When more than 162 young harbor seals were discovered stranded or dead on New England beaches in the fall of 2011, it was officially declared by the federal government as an Unusual Mortality Event (UME). For marine mammals, a UME is a stranding that is unexpected, involves a significant die-off of the population, and demands an immediate response.
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The National Oceanic and Atmospheric Administration (NOAA) assembled a team of scientists to investigate. Wildlife experts from the USGS National Wildlife Health Center contributed their expertise by isolating the virus from the tissues of the seals. They were able to characterize the virus as a type of influenza virus most closely related to the avian influenza H3N8 viruses commonly found in wild birds.
Collectively, the team of scientists determined that the H3N8 seal virus is likely to have caused the 2011 mortality event in New England. Further, it may pose a continued threat to marine mammals on the nation’s coast. Dr. Hon Ip, a USGS virologist at the National Wildlife Health Center, said, “What was surprising was that the seal virus contained genetic changes that have been shown to increase mammalian infection. Of the influenza viruses that have been previously isolated from seals, none shows this pattern of genetic change toward adapting to mammals.”
Katie Pugliares and Michael O’Neil with the New England Aquarium preparing a harbor seal carcass for necropsy. Photo Credit: New England Aquarium.