| Updated at: 1508 PST, Monday, September 20, 2010|
LOS ANGELES: A precursor to the human immunodeficiency virus (HIV) has been circulating for at least 32,000 years - much longer than scientists previously thought, new research from the University of Arizona shows.
The discovery raises an important question for scientists: If the simian immunodeficiency virus (SIV) was circulating in monkeys for thousands of years, what changed that made it suddenly cross into humans in the 20th century? Scientists believe HIV evolved from SIV.
Also of note, the findings suggest it could take many more generations for HIV to mutate into a less lethal form.
"Clearly the virus had been kicking around in primates for a long time before it crossed over," Michael Worobey, an associate professor of ecology and evolutionary biology at the UA, said in an interview Friday. "This is more of a good news story. It's not so good that the virus jumped into humans. Yet there was a time when it wasn't able to spread into humans. So it may be possible to drive the virus back into a situation where it can't spread successfully."
Worobey's research, completed with scientists at Tulane University, appears in the Sept. 17 issue of the journal Science.
Worobey and virologist Preston Marx of Tulane University conducted a genetic analysis of unique SIV strains found in monkeys on Bioko Island, a former peninsula that separated from what is now Cameroon about 10,000 years ago when sea levels rose at the end of the last ice age.
Scientists had previously thought the SIV virus was just a few hundred to 2,000 years old. And had that been true, it could also be true the virus became less virulent over a shorter period of time.
But Worobey and Marx's research showed the opposite - if HIV is going to mutate to a lower virulence, it's unlikely to happen anytime soon.
Marx's research team collected bush meat samples from Bioko drills monkeys. The scientists found four different strains of SIV that were highly genetically divergent from those found on the mainland. Worobey then compared DNA sequences of the viruses with the assumption that the island strains evolved in isolation for more than 10,000 years.
The computer modeling showed the rate of mutation to be much slower than previously thought, indicating that the virus is between 32,000 and 75,000 years old. These dates set a new minimum age for SIV, although it is likely to be even older, Marx told UA News.
"HIV is not tremendously contagious compared to flu and other viruses, so anything you do to disrupt the channels, whether it's condom use or antiretrovirals or circumcision, has a huge effect," Worobey said. "You put those things together in a really organized and aggressive way and we could knock it (HIV) down to low levels."
Worobey plans to advance his research by studying virus evolution in flu viruses, among other things.
He believes a key factor in HIV spreading among humans was the formation of large cities and transportation networks in Africa in the early 20th century.
"It's good to bear in mind that animals, particularly in this region, do carry viruses and other pathogens that can cross into people. It's a tricky thing. It's a source of food for people so you don't want to say it's bad to eat these animals, but it's good to know the possibility," said Worobey.
"The second thing is the idea of using evolutionary understanding to realize HIV has one weak spot of being poorly transmitted.
"There's a huge amount we can do before a (HIV) vaccine to control the epidemic. It comes down to preventing transmission in the most efficient ways. Sometimes people get overwhelmed and think because we haven't been very successful to date we're not going to be until we get a vaccine. I don't think that's true."