Updated 11/18/25

Bird flu (avian influenza, H5N1) has gotten a lot of headlines over the last year. If you’re a subscriber to our free monthly newsletter, you’ve read a lot about it. [And if you’re not… go here to sign up right now!  littlebigcat.substack.com]

1/5/26 Update: The USDA reports new bird flu outbreaks in five states, including two backyard flocks, a game-bird farm, and a broiler operation. The “good” news is that these were caught early, but the bad news is that there have also been die-offs in wild flocks of swans and Canada geese. Two infected domestic cats were also reported by USDA in November (North Dakota) and December (Denver, CO), but no details are available.

11/1/25 Update: As wild birds migrate south for the winter, the summer “pause” in bird flu outbreaks is over, according to the USDA (which, unlike CDC, is still tracking!). Multiple commercial and backyard flocks have recently been infected. Be sure to prevent your cat from hunting critters (including mice) who can carry this nasty flu virus!

Bird Flu Basics

Avian influenza is a common virus with many, many variants. The version of current concern, H5N1, has been circulating since 1996 when it was first seen in China. It bumped along at a low level for years until about 2005, when wild birds spread it to Europe, Africa, and the Middle East. It didn’t reach North America until 2013; and even then wasn’t a big deal until 2021 when it really took off.

Cats (domestic, wild, exotic, and big cats) are unusually susceptible to this bird flu. But it’s not just cats–carnivores in general seem more vulnerable to this flu. More than 200 species have been affected. (Only a handful of cases in domestic dogs have been documented, none in the U.S.)

Viruses are classified in “clades” (a strain or version). Last year, the 2021 strain developed a new clade, a mutation known as 2.3.4.4b within the B3.13 genotype (sorry if that’s “TMI”!). This mutation gave it the ability to jump from birds to mammals. The B3.13 virus suddenly turned up in dairy cows. Not a lot of viruses can cross species (rabies being a notable exception), so this was worrisome.

Like most influenzas, bird flu is likely transmitted through the air. This has been found to be the case in dairies, and is undoubtedly true in overcrowded poultry facilities as well. Much like its attitude with mad cow disease, the USDA does not want this to be true, and is working very hard to blame other sources. (See this ProPublic article; warning, it’s a bit graphic.) There are vaccines available for poultry, but they are being used because they could negatively affect international trade.

The other unusual ability of this clade is transmission by ingestion. Most viruses move around via secretions like eye and nose discharges, saliva, urine, or feces. But cats were getting this virus by eating it. Specifically, they were getting sick from drinking milk from infected cows. This virus has an affinity for mammary tissue, and collects in large quantities in milk. Cats drinking that milk were getting a massive viral load. The first clue anyone had that there was a problem, in fact, was a sudden spate of dead cats on dairy farms.

Bird flu, of course, primarily affects birds, and has run rampant among wild birds (especially ducks, geese, and gulls–the major transmitters across the world) as well as chickens,  turkeys, ducks, geese, and even emus–both large commercial operations and backyard flocks. Raptors and scavenging birds, like hawks, vultures, and crows, can also be infected. Songbirds, jays, cardinals, and robins can get avian flu, although in this outbreak they have been less likely to get ill. But they can still carry the more deadly virus varieties.

Signs of Bird Flu in Cats

The symptoms of bird flu can look like many other diseases, and can present with a wide variety of symptoms, including:

  • Lethargy/depression
  • Poor or no appetite
  • Fever
  • Conjunctivitis (red, puffy, or inflamed eyes)
  • Discharge from the eyes or nose
  • Sneezing
  • Coughing
  • Difficulty breathing/dyspnea
  • Neurologic signs like tremors, seizures, unsteadiness, wobbly gait, weakness, or blindness

Bird flu usually starts with loss of appetite, lethargy, and/or upper respiratory signs (red or irritated eyes, nasal discharge. It can progress very fast to neurological signs. Cats can die within 24 hours of developing symptoms. If you see these signs, and your cat has any possibility of exposure, seek veterinary care immediately.

Bird Flu Transmission

As mentioned, bird flu is transmitted easily to cats via raw milk. There have been no documented cases of milk causing disease in any other species, including humans. If you’re in a state where raw milk is legal, like California, DO NOT give it to cats. More than 1,000 dairies in the U.S. have documented bird flu cases. (Raw milk can transmit other disease-causing bugs, too, so do use caution for all species.) Fortunately for the cows, most of them don’t get very sick, and the vast majority recover.

There have also been cases where cats and other animals have gotten bird flu from raw meat. Now, before anyone gets on their high horse about “it could have gotten into the meat from the air!” let me assure you that the science is very solid. The genetic fingerprint of the virus from the meat and the dead eaters of that meat is specific down right to a particular molecular trigger. It is a red hot, smoking gun.

In the first well-publicized case, it wasn’t just two housecats, it was 17 animals, including 15 exotic and big cats and one fox. The virus was tracked to the exact farm where the infected turkeys were raised. The same meat was consumed in all cases.

Two other batches of infected raw cat food from other companies were subsequently recalled after deaths were reported. Fortunately one cat did survive.

Whether bird flu can be transmitted between mammals is controversial. The evidence suggests that it can be, but it’s not common. Fomites (inanimate objects like buckets, boots, or milking equipment) are the most likely culprits in dairies. Nobody is entirely certain exactly how the cows got it in the first place, though wild birds are sure to be involved.

While research is still in its early stages and not nearly enough testing has been done, we also know that mice, rats, and squirrels can also get, and likely transmit, bird flu. Therefore it’s very important to prevent cat predation on rodents as well as birds.

It’s also important to know that the bird flu in cats is very unlikely to mutate into a form that will cause a human pandemic. Humans’ body temperature is lower than most other affected species, and the virus does not survive in our nasal passages. It is most likely a dead-end infection in cats. (Infections in other animals, like birds and pigs, who are essentially mutation factories, are a far bigger concern!)

Testing

There is a good test for bird flu, and every state diagnostic lab in the U.S. has it, because H5N1 has been found in all 50 states.

Unlike rabies, which requires the cat to be dead for testing, living cat samples (blood, urine, saliva, eye or nasal discharges) are totally acceptable and accurate for testing.

If you have a cat with signs of bird flu and a history of possible exposure (for example, my cat Perry Christmas was very good at catching mice inside the house), your veterinarian can submit samples. USDA has even been paying for testing at the state lab (but it’s only $50 if they don’t). We really need the data!

The Big Conundrum

A lot of media and even some reputable research institutions have been very alarmist about bird flu. No doubt it’s a serious disease, and it can be fatal to many species besides cats, including humans.

Some headlines have trumpeted a supposed 90% fatality rate in cats. This is absolutely false and I don’t want you to worry about that! There have been many cases of exposure where the cats didn’t get bird flu at all, and many cases where cats have had milder cases and recovered.

The 90% estimate comes from cases where the cat progressed to neurological disease. This can happen very quickly. And indeed, 90% of neuro cases will in fact die.

But I suspect that there is a lot more bird flu going around in cats than anyone thinks. The symptoms mimic several other viruses, including the very common feline herpes and calici viruses, which almost all cats carry, and veterinarians see every single day. Vets are not going to send samples from every weepy-eyed, snotty-nosed cat to the diagnostic lab. If symptoms progress, that’s the time to consider avian flu and to take more serious steps to diagnose (and, of course, provide major supportive treatment!).

But more testing of symptomatic/exposed cats can only increase our database and help us understand the scope of the problem. Then we can do a reality-based assessment and not go around fear-mongering like some are fond of doing!

The Current Situation

As of September, 2025, 144 cats have died from bird flu. Many infections were associated with raw milk and raw meat. The most recent case (July 2025) was a cat in San Francisco that had eaten a raw chicken-based cat food. Two other unrelated cases occurred in July.

Since 2022, 648 cases have been documented in the U.S. in wild, captive, and domestic mammals, including mice, foxes, bears, dolphins, seals, and skunks. H5N1 is still globally widespread.

Infected poultry are still being found. When that happens, all the birds in that facility are killed. (This is unfortunate but necessary. Poultry do not live long enough to develop herd immunity.) Just since mid-September 2025, infection was confirmed in 28 commercial and 19 backyard flocks. Just this week (10/17/25) three large turkey farms in Minnesota lost 183,400 birds. Expect very expensive holidays this year if you’re not a vegetarian! The virus has also infected more than 1,000 dairies. Cows have a very high survival rate, and provide a reservoir of infection for wild birds from waste lagoons. Avian influenzas can circulate for years, and this one will persist for quite some time.

Preventing Bird Flu

So now that you know more about bird flu than you ever wanted, let’s talk about how to prevent it. Even if most infections are mild, you don’t want your cat to get it!

I’ve been contemplating and refining my recommendations for the past year. They are based on the latest science, my own knowledge base, and many conversations with scientists, diagnosticians, and colleagues. I am more cautious (okay, a little paranoid) than others, especially about raw meat. Perhaps I know more than is good for me about how meat is grown and processed (and especially about the pet food industry), that makes me much less trusting. But I’ve been directly involved in the pet food industry for over 20 years and this is where I’ve landed.

My biggest concern is for cats who go outdoors or hunt at all. Preventing access to wild birds and rodents is key.

Here are my current tips for keeping your cat safe:

  1. Keep cats away from backyard chickens, wild birds,  mice, rats, shrews, voles, squirrels. Put fine mesh screens on all outdoor catios and habicats to keep out tiny prey.
  2. Never feed cats raw milk or cheese made from raw milk. The virus can persist in these foods for many months.
  3. Preferably choose commercial raw food that has undergone HPP (high pressure pasteurization) .
  4. Cook grocery store poultry and non-HPP raw cat food to 140oF (60oC).
  5. If you are cooking a balanced commercial raw food, add a small amount of B-vitamins and extra water or broth to make up for what’s lost in heating.
  6. Whole cuts of beef, lamb, rabbit, elk, and other non-poultry meats (except pork and seafood) are probably safe to feed raw.