The recent incursion of Highly Pathogenic Avian Influenza A (H5N1) virus into North America and subsequent dissemination of virus across the continent, has had significant adverse impacts on domestic poultry, and has led to widespread mortality in many wild bird species. Here we report the recent spillover of H5N1 into marine mammals in the northeastern United States, with associated mortality on a regional scale. This spillover is coincident with a second wave of H5N1 in sympatric wild birds also experiencing regional mortality events. Viral sequences derived from both seal and avian hosts reveal distinct viral genetic differences between the two waves of infection. Spillover into seals was closely related to virus from the second wave, and one of eight seal-derived sequences had the mammalian adaptation PB2 E627K.

H ighly pathogenic avian influenza (HPAI) viruses are of concern because of their pandemic potential, socioeconomic impact during agricultural outbreaks, and risks to wildlife conservation. Since October 2020, HPAI A(H5N1) virus, belonging to the goose/Guangdong H5 2.3.4.4b clade, has been responsible for >70 million poultry deaths and >100 discrete infections in many wild mesocarnivore species (1). As of January 2023, H5N1 infections in mammals have been primarily attributed to consuming infected prey, without evidence of further transmission among mammals.We report an HPAI A(H5N1) virus outbreak among New England harbor and gray seals that was concurrent with a wave of avian infections in the region, resulting in a seal unusual mortality event (UME); evidence of mammal adaptation existed in a small subset of seals. Harbor (Phoca vitulina) and gray (Halichoerus grypus) seals in the North Atlantic are known to be affected by avian influenza A virus and have experienced previous outbreaks involving seal-to-seal transmission (2-7). Those seal species represent a pathway for adaptation of avian influenza A virus to mammal hosts that is a recurring event in nature and has implications for human health. The StudyThe first detections of HPAI clade 2.3.4.4b viruses in North America were in wild and domestic birds in November 2021 in Canada and late December 2021 in the United . Starting on January 20, 2022, avian oropharyngeal or cloacal samples were collected from wild birds by personnel in 4 wildlife clinics in Massachusetts. Additional opportunistic samples were collected in Maine and Massachusetts in response to suspicious avian deaths in seabird breeding colonies. We screened samples from 1,079

Recent marine mammal recovery and growth of human populations in coastal areas has led to increased human harassment of protected pinniped populations.Yet, current monitoring approaches lack the necessary resolution to describe this emerging issue. We therefore propose a new classification scheme for monitoring

Over the past several decades, the Gulf of Maine has experienced significant socio-ecological change. Coastlines have become more densely populated and developed, rapid and dramatic climate change has affected coastal ocean environments, and seal populations have grown as a result of federal protections. Long-term data sets from marine mammal stranding networks represent a valuable resource for investigating indicator species for coastal ocean health during this period of change. Using data collected from stranded harbor (Phoca vitulina), harp (Pagophilus groenlandicus), and gray (Halichoerus grypus) seals from 2002 to 2017 in Massachusetts, New Hampshire, and Maine, we tested for spatiotemporal correlations between stranding density and human population density, size of and proximity to seal haul-outs, sea surface temperature, North Atlantic Oscillation, snowfall, and sea ice extent. We found that in the Gulf of Maine proximity to coastal human population centers and large seal haul-outs are the greatest drivers of reported seal stranding density. Environmental factors played an important role only for harp seals, which do not breed in the study area, although recent shifts in the environmental seascape have the potential to affect all seal species in the Gulf of Maine.