The first case of transmission of the H5N1 avian influenza virus from a domestic cat to a human has been discovered in the United States : the feline became ill after consuming raw animal products and subsequently infected a veterinarian who examined him without wearing adequate eye and respiratory protection.
The man, however, was found to be asymptomatic, according to a study conducted by the Los Angeles County Department of Public Health in collaboration with the U.S. Centers for Disease Control and Prevention (CDC). The news was reported on the website of the American Veterinary Medical Association (AVMA).
The study looked at 19 cats who became ill after consuming raw milk, raw meat, or raw pet food purchased between November 2024 and January 2025.
Nine cats were tested, and all tested positive for the H5N1 clade 2.3.4.4b genotype B3.13, the same virus responsible for most human H5N1 infections. The remaining cases were identified through veterinary reports, laboratory reports, or routine testing.
In light of these infections, the researchers interviewed 139 people: 11 pet owners from five households with affected cats, 126 people from 10 veterinary clinics where 14 of the cats had been seen, one person from an animal control agency involved in transporting the cat carcasses, and one person from a local health department. All were initially monitored for symptoms, and although 30 people reported flu-like symptoms, none tested positive by RT-PCR.
A few months later, people who had been exposed to infected cats were invited to participate in an H5N1 serological survey. Of the 25 people who were tested, only one tested positive for antibodies. This person, as mentioned, was a veterinarian who had examined an infected cat without using protective equipment. The man, for whom other known risk factors for infection were ruled out, did not report flu-like symptoms.
"These findings provide evidence of zoonotic transmission of influenza A(H5N1) from domestic cats to humans," the study authors write. Veterinarians should be aware of the risks of infection, use appropriate personal protective equipment, and follow recommended infection control practices to reduce the risk of zoonotic transmission of influenza A(H5N1)."
