According to the latest research, the AIDS virus invaded the United States from Haiti, sometime around 1969, it then flourished and spread worldwide.
Scientists say it was probably brought into the country by a single infected immigrant, setting the stage for it to become the tragic epidemic which has since swept across the world.
Michael Worobey, who is based at the University of Arizona (UA) says the 1969 U.S. entry date is earlier than some experts had suggested and is the first human immunodeficiency virus discovered.
The HIV-1 group M subtype B, is the dominant strain of the AIDS virus in most countries outside sub-Saharan Africa and almost all the viruses are descendants of the one that emerged from Haiti.
A study by the assistant professor of ecology & evolutionary biology suggests that HIV infections were occurring in the United States for about 12 years before AIDS was first recognized by scientists as a disease in 1981 and by then many had died.
Worobey and his colleagues carried out a genetic analysis of stored blood samples from early AIDS patients in order to determine when the human immunodeficiency virus first entered the United States.
They discovered that HIV was brought to Haiti by an infected person from central Africa in about 1966, which ties in with earlier estimates; it then came to the United States in about 1969.
The researchers suspect the culprit was an unknown single infected Haitian immigrant who arrived in a large city such as Miami or New York; the virus circulated for years, initially in the U.S. population and then to other nations.
Experts say it can be several years after infection before a person develops AIDS.
Worobey says that single infection would have become two and then doubled again until over a number of years as a hundred or more were infected.
Worobey says from then on it multiplied until hundreds of thousands were infected before AIDS was recognized in the early 1980s.
The route the virus traversed as it spread from nation to nation has always been a topic for debate and Dr. Arthur Pitchenik, a co-author of the study says that as early as 1979 Haitian immigrants in Miami, who died from a mystery illness, had AIDS.