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Thursday, 11 May, 2000, 17:54 GMT 18:54 UK
Seals pose influenza threat
BBC Wild
The seals could "store" the virus
By BBC News Online's Damian Carrington

The influenza B virus has been found in animals for the first time, with the scientists who made the discovery saying it "may pose a direct threat to humans".

The virus was found in up to 2% of seals on the Dutch coast in 1999 and was identical to the virus prevalent in humans in the Netherlands in 1995.

The B virus is not a mild virus - it is dangerous.

Albert Osterhaus

The virus is being harboured unchanged by the seal. And because the human immune response to a particular virus strain fades with time, any later reintroduction of that strain might have a serious impact.

Team leader Professor Albert Osterhaus, from the National Influenza Centre at Erasmus University, told BBC News Online: "My message is that if you find these animals at the beach, just don't touch them. Stay away and wait until a professional comes."

Reservoir seals

There are three types of influenza virus, A, B and C. The A type is harboured in birds and also infects humans. It has been responsible for the last century's major pandemics.

Until now, the B type was thought to be an exclusively human disease.

Grey seal pup
Grey seal were also studied
Dr Alan Hay, Head of the WHO Influenza Centre at the UK National Institute for Medical Research said: "The idea of an animal reservoir would be controversial."

Animal reservoirs are important because they harbour the viruses, allowing infections to resurface after quiet periods. They can also allow viruses to mutate and become more virulent.

No kisses

This had not happened in the Dutch seals - the virus had remained the same for four years. But the human virus, and the human immune response, changes every year. If the old virus resurfaced at a later date, it could be much more potent than the annual human virus because, in effect, people's bodies had "forgotten" it.

Professor Albert Osterhaus said: "The virus is in an evolutionary stasis, apparently for five years. If this continued for another five or ten years and then it came back into the human population, then the immunity may have dwindled. That's an interesting thing to realise.

"The B virus is not a mild virus. For example, in the Netherlands more people die of flu than in road accidents and that is caused by B viruses. These are dangerous viruses."

However, Dr Hay noted: "One of the major requirements for infection is close contact - and we don't go around kissing seals, do we?"

Caught by cough

In 1999, the Dutch scientists found 12 seal pups with breathing difficulties, stranded on the coast. They took them to the Seal Rehabilitation and Research Centre in Pieterburen and tested them for viruses.

To their surprise they found influenza B and they are confident they have ruled out the possibility of laboratory contamination.

They then tested 971 stored blood samples, taken from seals admitted to the centre since the 1980s. Before 1995, none of the 580 samples contained influenza B. But from 1995 onwards 2% of the 391 samples showed evidence of the virus.

This data, and the fact that the virus was a 1995 strain, shows that the seals caught a human virus in 1995.

Professor Osterhaus thought it unlikely the infection occurred in a rehabilitation centre as workers wear protective clothes and take other precautions: "I think its much more likely that someone found a seal stranded on a beach and accidentally coughed into its face."

The research is published in the journal Science.

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See also:

29 Oct 99 | Health
Pig flu sparks epidemic fears
02 Dec 99 | Sci/Tech
Predicting the flu of the future
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08 Apr 99 | Medical notes
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