New York, Sep 6 (IANS): The avian H3N8 virus that killed more than 160 harbour seals along the New England coast in 2011 can spread through respiratory droplets and poses a threat to humans, says a study.

"This study highlights a gain-of-function experiment that occurred in nature and shows us there are avian flu viruses out there beyond H5N1 and H7N9 that could pose a threat to humans," said corresponding author Stacey Schultz-Cherry from the St. Jude Children's Research Hospital in the US.

The researchers found that the virus spread in ferrets though respiratory transmission, which is uncommon for avian flu viruses.

It raises concerns about possible person-to-person airborne spread of the harbour seal virus, as the researchers found no evidence of human immunity to the strain.

"Avian H3N8 viruses are established in horses and dogs. This study raises a red flag about the threat this strain poses to humans exposed to animals infected with the virus," Schultz-Cherry noted.

In this study, two of the three animals exposed to the harbour seal virus became infected via respiratory transmission, although the symptoms were mild.

Airborne transmission did not occur with the five other avian viruses tested, but two of the viruses spread in ferrets that shared cages.

In recent years, human cases of the highly pathogenic avian H5N1 and H7N9 flu have been confirmed in countries around the world, with mortality rates approaching 60 percent.

"The transmissibility of the seal H3N8 virus coupled with the apparent lack of immunity makes this strain a concern," the researchers noted.

The study appeared in the journal Nature Communications.