A new report says two domestic cats in Michigan were infected with the bird flu virus in 2024. (Photo by photographer Basak Gurbuz Derman via Getty Images)
Editor's note: This is developing information. Live Science is in contact with the CDC and will update as it receives responses.
Two “exclusively domestic” cats from separate Michigan households became infected with the H5N1 bird flu virus and eventually died, according to a new report. The cases raise the possibility that the virus can spread from humans to cats, but a lack of data complicates the situation.
The cases were described in a new Morbidity and Mortality Weekly Report (MMWR) published Thursday (Feb. 20). Some of the paper's authors are scientists affiliated with the Centers for Disease Control and Prevention (CDC), while others work at Michigan health and agricultural institutions or universities.
H5N1 is known to infect both wild and domestic cats, causing severe symptoms including neurological disorders that can be fatal. Since May 2022, the USDA has documented multiple cases of H5N1 infection in wild and domestic cats across the country. There have also been reports of domestic cats becoming infected with bird flu through contaminated raw pet food.
In the first of two recent cases involving a family of three domestic cats, one of the cats became ill in May 2024. The 5-year-old female initially showed a lack of appetite, as well as lethargy and disorientation. The cat was taken to a local veterinarian and then to the Michigan State University (MSU) Veterinary Medical Center, where advanced treatments are available. However, due to “rapid disease progression,” the cat was euthanized.
At the time, cases of bird flu had already been reported on some Michigan dairy farms, and the cat's owner worked on one of the dairy farms, although he had no direct contact with the animals. The cat's body was sent for further testing after euthanasia, and swabs from the brain and nose tested positive for H5N1. Virus samples from the cat matched viruses found in local cattle.
The discovery led to a broader investigation, during which officials learned that another domestic cat in the home developed potential bird flu symptoms after the first cat became ill. Symptoms included decreased appetite and watery eyes, but the cat eventually recovered without specific treatment. Samples from the second cat have not been tested for H5N1, but the timing of the illness may indicate possible transmission.
Although the dairy worker declined to be tested for avian influenza, he reported vomiting and diarrhea the day before the first cat fell ill. Three other members of the worker's household tested negative for influenza A, a member of the broad H5N1 family of viruses.
To complicate matters, one of the family members — a teenager who had “regular contact” with the sick cat — became ill about six days after she became ill. His symptoms included a cough, sore throat, headache, and muscle aches. However, the teen tested negative for the flu and instead tested positive on a test that looks for other common viruses, such as cold viruses. So while the timing of the teen’s infection may be concerning, based on these test results, it’s possible that he had a common respiratory allergy illness.
Around the same time, in another home in Michigan, a second house cat also became infected with bird flu.
The cat, a 6-month-old male, was also a pet-only cat. His owner brought the cat to MSU after he experienced “progressive neurological deterioration,” facial swelling, and loss of appetite over the course of one day. The cat died within 24 hours of the onset of these symptoms. M
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