ETIDIOH - NEW

  Abstract Highly pathogenic avian influenza (HPAI) H5N1 clade 2.3.4.4b has expanded rapidly across the Southern Ocean since 2023 , causing extensive mortality in sub-Antarctic wildlife . Yet its penetration into Antarctica and impacts on ice-dependent species remain poorly resolved primarily due to surveillance constraints . We report the first confirmed H5N1 infection in an Antarctic ice-dependent seal (crabeater seal; Lobodon carcinophaga) and document mortality of crabeater seals across the northern Weddell Sea during November-December 2024 . Combining genomic, serological and observational data across nine species, we detected H5N1 RNA in a crabeater seal and a kelp gull (Larus dominicanus), and recovered complete HA, NA and M2 gene sequences from both. Phylogenetic analyses allowed us to identify at least two independent introductions of HPAI H5N1 clade 2.3.4.4b into the northern Antarctic Peninsula region. Serology provided strong evidence of prior exposure in scavenging bir...

  Abstract Highly pathogenic avian influenza (HPAI) A(H5N1) clade 2.3.4.4b has recently emerged as a major threat to wildlife , agriculture, and public health due to its expanding host range and the increasing frequency of spillover into mammals . In July–August 2023, the mass death of over 3500 northern fur seals (Callorhinus ursinus) and at least one Steller sea lion (Eumetopias jubatus) was recorded on Tyuleniy Island in the Sea of Okhotsk, Russia. Two HPAI A( H5N1 ) viruses were isolated from fur seal carcasses and designated A/Northern_fur_seal/Russia_Tyuleniy/74/2023 and A/Northern_fur_seal/Russia_Tyuleniy/75/2023. Both viruses exhibited high pathogenicity in chickens (IVPI 2.7–3.0) and mice (MLD50 1.9–2.5 log10EID50/mL), with distinct differences in disease progression, histopathology, and organ tropism . Experimental infection of mice revealed that strain A/74/2023 induced more severe pulmonary and neurological lesions than A/75/2023. Whole-genome sequencing and phylogeneti...

  Abstract The global spread of highly pathogenic avian influenza A(H5N1) clade 2.3.4.4b viruses has recently extended to include diverse mammalian species , raising new concerns about pandemic risk . In 2023, this clade was first detected in Russian marine mammals during a mass mortality event among northern fur seals in the Far East . Genetic analyses revealed the causative viruses to belong to genotype A3 of European origin , which is known to have circulated in wild birds across the Far East since 2022. Notably, these isolates harbor the mammalian-adaptive substitutions PB2-K482R and NP-N319K—mutations previously linked to enhanced virulence in non-H5 avian influenza viruses , but whose impact on A(H5N1) clade 2.3.4.4b viruses remained to be characterized. The heightened virulence of A3 genotype viruses is confirmed by data obtained via a mouse model . However, despite these adaptive changes, ferret transmission models showed no evidence of airborne transmission of the fur seal...

Abstract Highly pathogenic avian influenza A(H5N1) clade 2.3.4.4b virus infections have caused substantial mortality events in marine mammals in recent years. We hypothesized that the high number of infections and disease severity could be related to cell tropism in respiratory tracts . Therefore, we examined the attachment pattern of an H5N1 clade 2.3.4.4b virus (H52022) as a measure for cell tropism in the respiratory tracts of harbor seals, gray seals, harbor porpoises, and bottlenose dolphins and compared it with an H5N1 clade 2.1.3.2 virus (H52005) and a human seasonal H3N2 virus using virus histochemistry. Both H5 viruses attached abundantly to olfactory and respiratory mucosa in the upper respiratory tract of both seal species. H52022 attached more abundantly than H52005 to epithelial cells in the lower respiratory tract of all species. The observed attachment possibly explains the susceptibility of marine mammal species for recent H5N1 viruses and the observed development of se...

Abstract H5Nx clade 2.3.4.4b high pathogenicity avian influenza viruses (HPAIV) have been detected repeatedly in Great Britain (GB) since autumn 2020, with H5N1 dominating detections but with low level detection of H5N5 during 2025. Globally, these viruses have caused mass mortalities in captive and wild avian and mammalian populations , including terrestrial and marine mammals . H5N1 has been the dominant subtype, and whilst incursions have overlapped temporally, occurrences have often been spatially distinct. Here, we report the detection of a mortality event in wild birds on the Norfolk coastline in the east of England, where H5N1 HPAIV was detected in five Great Black-backed Gulls (Larus marinus) and a Northern Fulmar (Fulmarus glacialis). Interestingly, at the same site, and as part of the same mortality event, a total of 17 Great Black-backed Gulls, one Herring Gull (Larus argentatus), one Atlantic Puffin (Fratercula arctica) and one Northern Fulmar tested positive for H5N5 HPAIV...

  Abstract Highly pathogenic avian influenza A viruses subtype H5N1 (HPAIV H5N1), subclade 2.3.4.4b infect multiple avian and mammalian species , posing a potential pandemic risk . Here we describe the outcomes of infection of ferrets with a HPAIV H5N1 virus, isolated from a European grey seal in 2023, compared with an older HPAIV H5N1 (A/Indonesia/05/2005). Overall, infection of ferrets with A/grey seal/Netherlands/302603/2023 caused more rapid mortality than infection of ferrets with A/Indonesia/05/2005. Animals developed severe pneumonia and irreversible hypothermia , associated with high levels of virus replication and histopathological changes in the respiratory tract and peripheral organs. As animal models for severe avian influenza virus infections in humans play a key role in the development of intervention strategies against these infections, these findings highlight the importance of using updated ferret models based on circulating virus strains. Source: Journal of Infect...

Abstract Thousands of outbreaks of the highly pathogenic avian influenza A(H5N1) virus in birds and an increasing number of mammal infections are registered annually. In 2023, multiple avian influenza outbreaks were registered among wild birds, poultry and seals in Russia . The genetic characterization of seventy-seven avian viruses and three viruses from seals showed that they belonged to the 2.3.4.4b clade and represented four distinct reassortant genotypes . The majority of viruses represented genotype BB , which was widespread in Europe in 2023. Viruses from seals and four viruses from birds , isolated from outbreaks in the Far East region , belonged to the G1 (A3) genotype and had the amino acid substitution N319K in the NP protein , previously associated with an increased virulence for mammals . In addition, one virus of the G10 genotype and two viruses, representing a previously undescribed genotype (designated as Ru-23-G4) were identified. The viruses analyzed showed normal inh...

 Forty Southern elephant seal (WILD), Sealion Island. Source: WOAH,  https://wahis.woah.org/#/in-review/6118 _____