A team of scientists, whose work was published in the journal Proceedings of the National Academy of Sciences, has found that a specific strain of the HIV virus passed from Haiti to the United States in about 1969 before spreading further.

The strain, called subtype B, predominates in the United States, Europe, large parts of South America, Australia and Japan.
 
The team traced the virus by examining archived blood samples from five early AIDS patients - all of them Haitian immigrants to the United States - and analyzed genetic sequences from another group of patients from around the world.

Using the data, they developed a map of the virus, which they believe shows conclusively that the strain came to the United States via Haiti, probably by a single person, in around 1969.
 
Michael Worobey of the University of Arizona in Tucson is one of the study's authors.  He says once in the United States, it appears the HIV virus circulated undetected for about a dozen years*.
 
He says the path of the virus he and his colleagues constructed corresponds with the start of the global pandemic and recognition of the first cases of HIV in 1981.

"AIDS came to the attention of the world through this form of the virus," he noted.  "This was the form of the virus that was killing young gay men in Los Angeles and in New York.  And that was what finally alerted people to the fact that we had something new on our hands here.  And the fact is that was just the first sort of tip of the iceberg. The iceberg went much deeper.  The virus had a much longer history even before it was noticed."

Scientists are certain that the AIDS virus developed somewhere in Africa after a virus jumped from monkeys to humans. But there are still questions about the history of HIV and how it incubated in Africa before moving on to the rest of the world.

Worobey and his team now want to trace the strain back further. His suspicion is that it probably arrived in Haiti from the Congo from Haitians who were working in Africa during those years.
 
Worobey says understanding the origins of this and other strains of HIV will enable scientists to predict how the virus may mutate in the future.

"If you look back in time about how the virus colonized different parts of the world it then helps you look forward in time to try to predict ok, in 10, 20, 50 years from now," he added.  "What's the pandemic going to look like?  How many different strains of the virus are going to be circulating in each area and so forth?"

Worobey says the AIDS strain in question has a deeper history in Haiti than in all the other countries it traveled to. Its genetic diversity is more extensive, he says, making development of a one-size-fits-all vaccine extremely difficult.

* - edited for clarification 02 Nov 07