Some species of primate have been infected with HIV-like viruses for millions of years longer than previously thought, research suggests.

Some species of primate have been infected with HIV-like viruses for millions of years longer than previously thought, research suggests.

The new findings could help reveal why non-human primates do not develop Aids and lead to new treatments for the disease, scientists claim.

Scientists had traditionally believed that lentiviruses, the family of virus including HIV, started infecting primates only in the past million years.

But a team of scientists led by Stanford University School of Medicine, California, discovered that lentiviruses may have been present in some primates for 15 million years and possibly as long as 85 million years.

The team discovered that the grey mouse lemur, found in Madagascar, has genes in its DNA matching the modern lentivirus.

Ancestors of the lemur colonised Madagascar 75 million years ago and the island separated from mainland Africa 14 million years ago, enabling lemurs to evolve separately from other primates.

The presence of the lentivirus in the grey lemur's DNA suggests lentivirus has evolved with the lemurs for at least 14 million years and may help explain why primates do not go on to develop Aids when they are infected with a simian version of HIV.

Scientists on the project hope that the findings will help reveal how ancient immune defences have evolved to fight retroviruses.

This could, in turn, have implications for vaccines and treatments for people with HIV.

Professor Beatrice Hahn, from the University of Alabama, said the findings could prove vitally important.

She explained: "The research raises a bunch of interesting questions about how mammals have dealt with these types of viruses over a minimum of 14 million years, what kind of defences they have developed and why some mammal species have lost these type of viruses.

"This is molecular archaeology; there may be a lot of gold in these sequences that hasn't been mined yet."

The study was published in the Proceedings of the National Academy of Sciences.