for National Geographic News
HIV went directly from Africa to Haiti, then spread to the United States and much of the rest of the world beginning around 1969, suggests an international team of researchers.
The findings settle a key debate on the history and transmission route of the deadly virus, the scientists say.
Even before HIV was identified as the cause of AIDS, Haiti's role in the disease epidemic had been hotly debated.
When AIDS was officially recognized in 1981 in the U.S., for instance, the unusually high prevalence of the disease in Haitian immigrants fueled speculation that the Caribbean island was the source of the mysterious illness.
Another theory held that the AIDS epidemic spread from the U.S. in the mid-1970s after Haiti became a popular destination for sex tourism.
Scientists led by Michael Worobey, an evolutionary biologist at the University of Arizona, Tucson, tried to solve the puzzle by tracing back the family history of the virus subtype blamed for the epidemic in North America.
The findings suggest that native Haitians carried the disease back to their island from Africa soon after the virus's emergence there. (Related: "AIDS Origin Traced to Chimp Group in Cameroon" [May 25, 2006].)
The new study appears online this week in the journal Proceedings of the National Academy of Sciences.
Root of the Epidemic
HIV is commonly transmitted through tainted blood transfusions, dirty needles, and unprotected sex. Infections often lead to a life-threatening condition in which the body's immune defenses are systematically disabled.
Two species of HIV can infect humans—HIV-1 and HIV-2. The former is more virulent, more easily transmitted, and accounts for the lion's share of global HIV infections. HIV-2 is less infectious and is largely confined to parts of Western Africa.
Based on differences in one of the nine genes that make up the virus, HIV-1 is placed in three major groups. The most prevalent, Group M, has eight geographically distinct subtypes.
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