View Full Version : HIV's complex family history unravelled

13th June 2003, 02:55 AM
James Randerson

The parent of the HIV virus was the product of a union between two monkey viruses, genetic detective work has revealed.

This genetic mixing occurred in a chimpanzee at least one million years ago, although it is thought that HIV did not cross into humans until the 1930s. But the discovery has prompted researchers to speculate that chimps may still harbour other HIV-like viruses that could jump to humans.

The complex genetic history of HIV viruses came to light when researchers tried to construct family trees connecting the different genomic elements in the viruses. If the viruses shared the same genetic history, you would expect these trees to match up, but they did not.

"Trees stemming from different parts of the genome put the virus in different places," says Paul Sharp, an expert on HIV evolution at the University of Nottingham, UK.

The Simian Immunodeficiency Virus (SIV) found in chimps, and which led to the most widespread human strain HIV-1, has elements of two other SIVs. These strains are found in red-capped mangabeys and greater spot-nosed monkeys, but it was not clear which of the SIV strains were the originals.

Gene swapping

Now Sharp and his team have constructed numerous family trees based on different assumptions about the order in which genetic mutations occurred during the evolution of the viruses. These indicate that the chimp SIV is the product of gene swapping between the monkey viruses.

Chimps are known to hunt a variety of monkeys and probably became infected with both the monkey SIV strains by eating their flesh. They could then swap genetic material and produce the virus that eventually crossed into humans.

Sharp believes the gene mixing happened at least a million years ago because the chimp SIV virus is present in two sub-species of chimpanzee that diverged at that time. They probably inherited the virus from their common ancestor.

The finding raises the possibility that chimps are infected with other combination viruses that could be dangerous to humans. "Clearly, with humans continuing to hunt chimps, there could be the chance for the next jump," says Sharp.

Journal reference: Science (vol 300, p 1713)

13th June 2003, 03:26 AM

I admit to being pretty ignorent in the field of genetics, but something about this theory seems a little tenuous to me, do we really know that much about gene swapping/mutation to say that this is what happened? or can we only really say that this would fit current understanding?

Interesting though that they have traced human HIV back to the 30's. The scientific basis for this does seem a lot more solid, though as this can only be based on blood samples etc, it does make you wonder how much further back it might go?