Yesterday, I discussed a situation where avian flu was suspected in the deaths of a reasonably large number of cats in Poland. “We need more information” was a big part of that, and as of today a few new pieces of the puzzle have come to light.

It’s now reported that H5N1 was detected in 9 of 11 samples from cats. Positive samples were from three different cities, which is a very important finding. A reasonably large number of cats affected (and this likely being the tip of the iceberg) from multiple different cities definitely raises concern, since this wasn’t just one group of cats exposed to the same infected bird or group of birds. Bird-to-cat jumps must have happened multiple times in multiple locations, and that’s not good.

Why might there be a large number of affected cats in this case?

The most logical explanation to me is that there’s a big outbreak of avian flu in the types of birds with which cats have more contact. Birds that live in cities and are more likely to be caught and eaten by cats. In parallel, there could be greater awareness of the risk of transmission of H5N1 to cats, so people are looking for and testing sick cats.

Regardless, this shows us we need to keep investigating. “Dozens” of potentially affected cats is still a pretty small number in the grand scheme of things, but it’s a lot for an infection that has been assumed to be a rare event, particularly considering we likely detect only a small minority of spillover events into animals. Every spillover to a mammal creates more opportunity for the virus to adapt to mammals (including humans), and when the virus infects domestic animals or animals with which people or domestic animals have more contact, spillovers increase the risk of human exposure. We’ve been fortunate that the serious impacts on mammals have, so far, avoided people. However, it’s a dynamic situation and we need to be vigilant (but not paranoid).

  • We need continued research to figure out what’s happening.
  • We need to use basic preventive measures to reduce spillover into domestic animals.
  • We need to prioritize vaccine development for humans and domestic animals in case it’s  needed.

A couple of days ago, there was a ProMed request for information following a report of a large number of dead cats in Poland. The cats were reported to have had respiratory and neurological disease, so my thought process went to “that fits with avian flu spillover,” then “but that large of a number would be really surprising.” However, it had to be on the radar given the clinical signs, limited other diseases that would cause that type of clinical presentation in otherwise healthy adult cats, and the dynamic nature of this massive international H5N1 avian flu pandemic.

Details are still pretty sparse, but there are now various reports that “flu” or “avian flu” were identified in at least some of the dozens of dead cats. That obviously raises concern and highlights a need for more detailed information.

It also gets me thinking about a few big questions:

  • Were these actually H5N1 avian flu infections?
  • Was this one transmission event (e.g. a bunch of cats exposed to the same source of virus) or multiple spillover events?
  • Was this likely all bird-to-cat or was cat-to-cat transmission also involved?
  • Have there been less severe infections in cats in the same area?

The last question is a big one. Right now, we know very little about the range of clinical signs in infected cats (and other species). The risk calculus is a lot different if this virus always causes severe/fatal disease versus if it causes a range of disease. We are more likely to find severe disease, especially in wildlife and feral animals, because we don’t notice mild illness as well in those species. Very sick or dead animal are much more likely to be caught and tested.

  • If there was group of 10 dead cats, odds are pretty high that would be recognized and at least some of the cats would be tested.
  • If there was a group of 10 cats with transient fever, cough and lethargy, that’s much less likely to be noticed (and the cats are less likely to be caught and tested).

That second group might be really important though. From a population standpoint, a virus that kills consistently and quickly is generally less likely to spread compared to one that causes more mild, prolonged illness, especially if the animal is still moving around and interacting with other animals.

Said another way, a big question is whether severely ill cats are the norm for H5N1 spillovers or whether they are just the tip of the iceberg. If the latter, then we have a much greater need to figure out what the risk of spread from them is. We haven’t really been able to explore this well yet here in Ontario because of logistical challenges, but the situation in Poland may help shed some light on the matter if more testing of live cats is done as part of the investigation.

(TL:DR… check out the TikTok version at the bottom)

When I was a newly graduated veterinarian in general practice, I gave puppies and kittens their first rabies vaccine at 16 weeks of age. That was the standard at the clinic and a common practice elsewhere. Now, if I ask audiences of veterinarians when they vaccinated against rabies, I’d say a majority still say 16 weeks.

But is waiting until 16 weeks to vaccinate against rabies a good approach?

When we vaccinate young animals, we’re aiming for the sweet spot of vaccinating them as young as possible, but at a time when we’re confident the vaccine will work. Antibodies that animals get from their mothers can interfere with vaccines, but those antibodies wane over time. We give a series of “core” vaccines (e.g. parvovirus and distemper virus in dogs) starting at a young age, knowing that they may not respond initially but eventually will, as maternal antibody interference disappears.

For core vaccines, we want to give at least one dose at 16+ weeks of age. However, rabies vaccine can be given earlier. Rabies vaccines in Canada are licensed for use at 12 weeks of age. In Ontario, the legal requirement is vaccination of all dogs and cats (and ferrets) against rabies at 3 months (12 weeks) of age.

So, why are puppies and kittens commonly vaccinated for rabies at 16 weeks?

The main reason is probably habit – “that’s what we’ve always done so that’s what we do.” Another reason is a focus on getting puppies and kittens back for that critical 16 week core vaccine. There’s concern that if people are fixated on the need for rabies vaccination for their pet, if they get it at 12 weeks, they may not be motivated to come back at 16 weeks, and therefore might put their pet at high risk of getting other serious disease like parvovirus or distemper.

12 weeks vs 16 weeks… what difference does 4 weeks make?

Most of the time, nothing, but sometimes, it’s life-and-death. Earlier vaccination means earlier protection from rabies. However, probably as importantly, earlier vaccination reduces the risk of significant isolation requirements if the animal is exposed to a potentially rabid animal.

For example, let’s say a 16 week old puppy was outside in the yard and night, and fought with an abnormal-acting raccoon. The puppy has some bite wounds, but the raccoon ran off and can’t be tested for rabies. This would typically be considered a potential rabies exposure.

Scenario 1: Puppy was vaccinated at 12 weeks of age. It’s been more than 28 days since the vaccine, so we’re quite confident it’s protected. In Ontario, that means we would give a booster vaccine within 7 days, and they there would be a 45 day observation period. That’s pretty minor and mainly means minimizing the animal’s contacts outside the household and keeping it on a leash when off the property.

Scenario 2: Puppy hasn’t yet been vaccinated (or was vaccinated so recently that it’s not considered protected). There are major implications here. If the puppy gets a rabies vaccine within 7 days, it gets a 3 month “precautionary confinement period” (basically, quarantine, but there are legal connotations to that word so government guidance avoids it). If a post-exposure vaccine isn’t given, the confinement period is extended to 6 months. This is a much bigger deal than Scenario 1 because it requires keeping the puppy at home at all times (unless medical attention is required), limiting contact to one age-appropriate caretaker, preventing contact with other people or animals, only going outside on a leash and in a fenced area (double barrier to escape) and keeping the puppy in a secure indoor area that allows the caretaker to observe the animal before direct contact and prevents accidental escape when indoors (for example, double door entry).  That’s tough to do with a puppy and sometimes, euthanasia is elected instead. Even if owners chose to proceed with confining the puppy, it can have a major impact on the puppy’s socialization and increase the risk of behavioural issues later in life.

So, from my standpoint (plus the legal requirement here), we want to vaccinate puppies and kittens as close to 12 weeks as possible. It’s rare that a 4 week delay would cause a problem, but when it does it can be major. We also want to make sure that doesn’t result in puppies and kittens failing to come back for that critical 16 week core vaccine, but we can educate owners about the need for that.


What age should puppies and kittens be vaccinated against rabies?

♬ original sound – Scott Weese – Scott Weese

There’s nothing too earth-shattering here, but a few useful changes pertaining to rabies regulations are coming to Ontario as of July 1, 2023.

  1. Medical officers of health (MOHs) will have the ability to require rabies testing of animals that have died or are euthanized during their 10 day observation period after they’ve bitten someone.

When a person is bitten by a dog or cat, it needs to be reported to public health, and the animal undergoes a 10 day observation period. Based on what we know about rabies shedding, if the animal is still alive and neurologically normal on day 10, it could not have transmitted rabies to the person via the bite on day zero. That means the bite victim can relax and doesn’t require rabies post-exposure prophylaxis (PEP).

Previously, if an owner animal died or had to be euthanized during this period, MOHs didn’t actually have the authority to require testing. They could recommend, ask, cajole… but the wording was vague enough that animal owners could refuse to have their animal tested. In the past, owners consented to the testing most of the time, but not always. Now, testing can be mandated, since otherwise, we couldn’t rule out rabies and the person that was bitten might have had to undergo unnecessary PEP.

  1. Rabies vaccination requirements will allow for vaccination outside of Ontario, under certain conditions.

The current wording in Regulation 567 requires all dogs, cats and ferrets over three months of age (and certain horses, cattle and sheep) to be vaccinated for rabies by a veterinarian that’s licensed in Ontario and with a vaccine that’s approved in Canada (I think a lot of veterinarians in Ontario don’t actually realize this). It makes sense to require re-vaccination of many imported dogs, but not all, especially those vaccinated in the US where veterinary training, vaccines and documentation requirements are basically the same.

After July 1, rabies vaccination will be considered adequate if performed by a veterinarian licensed anywhere in Canada or the US, with a vaccine licensed in the same jurisdiction, and accompanied by proper documentation (i.e. a vaccination certificate that meets the requirements listed in the Ontario Regulation 567).

So, the retired person that spends the winter in Florida and gets their dog vaccinated there doesn’t need to get the dog re-vaccinated again upon returning to Ontario (at least until the US vaccination expires). The imported dog from overseas where we may have less confidence in the reliability of the vaccine, documentation or reporting still needs to be re-vaccinated on arrival in Ontario.

The Ministry of Health and College of Veterinarians of Ontario have provided a decision tree to help clarify rabies vaccination requirements in imported animals:

Yes, I’m prone to making typos. No, this title isn’t one of them.

While we’re in the midst of an unprecedented international outbreak of H5N1 avian flu (with ongoing spillover into mammals), there’s a new kid on the block: H5N5 influenza. I think recent reports of H5N5 were glossed over by some who didn’t realize we’re talking about a different strain from the H5N1 we’ve been dealing with the last couple of years. While it’s not necessarily a game-changer, we need to pay attention to new strains like this.

The story starts with the finding of H5N5 flu in birds in Atlantic Canada, which started in January 2023. The genetic makeup of the virus indicates it’s a Eurasian lineage that’s circulating in birds in Europe. It’s suspected that it made it to Canada via migratory birds last fall.

More recently, and more concerningly, this H5N5 strain was identified in two raccoons in Charlottetown, Prince Edward Island. As far as I know, this is the first report of H5N5 in mammals. Presumably the raccoons were infected from eating infected birds, which is how we suspect most mammalian wildlife with H5N1 get infected too.

With reports of “new” diseases, we always have to consider surveillance bias. We’re looking and testing a lot more now because of H5N1, so we’re more likely to find other things (such as other strains, like this) as well. That raises the question of whether this is truly something new or just something we’ve found now because we’re looking harder. Based on the genomics of the virus (being a Eurasian lineage), it’s probably something new for this region.

Regardless, the presence of yet another avian flu strain and more spillover into mammals is a bit disconcerting, to say the least. Recent genetic study of this H5N5 virus has indicated that it’s likely also capable of long-term circulation in birds and recombination with other flu viruses, so this is a virus to watch.

That’s not to say that we’re heading into a massive H5N5 outbreak. It’s one more flu virus in the mix, one more flu virus with the potential to recombine with other (human, avian, swine, equine, canine, etc.) flu viruses, and one more flu virus that can (even in its current state) spillover into mammals. So we need to stay on alert. There are lots of influenza viruses out there: some are nasty, they are prone to changing, and sometimes that can be bad for humans or other species.


I get a surprising number of emails from people concerned about Baylisascaris procyonis, the raccoon roundworm. Some are just a bit concerned while others are almost paralyzed by fear at the thought of this parasite lurking in the environment. Most of my responses are largely re-assuring people that the risk is very limited and there are some easy things that the average person can do to avoid infection with this parasite. However, it can cause serious disease, so we can’t dismiss it entirely.

A recent paper in Emerging Infectious Diseases (Lipton et al. 2022) highlights both sides of the story: that Baylisascaris infection is a potentially nasty disease, but it’s really rare in people and largely restricted to some extreme situations.

What is Baylisascaris procyonis and what is the concern?

  • This is the raccoon roundworm, an intestinal parasite that normally lives in the gut of raccoons (the “definitive host”). Dogs can also be definitive hosts, but this is very rare.
  • Roundworm eggs are passed in feces of definitive hosts. Then they become infectious after 2-4 weeks in the environment, and if a definitive host (like another raccoon) or a typical paratenic host (like a rodent) then ingests them, the life cycle continues.
  • However, when roundworm eggs are ingested by other species (accidental hosts), the parasite can do strange (and nasty) things, because it doesn’t follow its normal life cycle. In these cases, after the eggs hatch in the gut, the larva migrate through the body and keep migrating, potentially damaging various tissues depending on where they go (a condition known as larva migrans). If they go to the brain, the damage can cause serious neurological disease. When that individual is a small animal and is eaten by a definitive host, that also perpetuates the life cycle.
  • For people, the concern is migration of the parasite larvae through sensitive tissues (e.g. brain, eye).

The Lipton et al. (2022) report describes severe neural larva migrans in a 7 year old autistic child. The fact that the child had autism and developmental delay is a key part of the story, since this child was predisposed to eating abnormal things (pica), which can lead to ingestion of things like feces encountered in the environment.

The child started exhibiting periods of abnormal neurological signs including impaired movement, lethargy and difficulty responding to commands. If you want more clinical and diagnosis details, they’re in the paper, but the child was ultimately diagnosed with eosinophilic encephalitis. Eosinophilic disease often points towards a parasitic cause, and treatment with albendazole was started. The child was reported to have played in a sandbox that had feces in it, and had been around farm animals, leading to concerns about a zoonotic infection. A blood test detected antibodies against B. procyonis, rounding out that suspicion.

After about 12 days in hospital, the child was discharged, with ongoing but improving symptoms reported a month later. This is actually a really positive outcome for neural larva migrans. Severe infections resulting in death or severe long term impairment are common. Whether the milder disease was because of a lower level of parasite ingestion, few larvae making it the brain, early treatment or some other factor isn’t known, but it was good to hear the child was recovering. Only time will tell if he fully recovers.

Upon further investigation, a raccoon latrine (a place raccoons defecate and where there can be a large amount of accumulated feces) was found at the patient’s house. The parents also recalled seeing the child put something from the ground in his mouth in the area near the latrine. Some raccoon fecal samples were subsequently collected from the area and the parasite was identified.

How common is B. procyonis in raccoons?

  • Very. The majority of raccoons in some (maybe all) regions are infected. It’s reasonable to assume that any raccoon is infected and that any raccoon feces potentially contain B. procyonis eggs.

How common are B. procyonis infections in people?

  • Really rare. The total number of reported cases in people in the dozens. However, we have to assume that there are other serious cases that don’t get reported, as well as likely a larger number of mild infections that never get identified. Still, considering it’s pretty much ubiquitous in raccoons and that we have close indirect contact through shared environments, it’s a very rare disease.

How do people get infected with B. procyonis?

  • This is a don’t eat poop” disease. Actually, it’s a “don’t eat raccoon poop that’s been sitting outside for more than 2 weeks” disease. Exposure to fresh raccoon feces poses no risk since it takes time for the parasite to become infective after it’s been passed in feces.

Does it take a lot of exposure to get infected with B. procyonis?

  • Presumably yes, it takes a lot of exposure to develop a clinical infection that causes signs of disease. Since there are lots of people who work a lot with raccoons (e.g. raccoon rehabbers) and in areas where raccoon defecate, but disease in people is really rare, that speaks to the limited risk, even with exposure to highly contaminated areas. It’s quite likely that there’s a much larger number of people that get exposed, mount an immune response and never get sick. A study from a few years ago reported antibodies against B. procyonis in about 7% of people tested in Santa Barbara, California. However, those were healthy people, so even if they were infected, it’s not a big deal if it doesn’t cause disease.
  • The main risk of disease, as seen the case reported above, is likely when a large volume of raccoon poop is ingested. That’s typically a concern in people with developmental disorders that lead them to eat atypical things. Avoiding that type of exposure is the key.

What can the average person do to avoid B. procyonis?

What about someone living with a person prone to pica?

  • It takes diligence to be on the lookout for lots of things that can pose problems for someone with pica. Caretakers need to be very diligent about looking for feces in the environment, picking up feces so that eggs cannot become infective, discouraging raccoons from setting up residence in structures (e.g. sheds, attic), looking for raccoon latrines and (if identified) both cleaning them up properly and discouraging raccoons from coming back.

What if someone is known to have ingested raccoon feces?

  • I get called about these situations periodically, and it leads to a decision by the physician whether preventative treatment is indicated. I’ve known parents to have pulled feces out of kids’ mouths (to reduce exposure and have something to test). Ultimately, it comes down to whether the physician thinks the exposure risk was high, and if so, treatment is often provided. More information about B. procyonis for health professionals is available on the CDC website.

So, the messaging about this parasite in people is often a challenge:

  • It’s a parasite that can cause fatal or debilitating disease, but it rarely does so.
  • Eggs can be present in many environments, but the risk is probably mainly in high risk sites like raccoon latrines.
  • We don’t know the infective dose, but for disease to occur in people it’s probably quite high.
  • Any pile of raccoon feces can be contaminated, but fresh (less than 2-4 week) feces pose no risk.
  • Common sense practices to keep raccoons away and keep feces out of peoples’ mouths are the key. It’s nothing fancy but some basic hygiene can go a long way.
  • Awareness is good, but this isn’t a disease to keep you up at night worrying.

Image from https://www.cdc.gov/parasites/baylisascaris/biology.html

While I get lots of interesting infectious disease questions every day, most aren’t new.


This one was.

To paraphrase, the question was basically “If we want to minimize the number of injections when vaccinating a dog, can we mix rabies and core (e.g. distemper, parvovirus, adenovirus) vaccines in the same syringe, using rabies vaccine as the diluent for the core vaccine?”

Some animals are hard to inject once, let alone twice. Mixing two vaccines into one syringe would make it a one-shot deal, which has appeal. But are there potential downsides?

There are probably at least a couple of major downsides to consider.

Rabies vaccine is a killed vaccine. “Core” vaccines are infectious (modified live) vaccines. For infectious vaccines to work, the modified (weakened) viruses must still be able to cause a low grade infection, to induce an immune response. If rabies vaccine is mixed with the modified live vaccine, I have no idea what would happen to the modified live organisms. It’s plausible that components of the rabies vaccine (which are not designed to support microbial growth and may contain preservatives to inhibit microbes) could inhibit the core vaccine. So, I wouldn’t have confidence that the core vaccine would work as expected.

Would the rabies vaccine work?

I’m less concerned about the killed rabies vaccine being impacted by the live core vaccine, but the key is I don’t know, and I doubt anyone has any data on that. That creates a couple of different levels of risk.

  • If we (veterinarians) use a product in a manner not according to the label, we’re getting into unknown territory. Consider whether the owner would be told that we’re doing something that might inhibit the vaccine(s) from working. We can’t state with confidence that what we’re doing (and charging for) is likely to be effective.
  • From a regulatory standpoint, the bigger issue is whether the rabies vaccination would be effective. The expectation is that we are giving rabies vaccine as per the label. If we don’t, but we indicate that the animal is properly vaccinate, that’s dodgy. A rabies vaccination certificate assumes the vaccine was given according to label directions. If the dog was exposed to rabies, it’s far from guaranteed that it would be properly protected, which leads to significant issues with quarantine / confinement periods and managing the risks to the people / animals in contact with the exposed dog.

So, while I completely understand the desire to limit the number of injections, doing something like mixing vaccines in the same vial or syringe is something I’d stay away from.

For cats, there’s an easier solution. There’s a licensed vaccine that includes feline core vaccines and rabies vaccine. For dogs, if we want to give multiple vaccines, we need to give multiple injections to help ensure they’re effective,

As per usual, the annual US rabies state-of-the-union has been published in the Journal of the American Veterinary Medical Association (Ma et al. 2023). It’s the same general information every year, but always a good reminder of the ongoing challenges with rabies here in North America.

Here are some highlights from the animal-related statistics:

  • 3663 rabid animals were identified in 54 US jurisdictions in 2021.
  • Cases included the typical mix of rabies virus variants (strains). See the map below for details on the geographic distribution of the different variants.
  • Most affected animals were wildlife. Cases are always going to be significantly underestimated when wildlife are involved, since we only see and test a fraction of those animals.
  • The number of rabid wildlife was down 18% from 2020. I don’t put a lot of stock in a result like that, since testing patterns can have a huge impact on the numbers. Rabies in wildlife isn’t going away.
  • Rabid bats were found everywhere but Alaska, Hawaii and Puerto Rico.
  • Raccoons were the 2nd most common species affected (if we consider all the bat spceies together). Most rabid raccoons were in the northeast, where raccoon rabies has been a problem for a while.
  • Skunks were the next most commonly infected species, followed by foxes. All those species have their own rabies virus variant(s) and are considered rabies reservoir species.
  • Domestic animals were less commonly affected, but the consequences of infection in a domestic animal can be much greater because of the degree of exposure to humans and other domestic animals.
  • 216 rabid cats were identified, mainly from Pennsylvania, Texas, New York, Virginia, Maryland, Georgia and New Jersey. There were 36 rabid dogs detected, over half of which came from Puerto Rico, Texas, Georgia and South Carolina. One dog was imported from Azerbaijan and was infected with a rabies virus strain found there.
  • Other domestic species affected included cattle (40), horses (17), a mule and a goat.

Here are some of the human-related statistics:

  • Five people were diagnosed with rabies in the US in 2021. They all died.
  • Four were infected with bat rabies variants, and infection occurred as a result of direct contact with bats.  One person had a canine rabies virus variant that is found in the Philippines, and was infected as a result of bites from a dog while visiting that country.
  • Only 1 person sought post-exposure prophylaxis (PEP) to prevent rabies. Normally, PEP is almost 100% effective. The person who developed rabies despite PEP was a noteworthy event that was previously reported, and it was likely due to a previously unrecognized immune disorder.

As in the past, the report also includes quick blurbs about rabies in Canada and Mexico:


  • Still lots of wildlife rabies, with bats leading the way, followed by skunks and foxes (now that Ontario’s raccoon rabies situation is more under control).
  • Domestic animals that were infected included 2 cattle, 1 goat, 1 llama, 2 cats and 5 dogs. The imported dog that developed rabies that we’ve talked about here before is on top of that.
  • There were no human cases of rabies in Canada in 2021.


  • There’s continued surveillance for canine rabies, since Mexico has eradicated that rabies virus variant (last case in 2016). No canine rabies variant cases were found.
  • Two rabid kittens were identified, along with 67 domestic livestock with rabies.
  •  As in Canada, there were no human cases of rabies in Mexico in 2021.

As the unprecedented global H5N1 avian flu outbreak continues (with no real end in sight), and as we get the spring mix of migrating birds, mingling bird populations, more active wildlife and a pending crop of baby wild critters, concerns about spillover infections from birds to mammals are on the rise.

The current H5N1 influenza A virus has infected an impressive array of mammals. That doesn’t necessarily mean it’s worse (for mammals at least) than previous H5N1 influenza strains, as the higher number of spillover infections in mammals may just be because there are so many infected birds involved in this ongoing outbreak. However, it’s still concerning.

  • The good news is that the currently circulating strains are quite poorly adapted to infect and transmit between mammals.
  • The bad news is that could change.

There are various animal populations and situations to considered. One is animal shelters, because they handle lots of animals, many with outdoor access (and therefore access to wild birds) and with unknown histories. Diseases are common in shelter animals, and teasing out high-consequence infections from “routine” diseases is a daily challenge. Many shelters also take in birds, including wild birds and domestic birds like backyard poultry (a particularly high risk group when it comes to exposure and susceptibility to avian flu).

What do we need to think about when in comes to avian flu and animal shelters?

As with any emerging disease situation, answers to some common questions may change over time as we learn more and as the disease evolves, but here are some initial thoughts:

How common are H5N1 infections in mammals?

Spillover infections to mammals are rare. The exact incidence is impossible to say. Even if the spillover risk is really low, with millions of infected birds, we’re bound to see at least some transmission to other species – that part is just a numbers game. Some mammalian species seem at higher risk (e.g. foxes), maybe because of combinations of more frequent / higher exposure (e.g. scavenging infected birds) and greater inherent susceptibility. However, we probably need to consider all mammals to be at some degree of risk. At that same time, we have to remember that the vast majority of mammals with respiratory or neurological disease don’t have flu.

What are some flags in shelter animals that flu might be a concern?

There are two major things to think about here. One is risk factors for disease exposure, which are primarily related to the animal species (e.g. waterfowl or contact with waterfowl) and the local situation (e.g. lots of dead birds in the area).

The other factor to consider is the clinical status of the animal. We’re still learning about what this virus does to different species, and clinical signs can be highly variable. I’m going to be most concerned about animals with severe respiratory and/or neurological disease. There are other things that can cause these signs, and not all H5N1 infected animals will have these kinds of signs (especially early in disease), but a dog that’s in an area with dead birds that has respiratory disease and is starting to develop neurological disease would set off a lot of alarm bells in my head.

What’s the risk of spread of H5N1 from mammals in shelters to humans?

Human risks are low but not zero. The same applies to other mammal-to-mammal transmission. The currently circulating strains are still very poorly adapted to people and other mammals, so spillover infections are rare and transmission risks from a spillover infection (e.g. an infected cat infecting another animal or a person) are very low.

What’s the risk of spread of H5N1 between mammals in a shelter?

As for humans (another mammal), the risk is probably very low. This virus isn’t currently adapted for mammal-to-mammal transmission, so most mammalian spillover infections are probably “dead ends,” meaning the mammal can’t infect anyone else and the virus dies out when the animal recovers, or succumbs. However, “probably” dead ends is far from definitive. We have no real idea of the risk, because the infections are so rare and are difficult to study. Viral loads in some infected mammals (inferred by PCR results) seemed pretty high – high enough that I think transmission risk is plausible during some stages of infection in some animals.

So, we should assume that there is some degree of risk from any infected animal, albeit relatively low and probably fairly easy to mitigate.

Are there any issues with disinfection in a shelter if H5N1 may be present?

No. Surfaces pose limited risk (especially compared to handling an infected animal) and influenza virus doesn’t survive long outside the host. Any routine disinfectant will deactivate the virus – it’s just a matter of actually doing a good job of cleaning and disinfection so that the disinfectant can work.

How should H5N1 suspects be housed in a shelter?

Ideally, they aren’t. High risk cases (e.g. wild bird with neurological disease in an area with flu activity) are best triaged outside, and, if they are to be housed, for that to be done outside the main shelter. Setting up a secure outdoor triage area and housing area (even just for short term housing while testing is being done and more information is being gathered) can be invaluable, whenever possible. It helps protect individuals in the shelter, and also avoids any risk of other animals at the shelter potentially needing to be quarantined or euthanized by preventing exposure to infected animals.

If suspect animals have to be housed in the shelter, they should be isolated, ideally individually (though isolation of a group from the same area with the same flu risk is also reasonable). That would seem to be intuitive but it’s not always the case in shelters, since sometimes isolation units house a variety of different potentially infectious cases (e.g. all sneezing cats go into the same ward). However, we don’t want that here since we don’t want our flu suspect to be in the same room with another animal that has little chance of having flu. So, housing them in individual isolation is best, ideally a room with separate ventilation. Adding a HEPA filter to the room is never a bad idea (flu or otherwise).

How should H5N1 suspects be handled?

Handle suspects using contact precautions, including gown, gloves, mask (ideally N95/KN95/FFP2) and eye protection or a face shield.

And handle them as little as possible.

What about testing of animals for H5N1 (or other influenza A strains)?

Testing is great. Negatives are not a guarantee that an animal is truly not infected, but testing helps us identify infected cases so we know what’s going on, helps with getting compliance with infection control measures, and helps us to better understand the broader risks.

For domestic animals, testing is most often going to be at the shelter’s expense (despite the value of supporting testing in high risk situations). Shelters can burn through a lot of money testing every dog and cat with respiratory disease, so realistically testing would focus on animals with severe or atypical disease, especially respiratory and neurological disease combined, and where there’s a plausible chance of exposure to wild birds.

What to test is still a grey area because we don’t have much data. At this point, I’d recommend oropharyngeal, nasal and rectal swabs (in that order of priority). Also remember that the lab test must be able to detect H5N1. Not all tests do that, so it’s important to ask about the test itself before sending off a sample.

Remember: Sample collection is probably one of the highest risk human-animal interactions. Everyone involved in sample collection should wear proper personal protective equipment (PPE), including face/eye protection.

What is the risk to staff that have to recover animals from the field?

This work creates a few high risk situations, such as close contact with a struggling animal (e.g. if the animal needs to be caught and restrained) and being the same vehicle (enclosed space) for transport back to the shelter.

  • PPE should be worn for any contact with high-risk flu suspects.
  • For transportation of any suspect animals, maximizing ventilation (e.g. opening vehicle windows or maximizing flow-through air) is a good idea, and it’s reasonable to have anyone in the vehicle wear a mask (ideally N95/KN95/FFP2) and ideally also eye protection. The size of vehicle, position of the animal, type of animal, animal behaviour (e.g. barking) and travel time would influence risk.

Should flu vaccination of shelter staff be recommended or required?

Vaccination of staff is a great recommendation for a few reasons. One is just because human flu is an important cause of disease. Current human flu vaccines likely provide little to no protection against H5N1, but they are still useful in the context of this outbreak because we don’t want to create situations where multiple flu viruses can get together and make a new flu virus. The more people with human flu that are exposed to animals with avian flu, the greater the risk of multiple flu viruses recombining. Odds of that are very low in a shelter but they’re not zero, so it’s great to have high flu vaccine coverage of staff.

Related to that, people with potential human flu shouldn’t be at a shelter, for the sake of both routine protection of other personnel and to avoid making the shelter a human/avian flu mixing vessel.

What about vaccination of animals against H5N1?

For dogs, we have H3N2 and H3N8 vaccines, but those would offer little to no protection against H5N1. As with people, we want to avoid different flu viruses getting together in the same animal, so having the dog population protected against canine flu is never a bad idea. However, given vaccine availability issues, limited impact on virus shedding, the time required to have protective immunity from the two dose series, and cost considerations, it’s pretty low yield in this scenario.

That’s it for this morning’s flu thoughts. There will probably be a “Part 2” since I’m sure I’ll realize I missed a lot of questions as soon as I post this.

barn cat on wooden fence

The other day, I said that finding H5N1 avian flu in dogs was unsurprising. That also applies (probably even more so) to cats. We’ve known for years that cats are susceptible to H5N1, and since some cats spend a lot of time unsupervised outside and interact with (and eat) birds, they have lots of chances for (sometimes quite high) exposure.

The Wyoming State Veterinary Laboratory recently identified H5N1 in a barn cat from central Wyoming. It is suspected the cat was infected by eating infected waterfowl. Whether or not the cat was sick isn’t mentioned, but since it was a barn cat and testing for this virus isn’t common in cats, I’d guess that the cat was either very sick or died, and that’s why they tested it.

This follows a report from February 2023 of H5N1 in two cats in Nebraska. The first cat was an outdoor cat that died from severe and rapidly progressive neurological disease. Another outdoor cat in the same household also developed neurological disease shortly thereafter and was euthanized. The H5N1 virus was found in the brain tissue in both cases. Whether the two cats were infected from the same source or whether there was cat-to-cat transmission would be pretty hard or impossible to differentiate. The other two cats in the household were healthy and tested negative on nasal swabs.

Reports of this virus in cats aren’t overly surprising, and reflect rare spillover during a period when there’s an unprecedented amount of virus circulating in birds internationally. However, these rare cases still highlight the animal health risks from spillover infections, and the potential for domestic animals to act as a bridge between wildlife and humans.

So what should we do now?
Not really anything different from what we’ve already been recommending.

Keep domestic animals away from wildlife as much as possible. That’s tough with outdoor cats, but keeping cats indoors whenever possible (especially with avian flu is in the area) would be a good start. Some cats can’t stay indoors and there’s less we can do about them. Making sure outdoor cats are well fed helps but won’t stop them from hunting altogether, so we can’t eliminate the risk of exposure. Considering influenza infection in cats that have outdoor access and develop severe neurological or respiratory disease is important for surveillance purposes.

Can cats infect other cats or people with H5N1?

It’s hard to say. We generally assume that spillover infections are lower risk for transmission since the virus isn’t infecting its typical host. However, the first Nebraska cat had a really high viral burden in the brain, based on the PCR test results. It’s hard to say how much virus a cat with a central nervous system infection would shed in its respiratory secretions, but it’s still fair to assume there’s some degree of risk.

Should we take extra precautions when handling sick cats with outdoor access?

Sure. Based on what’s been reported to date, neurological disease is probably a big component of these infections, so we should already be taking precautions with these animals because rabies would be another possible cause of acute neurological signs. The same precautions will help prevent transmission of flu from such a cat. Outdoor cats with severe respiratory disease probably don’t have flu (since there are other more likely causes), but taking added precautions in veterinary clinics (e.g. keeping the cat isolated from other animals, use of PPE) and households (e.g. limiting close contact, attention to hand hygiene) are certainly reasonable.