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(Agencies)
Updated: 2007-10-30 10:22

WASHINGTON -- The AIDS virus invaded the United States in about 1969 from Haiti, carried most likely by a single infected immigrant who set the stage for it to sweep the world in a tragic epidemic, scientists said on Monday.

Vivian Voyles places a rose on the Circle of Friends at the National AIDS Memorial Grove on World Aids Day in San Francisco, California, December 1, 2006. The AIDS virus invaded the United States in about 1969 from Haiti, carried most likely by a single infected immigrant who set the stage for it to sweep the world in a tragic epidemic, scientists said on Monday. [Agencies]

Michael Worobey, a University of Arizona evolutionary biologist, said the 1969 US entry date is earlier than some experts had believed.

The timeline laid out in the study led by Worobey indicates that HIV infections were occurring in the United States for roughly 12 years before AIDS was first recognized by scientists as a disease in 1981. Many people had died by that point.

"It is somehow chilling to know it was probably circulating for so long under our noses," Worobey said in a telephone interview.

The researchers conducted a genetic analysis of stored blood samples from early AIDS patients to determine when the human immunodeficiency virus first entered the United States.

They found that HIV was brought to Haiti by an infected person from central Africa in about 1966, which matches earlier estimates, and then came to the United States in about 1969.

The researchers think an unknown single infected Haitian immigrant arrived in a large city like Miami or New York, and the virus circulated for years -- first in the US population and then to other nations.

It can take several years after infection for a person to develop AIDS, a disease that ravages the immune system.

DISEASE MULTIPLIES

"That one infection would have become two, and then it doubles again and the two becomes four," Worobey said. "So you have a period -- probably a fair number of years -- where you're dealing with probably fewer than a hundred people who are infected.

"And then, as with epidemic expansion, at some point the hundred becomes 200, you start getting into thousands, tens of thousands. And then quite rapidly you can be up into the hundreds of thousands of infections that were probably already there before AIDS was recognized in the early 1980s."

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