Summary
A bioRxiv preprint reports H5N1 and H5N5 infections in six red foxes in Norway between 2022 and 2024. The investigation found systemic infection and detected a mammalian-adaptation marker in two H5N1 viruses.
A bioRxiv preprint reports six cases of highly pathogenic avian influenza in red foxes in Norway during 2022–2024, involving H5N1 and H5N5 viruses. Pathological and virological investigations found systemic infection, with prominent lesions in the brain and/or lungs. The report describes infections in individual foxes; it is not a population-level estimate of how commonly foxes were infected.
The finding adds to evidence that highly pathogenic avian influenza viruses can infect mammals. Since 2020, H5Nx viruses in clade 2.3.4.4b have spread globally among domestic and wild birds, with spillovers into mammals. Human infections remain rare, according to the preprint, but the viruses’ potential to infect people is a public-health concern.
What the investigation found
The researchers analysed six fox cases and identified both H5N1 and H5N5. Phylogenetic analyses found high similarity between the viruses detected in foxes and viruses circulating in wild birds at the same time. This is a genetic comparison; the abstract does not identify how the foxes acquired infection.
The team also reported the PB2:E627K marker in one H5N1 virus and as a minority variant in a second. PB2 is a protein involved in influenza-virus replication, and E627K is a change in that protein tracked as a marker of mammalian adaptation. Its detection is a genetic finding within this case investigation.
A signal for wildlife surveillance
The combination of systemic infection, lesions in the brain and/or lungs, and genetic similarity to viruses circulating in birds makes the fox cases relevant to monitoring how avian influenza reaches and affects mammals. The PB2 finding adds a specific viral feature for surveillance teams to track in sequence data.
The report is a preprint, and its findings concern six foxes in Norway. The cases document infections and associated pathology, while the available abstract does not establish the route of infection or its frequency among foxes.