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An AIDS ward in Haiti.

Malcolm Linton

How HIV Took the World by Storm

Five HIV isolates that had been forgotten in freezers for 2 decades are revealing new details about how and when the virus spread from Africa to Haiti and then exploded on the world scene.

Much controversy has swirled around the origins of the AIDS epidemic. Because some of the first AIDS cases surfaced in Haitian immigrants to the United States, the Atlanta, Georgia-based Centers for Disease Control and Prevention (CDC) once wrongly lumped Haitians together with hemophiliacs, heroin users, and homosexuals--the "4H Club"--as being at especially high risk of contracting the disease. As a result, Haitians were blamed for spreading the disease to the United States.

Since then, the focus has turned away from blame to understanding the epidemic's origins. To that end, evolutionary biologist Michael Worobey of the University of Arizona in Tucson and colleagues analyzed blood samples saved from five Haitian AIDS patients treated in Miami in 1982 and 1983. "It was the next best thing to being able to travel back in time," he says. In a paper published online this week in the Proceedings of the National Academy of Sciences, Worobey and co-workers focused on what's known as HIV-1 subtype B. "This was the variant that led to the discovery of AIDS and so much of the story that reared its head after 1981," says Worobey.

Molecular analyses of the archival isolates confirmed earlier reports that subtype B traveled from central Africa to Haiti about 1966, entering the United States 3 years later. The researchers' estimated probability that the virus instead traveled from the United States to Haiti--0.00003--is infinitesimal.

Beatrice Hahn, a virologist at the University of Alabama, Birmingham, says the study offers the clearest picture yet of how the young epidemic matured: "It's a very nice piece of evolutionary sleuthing." One provocative finding, says Hahn, suggests that although several different isolates of subtype B came from Haiti to the United States, only one got a foothold. It had not evolved ways to transmit more readily, says Worobey, and appears to have been "lucky" to have spread among high-risk populations--primarily, gay males in the United States. It then spread to Canada, South America, Europe, Asia, and even back to Africa.

Some are not persuaded. Jean "Bill" Pape, who heads the largest AIDS research program in Haiti, says Worobey and co-workers simply "restate prejudices advanced 2 decades ago." Pape notes that the authors offer no details about the sexual histories of the five Haitian immigrants, who he contends could have been infected by Americans. He also questions whether HIV arrived in 1966, pointing to retrospective studies in Haiti that did not find an AIDS case until 1978.

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