to track at least 13 transmissions from apes to humans, but only one transmision involved the HIV-1 virus group that has resulted in some 75 million human infections to this time.
The team of scientists involved in this study see the following factors being involved in the development of the pandemic. Between the 1920s and 1930s, there were more human mobility due to new railway networks (during the Belgian colonial rule), people moved to cities away from traditional life, and most importantly for this virus, a mobile population, living in new cities, led to a more dynamic sex trade (think, more prostitution) and eventually to someone near you dying from Aids.
The full story of the research conducted at the University of Oxford,
can be read at: http://www.sciencedaily.com/releases/2014/10/141002141759.htm