The strain, called H3N8, was found in New England harbor seals. The study authors identified it from a DNA analysis of a virus that was linked to the die-off of 162 New England harbor seals in 2011. The DNA test was done on samples taken during autopsies on 5 of the seals.
Analysis reveals the new strain is able to target a protein in the human respiratory tract.
Anne Moscona, a pediatrician who researches emerging viruses at Weill Cornell Medical College in New York City, edited the study report. She told the press:
"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."
The study authors, from Columbia University and the National Oceanic and Atmospheric Administration Outbreaks, and other research centers, point to the importance of monitoring new strains of flu that start in birds and adapt to infect mammals.
By studying and following the progress of the virus, scientists stand a better chance of being able to predict any emergent strains that could pose a threat to humans and start a new pandemic.
Cause for ConcernThe study authors say we should be concerned about this new strain because it seems to have followed a similar path as the H1N1 "swine flu", that probably came from a reassortment of flu viruses in birds, pigs and humans.
It could be the first sighting of a new group of flu viruses with the potential to persist and move between species, they note.
The new virus appears to be a close relative of a flu strain that has been circulating in birds in North America since 2002, but adapted to living in mammals.
The virus has mutations that are known to make flu viruses more transmissible and cause more severe disease.
For instance, it is able to target a receptor called SAα-2,6, a protein found in the human respiratory tract. Scientists have suggested, that should for instance, the bird flu virus H5N1 adapt to human hosts, then the first step is likely to be a switch to bind to human rather than bird cell receptors.
Need to Consider New RoutesMoscana says these findings raise two reasons to be concerned about H5N8.
First, it is a new virus that infects mammals, and it may cross the species barrier and pose a threat to humans.
Second, the possibility that the threat from bird flu would come through seals has not been widely considered before.
She says pandemic flu can emerge unexpectedly via routes we have not thought of, and we need to be ready for that.
"Flu could emerge from anywhere and our readiness has to be much better than we previously realized," says Moscona.
"We need to be very nimble in our ability to identify and understand the potential risks posed by new viruses emerging from unexpected sources," she adds.
Seal Deaths Not UnusualIt is not unusual for large numbers of seals to die from flu-virus infections.
Last year, a report in the Boston Globe highlighted how the past few decades have seen notable seal die-offs in the Northeast of the United States, including a rash of flu deaths in 1979 and 1980. A link to bird flu was suspected then as well, the theory being that the mammals picked up the virus while sunning themselves on rocks covered with bird droppings.
In 2006, a morbillivirus (from a family of viruses that includes the one that causes measles in humans) killed hundreds of harbor and gray seals in New England. The same virus was behind the death of 20,000 seals a few years earlier in the United Kingdom.
Harbor seals are year-round inhabitants of the coastal waters of eastern Canada and Maine and occur seasonally along the southern New England to New Jersey coasts from September through late May, although a recent report from by the National Marine Fisheries Service, suggests scattered sightings and strandings have been recorded as far south as Florida.
At the last survey in 2001, the estimated population of harbor seals along the New England coast was 99,340.
Written by Catharine Paddock PhD