Researchers said on Wednesday the deadly AIDS virus has been circulating among humans for nearly a century “” decades longer than scientists had first thought.
Genetic analysis pushes the estimated origin of HIV back to between 1884 and 1924, with a more focused estimate at 1908. The disease is thought to have originated in sub-Saharan Africa, just as modern cities were emerging in the region.
Scientists had originally estimated the origin at around 1930. AIDS wasn’t recognized formally until 1981 when it got the attention of public health officials in the United States.
“The new result is not a monumental shift, but it means the virus was circulating under our radar even longer than we knew,” said Michael Worobey of the University of Arizona, an author of the new work.
The newly calculated dates fall during the rise of cities in Africa, and the researchers suggest urban development may have promoted HIV’s initial establishment and early spread.
HIV is believed to have descended from a chimpanzee virus that jumped to humans in Africa, probably when people butchered chimps. Researchers say many individuals were probably infected that way, but so few other people caught the virus that it failed to get a lasting foothold.
Worobey suggested that the growth of African cities might have changed that by putting lots of people close together and promoting prostitution. “Cities are kind of ideal for a virus like HIV, providing more chances for infected people to pass the virus to others,” he said.
He believes that perhaps a person infected with the AIDS virus in a rural area went to what is now Kinshasa, Congo and “now you’ve got the spark arriving in the tinderbox.”
“I think the picture that has emerged here, is that changes the human population experienced may have opened to the door to the spread of HIV,” he said.
“Previous work on HIV sequencing had been done on frozen samples and there are only so many of those samples available,” Woroby said. The 1959 and 1960 samples are presently the oldest links to the HIV epidemic.
The research is based on 48-year-old gene fragments dug from a wax-embedded lymph node from a woman in Kinshasa in the Democratic Republic of Congo, formerly Zaire.
The 1960 sample is the second-oldest genetic sequence of HIV-1 group M, the main strain of the virus responsible for the AIDS pandemic.
The oldest sequence came from a 1959 blood sample given by a man in Kinshasa, formerly known as Leopoldville.
“Once you have two you can line them up and compare them and once you do that, you see these two sequences are very different. That means the virus had already been there for a long time even by 1959 or 1960,” Worobey said.
Researchers took advantage of the fact that HIV mutates rapidly. So two strains from a common ancestor quickly become less and less alike in their genetic material over time.
The research study used genetic data from the two old HIV samples plus more than 100 modern samples to create a family tree going back to these samples’ last common ancestor.
Worobey said researchers got various answers under various approaches for when that ancestor virus appeared, but the 1884-to-1924 bracket is probably the most reliable.
Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said the new work is clearly an improvement over the previous estimate of around 1930.
Fauci said disease prevention is one of the most important issues in HIV. “For every one person that we put on therapy, two to three people in the developing world get newly infected,” he said. “The only way we are going to get our arms around this is through prevention.”
Professor Paul Clark, a researcher into evolutionary history at the University of Edinburgh, said that while the finding was mainly of “historical interest”, it might provide more clues about how the virus changed over time.
“We can now paint a remarkably detailed picture of the time and place of origin of HIV-1 group M viruses and their early diversification, and thus of the prehistory of the AIDS pandemic.”
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