A new flu virus identified in American harbour seals has the potential to pass to other mammals, including humans, say experts.
The H3N8 strain was discovered following the death of 162 New England harbour seals last year when a post-mortem examination of five of the animals showed they were killed by a flu infection.
Researchers state that the strain is similar to one that has been circulating in birds – H3N8 influenza A virus – but it has adapted to living in mammals.
It's a combination we haven't seen in disease before
Because of the way the strain has evolved scientists fear a potential flu pandemic could emerge from unexpected sources.
The symptoms for humans could be incredibly severe, with the virus specifically having the ability to target a protein found in human lungs.
This could subsequently cause the immune system to go into overdrive and attack itself, as well as leaving lungs vulnerable to pneumonia and bacterial infections.
Dr Anne Moscona, from Weill Cornell Medical College in New York City, who led the researchers, said: "There is a concern that we have a new mammalian-transmissible virus to which humans haven't been exposed yet.
"It's a combination we haven't seen in disease before," she said, adding: "Flu could emerge from anywhere and our readiness has to be much better than we previously realised."
The report is published in the journal of the American Society for Microbiology.
The researcher continued that it was crucial to be alert to these new risks and be "ready to act on them."