Outbreak of Highly Pathogenic Avian Influenza Virus H5N1 in Seals in the St. Lawrence Estuary, Quebec, Canada

Abstract

We describe an unusual mortality event caused by a highly pathogenic avian influenza virus (HPAI) H5N1 clade 2.3.4.4b involving harbor (Phoca vitulina) and grey (Halichoerus grypus) seals in the St. Lawrence Estuary, Quebec, Canada. Fifteen (56%) of the seals submitted for necropsy were considered to be fatally infected by H5N1 containing fully Eurasian (EA) or Eurasian/North American genome constellation.Concurrently, presence of large numbers of bird carcasses infected with H5N1 at haul-out sites most likely contributed to the spill-over of infection to the seals. Histologic changes included meningoencephalitis (100%), fibrinosuppurative alveolitis, and multi-organ acute necrotizing inflammation. This is the first report of fatal H5N1 infection in pinnipeds in Canada, raising concerns about the expanding host of this virus, potential for establishment of a marine mammal reservoir, and the public health risks associated with spillover to mammals.

Massive outbreak of Influenza A H5N1 in elephant seals at Península Valdés, Argentina: increased evidence for mammal-to-mammal transmission

“…Since 2020, the world has witnessed an unprecedented global epizootic of H5N1 clade 2.3.4.4b viruses with a catastrophic ecological impact on wildlife species, including pinnipeds. Although H5N1 HPAI viruses were previously implicated in mortalities of harbor seals (Phoca vitulina) and gray seals (Halichoerus grypus) in Europe in 2016-2021 [28][29][30] and in North America in May-July 2022 17,19 , the magnitude of those mortalities (<200 deaths in total) would pale in comparison with the impacts that ensued when these viruses arrived in South America. At least 30,000 sea lions have died in Peru, Chile, Argentina, Uruguay and Brazil 10,[12][13][14]20,[22][23][24][25] .…”

“…The virus then spread to South America in 2022 via multiple introductions 9,10 , causing unprecedented large-scale mortality of seabirds, with an estimated death toll surpassing 650,000 individuals [10][11][12][13][14] . H5N1 HPAI sporadically caused mortality of pinnipeds and cetaceans in Europe 15,16 and North America [17][18][19] , but it was only upon reaching the Pacific coast of South America that the virus demonstrated an ability to cause large-scale mortality in marine mammals 10,20 . More than 30,000 South American sea lions (Otaria byronia) died as H5N1 virus spread along the coast of Peru and Chile in 2022-2023, with porpoises, dolphins and otters also being affected in smaller numbers 10,[12][13][14][20][21][22] .…”

“…H5N1 HPAI sporadically caused mortality of pinnipeds and cetaceans in Europe 15,16 and North America 17–19 , but it was only upon reaching the Pacific coast of South America that the virus demonstrated an ability to cause large-scale mortality in marine mammals 10,20 . More than 30,000 South American sea lions ( Otaria byronia ) died as H5N1 virus spread along the coast of Peru and Chile in 2022–2023, with porpoises, dolphins and otters also being affected in smaller numbers 10,12–14,20–22 .…”