Scientists track arrival of HIV in U.S.

In the decades since young gay men in the United States started dying from a mysterious disease in the 1980s, scientists have wondered how and when the AIDS virus arrived.

Now scientists reconstructing the genetic evolution of the deadly virus say they have traced its true path — concluding the insidious pathogen used Haiti as a steppingstone from Africa to the United States and arrived much earlier than had been thought. It then simmered silently here for more than a decade before it was detected, beginning its global spread along the way.

"This is the first time that we've been able to bring together the geographical picture with the timing picture to show with a pretty high degree of certainty where the virus went from Africa, and when," said Michael Worobey, a professor of ecology and evolutionary biology at the University of Arizona in Tucson, who led the research.

In addition to writing a key chapter in the history of the AIDS pandemic, the new insights into the genetic variability of the virus could aid the long-frustrated efforts to develop an effective vaccine.

"What this might tell us is how the virus might evolve molecularly," said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases in Bethesda, Md. "That might have an impact on the virus that you put in your vaccines."

It had been established that HIV originally jumped from chimpanzees to humans, possibly when hunters in Africa butchered animals infected with a version of the virus. In 2000, researchers found that the virus began to proliferate in Africans around 1930.

But the exact route the virus took as it crept out of Africa before exploding in other parts of the world has been the subject of debate and speculation.

Worobey extracted HIV from blood samples of the earliest Haitian AIDS patients in the United States and analyzed the viral genes. The researchers then compared their findings to molecular sequences of samples of the strain of HIV that is primarily responsible for the global spread of the pandemic outside of Africa. (Other strains, however, account for far more AIDS cases worldwide today.) The researchers used specimens from 19 countries, including the United States, Canada, Haiti and several in Europe, Latin America and parts of Asia, focusing on the diversity of mutations in two key genes.

Based on the analysis, the researchers reported last week in the Proceedings of the National Academy of Sciences that there is a 99.8 percent certainty that the virus moved first from Africa to Haiti and then leapt to the United States.

Because the mutations accumulate at a predictable rate, the researchers were able to use them as a kind of molecular clock to calculate when the virus arrived in each location. The results indicated that it appeared in Haiti in about 1966 and the United States in about 1969, before traveling to Europe, Canada, Latin America, Australia, Japan and other parts of the world.

"That doesn't mean the virus traveled directly from the U.S. independently to each of those other countries," Worobey said. "It might have gone from the U.S. to Germany and Germany to Estonia and so forth. But once it got into the U.S. population, Americans traveling to other countries and people traveling to America allowed it to flow to other countries. The United States probably served as a worldwide hub for this spread."

The virus may have made its initial jump from Africa to Haiti after the Democratic Republic of Congo won its independence in 1960 and many Haitians sought work there, Worobey speculated.

"There were a lot of Haitian teachers in the Congo. One of those workers may have brought the ancestral subtype B virus back to Haiti. We can't prove that, but it seems plausible. The timing is consistent," he said.