Scientists in the United States have identified a new strain of flu in seals that could pose a threat to human health.
H3N8, which has been associated with the deaths of seals in New England, is thought to have evolved from a type circulating in birds.
Researchers say the virus may have evolved from a type that had been circulating in birds.
They say the discovery highlights the potential for pandemic flu to emerge from unexpected sources.
researchers were puzzled by the mysterious deaths from pneumonia of 162 harbour seals around the coast of New England last year.
The BBC reports autopsies on five of the marine mammals indicate that they died from a type of H3N8 influenza A virus that is closely related to a strain circulating in North American birds since 2002.
Professor Ian Lipkin of Columbia University told the BBC that the virus has been circulating for a while.
'''We've found there have been mutations in this virus which enable it to bind to both bird receptors for flu as well as mammalian receptors for flu,'' he said.
As well as mutating to live in both animals and birds, the scientists say this flu has evolved to make it more likely to cause severe symptoms. The virus also has the ability to target a protein found in the human respiratory tract.