The findings were published this week in an online edition of the Proceedings of the National Academy of Sciences.
After using genetic techniques to study the evolution of the virus, the researchers came to believe that the AIDS strain moved from Africa to Haiti at some time during the mid-1960s. They think it circulated in Haiti for perhaps a few years before moving on to the United States in about 1969.
Doctors didn't begin picking up on the existence of the virus in the United States until 1981, when they noticed that some gay men were developing unusual diseases. "That leaves a 12-year period between when we think it came in, and people realized there was something new," he said.
What could explain that? It's possible that the virus was around and making people sick for a decade or more, but the number of people infected may have been tiny, Worobey said. After all, it can often take 10 to 12 years for someone to become ill with AIDS after being infected by the virus, he said.
Going back even earlier, some scientists suspect that AIDS stalked Africa since the 1930s. "It's not that surprising that it circulated for 30 years before we have any hard evidence of it," Worobey said. "In Africa, most people die of tuberculosis when they have AIDS, and that adds a whole layer of fog" to detecting HIV disease, he said.
What now? Scientists could use the findings about Haiti as they try to develop vaccines, Worobey said. The AIDS strain in question "has a deeper history in Haiti than in all these other countries (that it traveled to). Its genetic diversity is more extensive, and that should be considered when either testing or designing subtype B vaccines in the future."
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