The discovery of an infectious giant virus that had been entombed in Siberian permafrost for 30,000 years has led scientists to warn of other disease-causing viruses and microbes that may escape from the frozen earth once it has melted.

Scientists in France and Russia discovered the giant virus in samples of frozen earth taken from the far north-east of Russia. Tests in the laboratory showed that the virus was capable of infecting amoeba - single-celled micro-organisms - although it cannot infect multi-cellular animals and humans.

The virus is much larger than usual viruses and is so big it can be seen under ordinary optical microscopes. It is similar to two other known types of giant viruses, but its genetic material is different enough for it to be classified as belonging to a distinct species, Pithovirus sibericum, within a totally new group of viruses.

Researchers at the Russian Academy of Sciences in Pushchino and France's National Centre for Scientific Research (CNRS) in Marseille said that the virus was buried 30 metres (100 feet) below ground in the Chukotka autonomous region of Siberia and must have been frozen for at least 30,000 years before it burst back into life when offered the "bait" of living amoeba in a laboratory experiment.


"This study demonstrates that viruses can survive in permafrost - the permanently frozen layer of soil found in the Arctic regions - almost over geological time periods, that is for more than 30,000 years," a CNRS spokeswoman said.

"These findings have important implications in terms of public-health risks related to the exploitation of mining and energy resources in circumpolar regions, which may arise as a result of global warming," she said.

"The re-emergence of viruses considered eradicated, such as smallpox, whose replication process is similar to Pithovirus, is no longer the domain of science fiction. The probability of this type of scenario needs to be estimated realistically," she added.

The virus was last active at a time when mammoths roamed the Siberian steppes and the last Neanderthals were on the verge of extinction in the Iberian peninsula. The virus particle survived by being encased in a protective protein coat, measuring 1.5 thousandths of a millimetre long.

The giant Pithovirus replicates inside the part of the amoeba that lies outside its cell's nucleus. This form of cytoplasmic replication is similar to the way large DNA virus replicate, including the Variola virus which causes smallpox.

Chantal Abergel, a CNRS scientist who helped to carry out the work, said that there may be other viruses frozen in the permafrost layers of the Arctic that could become active again when disturbed either by drilling or by the melting of the frozen ground.

"It may be possible to find other viruses that may be able to infect other kinds of host organisms other than amoeba. We need really to study the DNA of permafrost samples to directly study the kind of microbes that exist there," Dr Abergel said.

"We don't know what is there in the permafrost but we need to be careful when prospecting for oil, minerals or whatever we are looking for. The message should be 'think before you drill'. And if someone does get sick on the spot, the last thing is to send them back immediately to New York or London or any other city where a virus infection can spread," she said.

The Pithovirus, which is named after the Greek word to describe the amphora handed by the gods to Pandora, was found by drilling horizontally half way down a 60 metre cliff formed by the River Anyuy in the Kolyma region of Siberia.

The lead researchers in Russia were Lyubov Shmakova and Elizaveta Rivkina of the Institute of Physicochemical and Biological Problems in Soil Science in Pushchino.

- UK Independent