Figuring out which path HIV/AIDS took as it began its world travels and when it moved from one country to another has long been a topic of scientific investigation and debate.
Worobey and his colleagues tackled the problem by using archived blood samples from AIDS patients to construct genetic family trees for HIV.
The team analyzed blood from five of the first AIDS patients identified in the U.S., all of whom were recent immigrants from Haiti. The team also analyzed genetic sequences from another 117 AIDS patients from around the world who were infected with subtype B, the virus strain that has spread most widely.
Once all 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. The researchers 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 percent -- 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 percent, almost 100 percent.
The analysis also shows that the ancestry of most viruses in the U.S. can be traced back to one common ancestor -- the virus that came from Haiti in about 1969.
"Before this study, that had not been nailed down," Worobey said.
The research also reveals that Haiti has a much larger genetic divers
|Contact: Mari N. Jensen|
University of Arizona