Global warming will release dormant germs from ice?

Dec 4, 2006 14:31 GMT  ·  By

An international team found flu viruses in the ice of Siberian lakes, fact that warns about the possibility that global warming may release germs locked in glaciers for decades or even centuries.

Long-dormant strains of viruses, bacteria, and fungi, wrapped in ice in remote zones, may be released by melting ice and migratory birds. "Our hypothesis is that influenza can survive in ice over the winter and re-infect birds as they come back in spring," says Dr. Scott Rogers of Bowling Green State University, Ohio, US.

Many of these glaciers are on the flight pathways of migratory birds, which will lay virus onto the ice with their droppings, where it freezes. "We've found viral RNA in the ice in Siberia, and it's along the major flight paths of migrating waterfowl, whose pathways take them to North America, Asia and Australia, and interconnect with other migratory paths to Europe and Africa," explains Rogers. Frozen lakes may act as "melting pots" for flu viruses, permitting viruses from one year to mix with those from previous years. Germs preserved in ice over long periods of time and released decades later may find humans no longer immune to them. E.g., survivors of the Spanish flu pandemics of 1918 had immunity to that strain - called H1N1 (image)- but that immunity vanished with them, meaning a revival of that virus could be epidemic.

The American-Russian-Israeli team sought pieces of genetic material from flu viruses in ice taken from three north-east Siberian lakes that freeze and thaw each year and where migratory water fowl stop. In the most bird-visited lake, they discovered fragments of RNA encoding haemagglutinin, the protein that allows influenza viruses to bind to the cells they attack.

This is the first time viral RNA from a human infecting strain was found in ice. The team collected water and froze it in the summer, and in the winter, they cut ice samples with a sterilized saw. The haemagglutinin of the ice-discovered H1 virus is closest to a strain active from 1933-38 and again in the '60s. "These certain strains come back from time to time," said Rogers. "People have studied the biotic (transmission) cycle over the years, but it's been clear that some of the virus should be mutating faster. But some of the strains come back, and they haven't mutated."

"We're at a really basic level right now," Rogers adds, explaining that the researchers still can not say if the frozen viruses are still alive. "We think they can survive a long time in ice, tomato mosaic virus has been found in 140,000-year-old ice in Greenland." said Rogers. "The idea is plausible", says Jonathan Stoye, head of virology at the UK National Institute for Medical Research in London. "The important issue is whether or not there's infectious virus in the ice, rather than just fragments of RNA."

The team thinks that the World Health Organization - which annually considers what flu strains are emerging in the hope of tailoring vaccines accordingly - should use this information to help develop inoculation strategies for the future. "We thought that by looking at what's melting and what birds are picking up better guesses for the next year might be possible." said Rogers.

The viruses may have survived depending largely on how they were frozen. Water-frozen viruses are likely to be inactivated by the water's relatively low pH. "But if the virus was in droppings, which presumably is how it was deposited, there seems to be no reason why it should not freeze and survive at low temperatures." added Rogers.

Viruses are more likely to survive if they freeze and thaw only once, as the freeze-thaw process kills more than 90% of the viruses. "The kind of consistently freezing conditions you would expect to need to preserve a virus are unlikely to be found in places that are heavily populated with people," said Karen Lacourciere, program officer for influenza at the US National Institute of Allergy and Infectious Diseases.

The first ancient virus discovered in ice was found in 1999 in the Arctic by Rogers and a team from Syracuse University in New York, US. Another team has revived a 32,000 years old dormant bacterium from a frozen pond in Alaska, while a 250-million-year-old bacterium from salt has also been revived.

The scientists are going to expand their research to Canadian, Wyoming (US), Himalaya and Alaskan lakes, after they have already done researches in Greenland, Antarctica and Siberia.