HIV-1 in U.S. traced back to Haiti

The AIDS virus entered the U.S. via Haiti, probably arriving in just one person in about 1969, earlier than previously believed, according to research by the University of Arizona, Tucson. After the virus, HIV-1, came into the U.S., it flourished and spread worldwide.

The research is the first to pinpoint definitively when and from where HIV-1 entered the U.S. and shows that most HIV/AIDS viruses in this country descended from a single common ancestor. The actual ancestral HIV entered America long before the storied "Patient Zero," asserts Michael Worobey, assistant professor of ecology and evolutionary biology. "Once the virus got to the U.S., then it just moved explosively around the world."

The strain that migrated to the U.S. in 1969, HIV-1 group M subtype B, is the first human immunodeficiency virus discovered. It is the dominant strain of the AIDS virus in most countries outside sub-Saharan Africa. Almost all the viruses in those countries descended from the one that emerged from Haiti. Worobey and his colleagues figured out when HIV reached the U.S. by conducting genetic analyses of archived blood samples from early AIDS patients. Learning more about the genetic makeup of the various strains of HIV could help vaccine development, Worobey contends.

Figuring out which path HIV/AIDS took as it began its world travels and when it moved from one country to another long has been a topic of scientific investigation and debate. The team analyzed blood from five of the first AIDS patients identified in the U.S., all of whom were recent immigrants from Haiti, as well as the genetic sequences from another 117 patients from around the world who were infected with subtype B, the virus strain that has spread most widely. Once the sequences were assembled, the researchers loaded the data into a computer and used Bayesian statistics to investigate all the family trees that were consistent with the genetic data. They then evaluated all possible HIV family trees to determine how probable a particular family tree is.

For the hypothesis that, from Africa, HIV went to the U.S. first, the probability is 0.003%--virtually nil; that HIV moved first from Africa to Haiti and then on to the U.S., the probability is 99.8%.

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The analysis also shows that most viruses in the U.S. can be traced back to a common ancestor--the one that came from Haiti in about 1969. "Before this study, that had not been nailed down," Worobey affirms.

The research reveals that Haiti has a much larger genetic diversity of subtype B than does the U.S. The virus moved from Africa to Haiti in about 1966. Haiti has more diversity of HIV because the virus has been there longer and had more time to mutate.

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