Genetic evidence clears HIV’s ‘Patient Zero’

AIDS virus already in U.S. when airline steward infected.

The Canadian flight attend a n t wi d e l y b l a med f o r bringing HIV to the United States and triggering an epidemic that has killed nearly 700,000 people has been exonerated by science, more than 30 years after his death.

I n a s t u d y p u b l i s h e d Wednesday in the journal Nature, researchers used new genetic evidence to show that Gaet an Dugas — who has been dubbed “Patient Zero” — could not have been the first person in the United States to have the virus that causes AIDS.

I n s t e a d , t h e re s e a rc h - ers report that Dugas was one of thousands of people who were infected with the human immunodeficiency virus by the late 1970s, years before it was officially recognized by the medical community in 1981.

The genetic analysis also reveals the path taken by the most common strain of the virus after it traveled from the Caribbean to the United States. Upon arriving in New York Cit y around 1970, it circulated and diversified for about five years before being dispersed across the country.

“There really is no question about the geographical direction of movement,” said study leader Michael Worobey, an evolutionary biologist at the University of Arizona in Tucson.

The new evidence comes from two caches of blood serum samples taken from gay men in New York City in 1978 and 1979, and in San Francisco in 1978.

The men were participating in a study of hepatitis B, which was prevalent in the gay community at the time. They weren’t tested for HIV because it wasn’t known to exist back then. However, if any of them had it, there should be evidence in their blood in the form of antibodies, the proteins that our immune systems make to fight an infection.

To see if any of the men in the hepatitis B study had contracted HIV, a different group of researchers analyzed the New York City samples and found that, indeed, 6.6 percent of them contained HIV antibodies. Inspired by this work, Worobey and his team did a similar test for the West Coast samples and discovered HIV antibodies in 3.7 percent of them.

The presence of antibodies can show whether a person has contracted a certain virus, but they can’t provide much detailed information about the virus itself, Worobey said. So his group’s next step was to scour the serum samples for fragments of HIV RNA that may have been circulating in these men’s bloodstreams.

It was a long shot. The samples were decades old, and RNA is generally too fragile to survive for long periods.

But the researchers were persistent. They selected 53 samples for attempted genetic sequenc ing, and they were eventually able to cobble together the full HIV genomes of eight of them — three from San Francisco and five from New York.

Geneticists measure how many mutations occur in the genome in a given time period. Thi s i s how they determined that HIV was first transmitted from a chimpanzee to a single human early in the 20th century in sub-Saharan Africa.

The HIV molecular clock also allows researchers to trace landmark moments in the evolution of the virus. After the initial transmission from chimp to human, the next one came when HIV began c irculating in Kinshasa, the capital of the Democratic Republic of Congo. By 1960, viral samples from the city were tremendously diverse, suggesting HIV had been present in the area for a long time, Worobey said.

Around 1967, a branch of the virus known as HIV-1 group M subtype B took hold in the Caribbean and diversified in Haiti.

The new work makes clear that this strain first jumped from the Caribbean to New York City in 1970 or 1971.

By the late 1970s, when the eight serum samples were collected, the five viral genomes from New York already had a high degree of genetic diversity; the three from San Francisco did not. This indicates HIV probably was in New York much longer than it was in San Francisco.

“New York City acts as a hub from which the virus moved to the West Coast — and eventually to Western Europe, Australia, Japan, South America and other places,” Worobey said.

As part of this study, the authors assembled the complete HIV genome from a serum sample collected from Dugas in 1983, a year before his death at the age of 31.

T h e ge n o me wa s t y p - ic al of HIV strains in the United States at the time, the researchers reported, and there was nothing to indicate that it had set off the epidemic here.

“We found no evidence that Patient Zero was the first person infected by this lineage of HIV-1,” they wrote.