Background: Clade 2.3.4.4b highly pathogenic avian influenza A(H5N1) (HPAI H5N1) viruses have spread prolifically in dairy cattle in the US, resulting in dozens of human infections, some without well-established links to animal contacts. Many wild mammals have also been affected, including peridomestic house mice.

Methods: Here, we evaluated susceptibility, tissue tropism, and shedding in female PWK/PhJ and BALB/cJ mice, two laboratory strains derived from house mice that differ in expression of the antiviral restriction factor Mx1. PWK/PhJ mice, which were selected for their natural expression of Mx1, better reflect the antiviral capacity of most wild house mice, whereas BALB/cJ mice lack functional Mx1.

Findings: We found that, regardless of Mx1 expression status, mice are susceptible to infection by dairy cattle HPAI H5N1 viruses, that infection leads to systemic spread to non-respiratory sites, and that infected animals shed virus into the environment via urine. Shed virus remained infectious in urine for at least 24 h at room temperature.

Interpretation: These findings suggest that wild house mice could contribute to HPAI H5N1 environmental contamination and may play a role in transmission to other hosts.