The AIDS virus entered the United States via Haiti in about 1969 -- earlier than previously believed -- concludes new research.
"Once the virus got to the U.S., then it just moved explosively around the world," said senior study author Michael Worobey, an assistant professor of ecology and evolutionary biology at The University of Arizona.
The research, published in the journal Proceedings of the National Academy of Sciences, is the first to definitively pinpoint when and from where HIV-1 entered the United States and shows that most HIV viruses in the U.S. descended from a single common ancestor.
The timeline laid out in the study suggests that HIV infections were occurring in the U.S. for roughly 12 years before AIDS was first recognized by scientists as a disease in 1981. By that point, of course, many people had died.
Worobey believes HIV developed in central Africa, perhaps as early as 1930, then moved to Haiti in the 1960s, where it mutated and flourished. It then moved to the U.S. and from there, the rest of the world.
The strain that migrated to the U.S. is called HIV-1 group M subtype B, and was the first human immunodeficiency virus discovered. It is the dominant strain of the AIDS virus in most countries, except sub-Saharan Africa.
To conduct the study, Worobey's team performed a genetic analysis of stored blood samples from the earliest AIDS patients, all of whom were recent immigrants from Haiti. The researchers also looked at genetic data from 117 more early AIDS patients from around the world.
Once all the genetic data was assembled, the researchers loaded it into a computer and used Bayesian statistics to analyze it.
For the hypothesis that HIV went from Africa to the U.S. first, the probability turned out to be 0.003 per cent -- virtually nil. For the hypothesis that HIV went from Africa first to Haiti and then on to the U.S., the probability is 99.8 per cent.
Worobey's team believes that HIV was brought to Haiti by an infected person from central Africa in about 1966, which matches earlier estimates. That unknown single infected Haitian immigrant then likely arrived in a large U.S. city like Miami or New York in 1969.
Since it can take several years after infection for a person to develop AIDS, the virus likely circulated for years before it manifested itself in AIDS.
HIV has gone on to infect tens of millions around the world and AIDS has killed more than 25 million people.
Learning more about the genetic make-up of the various strains of HIV could help vaccine development, Worobey said.
"The main challenge of developing a vaccine against HIV is its tremendous genetic diversity," he said.
