Encephalitis and Death in Wild Mammals at a Rehabilitation Center after Infection with Highly Pathogenic Avian Influenza A(H5N8) Virus, United Kingdom

Abstract

A n episode of unusual disease resulting in deaths in different species at a wildlife rehabilitation center in the United Kingdom during late 2020 led to the retrospective detection of infl uenza A virus subtype H5N8 of avian origin in 5 mute swans, a fox, and 3 seals. The wildlife rehabilitation center admits >6,000 animals each year. New arrivals are initially housed in a quarantine facility upon admission. Four juvenile common seals (Phoca vitulina), 1 juvenile gray seal (Halichoerus grypus), and 1 juvenile red fox (Vulpes vulpes) died or were euthanized over a 2-day period. The fox died suddenly after a short period of nonspecifi c malaise and inappetence. The seals exhibited sudden-onset neurologic signs, including seizures before death or euthanasia (Figure 1). This mortality event occurred ≈1 week after the deaths or euthanasia of 5 mute swans (Cygnus olor) held in isolation at the center because of acute-onset malaise and terminal seizures. The 5 swans were submitted for examination and testing under the Avian Infl uenza Wild Bird Surveillance Scheme (undertaken by the United Kingdom's Animal and Plant Health Agency) (1), and they tested positive for highly pathogenic avian infl uenza A(H5N8) virus.The unusual spatiotemporal cluster of unexplained death and neurologic disease in multiple avian and nonavian species warranted further investigation. Infl uenza of avian origin was not suspected in the fox and seals, and none of the other captive birds at the center showed any clinical signs of disease. The linkage between the mortality event in the swans and that observed in the fox and seals was not

Infections with highly pathogenic avian influenza A virus (HPAIV) H5N8 in harbor seals at the German North Sea coast, 2021

“…Serological investigations did not provide evidence for a wide distribution of these viruses in healthy seals. Similar to very recently reported findings in captive seals in the UK [ 7 ], our results show that HPAIV H5N8 of clade 2.3.4.4b can induce fatal CNS infections in seals under natural conditions. Experimental infection of cats has elucidated that HPAIV reaches the brain through the gut, Plexus Auerbachii , and Nervus vagus [ 13 ].…”

“…During a previous IAV (H10N7) outbreak in seals associated with pneumonia and slightly increased mortality [ 6 ], and in context of HPAIV H5N8 infection in lung tissues of two dead grey seals ( Halichoerus grypus ) found at the Polish Baltic coast in 2016 [ 4 ], no evidence for an infection of the brain was found. Currently circulating HPAIV H5N8 has been very recently reported to cause unusual neurological infection with fatal outcome in four harbor seals and one grey seal kept in a wildlife rehabilitation centre [ 7 ].…”

“… Phylogenetic analysis of hemagglutinin (HA) encoding sequences of highly pathogenic avian influenza viruses (HPAIV) subtype H5N8. (A) Complete H5 encoding nucleotide sequences obtained from brain tissues of three seals determined within this study (indicated in bold) were compared to sequences of H5N8 HPAIV previously detected in seals from Poland (2016), England (2020) and a human case (2020) from Russia [ 4 , 7 , 14 ]. In addition, a representative set of H5 sequences affiliated to clade 2.3.4.4b is included.…”

A case of avian influenza A(H5N1) in England, January 2022

“…Virological characterisation of recent human zoonotic H5N6 viruses shows that H5N6 Eurasian viruses have a haemagglutinin (HA) protein which groups into clade 2.3.4.4h, which is distinct from the HA of the circulating European viruses, which groups into clade 2.3.3.4b [ 7 ]. HPAI H5N6 and H5N8 subtype candidate vaccine viruses have been developed or recommended for pandemic preparedness including clade 2.3.4.4b CVV (A/Astrakhan/3212/2020-like) [ 8 ]. This is of increased importance given the recent detection of clade 2.3.4.4b viruses in mammals in Europe [ 9 ].…”

Evolutionary and Mutational Characterization of the First H5N8 Subtype Influenza A Virus in Humans

“…To date, it is the first report that an H5N8 virus can cross the species barrier and infect humans. Before this case, H5N8 viruses had been reported to infect other mammalian hosts, including domestic and wild pigs, foxes, and gray seals [12][13][14][15]. Although all infected individuals were asymptomatic, the World Health Organization emphasized the demand for further risk assessment towards pandemic preparedness.…”