20.06.2025

Viruses 2025, 17, 855

Domestic cats have traditionally been overlooked as potential hosts for influenza A viruses (IAVs). However, the global dissemination of highly pathogenic avian influenza (HPAI) H5N1, particularly clade 2.3.4.4b, has raised renewed concerns about cross-species transmission. This viral clade has been associated with numerous spillover events into mammalian hosts, including mink, sea lions, and dairy cattle, and has now been implicated in severe and fatal outbreaks among felids. Prior to 2023, feline H5N1 infections were considered sporadic and typically associated with direct contact with infected birds. However, recent cases in South Korea, France, and the United States, including outbreaks among shelter cats and pets exposed to infected cattle or contaminated food, have highlighted the potential for broader feline involvement. Notably, the 2023 outbreak in Poland marked the first large-scale epizootic among cats, suggesting either increased environmental exposure or ongoing viral adaptation. These developments underscore the importance of elucidating feline susceptibility, transmission dynamics, and the role of cats in the ecology and evolution of influenza viruses.
A new study published in Viruses conducted a cross-sectional seroepidemiological investigation to assess the seroprevalence of IAVs - particularly H5Nx subtypes - in Polish domestic cats during the 2023 HPAI H5N1 outbreak. A total of 835 serum samples collected in June 2023 were screened using competitive ELISAs targeting the IAV nucleoprotein and H5 hemagglutinin. The apparent seroprevalence of IAV was 8.5%, with 2.8–3.1% of cats testing positive for H5-specific antibodies. Notably, H5 seropositivity was significantly associated with younger age (≤8 years) and male sex, suggesting distinct risk profiles and transmission pathways for H5 versus non-H5 subtypes. In contrast, non-H5 IAV antibodies were more prevalent in older cats, potentially reflecting prior exposure to human seasonal influenza strains.
These findings indicate that subclinical or mild H5N1 infections in cats are more common than previously recognized and highlight the species’ potential role in interspecies transmission. Given the risk of co-infection and possible reassortment with human IAVs, the study emphasizes the need for enhanced surveillance in feline populations, particularly in areas affected by HPAI. It also supports public health recommendations to limit outdoor access for domestic cats in endemic regions.