But Castello says they probably needed their coats to survive for hundreds of years in the ice. The team says that a brief rise in temperature could unleash the entombed viruses. If released, they could cause outbreaks of disease. He has already found evidence that caliciviruses, which can cause diarrhoea, periodically re-emerge from the oceans, causing new infections. The findings may answer some puzzling questions, Smith adds.
Viruses evolve fast, continually changing their protein coats.
Yet identical caliciviruses have appeared at 20-year intervals on opposite sides of the US, he says. He thinks they might have spent years trapped in polar ice before re-emerging to strike again. Such exchanges could put a spanner in the works of viral evolution studies. Castello says that instead of representing the endpoint of steady evolution, modern populations of viruses might be a complex mishmash of highly evolved ones and others that have taken a holiday from evolution in cold storage. The New York team plans to use other techniques to find out if viruses in other cores are still viable.