Highly Pathogenic Avian Influenza

Avian influenza is a flu virus that circulates naturally in wild birds. Waterfowl and shorebirds are its usual hosts, and certain strains can also infect domestic poultry, a range of wild and domestic mammals, and, rarely, people. The word "highly pathogenic" describes how severe the virus is in poultry, where it spreads fast and kills large numbers of birds. H5N1 is the strain of most concern, and most wild birds carry it without looking ill, which is how it travels along migration routes. Since 2020 one particular family of H5N1 viruses (clade 2.3.4.4b) has spread across continents in birds and has also moved into mammals, including dairy cattle in the United States.

For pet owners, the part that matters is what happens when the virus reaches a cat. Cats are unusually susceptible to severe illness from H5N1, and infection is often fatal. Reported signs include fever, marked tiredness, heavy discharge from the eyes and nose, laboured breathing and neurological problems such as wobbliness, tremors or seizures, and illness can worsen very quickly. Because those neurological signs overlap with rabies, a vet will usually want to rule that out too. Dogs can also be infected, but they typically show mild signs and rarely die from it.

Cats mostly get infected by eating something contaminated rather than by breathing it in. Investigations have repeatedly traced feline cases to raw poultry and to unpasteurised milk, in both pet cats and wild felids. Cases have been linked to commercial raw frozen cat food, to raw duck meat in shelter cats in South Korea, and to shop-bought raw cow's milk, with virus later found in the surviving cat's urine. Hunting or scavenging dead wild birds is another route. No pet-to-human transmission has been reported, but handling contaminated raw food or a sick animal is treated as a genuine risk to people, which is why hand washing and gloves come up in official advice.

Lowering the risk

Prevent your pet from eating dead birds or other wildlife, and avoid feeding raw meat, raw poultry or unpasteurised milk. The AVMA also advises keeping cats indoors where possible and keeping pets that do go out away from wild birds, poultry and cattle and the places those animals live. If you feed garden birds or walk where birds gather, changing or cleaning your shoes before coming inside is a sensible extra step. There is currently no vaccine to protect cats against H5N1, so avoiding exposure is the whole strategy.

Bird flu is a notifiable disease in most countries, meaning suspected cases must be reported to the authorities, and local rules and outbreak levels differ from place to place. If your cat has eaten a raw poultry diet, raw milk or a wild bird and then becomes unwell, phone your vet before arriving so the practice can prepare, and mention the exposure. This is general information, not a diagnosis: testing and treatment decisions belong with your vet.