An analysis of 25-year-old blood samples pushes the arrival of HIV in the United States back to about 1969, 12 years before AIDS was first described by a doctor in Los Angeles. The virus came from Haiti, which served as a Western Hemisphere toehold for the early stages of the epidemic starting in the mid-1960s, according to the analysis.
“There have been some suggestions that the virus may have been [in the United States] before the mid-1970s,” says Michael Worobey, a microbiologist at the University of Arizona in Tucson, who led the study. “But there’s also been lots of skepticism.” He says that his research provides the first “rigorous” evidence of an earlier U.S. arrival of HIV.
“I’m convinced,” says Beatrice Hahn, a microbiologist at the University of Alabama School of Medicine in Birmingham. “It’s a very nice piece of work that accounts for all the variables.”
The new study fills in a crucial segment of the HIV time line. Earlier research by Hahn and others pointed to 1930 as the date when HIV jumped from West African chimpanzees into people, likely via hunters who butchered the apes. An unrecognized outbreak percolated in Africa for decades before jumping to Haiti, according to that research.
There, the virus evolved into several variants. Most were dead-ends, causing few infections. But the new study, which appears online and in an upcoming Proceedings of the National Academy of Sciences, shows that a variant dubbed subtype B jumped from Haiti to the United States before igniting the current pandemic.
Worobey and his team reached their conclusions by listening to the ticking of HIV’s “molecular clock”—the rate at which the virus accumulates genetic mutations. The pattern of these mutations tells researchers on which branch of an evolutionary tree to place individual viruses. The molecular clock allows the scientists to peer into the past to see when the branches split from a common ancestor.
Over the past several years, researchers have improved their clock-watching skills by building a database of HIV samples from around the world. Worobey tapped into this database to examine the genetics of 109 subtype B viruses.
He then added data from five Haitian AIDS patients treated in Miami in the early 1980s, before HIV had been identified as the cause of the disease. Arthur Pitchenik, the pulmonologist who treated the patients, sensed an important trend and sent blood samples to the Centers for Disease Control and Prevention in Atlanta. “It was a no-brainer to freeze the blood for further study,” he says.
From those samples, Worobey fished out DNA made by the Haitians’ HIV. This evidence added several branches to the existing HIV evolutionary tree and proved that the virus arrived in the United States from Haiti in 1969, give or take a few years, says Worobey.