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Abstract The discovery of several novel hepatovirus species in marine and terrestrial mammals has expanded the recognised members of the genus Hepatovirus and has provided better understanding on the evolutionary origins of human hepatovirus A (HAV). Using high throughput sequencing we detected a seal hepatovirus (SealHAV_NL/PV/21), in liver tissue of a deceased harbor seal (Phoca vitulina) originating from the Dutch North Sea coast. RT-PCR screening of liver samples of 88 harbor seals and 12 grey seals (Halichoerus grypus) from the same region identified seal hepatovirus in nine juvenile harbor seals in which minor sequence variation was observed in the VP1 gene. Whole-genome sequence analysis showed that SealHAV_NL/PV/21 displayed 95.6% nucleotide indentity to New England seal hepatovirus but had a 5′-UTR which contained additional 51 bp. Phylogenetic analysis showed that seal hepatoviruses clustered in a monophyletic group separate from other hepatovirus species that have been identified in terrestrial mammals. Assessment of seal hepatovirus RNA loads in organs of all infected animals showed that the liver had the highest number of RNA copies with up to 107 RNA copies per mg of tissue. Seal hepatovirus RNA was readily detected by in situ hybridization in hepatocytes in the liver but was not associated with pathological lesions. Serological screening of 90 contemporary seal sera using a HAV-based ELISA showed the presence of hepatovirus antibodies in 14 harbor seals and one juvenile grey seal. These findings collectively show that seal hepatovirus is enzootic among seals of the North Sea, causing quiescent infections in young animals.

Analysis of liver tissue from a Cape penguin that died with hepatitis at a zoo in Germany revealed Umatilla virus. Testing uncovered Umatilla virus RNA in samples from 2 other deceased Cape penguins at the zoo. Our results expand knowledge of the prevalence of this virus in bird species across Germany.

Recent reports documenting sporadic infections in carnivorous mammals worldwide with highly pathogenic avian influenza virus (HPAIV) H5N1 clade 2.3.4.4b have raised concerns about the potential risk of adaptation to sustained transmission in mammals, including humans. We report H5N1 clade 2.3.4.4b infection of two grey seals (Halichoerus grypus) from coastal waters of The Netherlands and Germany in December 2022 and February 2023, respectively. Histological and immunohistochemical investigations showed in both animals a non-suppurative and necrotising encephalitis with viral antigen restricted to the neuroparenchyma. Whole genome sequencing showed the presence of HPAIV H5N1 clade 2.3.4.4b strains in brain tissue, which were closely related to sympatric avian influenza viruses. Viral RNA was also detected in the lung of the seal from Germany by real-time quantitative PCR. No other organs tested positive. The mammalian adaptation PB2-E627K mutation was identified in approximately 40% of the virus population present in the brain tissue of the German seal. Retrospective screening for nucleoprotein-specific antibodies, of sera collected from 251 seals sampled in this region from 2020 to 2023, did not show evidence of influenza A virus-specific antibodies. Similarly, screening by reverse transcription PCR of tissues of 101 seals that had died along the Dutch coast in the period 2020–2021, did not show evidence of influenza virus infection. Collectively, these results indicate that individual seals are sporadically infected with HPAIV-H5N1 clade 2.3.4.4b, resulting in an encephalitis in the absence of a systemic infection, and with no evidence thus far of onward spread between seals.

We conducted a severe acute respiratory syndrome coronavirus 2 antibody seroprevalence study among >2,000 domestic cats from 4 countries during the first coronavirus disease wave in Europe. We found 4.4% seroprevalence using a virus neutralization test and 4.3% using a receptor-binding domain ELISA, demonstrating probable human-to-cat transmission.

The current outbreak of HPAI H5N1 virus infections in dairy cattle in the USA underscores the need for easily accessible methods to rapidly assess host susceptibility for infection with known and emerging influenza viruses. Here we show that ex vivo lung slice cultures from calves provide a useful method to rapidly screen host susceptibility to a range of influenza A viruses.