AIDS Virus Traveled to Haiti, Then U.S., Study Says
for National Geographic News
|October 29, 2007|
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.
Worobey and his colleagues looked at subtype B. Though it is found mainly in North America and Europe, the strain is present in the most number of countries.
The researchers analyzed tissue samples from five Haitian AIDS patients collected in 1982 and 1983. All five had then recently immigrated to the U.S. and were among the first recognized victims of AIDS.
A family tree constructed from the HIV-1 genes of the five Haitians and subtype B gene sequences from 19 other countries place the Haitian virus at the root of all branches.
"This is strong evidence that HIV-1 subtype B arrived and began spreading in Haiti before it did elsewhere," Worobey said.
It is generally thought that the virus arrived with Haitian professionals returning from Zaire (now the Democratic Republic of the Congo) following a wave of nationalism there in the 1960s.
Using advanced statistical techniques, Worobey and his colleagues estimated that the subtype B strain reached Haiti sometime around 1966 and the United States around 1969.
"Until AIDS was initially recognized in 1981, the virus was cryptically [hiddenly] circulating in a sophisticated medical environment for the better part of 12 years," Worobey said.
Beatrice Hahn is a microbiologist at the University of Alabama in Birmingham who was not involved with the study.
"The paper is a nice piece of evolutionary sleuthing,'' she said. "It shows how chance events can shape a major epidemic and that one virus introduced under the right circumstances can create major havoc."
"The findings are significant," added Robert Garry, a microbiologist at Tulane University. They indicate "an important lineage of subtype B HIV was present in Haiti, which eventually spread elsewhere," he added.
But he is not fully convinced that a Haitian origin is the only explanation for subtype-B strains in the Americas, however.
It is quite likely that other B lineages appeared in the Americas prior to and in all likelihood independently of the Haitian lineage, he said.
"It is possible that HIV made many incursions into the United States. Most of these likely never spread or spread cryptically for a while and burned out," he added. "The one discussed in this paper appears to have been the bomb that actually went off."
Study leader Worobey, a former forest firefighter, likes to use a wildfire analogy.
"It is like a forest fire, it often produces sparks that fly out in front of a fire. Some of those sparks ... die out. But every once in a while one of those sparks ... can start a new wildfire. And that is what we are seeing in this case."
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