Wednesday, September 1, 1999 Published at 17:48 GMT 18:48 UK
Virus found in Arctic ice
Greenland, where viruses can survive for centuries.
By Environment Correspondent Alex Kirby
The discovery of the first virus preserved in the Arctic ice has prompted a warning that there may be more, and that warm weather may release them to start epidemics.
The virus, a tomato mosaic tobamovirus (ToMV) was found by a team of American researchers.
The discovery, reported in the magazine New Scientist, suggests that other viruses, possibly including 'flu, smallpox and polio, may also have survived in the ice.
One of the team, Tom Starmer, of Syracuse University, said: "We don't know the survival rate, or how often they get back into the environment. But it certainly is possible."
His colleagues, Scott Rogers and John Castello, of the State University of New York in Syracuse, had earlier found ToMV, a common plant pathogen, in clouds and fog.
It can survive in such environments because it belongs to a family with very tough protein coats.
So they examined four ice cores, from three sites in Greenland, containing ice between 500 and 140,000 years old.
To prevent contamination they first disinfected the outside of each core using ultraviolet light, and then searched the inner core for RNA from the tomato pathogen using the polymerase chain reaction (PCR).
As they had suspected, the RNA was present - and sequencing revealed 15 strains of the virus.
The PCR method destroys organisms as it amplifies their genetic material, so the team is not certain the viruses had retained the protein coats that help them to invade cells.
But John Castello says they probably needed the coats to survive for centuries in the ice.
The team says a brief rise in temperature could let loose any viruses and cause disease.
Scott Rogers told BBC News Online: "We think micro-organisms are being released constantly, during periods of warming, and when glaciers calve".
"It's very possible that more frequent and intense warming, caused by climate change, will lead to more releases."
He has found that caliciviruses, which can cause diarrhoea, emerge from time to time from the sea to cause new infections.
Identical caliciviruses have appeared at 20-year intervals on opposite sides of the USA, he says, and could have spent years in the polar ice before re-emerging.
"How did these viruses stay the same for so long? Where have they been hanging out?"
Mystery of viral evolution
John Castello says the discovery could mean that modern viruses might be a mixture of highly evolved ones and others that have been frozen for centuries.
"Perhaps they are actually ancient populations that have been recycled over and over again. How can you do evolutionary studies if that's true?"
He and his colleagues now plan to use other techniques to see whether viruses in other cores are still viable.
They will look not only at Arctic cores, but also at ice from the Antarctic that is up to 400,000 years old.