A widely-held theory of how Aids arrived in the west - as an infection carried by a promiscuous gay Canadian flight attendant - is overturned by a study published today that shows the American epidemic was born two decades earlier, during the sixties.

The western epidemic was first recognised in 1981 with an outbreak of a rare form of cancer among gay men in New York and California, along with a rash of seemingly healthy young men presenting with fevers, flu-like symptoms, and a rare pneumonia.

In his book, And the Band Played On, American journalist Randy Shilts identified "Patient Zero" as a gay Canadian flight attendant named Gaëtan Dugas, who died in 1984 after spreading the virus out of Africa to a number of homosexual partners in the west. advertisement

This theory, which made Gaetan a notorious benchmark for the spread of an epidemic that now affects 40 million people worldwide, is overturned today by a study in the Proceedings of the National Academy of Sciences which concludes the virus was incubating in the American population for much longer.

The path the strain took from its central African origins has long been debated, but the new study suggest that the simplest explanation is that the virus entered Haiti first, and then was transmitted to the United States, in or around 1969. Then HIV-1 circulated in the US for around a dozen years before the formal recognition of AIDS by doctors in 1981.

"Our results show that the strain of virus that spawned the U.S. AIDS epidemic probably arrived in or around 1969. That is earlier than a lot of people had imagined," said senior author Michael Worobey of the University of Arizona, Tuscon.

The research is the first to definitively pinpoint when and from where HIV-1 entered the United States. "Patient Zero", ever since Shilts's book, has taken on an importance greater than perhaps deserved," Worobey told the Daily Telegraph.

"He was originally designated "patient O" as in "OUT of California" but that evolved into Patient Zero. He was certainly an early victim, and one linked to many other early cases," he said, though he added there is "no reason to mark him out as the likely index case for the US epidemic."

In fact "Haiti was the stepping stone the virus took when it left central Africa," said Worobey. "Once the virus got to the US then it just moved explosively around the world." The strain that migrated to America in 1969 is the first human immunodeficiency virus (HIV) discovered and the dominant strain of the AIDS virus in most countries outside sub-Saharan Africa. Almost all the viruses in those countries descended from the one that emerged from Haiti, he said.

The team, which includes Andrew Rambaut at the University of Edinburgh, based on the conclusion on genetic analyses.

The team analysed blood from five of the first Aids patients identified in the US, all of whom were recent immigrants from Haiti. The team also analysed genetic sequences from another 117 AIDS patients from around the world. The team used statistical methods to investigate all the family trees that were consistent with the genetic data. For the hypothesis that, from Africa, HIV went to the US first, the probability is 0.003 percent -- virtually nil. For the hypothesis that HIV went from Africa first to Haiti in around 1966 and then on to the US, the probability is 99.8 percent, almost 100 percent.

"I am not sure the Gaetan idea is given much credence these days - our paper really more generally rules out the idea of specific individuals causing these epidemics," said Rambaut. "It is not the entry into the USA that is relevant here but the crossing of the virus into US risk groups."

Learning more about the genetic make-up of the various strains of HIV could help vaccine development, Worobey added. "The main challenge of developing a vaccine against HIV is its tremendous genetic diversity," he said. Knowing the gamut of diversity could be important.

© Copyright of Telegraph Media Group Limited 2007. Reprinted from The Telegraph of Monday, October 29, 2007.