Examinations of ice cores up to 140,000 years old from Greenland have yielded a virus that attacks plants. Now, some scientists think, strains of influenza, smallpox and polio from millennia ago could be waiting to create fresh epidemics when they thaw. "We don't know the [viruses'] survival rate, or how often they get back to the environment," Tom Starmer, of Syracuse University in New York, told New Scientist magazine. "But it certainly is possible."
Scott Rogers, a colleague of Professor Starmer, said global warming could lead to a significant threat as the viruses were exposed again to the world. Calvin Smith, a virologist at Oregon State University, said: "If you've got these things lying in the ice for a thousand years or more and their usual host has not had to deal with them, this may be a source of epidemics."
The New York team established that RNA, the genetic material of the virus, was present by using a test which "amplifies" even small amounts of genetic material.
But David Onions, a Glasgow University virologist, doubted long-buried viruses would still retain their vitality and that they would be any more dangerous than present-day ones. "Some virus groups ... could survive long periods as structures in ice. But whether they would be infectious after that is another question. It's not surprising that they could amplify the genetic material. But any danger would be extremely remote."
Viruses interact with their hosts and almost all the variants of any virus are reckoned to exist at any time; the factor which changes is the human immune response. "It's unlikely there's anything there that poses a risk," said Professor Onions. "Then again, in science you never say never."
Dr Smith reckons one sort of virus, the calcivirus, which can cause diarrhoea, periodically spends decades trapped in polar ice before re-emerging. He has already shown that strains of calcivirus periodically disappear and then re-emerge from the oceans.
Last year a team tried to find frozen copies of the influenza virus which caused a pandemic in 1917 in the bodies of miners buried on an island off Norway. But they had decomposed, forestalling the work. The American team which has done the latest work in the Arctic now intends to examine ice cores from the Antarctic.Reuse content