Aids virus affecting people for more than 100 years, reveals study

THE Aids virus has been affecting people for about 100 years, decades longer than scientists had thought, a new study said yesterday.

Genetic analysis pushes the estimated origin of HIV back to between 1884 and 1924, with a focused estimate at 1908.

Previously, scientists had estimated the origin at about 1930. Aids was not recognised formally until 1981 when it got the attention of public health officials in the US.

The new result is “not a monumental shift, but it means the virus was circulating under our radar even longer than we knew”, said Professor Michael Worobey of the University of Arizona, an author of the new work.

The results appear in today’s issue of the journal Nature.

Scientists say HIV descended from a chimpanzee virus that jumped to humans in Africa, probably when people butchered chimps. Many were probably infected that way, but so few other people caught the virus that it failed to get a foothold, researchers say.

But the growth of African cities may have changed that by putting people close together and promoting prostitution, Professor Worobey suggested. “Cities are kind of ideal for a virus like HIV”, providing more chances for infected people to pass on the virus, he said.

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”, he said.

Key to the work was the discovery of an HIV sample taken from a woman in Kinshasa in 1960. It was only the second such sample found from before 1976; the other was from 1959, also from Kinshasa.

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. That allows scientists to “run the clock backward” by calculating how long it would take for various strains to become as different as they are observed to be. That would indicate when they both sprang from their most recent common ancestor.

The work 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. Researchers got various answers under various approaches for when that ancestor virus appeared, but the 1884-to-1924 bracket is probably the most reliable, he said.