Aids precursors SIV millennia older than imagined

Surprisingly old age and low mutation rate raise new questions about the origin of HIV

Mandrills are carriers of SIV © Tulane University, Preston Marx
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The SI virus, which is considered a precursor to the human AIDS virus, is between 32, 000 and 75, 000 years old, thousands of years older than previously thought. This is shown by a now published in "Science" gene analysis infected "Bushmeats" from the African island of Bioko. She also raises the question of why the AIDS epidemic broke out only in the 20th century, although humans must have been in contact with SIV-infected monkeys for millennia.

Simian Immunodeficiency Virus, or SIV for short, is the monkey-derived form of HIV and is widely regarded as the evolutionary progenitor of the AIDS virus in humans. However, in contrast to the human variant, SIV does not cause AIDS in infected animals but is benign. In the course of evolution, monkey virus and the host have become balanced because the pathogen benefits more from the survival of the monkey than from its death. How long this mitigation took was previously unclear, as the age of the SIV could not be determined exactly. A recent study based on a DNA comparison found that it was only a few hundred years old, but remained controversial.

Bushmeat from isolated island

Now, American researchers led by virologist Preston Marx of the Tulane National Primate Research Center have provided new data that completely contradicts this earlier study and provides a whole new picture of the evolution of AIDS viruses. The scientists analyzed DNA samples of the virus from a monkey population on the island of Bioko. More than 10, 000 years ago, a peninsula, bioco and the living on her fauna since then isolated from the African mainland. For DNA analysis, the researchers collected samples of SIV-infected "bushmeat", the meat of Mandrillus Mandrillus leucophaeus native to Bioko. This included four strains of SIV, all of which were highly different from the SIV strains found on the mainland.

Analysis of a bushmeat sample Science / AAAS

SIV at least 32, 000 years old

A comparison of the island and mainland sequences and the reconstruction of the mutation rates shows that mutations appear to be much slower and less common in SIV than previously thought. Calculations using a computer model indicated an age of the SIV virus of at least 32, 000 to 75, 000 years. SIV may even have been created more than a million years ago.

HIV: No decrease in virulence in sight

These results also shed new light on the evolution of the human HI virus. Because if SIV has had thousands of years to develop into its current mild form, then this HIV-related process could take longer than previously hoped for in HIV. "If SIV emerged recently, as previously thought, then it has lost its virulence within a relatively short period of time, " explains Michael Worobey of the University of Arizona. But our results show the opposite. If HIV also develops a lower level of virulence, it probably will not happen very soon. Ad

Island of Bioko - separated from the mainland for 10, 000 years Science / AAAS

Triggers of the HIV epidemic again mysterious

The study also raises questions about the origin of HIV. So far, researchers suspect that the human AIDS virus is derived from the SIV. But if mankind had been in contact with SIV-infected monkeys for thousands of years, why did the AIDS epidemic only start in the 20th century? "It's like finding a fossil piece of virus evolution, " Worobey said. We have this little island that gives us clues to SIV and says, It is old . Now we know that people have almost certainly been exposed to the SIV for a very long time, maybe even hundreds of thousands of years. "

Such a long exposure would normally require that either the human develops some immunity to the virus, or that the human form of the virus gradually diminishes not to kill all its hosts before they can pass on the pathogen. "Something must have happened in the 20th century to turn this relatively benign monkey virus into something that was much more potent and could trigger the epidemic, " explains Marx. "We do not know what this trigger was, but there must have been one."

(University of Arizona / Science, 17.09.2010 - NPO)