Bette Korber, who keeps a database of HIV genetic information at the lab, calculated HIV's family tree by looking at the rate the virus mutates over time. Dr. Korber assumed these genetic changes happen at a constant rate and used a supercomputer to clock the mutations back through time to a common ancestor.
Dr. Korber estimates that the current pandemic goes back to one or a small group of infected humans around 1930, though this ancestor virus could have emerged as early as 1910 or as late as 1950. From this single source, this researcher suggests, came the virus that now infects roughly 40 million people all over the world.
"This offers a small piece in a larger puzzle concerning the origins of HIV", Dr. Bette Korber stated. Her findings were released at a scientific conference in San Francisco. Experts believe that HIV's ancestor is a virus that ordinarily infects chimpanzees. Somehow it spread to people, perhaps through a bite or hunting mishap, in west equatorial Africa.
Just when this happened, though, is still a mystery, according to Dr. Korber. The leap from chimp to man could have been around 1930. Or it may have occurred much earlier and the virus stayed within a small group of humans. The work challenges a theory that AIDS actually began in the 1950s, when HIV was accidentally mixed with the polio vaccine.
In last year's book "The River", Edward Hooper theorises that HIV contaminated batches of the vaccine that were grown in chimp tissue. This then spread when the vaccine was tested in the Belgian Congo. Dr. Korber however claimed this is highly unlikely, since it would require the introduction of at least 10 genetically separate strains of the virus into the vaccine from different chimps.
Dr. Steven Wolinsky of Northwestern University called Dr. Korber's project "a computational tour de force". Dr. Korber based her work on the genetic codes of 160 different copies of the AIDS virus. She analysed them on a Los Alamos supercomputer, called Nirvana, which can perform 1 trillion computations per second.
The earliest existing sample of HIV was found in a blood specimen obtained in Leopoldville, now Kinshasa, in 1959.