New Flu Virus in Seals: Could it be the Source of the Next Pandemic?

Swine flu is sooo three years ago. Should we be concerned about seal flu now?

It is literally impossible to find a photo of a threatening-looking seal.

Possibly. A new strain of influenza virus found in harbor seals could well represent a threat to wildlife and human health, according to the authors of a study in mBio this week. It is crucial to monitor viruses like this one, which originated in birds and adapted to infect mammals, the authors say, so that scientists can better predict the emergence of new strains of influenza and prevent pandemics in the future.

The study focuses on a virus associated with a die-off of 162 New England harbor seals in 2011. Autopsies of five of the seals revealed they apparently died from influenza. The authors sequenced the full viral genome using DNA extracted from infected tissue and compared the sequences with known flu strains from a variety of animal and human sources. The phylogeny of the virus paints a complicated family tree, but it is most closely related to an H3N8 virus that has been circulating in North American waterfowl since 2002.

Unlike the strain in birds, this H3N8 virus has adaptations to living in mammals and has mutations that are known to make flu viruses more transmissible and cause more severe disease. The virus also has the ability to target a receptor called SAα-2,6, a protein found in the human respiratory tract.  

The authors, who hail from several different institutions, including Columbia University and the National Oceanic and Atmospheric Administration Outbreaks, say transmissible and pathogenic flu viruses in mammals, like the one in this study, clearly pose a concern for human health. In 2009, for instance, the H1N1 "swine flu" virus that emerged in humans apparently originated from a reassortment of flu viruses found in birds, pigs, and humans. The H3N8 strain in New England harbor seals may come to represent the first sighting of a new group of influenza viruses with the potential to persist and move between species.

The editor of the report, Anne Moscona of Weill Cornell Medical College in New York City, says it raises two concerns about flu. First, this strain is a novel virus that infects mammals and may well pass from animal to animal, a combination of traits that make it a potential threat to humans.

"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," Moscona says.

Also, says Moscona, the possibility that a bird flu virus would infect seals hadn't been widely considered before, highlighting the fact that pandemic influenza can crop up in unexpected ways. Moscona emphasizes the need for readiness.

"Flu could emerge from anywhere and our readiness has to be much better than we previously realized. We need to be very nimble in our ability to identify and understand the potential risks posed by new viruses emerging from unexpected sources," says Moscona. "It's important to realize that viruses can emerge through routes that we haven't considered. We need to be alert to those risks and ready to act on them."