A team of American researchers discovered that an H3N8 influenza A virus of avian origin was responsible for the outbreak of pneumonia that killed 162 harbor seals along the New England coast, between September and December 2011. The results of their analysis has been published on mBio, the online journal of the American Society for Microbiology.

The seal H3N8 and avian H3N8 viruses are separated by a total of 37 amino acid substitutions, some of which reflect adaptation to mammalian hosts. Also, these mutations are known to increase virulence and transmissibility in avian H5N1 viruses infecting mammals. Although no sufficient proofs of seal-to-seal transmission were found, some data seem to suggest that mammalian spread might already have occurred. Further studies will be required to establish the functional significance of these mutations.

Seals, as much as pigs, can be infected by multiple influenza virus subtypes; this means that they could become “incubator” for new hybrid strains. As stated by Dr. W. Ian Lipkin from the Mailman School of Public Health of Columbia University, one of the authors of the study, “If it adapts better to mammal hosts, it may well start to move into humans. This is clearly a virus for which we need some surveillance.”