The virus could therefore very well be transmitted to humans

Eric Delaporte

It has been dubbed SIVgsn by the researchers from the Research Institute for Development (IRD) in Montpellier, France, who discovered it.

It is similar to HIV-1, a strain that causes Aids in humans, and to a form of the virus found in chimpanzees.

The IRD's Eric Delaporte said it might help to explain the connection between SIV and HIV.

Chimpanzees eat greater spot-nose monkeys, and the research suggests that this is how they originally became infected with SIV.

However, the meat of the smaller monkey is also sought after by humans.

It might be that HIV began when some individuals became infected with SIVgsn - possibly by cutting themselves while preparing infected meat.

Crucial gene

The French researchers found that SIVgsn contains a particular gene which controls the way it reproduces itself, and which gives it the potential to jump from monkeys to man.

Dr Delaporte said: "The virus could therefore very well be transmitted to humans, or other monkeys, to create either new strains of divergent HIV viruses, or it could combine with existing viruses thus complicating the virological specter of HIV."

He said the next step would be to develop tests to screen all simian viruses to evaluate the risk to people.

Preventing spread

John Godwin, head of policy and advocacy, National AIDS Trust, said: "We have known for some years now that in all likelihood HIV jumped the species barrier between monkeys and humans sometime last century. Since that time over 60 million people have been infected.

"The crucial issues for us now are how to prevent the further spread of HIV in humans and how to develop better treatments and eventually a cure and vaccine.

"If research into the origins of the virus can assist this task than greater knowledge in this area is welcome."

To date, numerous strains of SIV, regrouped into six types, have been identified in around 30 species and sub-species of African monkeys.

Unlike humans, monkeys are natural carriers of the virus without developing Aids.

The research was presented at the ninth Conference on Retroviruses and Opportunistic Infections in Seattle.