When the bird flu virus began striking dairy farms last year, dead barn cats were often the first sign.
A new report from the Centers for Disease Control and Prevention suggests that cats may also be bearing the brunt inside U.S households: When cats die unexpectedly, there may be the H5N1 bird flu virus in the house.
The study, parts of which were accidentally released this month, details a public health investigation in Michigan from May 2024 involving dairy workers with bird flu symptoms and their pet cats.
The investigation was launched as a result of veterinarians who saw sick cats, and realized that those cats belonged to dairy workers — making the connection to the animals’ illness and the H5N1 outbreak that was infecting Michigan dairy herds.
The two dairy industry workers declined to be tested for the virus, so investigators were unable to definitively show the spread of infection. However, both workers had shown symptoms suggestive of infection, the study said.
In one case, a worker who wasn’t employed on a farm but transported unpasteurized milk between farms reported conjunctivitis. The other person worked on a dairy farm and reported seeing several dead barn cats on the premises. He suffered gastrointestinal symptoms, such as diarrhea and vomiting the day before a pet cat became sick.
Both workers also ended communication with health officials before the investigation was over, with one citing fear of losing employment for implicating dairy farms, according to the study.
Two adolescents living in one of the worker’s homes also became sick. Both tested negative for the virus.
Jennifer Nuzzo, director of the Pandemic Center at Brown University in Providence, R.I., said the paper raises more questions than it answers.
“We’ve known that cats can become ill with H5N1,” she said. “This paper raises, but does not answer, the question of whether farmworkers may spread H5N1 to their cats. We need to know more about how this may have occurred, as it could inform our understanding of whether people can spread the virus to other animals, including other humans.”
Because the workers declined to be tested for the virus, the authors could not conclude that they had passed the virus to their pet cats.
According to the study, a 5-year-old indoor cat belonging to one of the dairy workers was brought to a local veterinary clinic after showing decreased appetite, disinterest in grooming, disorientation and tiredness. After not improving over two more days, the cat was referred to the Michigan State University Veterinary Medical Center., where the cat was euthanized after “rapid disease progression.”
Because the cat’s owner was a dairy farm worker, and there were reports of H5N1 in local dairy farms, the cat’s body was sent to the university’s diagnostic laboratory, where tests confirmed the presence of the virus. That discovery triggered the investigation by state public health officers.
In the second dairy worker household, a 6-month-old Maine Coon cat that lived exclusively indoors was brought directly to the Michigan State veterinary clinic. The cat also tested positive for the virus and died 24 hours later.
A second cat in the household had no symptoms and tested negative for the virus.
The cats’ owner reported not wearing protective equipment and being frequently splashed by milk in the eyes and face, and on clothing. The worker told investigators that the Maine coon cat would often roll in those clothes, something the second cat never did.
The owner reported experiencing eye irritation that began two days before the coon cat got sick. The owner wasn’t tested for influenza, declined antiviral treatment and ended communication with the investigators.
“This is depressing and will continue until we have more severe illnesses reported that scare people,” said John Korslund, a retired U.S. Department of Agriculture veterinarian and researcher.
He said his biggest concern is the time lag among infection, symptoms and testing, which can be on the order of three days to two weeks — a pause that enables the virus to move undetected through farms and the environment.
“We are consistently testing humans much too late — after cow herds have shown clinical signs and workers have ‘recovered,’” he said. “If we want to get serious about finding human H5 infections, we’ll need to use rapid tests in [workers’] homes when the eyes first are red, independent of what is happening in the herd on the farm.”
“The workers, the cats, and the bulk milk samples are the best sentinels for early dairy herd diagnoses,” he said.
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