Avian Influenza Outbreak in Illinois Farm Affects Domestic Cat and Wild Rats

In March 2025, the farmer lost 100 out of 105 birds in his backyard flock and subsequently brought samples of five birds and a rat to the University of Missouri for testing. The farm, situated near a reservoir lake, was prone to infections from wild waterfowl. Testing confirmed that a sample from one of the chickens was positive for avian influenza. Four days later, the farmer’s veterinarian sent the remains of a cat and another rat to the University of Illinois for further examination, considering several reports of cat infections at that time.

Dr. Leyi Wang, the virology section head at the University of Illinois, noted that the spread of the virus to the cat and rat likely occurred through contact with infected birds. The lab tests revealed that both the cat and rat were infected with the same strain of H5N1 avian influenza found in the chickens, with extensive infections observed in both animals' tissues.

Wang expressed surprise at the rat's infection, highlighting the potential role of rodents in transmitting the virus between wild birds and livestock. The findings showed that all tissues tested from the cat were positive for infection, as were 11 out of 15 from the rat, with viral RNA also detected in the rat’s urine.

Sequencing of the viral genomes from the chicken, cat, and rat indicated they shared a common source, likely a spillover from poultry to the other animals. Importantly, the viral strains showed mutations that facilitate adaptation to mammals, which raises concerns about the potential for further transmission.

The study, published in the journal Emerging Infectious Diseases, calls for increased vigilance among farmers, backyard flock owners, and veterinarians. Wang advises keeping poultry away from wild waterfowl, monitoring for sudden flock die-offs, controlling rodent populations, and preventing farm cats from scavenging dead birds.