Two cats that belonged to Michigan dairy workers became infected with bird flu and later died, but it’s unclear how they became sick, according to a new study published on Feb. 20 by the Centers for Disease Control and Prevention (CDC).
The cats lived in two separate households and developed severe illnesses after becoming infected with bird flu in May 2024. One cat was euthanized on day four and the other cat died within 24 hours of illness.
Both were indoor-only cats that had not been exposed to infected cattle or birds and didn’t consume unpasteurized milk, the CDC study said.
An investigation by the Michigan Department of Health and Human Services and Mid-Michigan District Health Department found that the cats had contracted Type A H5N1 bird virus, which has been found in U.S. dairy herds.
One of the cats (referred to in the study as cat 1A) lived in a household with two adults, one of whom worked on a dairy farm in a county known to have bird flu-infected cattle. Two adolescents and two other exclusively indoor cats also lived in the house, the CDC said.
The infected cat began showing symptoms, including decreased appetite, lack of grooming, disorientation, and lethargy on the second day of illness and was subsequently evaluated at a local veterinary clinic, according to the study.
On the fourth day, the cat was referred to the Michigan State University (MSU) Veterinary Medical Center (VMC), where it was euthanized because of rapid disease progression.
A second cat in that household also got sick but recovered after 11 days. A third cat in the household didn’t get sick and tested negative for bird flu.
The dairy farm worker reported experiencing vomiting and diarrhea for one day prior to the cat getting sick but declined influenza testing, the CDC said.
Additionally, according to the health agency, an adolescent in the same household got sick but tested negative for influenza A virus.
In the other household, a cat (referred to in the study as cat 2A) lived with its owner, a dairy farm worker, and one additional indoor cat.
The CDC said the owner had transported raw milk from various farms in a Michigan county, including farms with dairy cattle confirmed to be infected with bird flu. The owner had done so without wearing personal protective equipment (PPE) and reported frequent splashes of milk on the face, eyes, and clothing.
Unclear How Cats Became Sick, CDC Says
Additionally, the owner did not remove work clothing before entering the home when returning from work, the CDC said.
Cat 2A became sick and began displaying symptoms, including progressive neurologic deterioration, anorexia, lethargy, and facial swelling six days after cat 1A was referred to MSU VMC, the CDC study said.
“On initial physical examination of cat 2A, it was found to be obtunded, with abnormalities of cranial nerve function, abnormal motor function, puffiness of the eyes and nose, and minimal movement,” the study said.
The cat tested positive for influenza A virus and died within 24 hours of onset of illness signs, the CDC said. The other cat in that household tested negative for the virus.
Cat 2A’s owner reported that the animal would roll in the owner’s work clothes, whereas the other cat in that household did not exhibit this behavior, according to the CDC. The agency also noted that the cat’s owner reported eye irritation, a possible symptom of bird flu, two days before the cat got sick.
“The owner did not receive testing for influenza and declined oseltamivir and further contact with public health officials, stating fear of losing employment as a consequence of communicating with public health officials and implicating farms that provided milk,” the CDC said.
Because the two dairy industry workers declined to be tested for the virus, it is still unclear exactly how the animals got sick or whether they spread the virus to people in the household.
The CDC also noted that 24 veterinary staff members were potentially exposed to the two sick cats, seven of whom reported signs or symptoms of illness following exposure. Only five agreed to testing, and they all tested negative for bird flu, according to the CDC.
The study concluded that while reports of bird flu infections in indoor cats are rare, “such cats might pose a risk for human infection,” and further studies are required.
While the CDC says the risk to human health remains low, the agency recommends that anyone with occupational or recreational exposure wear PPE when interacting with potentially infected animals.
The Associated Press contributed to this report.