Highly Pathogenic Avian Influenza

Bird flu, also called avian influenza, is a flu virus that circulates naturally in wild waterfowl and shorebirds. Most of these birds carry it without getting sick, which is how the virus travels along migration routes and turns up in new regions and species. "Highly pathogenic" describes how severe a strain is in poultry, where it can spread fast and kill large numbers of birds. H5N1 is the strain drawing the most attention right now, and since 2020 one branch of it, known to scientists as clade 2.3.4.4b, has spread across continents and into a growing list of mammals, including dairy cattle in the United States from 2024 onward.

For pet owners, the part that matters most is what happens when this virus reaches a cat. Cats are unusually vulnerable to severe illness from H5N1, and the Cornell Feline Health Center notes that up to 70% of infected cats die. Illness often starts with fever, loss of appetite and tiredness, then can worsen quickly into heavy discharge from the eyes and nose, breathing difficulty, and neurological signs such as wobbliness, circling, tremors, seizures or blindness. Because those neurological signs look similar to rabies, a vet will usually want to rule that out as well. Dogs can be infected too, but this appears to be rare, and reported cases have generally involved milder respiratory illness rather than the severe disease seen in cats.

Cats mostly get infected by eating something contaminated rather than by breathing the virus in. Investigations have repeatedly traced feline infections to raw poultry and to raw, unpasteurised milk or colostrum, including milk bought at the market that led to two cat deaths and virus later found in the surviving cat's urine. Commercial raw and frozen cat food has also been linked to cat deaths, and hunting or scavenging dead wild birds is another recognised route. Cat-to-cat spread has not been clearly confirmed, and the risk to people is generally considered very low, but a documented case of a cat infecting a veterinary professional shows it isn't impossible, particularly with close, unprotected contact with a sick animal. This is why handling a raw food product or a sick pet with hand washing and gloves is treated as sensible practice rather than an overreaction.

Lowering the risk

The clearest steps an owner can take are to avoid feeding raw poultry, raw meat and unpasteurised milk or dairy, and to stop pets eating dead birds or wildlife. Cornell's guidance also recommends keeping cats indoors and away from livestock, poultry and their environments, and washing your hands and changing clothing or footwear after contact with birds, farm animals, or places where they gather. There is currently no approved vaccine for H5N1 in cats, though researchers have reported early success protecting cats in trials of experimental vaccines, so for now avoiding exposure is the main defence available to owners.

How outbreaks are tracked and reported to authorities varies by country, so check what applies locally if you keep poultry or live near affected farms. If your cat has eaten raw poultry, raw milk, or a wild bird and then seems unwell, phone your vet before bringing the animal in, so the practice can prepare, and mention the possible exposure. This entry is general information, not a diagnosis: any decision about testing or treatment belongs with your vet.