Humanity has battled scores of infectious diseases throughout history and they are still around in certain areas. The Black Plague pops up now and then and Anthrax and Cholera and Yellow Fever still claim lives. Science has been well aware of all the diseases but all of a sudden a new virus pops up in the 1960's that nobody ever heard of. Genetic research was in it's infancy and the Cold War was going on and the Russians as well as the US and probably China were experimenting with biological weapons. There are bombing ranges in the US that post no trespassing because of explosive and biological hazards. It wasn't long ago that American Troops were used as guinea pigs without their knowledge for experiments in LSD and nuclear weapons. It doesn't take much imagination to conclude that HIV was manufactured in a lab and either intentionally released or escaped.