HIV's ancestor much older than previously thought

Washington, Sep 17 (ANI): A recent study has found that HIV's ancestor that infect monkeys is thousand of years older than previously thought which implies that HIV is not likely to stop killing humans anytime soon.

The University of Arizona and Tulane University researchers stated that simian immunodeficiency virus, unlike HIV, does not cause AIDS in most of its primate hosts.

If it took thousands of years for SIV to evolve into a primarily non-lethal state, it would likely take a very long time for HIV to naturally follow the same trajectory.

The simian immunodeficiency virus, or SIV, is at least 32,000 to 75,000 years old, and likely much older, according to a genetic analysis of unique SIV strains found in monkeys on Bioko Island, a former peninsula.

"HIV is the odd man out because, by and large, all the other species of immunodeficiency viruses impose a much lower mortality on their host species," said Michael Worobey of Tulane University.

"So, if SIV entered the picture relatively recently as was previously thought, we would think it achieved a much lower virulence over a short timescale," said Worobey.

"But our findings suggest the opposite. If HIV is going to evolve to lower virulence, it is unlikely to happen anytime soon," he said.

The study also raises a question about the origin of HIV, which scientists believe evolved from SIV.

"Something happened in the 20th century to change this relatively benign monkey virus into something that was much more potent and could start the epidemic," said Marx.

"We now have this little island that is revealing clues about SIV, and it says, 'It's old.' Now we know that humans were almost certainly exposed to SIV for a long time, probably hundreds of thousands of years," said Worobey.

Marx tested his theory that SIV had ancient origins by seeking out DNA samples from monkey populations that had been isolated for thousands of years. His research team collected bush meat samples from Bioko Drills (Mandrillus leucophaeus).

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 modelling 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, said Marx.

The findings appeared in the journal Science. (ANI)