We know deadly influenza can come from birds. We know it can come from pigs. Now it appears humans may face a danger of pandemic flu from seals, as well.
Writing Tuesday in the online journal mBio, scientists at Columbia University and several other institutions described an outbreak of a new strain of H3N8 flu in harbor seals.
Between September and December 2011, 162 of the seals — most under 6 months old — died in a pneumonia outbreak off the New England coast. The die-off represented a mortality rate four times greater than expected.
When researchers studied tissue samples from five of the seals, they discovered that all had been infected with a recently mutated form of avian H3N8 flu that had been present in North American waterfowl since at least 2002. Usually H3N8 is associated with birds, horses and dogs. Geneticanalysis of the novel strain indicated that A/harborseal/Massachusetts/1/2011 virus, as it is called, had only recently passed from wild birds to the seals.
The development was obviously bad news for the seals, who suffered skin lesionsas well as pneumonia during the outbreak. It also poses a worry for wildlife and people, the team suggested, because the new H3N8 strain "has naturally acquired mutations that are known to increase transmissibility and virulence in mammals."
Several of the mutations in seal H3N8 flu, for instance, are shared with human H3N2 flu.
The researchers also found that the new H3N8 flu was able to bind to receptors common in the respiratory systems of mammals as well as receptors common in the respiratory systems of birds — another indication that the virus could jump from species to species.
The adaptation to the mammalian receptors “is regarded as a significant driving force in the emergence of global pandemics, especially for viruses with phenotypes that confer increased virulence,” the team wrote, adding that further investigation would be needed to figure out if specific mutations actually would result in enhanced virulence and transmission.
The upshot for human animals? Keeping tabs on influenza outbreaks in a wider variety of species may be necessary to prevent new pandemics in people.
“Flu could emerge from anywhere,” said Anne Moscona, director of the Division of Pediatric Infectious Diseases at Weill Cornell Medical College in New York City, who edited the study for mBio, in a statement. “We need to be very nimble in our ability to identify and understand the potential risks posed by new viruses emerging from unexpected sources. It’s important to realize that viruses can emerge through routes we haven’t considered. We need to be alert to those risks and ready to act on them.”