The findings are unlikely to help scientists discover better treatments for AIDS, but they could provide insight into how HIV evolves and moves from place to place, said Michael Worobey, a professor in the University of Arizona's Department of Ecology and Evolutionary Biology and co-author of a study released Monday.
"It matters when these events occurred and how often colonizations of new locales occur," he said. "That helps us predict the future complexity of the HIV pandemic."
The study findings about the spread of HIV are "definitive," added Dr. Beatrice Hahn, a professor in the University of Alabama at Birmingham's departments of medicine and microbiology. Hahn, who studies how the virus developed, said the next step in research is to go "further back in time" and use old blood samples from central Africa to understand more about the early days of AIDS.
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.
In the new study, Worobey and colleagues studied a strain of the AIDS virus known as subtype B, which commonly affects people in many countries, including the United States. The researchers tried to figure out how the virus traveled by studying blood samples of Haitian immigrants to the United States who were among the first in the country to be diagnosed as suffering from AIDS.
"For the last few years, we've been thinking it would be good to try to collect and analyze as many archival human samples as possible," Worobey said. "We can travel back in time and look directly at the viruses that were circulating at early time points."
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."
More information
There's more on the history of HIV and AIDS at the U.S. Food and Drug Administration.
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