H5N1 Bird Flu Found in Polish Domestic Cats

July 21, 2023 – An outbreak of H5N1 bird flu in household cats was recently reported by the World Health Organization, underscoring that these viruses can infect and cause illness in household pets. Thirty-four domestic cats across eight provinces in Poland tested positive for avian influenza A(H5N1) virus (“H5N1 bird flu”). Many of the infected cats showed neurological signs (e.g., paralysis, seizures) and became severely ill or died. H5N1 bird flu viruses are widespread globally among wild birds and domestic poultry and have caused sporadic infections in mammals. It is important to note that a review of the genetic sequences of the viruses found in cats in Poland does not show any reason to change CDC’s risk assessment to human health, which remains low for the general public. Further, there is no evidence of cat-to cat-transmission.

While domestic animals, including cats, rarely become infected with H5N1, it has been reported, most often after eating raw, sick, or dead infected wild birds or poultry or being in environments contaminated by them. Among the infected cats, most lived inside with partial outdoor access (e.g., via balconies or terraces); however, some were primarily outdoor cats with potential exposures to wild birds. Some infected cats were fed raw poultry or poultry parts. Of the thirty-four infected cats, eleven died from their infection and fourteen were euthanized. The source of H5N1 exposure remains unclear. Investigators have not found evidence that this virus is spreading from cat-to-cat. Also, no illness has been reported in cat owners or other people exposed to the cats.

Preliminary genetic sequencing of the viruses isolated from cats indicate these are from the H5 2.3.4.4b clade, which are similar to the viruses that have been circulating in wild birds and poultry recently in Poland. The viruses include genetic changes that previously have been associated with more severe illness and better ability to spread in mammals. However, there are no changes that would suggest these viruses could easily bind to receptors in the upper respiratory tract of humans, nor any changes that would suggest the viruses were adapted to more easily spread to people. The latter changes would be needed to infect people more easily and to spread more easily among people.

Sequencing also found that these viruses are well-matched to a candidate vaccine virus (CVV) developed by CDC in 2022. CVVs are used to produce vaccine for people, if needed. The existing 2022 CVV would provide good protection against these viruses based on genetic sequencing.

Bird flu infections among domestic animals are rare. However, if your pet is showing signs of illness suggesting bird flu virus infection and has been exposed to infected (sick or dead) wild birds/poultry or has eaten raw food containing poultry products, you should immediately contact your pet’s veterinarian or state animal health official. Additionally, monitor your own health and the health of other household members with close contact with your pet for signs of infection, including fever, cough, difficulty breathing/shortness of breath, conjunctivitis (eye tearing, redness, irritation, or discharge from eye), runny or stuffy nose, or diarrhea. It unlikely that pet owners would get sick with bird flu through direct contact with their infected pet, but it is possible.

The risk to human health from H5N1 bird flu infections in cats is thought to be low. Current H5N1 outbreaks in poultry and birds (with occasional spillovers into mammals and people) continues to be mostly an animal health issue. However, people should avoid direct and close contact with sick or dead wild birds, poultry, and sick or dead wild animals.

CDC has information about precautions to take with wild birds and guidance for pet owners and people who may have direct contact with infected animals. More information about avian influenza is available on the CDC website.