By Andi Anderson
A recent study has revealed that a highly pathogenic avian influenza (H5N1) outbreak on an Illinois farm spread beyond poultry, infecting both a domestic cat and wild rats. The findings highlight the importance of monitoring all animals on farms during bird flu outbreaks and strengthening biosecurity measures.
The outbreak occurred in March 2025 when an Illinois farmer lost 100 of 105 backyard birds within a short period. The farm was located near a reservoir lake, an area frequently visited by wild waterfowl, which are known carriers of avian influenza viruses. Investigators believe the disease likely spread from wild birds to the backyard flock.
After the outbreak, samples from a chicken were tested and confirmed positive for H5N1 avian influenza. A few days later, the remains of a farm cat and a rat were collected and examined by researchers from the University of Illinois Urbana-Champaign Veterinary Diagnostic Laboratory and the University of Missouri Veterinary Medical Diagnostic Laboratory.
According to the analysis, both mammals tested positive for the same H5N1 virus subtype found in the infected chicken. Researchers discovered widespread infection throughout the animals' bodies. All 12 tissue samples collected from the cat tested positive, while 11 of 15 tissue samples from the rat contained the virus. Viral genetic material was also detected in the rat's urine.
“Bird flu does not stop at birds. On this farm, a cat and a rat were infected too, most likely after contact with dead or dying infected birds, and any wild animal that scavenges or handles carcasses could be exposed the same way,” said Dr. Leyi Wang, virology section head at the University of Illinois Veterinary Diagnostic Laboratory.
Researchers were particularly surprised by the rat infection.
“The cat was expected, but the rat is the surprise,” said Dr. Leyi Wang, who also is a professor of veterinary clinical medicine at the University of Illinois. “Since rats live on nearly every farm despite biosecurity, they may be an overlooked link between wild birds, poultry and other mammals. Rodents live close to people, livestock and feed, so infected, shedding rodents could contaminate the farm environment and create new exposure routes.”
Genetic sequencing showed that the viruses found in the chicken, cat, and rat were nearly identical, suggesting they originated from the same source. Researchers also identified a mutation associated with better adaptation of the virus to mammals.
“Because the mammalian-adaptation marker was already present in the bird virus, crossing into mammals may not require new mutations,” Wang said. “Shared changes arising in two mammalian species are exactly the kind of adaptation signal worth watching.”
The findings were published in the journal Emerging Infectious Diseases. Researchers emphasized the need for farmers, backyard poultry owners, and veterinarians to remain alert during bird flu outbreaks.
“For flock owners: keep poultry away from wild waterfowl, report sudden die-offs, control rodents and don’t let farm cats scavenge dead birds. For veterinarians: when poultry die of suspected HPAI, treat sick or dead mammals on the same premises as potentially infected and use appropriate precautions.”
The study demonstrates that avian influenza can affect multiple animal species on a farm and reinforces the importance of disease surveillance, rodent control, and preventive measures to protect animal and public health.
Photo Credit: gettyimages-branex
Categories: Illinois, Livestock, Poultry