Can flu viruses survive winter in frozen lakes?

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Can flu viruses survive winter in frozen lakes?

29 November 2006 NewScientist.com news service Brahic

Evidence of flu viruses frozen in Siberian lakes has prompted

researchers to examine the possibility that global warming may release

microbes locked in glaciers for decades or even centuries.

" Our hypothesis is that influenza can survive in ice over the winter

and re-infect birds as they come back in spring, " says of

Bowling Green State University, Ohio, US. He believes the frozen lakes

act as " melting pots " for flu viruses, allowing viruses from one year

to mix with those from previous years.

has spent decades searching ice for micro-organisms. He teamed

up with Dany Shoham at Bar-Ilan University, Israel, and

Gilichinsky, at the Russian Academy of Sciences, to obtain samples of

ice from Siberian lakes where migratory birds stop.

The group looked for pieces of genetic material from flu viruses in

ice taken from three lakes that freeze and thaw each year. In the lake

that is most visited by migratory birds, Lake Park, they found

fragments of RNA coding for haemagglutinin, the surface protein that

allows flu viruses to bind to the cells they infect.

Genetic analysis revealed the haemagglutinin was most closely related

to an H1-strain flu virus that was around in the 1930s and later

resurfaced in the 1960s.

Frozen droppings

' team is now looking at ice cores from glaciers in Alaska and

Wyoming in the US, and from Canada. They intend to study cores from

Siberia and the Himalayas as well.

Many of these glaciers are on the flight paths of migratory birds,

which will deposit virus onto the ice in their droppings, where it

freezes. believes there is a possibility that, as global

warming melts glaciers, they will release the viruses, and perhaps

other microbes such as bacteria and fungi that have otherwise

disappeared from our environment.

The idea is plausible, says Stoye, head of virology at the UK

National Institute for Medical Research in London. But he adds: " The

important issue is whether or not there's infectious virus " in the

ice, rather than just fragments of RNA. is collaborating with

researchers at sufficiently biosecure labs to try and answer this

question.

Freeze-thaw process

Stoye says that whether or not the viruses are infectious depends

largely on how the virus was frozen. Viruses frozen in water 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. "

He adds that viruses are more likely to survive in a frozen state if

they freeze and thaw only once, as the freeze-thaw process kills at

least 90% of virus each time.

Lacourciere, programme officer for influenza at the US National

Institute of Allergy and Infectious Diseases, which funded '

research, thinks the ice cores are unlikely to contain viruses shed by

humans.

" 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, " she says. She also notes the samples

has looked at so far are taken from the middle of lakes that

are almost exclusively visited by birds.

The first ancient virus discovered frozen in ice was found in 1999 in

the Arctic by and colleagues at Syracuse University in New

York, US, (see Back from the dead). Other researchers have revived a

bacterium in that sat dormant in a frozen pond in Alaska for 32,000

years (see Ice age bacteria brought back to life). And a

250-million-year-old bacterium stored in salt has also been brought

back to life

Journal reference: Journal of Virology (vol 80, p 1229).

http://www.newscientist.com/article/dn10676-can-flu-viruses-survive-winter-in-fr\

ozen-lakes.html