Image caption Harbour seals in New England were found to be infected with the new strain

Scientists in the United States have identified a new strain of influenza in harbour seals that could potentially impact human and animal health.

The H3N8 flu has been associated with the deaths of harbour seals in New England last year.

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.

We need to be very nimble in our ability to identify and understand the potential risks posed by new viruses from unexpected source Dr Anne Moscona, Weill Cornell Medical College

Researchers were puzzled by the mysterious deaths from pneumonia of 162 harbour seals around the coast of New England last year.

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.

One of authors of the research paper is Prof Ian Lipkin, from Columbia University in the US. He is a celebrated virus hunter who in the past has helped identify West Nile virus and Severe Acute Respiratory Syndrome (SARS). He told the BBC that finding this flu virus in seals was an interesting "new jump".

"It's something that's been circulating for a while in birds, but we've not had this sort of die off relating to this virus in the past. As we've looked at it in some detail, 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."

Media playback is unsupported on your device Media caption Dr Ian Lipkin: "We found that the virus had adapted"

Cause for concern

As well as mutating to live in both mammals 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.

Dr Anne Moscona of Weill Cornell Medical College in New York City edited the report and says that the new virus is a worry.

"There is a concern that we have a new mammalian-transmissible virus to which humans haven't yet been exposed. It's a combination we haven't seen in disease before."

One of the big concerns for Prof Lipkin is that seals are acting as a mixing vessel for viruses in a way that has previously happened in pigs.

"What was interesting about this is the seals are acting as an intermediary - they have receptors for both bird flu viruses and well as mammalian flu viruses, so you have a host in which this virus can adapt, evolve and become more mammalian in phenotype and more capable of causing disease in mammals.

"That's when we really need to be concerned that it's going to be spreading into humans."

The scientists who examined the dead seals had not suspected that an influenza virus was the cause of the die off. The finding surprised them and they argue that it highlights the fact that a pandemic influenza could emerge from a number of different routes.

"Flu could emerge from anywhere," said Dr Moscona, "and our readiness has to be much better than we previously realised. We need to be very nimble in our ability to identify and understand the potential risks posed by new viruses from unexpected sources."

The report is published in the journal of the American Society for Microbiology.