As with any emerging disease, we have more questions than answers, but we can make some interim assessments based on general principles of infection control, and what we’ve learned over the past couple years about this particular H5N1 influenza A virus that’s been circulating in wild birds all over the world, and spilling over into many different species of mammals (including cats), along the way. The details are likely to change over time as we learn more, but this is where I see things at the moment.

Cats can get infected with this H5N1 influenza strain

We’re known this for a while. There have been infected cats (big and small) in various countries over the past couple of years. It’s a bit cumbersome, but there’s good tracking of avian influenza cases in mammals worldwide on the WOAH (World Organization for Animal Health) website.  As with most infections, we no doubt only diagnose a small subset of infections that actually occur (just the tip of the iceberg).

Infections with H5N1 influenza in cats are rare

Notwithstanding my comment above about underdiagnosis of cases, we need to keep this in context. There have been millions upon millions of infected birds all over the world in the last few years. There are lots of cats in areas where infected birds have been present, and cat-bird contact is far from rare. So, there’s likely been lots of exposure, but disease (at least serious disease) in cats has been rare; that’s a bit of good news.

Although H5N1 infections in cats can be severe, social media claims of “100% mortality” are overblown

As we’ve seen in many other mammals with spillover infections (but fortunately not humans so far), infected cats can have very severe disease, including fatal infections, typically with severe neurological signs. It can be very bad, but it’s presumably nowhere near 100% fatal.

  • We’re missing a lot of context because of testing bias, because we’re mostly only testing cats with severe signs of illness, or cats that are found dead in areas where birds have avian flu.
  • We don’t do enough testing of other cats that have been exposed but are still healthy, or only have very mild disease. We just don’t know enough yet to say what the true morbidity or mortality rates are in cats.
  • For all the hype, getting samples from exposed cats to test is a challenge. I’ve been set up for a while to get samples from cats with wild bird contact, but despite there being lots of outdoor cats and lots of infected birds, I haven’t been able to get any samples. (But when the dairy cow news broke this week, I made sure my PAPR was charged and my sampling kit was ready, in case there’s now more motivation to test.)

We don’t know whether H5N1 infected cats can be infectious to others

With only a small number cats tested, it’s hard to gauge the risk of transmission from cats to other animals (or people). Hopefully we’ll get more information about the cats on infected dairy farms. A challenge with multiple cats being infected in a situation like this is sorting out if they were all exposed to infected birds, all exposed to infected cattle (especially contaminated milk) or whether there may have been some cat-to-cat transmission of the flu virus. There’s very little we can do to sort that out when investigating a single farm at a single point in time. We can infer some things from testing results (particularly from quantitative viral loads in respiratory and fecal samples), but it’s still a bit of a guess without more testing and epidemiological investigation.

What can the average cat owner do?

If possible, keep your cat inside, as it minimizes any risk of exposure to infected wild birds (which are still the main source of H5N1 influenza). That’s not always possible though, since some indoor-outdoor cats simply won’t tolerate being inside 24/7, and some outdoor cats can’t be moved indoors.

Take our three cats as examples:

  • Milo is an indoor only cat. He’s low risk.
  • Rumple was adopted through the Guelph Humane Society’s working cat program as a barn cat since he was deemed unsuitable for indoor living. He’s actually a huge suck and now spends a lot of time inside, but he wouldn’t tolerate it full time (I’m not sure he’s ever used a litter box).
  • Alice is an outdoor cat that Rumple adopted. She was a scrawny, completely feral cat who started living with Rumple in the garage, and on our deck. She’s a sweetie around us now, but only on her terms. She will take a few steps in the house (very warily) and then dart back outside, but when outside she’ll roll around on us and purr her head off. She cannot be moved inside. We can make sure she and Rumple are well fed (they’re both on the chunky side), but can’t guarantee they won’t hunt anyway. So they (especially Rumple) are a risk as a bridge from outside to inside. We know that and accept the risk.

People who have indoor/outdoor cats should assess the risk, the ability to change their cat’s living arrangements, and their risk tolerance.

We can also try to discourage mixing of cats and birds. Removing bird feeders from yards is a simple step that I’d recommend at this point.

What if an indoor/outdoor cat gets sick?

Most of the time, the cat won’t be sick from flu, but it’s a possibility, and the risk would be higher if the cat is a known hunter and if there’s recent flu activity in local wild birds. In that event, I think it’s reasonable for owners to limit close contact with the cat, consider wearing a mask if close contact is required, and talk to their veterinarian about testing (for flu and/or other causes). We can’t freak out every time a cat gets sick, but acute onset of severe respiratory and/or neurological disease in an adult indoor/outdoor cat would raise a lot of concern, since that’s uncommon in otherwise healthy mature cats. (Young kittens are a completely different story – they’re upper respiratory snot factories at the best of times.)

What should veterinarians when presented with a sick cat?

I don’t think we’re at the point of saying respiratory PPE should be worn for handling every sick cat. A risk assessment is always appropriate, and ideally there’s a triage process over the phone prior to any sick cat entering the clinic. If the cat has outdoor exposure, especially known exposure to wild birds, and the cat has an acute onset of respiratory or neurological disease, it makes sense to start off with enhanced PPE (e.g. mask, eye protection, gown, gloves) until the situation is sorted out

Are there any concerns about H5N1 influenza and raw meat diets?

Maybe. There are a variety of reasons why raw diets create disease risks (Salmonella being a big one), but there are some specific concerns about the H5N1 virus in these diets too. Last year, there were reports of outbreaks of H5N1 infection in cats linked to raw diets in Poland and South Korea. However, confirmatory data has been lacking, so it’s unclear how strong the link is. It’s probably also mainly or solely a risk from very fresh diets.

I’d use this as yet another reason to avoid raw diets. If someone wants to feed a raw diet, high pressure pasteurized diets should be considered as that likely eliminates influenza virus.

What am I doing about H5N1 influenza in cats right now?

I’ll keep an eye on Rumple and Alice for any signs of illness. If they get sick, I’ll keep them away from everyone, sample them, and go from there. If they have severe illness, I have a plan to manage that, but that’s more medical than I want to get into here. Beyond that, I’m staying aware of the situation and will act (and adjust) as necessary.

What about the risk of H5N1 influenza in dogs?

Separate species. Separate story. But, we know dogs can be susceptible to H5N1 influenza too (but likely even less commonly than cats). Keeping dogs away from potentially infected birds is important at this point, especially dead birds that are higher risk for having died from infection. (That’s something that’s important for me since we live in the country and own Labradors that consider basically anything (live or dead, organic or not) to be a potential snack.)