UN Integrated Regional Information Networks - December 16, 2008

Robert Shafer, a senior author of the research, told IRIN/PlusNews that the discovery "is one of the most important missing links" required for understanding the evolutionary history of HIV-related viruses.

It is widely believed that the two strains of HIV prevalent in humans, HIV-1 and HIV-2, were passed on by primates from Africa, and that these primates have harboured the disease for a million years at the most. But the discovery of a virus related to HIV in the genetic make-up of the tiny grey mouse lemur, found only in Madagascar, has turned these beliefs on their head.

The new findings, published in the Proceedings of the National Academy of Sciences on 1 December, suggest that lentiviruses, the family of viruses to which the HIV-1 and HIV-2 belong, have been present in primates for at least 14 million years. That was the last time the Indian Ocean island of Madagascar was linked to mainland Africa, allowing the disease to pass to lemurs.

"Our discovery means that primate lentiviruses have been present in Madagascar historically and may still be circulating there," Robert Gifford, an infectious disease researcher at the Stanford School of Medicine and lead author of the research, told IRIN/PlusNews. "Since Madagascar has been very isolated throughout evolutionary history, it's not clear how we could have these viruses present both there and in Africa, unless they are in fact many millions of years old."

Scientists now believe that lentiviruses could be at least 50 million years old, and that they may be found in primates throughout the world.

More than 25 million people across the world have died of AIDS-related illnesses since the HI virus was first identified in the United States 27 years ago. Two-thirds of the 33 million people infected with HIV globally live in sub-Saharan Africa, but Madagascar's HIV prevalence rate has so far remained below 1 percent. The prevalence of syphilis and other sexually transmitted diseases, however, suggest that the virus could spread rapidly.

The recent findings from Stanford University are unlikely to radically change the course of research into HIV and AIDS in the short term, but are expected to have a major impact on scientists' broader understanding of the virus.

"If we are ever going to properly understand the relationships between lentiviruses and disease, assess the risk of new epidemics occurring, and harness the body's natural defences to prevent and control HIV infections, we need to establish the proper ecological and evolutionary contexts," Gifford said.

He described the lentivirus material found in the genetic make-up of the grey mouse lemur as "molecular fossils" that show how viruses looked hundreds of thousands or even millions of years ago. This is important, as it helps scientists understand the functions of different genes within a virus, and to assess the limits of virus adaptation and potential vulnerabilities - information that could be used to help develop new ways to prevent and treat infections in humans.

However, Gifford warned that there was still a long road ahead. "Like many things in science, our findings raise as many questions as they provide answers," he said. "But the important thing is that they reveal something new and completely unexpected about the evolutionary relationship between primates and lentiviruses."

See also: Madagascar: The future at stake

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