Highly pathogenic avian influenza, or HPAI, has been all over the news. Also referred to as “bird flu” or “H5N1” this has been making waves in the recent months with infections in cats. So what is it, and what do you need to know as a cat owner?
What is it?
HPAI is a virus with high mortality, infecting birds and poultry such as chickens and turkeys. Other types of birds, such as waterfowl, can become infected and remain asymptomatic and shed the virus.
HPAI is not new, with cases dating back to the 1950’s. In most cases it was eradicated quickly, except for an outbreak in 1996. This was called Goose Guangdong virus, as it originated in a goose in Guangdong. This is likely the precursor to the current dominant strain. This outbreak led to cases in mammals – like cast and cattle- - due to mutations. Infectious risk to humans is currently low.
Transmission
Transmission occurs through close contact or aerosolized particles from infected birds. Humans can also act as fomites, where we track the disease on our clothes or skin. It can also be shed in the feces of infected birds, so anywhere a bird defecates is a potential source of infection.
The most common way it’s transmitted to cats is by eating an infected carcass, drinking raw milk or being exposed to droppings or fomites. While cats are extremely susceptible, dogs seem less likely to be infected.
Why are cats so susceptible? It has to do with the similarities in the respiratory tract with birds. Specifically, there’s a sialic acid receptor that this strain binds to. Cats also have sialic acid receptors in their GI tract, which is how ingestion of contaminated meat can lead to infection.
The most common current cause of HPAI in cats is due to ingesting raw food or raw milk. While HPAI is “avian influenza,” there’s been infections in multiple dairy cattle across the United States. Raw milk is never recommended for cats, partly due to disease transmission. There are several brands of raw cat food that have recalled their food after being linked to HPAI. Most of the formulations involve chicken, though there is evidence that HPAI can be found in the muscle meat of cows as well as the milk. Some of these companies are using ‘human grade’ meat, meaning these infected birds are making their way into the food chain. Additionally, methods such as HPP do not appear to rid the food of HPAI.
Outdoor cats with exposure to infected carcasses, such as dead birds, are another source of infection.
Cat to cat?
As of now, there is limited evidence of cat-to-cat transmission. There is a suspected case from May of 2024, where two cats in the household became ill. The first cat fell ill and was euthanized on day 4. On that same day, a second cat in the household began showing signs of an illness. That cat was never tested for HPAI, as it was deemed too sick to go to the veterinary clinic. A third, asymptomatic cat in the household was tested 11 days after the first cat became ill and was negative. Given the timeline of illness between cat 1 and cat 2, cat to cat transmission was suspected but never confirmed.
Earlier this year a second possible case of cat-to-cat transmission was noted. Valentino, a 1-year-old cat, became ill and was euthanized. He was sent for necropsy, which confirmed HPAI in multiple body systems. Contact tracing was performed, and it was noted he was in a kennel near another cat who was sick. That cat had a mild fever and was hospitalized, and its diet history included Savage Food Products. This brand was in the process of a recall due to its link to other HPAI cases in cats. Valentino was not a typical cat – he was diabetic and had FIP as a kitten. Still, this shows a potential cat to cat transmission.
Clinical Signs
Clinical signs of HPAI in cats is varied, with some cats dying within 2-3 days of showing clinical signs. Some cases present with a fever, others with respiratory signs, still others with neurological signs. In the case of the cat from May 2024, it started with decreased appetite and lethargy, then progressed to neurological deterioration. The other cat in the household had watery, purulent eye discharge, decreased appetite and breathing heavy. Other cats in literature have similar presentations – very acute onsets of illness, which rapidly progress. An owner in Oregon lost 2 of her cats to HPAI, which started with on and off fevers, decreased appetite and then neurological signs. The other infected cats in the household had signs of pneumonia.
Mortality rate is variable, with some reporting 50% of cats infected passing. However, it’s unknown how many cats have infection with mild signs, like the cat suspected to have infected Valentino. Additionally, given the exposure with outdoor cats there’s likely missed cases. At this time, it’s considered a disease with a high mortality rate in cats.
How can you protect your cat?
First – cats should be kept indoors. Anything that limits their exposure to infected bird carcasses or infected feces is ideal.
Second – avoid any raw food in cats. This includes raw milk. Cooking the food will kill the HPAI virus.
Lastly – don’t be a fomite. If you go to open air bird markets, if you walk areas where you track bird feces on your shoes, if you work at a dairy, you have the potential to be a fomite. Take your shoes off outside. Put all your clothes directly into the wash and don’t allow your cats to roll in them. Shower, wash your hands and practice good hygiene.
While HPAI is not new, the current outbreak is still very concerning. Make sure you follow trusted news sources, like the CDC or the AVMA when it comes to updates about HPAI. I’ll try to keep my social media and Substack accounts updated to reflect new information and changes with HPAI. I also encourage you to follow epidemiologists, such as Dr. Andrea Love, to learn more about how these diseases work.