Outbreak of avian influenza A(H5N1) at a poultry farm in the USA affected cats and rats

In March 2025, an outbreak of highly pathogenic avian influenza A(H5N1) clade 2.3.4.4b occurred at a poultry farm in Illinois, USA. Out of 105 livestock animals @@T0@@, 100 died. The farmer sent the remains of the livestock animals for veterinary examination. Specialists confirmed the presence of the virus in the poultry @@T0@@, and also identified cases of infection among small mammals on the farm territory — a domestic cat and wild rats.

During laboratory studies of cat and rat tissue samples using qRT-PCR and sequencing, positive results were detected in many tissues, including the brain, where the highest viral load was recorded. The virus was also isolated in the respiratory tract, kidneys, and, in the rat, in the urine. Analysis revealed the presence of the basic polymerase 2 E627K mutation, associated with mammalian adaptation, in all three studied species (chicken, cat, and rat).

Pathological and histological examination revealed pneumonia, nervous tissue lesions, and other pathologies in the animals. The obtained data indicate systemic dissemination of the virus in infected cats and rats. The detection of the virus in the kidneys and urine of rodents suggests that rodent urine may serve as a potential vehicle for transmission of infection, which requires further study.