Characterization of Avian-like Influenza A (H4N6) Virus Isolated from Caspian Seal in 2012

Marine mammals are widely distributed and can be found almost in all coastal waters and coastlines around the world. The interface areas between marine and terrestrial environments provide natural habitats for aquatic and semiaquatic mammals as well as for reservoir species of avian influenza viruses (AIV) (Runstadler et al. 2013). Previous studies showed that wild aquatic birds, the natural reservoir of AIV, are able to transmit the virus to various mammals, including seals, swine, horses, muskrats, and humans (Webster et al. 1992; Reperant et al. 2009; Gulyaeva et al. 2017). Close contacts between sea mammals and wild birds on breeding-grounds could promote both interspecies transmission of AIV and virus establishment in a new host (Fereidouni et al. 2014). Various AIV subtypes (A/seal/ Massachusetts/80(H7N7), A/Seal/MA/133/82(H4N5), A/Seal/MA/3807/91(H4N6), A/Seal/MA/3911/92(H3N3), A/harbour seal/Mass/1/2011(H3N8) and A/harbor seal/NL/ PV14-221_ThS/2015(H10N7) etc.) have been isolated from different species of marine mammals during the last 30 years. AIV isolated from marine mammals and wild birds are closely related, which suggests that wild birds are the major source of AIV infection (Fereidouni et al. 2014; Bodewes et al. 2015). In addition, AIV can cross species barrier and replicate well in experimental mammals without prior adaptation (Driskell et al. 2012).