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.

Labrador retriever in a field

I have Labrador Retrievers, so I’m well versed in dealing with the implications of what my dogs have been eating (Labs being prone to considering just about anything fair game for ingestion). Owning such a pair of environmental vacuums, the question of whether dogs might be at risk of H5N1 avian flu exposure from bird feces or other things in the great outdoors has a personal spin.

It’s a really common question these days, and we don’t have a really solid answer, and it’s a very hard thing to study. In natural settings, teasing out environmental exposure from direct bird-to-bird or bird-to-other-animal exposure is tough. We rarely have situations where we can clearly say “this individual was exposed to this and only this type of environment, and then did (or did not) get infected.” There’s also a species susceptibility component. Environmental transmission of H5N1 influenza to birds is likely very different from environmental transmission to mammals because of the lower susceptibility of mammals. Even within mammals, there’s likely a lot of variation in susceptibility of different species, and types / level of exposures they’re likely to have.

So is there cause for concern regarding exposure of dogs (and other mammals) to H5N1 flu from bird feces in the environment?

Yes, to some degree. Environmental exposure has been identified as a risk factor for human H5N1 infection in the past, but that’s usually from contact with very high risk environments like infected farms or markets, or where people live with poultry (e.g. in the household). More recently, environmental exposure was deemed to be the most plausible source of infection with H5N1 influenza in a person in Chile.

So, there’s a plausible risk of environmental exposure to this virus, but it’s hard to extrapolate those reports to common casual outdoor exposure to bird feces or other sources. We also have to remember that these are rare incidents during an outbreak where millions of birds have been infected, and have been shedding a vast amount of flu virus into the environment.

What types of environments are of greatest concern?

The more infected birds in a particular area, the greater the risk the virus will be present in the environment. That’s pretty obvious. One infected bird can shed a little bit of virus, ten thousand infected birds can shed a whole lot more. But the risk doesn’t depend solely on the amount of virus expelled by birds; it also depends on things like how well the virus survives in the environment, and how people or other animals are exposed.

Does the H5N1 influenza virus survive long in the environment?

Yes and no. Fortunately, flu viruses don’t usually survive well outside the body. If it’s dry and sunny, the virus will die pretty quickly (typically within hours). But, if the virus is in a nice protected environment, it can survive for longer periods of time (potentially days or weeks).

Can a dog get H5N1 influenza from eating bird poop?

Potentially. It would have to be fairly fresh poop from an infected bird, with enough of a viral load to cause infection (but we don’t know how much of a load that is for a dog). I’d say the risk is pretty limited in most situations. However, if a dog is “grazing” in an area with a lot of infected birds and a lot of bird poop, there’s going to be some risk.

Can a person or dog get infected from virus on someone’s shoes if they walk where infected birds have been?

This is getting into the “theoretically possible but extremely unlikely” area. It’s not impossible but there are bigger things to worry about. That said, if there are lots of birds in an area and flu is active, it’s wise to stay away (and not just to keep your shoes clean).

Overall, I’d say the risk of H5N1 influenza infection in dogs from normal activities like walking in a park is low. It’s not zero, but it’s low enough that people shouldn’t panic. Like most things, it’s a matter of balancing costs and benefits of preventive measures. A bit of common sense goes a long way:

  • Stay away from areas with lots of birds.
  • Be more restrictive about outdoor activities when flu is active in birds in the area.
  • Avoid direct dog-to-bird contact (including both live and dead birds).
  • Avoid situations where direct dog-to-bird contact is more likely to happen (e.g. lots of territorial or habituated geese, like in many public parks).
  • Avoid areas with obvious accumulations of bird poop.

And the most important measure:

  • Keep dogs away from sick or dead birds.

This can be filed under “concerning but not surprising,” but H5N1 avian influenza has been identified in a dog in Ontario

It’s concerning because any spillover into mammals raises concerns about continued adaptation of this virus to spread outside birds, and because spillover infections in mammals can be severe. 

It’s not surprising because when you have millions of infected birds internationally, it’s inevitable that domestic and wild mammals will be exposed. Even if transmission is rare, when there’s a lot of exposure, transmission becomes more likely to occur and to be detected.

The case at hand is a dog from Oshawa, Ontario that died several days after being found scavenging a dead goose. Both the dog and goose were tested for H5N1 highly pathogenic avian influenza (HPAI) virus, and both were positive. Sequencing of the virus at the National Centre for Foreign Animal Diseases was performed and the virus from both the dog and goose were the same, and were consistent with the H5N1 strain that’s circulating in wild birds and domestic poultry. Further testing is being performed to confirm the cause of death in the dog. Given what we know about spillover infections into related species like foxes, it’s certainly possible that avian flu could have contributed to the dog’s death.

What should people in Ontario (or anywhere else avian flu is circulating) do?

  • Relax. That’s the first thing. This is concerning but not a doomsday scenario. We know that spillover into various mammals is happening and it will continue to happen. Also, this was a pretty high-exposure scenario where a dog had a lot of direct contact with a bird that had died of avian flu. It’s a reminder of why we’ve been emphasizing the need to try to better understand this virus since the outbreak was first identified, and to try to prevent more spillover infections from wild birds.

The next step is to just take (or continue to use) some basic common sense measures to reduce the risk of exposure.

What can be done?

  • The big thing is keeping dogs (and other domestic animals) away from wild birds.  It’s a good general rule to keep dogs away from wildlife anyway (alive or dead). That’s particularly true when there’s avian flu activity in an area.

Can dogs be vaccinated against this flu virus?

  • No, at least not at this point. Canine flu vaccines target different flu strains (canine H3N2 and H3N8) and there’s not likely any relevant cross protection. 

What’s the risk to people from infected dogs?

  • It’s probably very low but this is an unknown. Spillover infections into other species are often “dead end,” where the infected individual can’t/doesn’t infect anyone else. However, there have been some wild mammal outbreaks where limited mammal-to-mammal transmission has been a concern. When litters of wild canids have been infected, it’s hard to say if they were all exposed to the same infected birds or whether there was mammal-to-mammal spread.
  • So, it’s a big unknown. With that, it’s reasonable to take precautions to reduce contact with potentially infected mammals. However, the risk is probably quite low.

Should sick dogs be tested?

  • Testing would be considered in situations where there’s a plausible concern about H5N1 flu, based on likely exposure and the signs of illness in the dog. Lots of dogs have respiratory disease from various viral and bacterial causes and there’s no use testing every coughing dog (especially since a mildly ill coughing dog isn’t going to be a classical presentation for this viral infection). Testing for H5N1 influenza can be done through veterinarians, typically by PCR testing of oro-pharyngeal (throat), nasal and/or rectal swabs. 

What about cats?

  • Basically, replace everything above with “cat” instead of “dog.” The risks and preventive measures are pretty similar. Keeping cats indoors (when possible) to reduce their exposure to wild birds, is the main measure. That will help protect both them and their human contacts.

We’ve been dealing with a major shortage of canine influenza vaccine for a while. That’s caused a few different hassles, some related to disease and others related to vaccination requirements.

A quick recap: There are a couple of different strains of dog-adpated flu internationally, but currently we’re really just worried about H3N2. This strain is present in Asia and the US (to which it was imported from Asia). It was introduced to Canada (specifically Ontario) a couple of times in 2018, but we were able to contain it and I’m not aware of any spread of it up here since then, but we remain on the lookout.

From an epidemiological standpoint, canine flu is different from human flu in that it’s not particularly seasonal, and it’s not as widely distributed. In the US, we see sproradic cases and outbreaks that seem to jump around the country (likely related to dog movement), often causing local outbreaks that tend to burn out. In contrast, human (seasonal) flu is more widely disseminated and most people are at some risk of exposure. Currently most dogs probably have little chance of encountering canine flu, but we have a hard time predicting which dogs will get exposed, since the virus jumps around geographically.

Canine flu vaccines are, well, just like other flu vaccines, in that they’re reasonably good at what they’re designed to do: reduce the likelihood and severity of disease. They’re not meant to stop the spread of the virus altogether, or contain an outbreak. They’re used to reduce severe impacts on dogs that get infected.

There are two main groups I think about in terms of dogs that benefit from canine flu vaccines:

  1. Dogs that are at increased risk of exposure to flu. Those include dogs that have contact with lots of other dogs, dogs that travel to areas where flu is spreading and dogs that have contact with dogs imported from high risk areas (e.g. Asia).
  1. Dogs that are at greater risk of severe disease or death if they get infected. Unfortunately this group is often overlooked. Older dogs are the main concern, since flu deaths tend to occur mostly in senior dogs. However, it also includes the very young, pregnant, immunocompromised, brachycephalic breeds (smushy faced breeds like bulldogs) and dogs with underlying severe heart or lung disease.

The first group is more likely to be exposed but the second group is more likely to be seriously impacted. So, if push comes to shove, I want to focus on vaccinating that second group. That protects more dogs from serious disease and doesn’t negatively impact control much (if at all), since flu vaccines are not a good tool to prevent transmission in the first place.

However, if we look at what dogs actually get vaccinated, it’s often dogs in low risk areas that go to kennels or group events. It’s not necessarily because of a high risk of exposure to flu or a high risk of complications, it’s because someone has made it part of admission requirements.

What’s the benefit of requiring flu vaccination for boarding or day care?

  • The benefits are pretty limited, from a facility standpoint. It might help reduce transmission if an infected dog gets in, but that’s probably marginal. Flu is really transmissible, so I doubt even having good flu vaccine coverage in a group of dogs will really prevent an outbreak. It will reduce the degree of illness in individual dogs, but not do a lot to protect the facility (and that’s the premise for requiring vaccination).

That means by vaccinating all these dogs, we’re burning through our limited vaccine supply for very limited gain. In a time of shortage, I’d rather see vaccine diverted to situations where it is more likely to have an impact:

  • Dogs at higher risk of serious disease
  • Situations where vaccination is needed for dog movement (e.g. someone moving to a country that requires flu vaccination of dogs prior to importation)

Would I like all dogs vaccinated against the flu? Sure. It’s not going to happen, though. So, while we’re in a period of vaccine shortage, here’s how I’d prioritize our limited supply:


An abstract in the upcoming European Conference on Clinical Microbiology and Infectious Diseases (ECCMID) has gotten a fair bit of press and led to a lot of questions because of some sensational headlines. I’ll hopefully be able to check out all the details at ECCMID (I’ll be there for the Global Leaders Group on AMR meeting), but let’s take a quick look at what we know so far…

First, we know there’s regular exchanging of bacteria between people and pets. That’s no surprise. We have close and prolonged contact with our pets, and many bacterial are adept at surviving in a variety of animal species in addition to humans. I’ve done various studies over the years looking at this with specific bugs like methicillin-resistant Staphylococcus aureus (MRSA) and Clostridium difficile.

There are some specific issues with certain bacteria, but there are also some common themes about how many of these bacteria behave:

  • Bacteria are periodically passed between people and pets, in both directions.
  • Bacteria may be more human-associated (e.g. Staphylococcus aureus) or dog-associated (e.g. Staphylococcus pseudintermedius), so when they move to another species, it’s often just a transient visit, such that they soon disappear again on their own.
  • If we look at multiple people and pets in the households, it’s typically more common to find human-associated bugs (like MRSA or C. difficile) in other humans, not pets.
  • When we drill down to see if the same strains of a bacterial species are present in both people and pets in a household, we often don’t find too much overlap.
  • Transmission of many concerning bacteria, particularly multidrug-resistant (MDR) bacteria that are most commonly associated with people, is probably mainly human-to-pet.

None of that is meant to dismiss the issue of transmission of MDR bacteria between people and pets. These strains that emerge and spread in people can spread to pets, and it’s possible for pets to spread them back under the right conditions. However, just finding the same bacterium in people and pets doesn’t mean the pet is an imminent risk. Much of the time, pets are innocent bystanders or victims, with humans being the source and posing a greater risk to other people that the pets. .

The ECCMID study, coordinated by Dr. Carolin Hackmann from Charite University Hospital Berlin, is a nice study of human-animal sharing of MDR bacteria. Here’s a summary of what we know so far about their work:

  • Researchers collected swabs from 2891 human hospital patients, 30% of whom harboured a resistant bacterium of some sort (no surprise).
  • Patients were then asked to submit fecal samples from their pets. Over 300 samples were collected from dogs and cats, of which 15% of dogs and 5% of cats harboured at least one resistant bacterium (no surprise there either, especially if they used a broad definition of a resistant bacterium).
  • In only four instances was the same bacterial species found in the human patient and their pet(s).
  • In only ONE instance (out of 2891 humans and over 300 pets) did a pet and person actually harbour the same bacterial strain, based on genomic testing. This was a MDR E. coli in a person and a dog.
  • In this one instance, nothing is reported in the press reports about directionality of spread. Presumably, there was no way to figure out who infected whom (or whether both person and dog were infected by someone/something else).

Was that dog a risk to other dogs or people? Potentially, just like many other dogs. The owner was probably a greater risk to others, but we can’t dismiss the potential for the dog to be a source of re-infection of the owner either (i.e. were the owner to get rid of the bacterium but then get re-exposed from contact with the dog).

It’s an interesting study and we need more work like this.

But, is this concerning?

Not really. It’s another piece of evidence that we live in a polymicrobial world as part of a vast ecosystem. Sometimes we share bacteria (and other microbes) with other members of that shared ecosystem. Usually, it’s benign; sometimes, it’s disastrous (i.e. SARS-CoV-2); and there are lots of gradations in between.

This doesn’t change my thinking or my behaviours, but adds one more piece of evidence to the notion that we have to look beyond people to control certain human diseases – something that is overlooked surprisingly often. At the same time, we need to maintain perspective and not over-react when we find certain microbes in pets that have close contact with people. There’s always going to be some infectious disease risk with any animal contact, but we can mitigate that risk significantly. When it comes to sharing MDR bacteria in households, the best things we can do are optimize health (both human and animal), improve antibiotic stewardship (to reduce the likelihood one of these bacteria will be present in any individual, human or animal), and use common sense basic infection control practices, like hand hygiene.

So, pay attention but don’t panic (and take headlines with a grain of salt).

Being asked to coordinate a paper for the Journal of Law, Medicine & Ethics wasn’t on my academic bingo card for the year, but like a lot of things in recent years, I’ve come to expect the unexpected. The paper in question is part of a special edition entitled Addressing Antimicrobial Resistance through the Proposed Pandemic Instrument. It has a great series of papers addressing a range of pandemic issues, the threat of antimicrobial resistance (AMR), how a pandemic instrument (meaning an international instrument like a treaty) can address pandemic prevention, and why AMR needs to be part of that.

Why are we talking about AMR and pandemics?

Antimicrobial resistance has been called the “silent pandemic,” since it currently causes substantial but often largely unrecognized harm around the world, and the scope of the problem is only getting worse. While peoples’ first thoughts about pandemic risks almost invariably jump to new viruses (which are absolutely important too), the ongoing pandemic of AMR is killing huge numbers of people, affecting countless lives and livelihoods, compromising advances in healthcare, impacting animal health and welfare, and having a tremendous economic impact. It doesn’t get much press, but it’s one of the biggest global health threats we are currently facing. If we don’t act aggressively, it’s going to get much worse.

The special edition of the Journal of Law, Medicine & Ethics has lots of great information about why AMR needs to be in the pandemic instrument, governance issues related to that, what a pandemic instrument might achieve, and what barriers might be present. If you’re interested in this area, I’d recommend checking out those articles.

Here I’ll comment on the article that we wrote for the series, entitled “Governance Processes and Challenges for Reservation of Antimicrobials Exclusively for Human Use and Restriction of Antimicrobial Use in Animals“. We were asked to write about how restriction of antimicrobial use (AMU) in animals and designation of certain antimicrobials exclusively for human use could be built into an instrument. However, we took a bit of a different tack, partly because governance isn’t my area, but more because there are a lot of nuances to the issue that need to be considered by people with expertise in governance.

Ultimately it sounds simple: just use fewer antimicrobials.

But that’s just part of the story, and there are many related issues. If we don’t dive into those, we can end up with ineffective or impractical efforts that may not be optimal, or worse may not help at all, or even worse yet may cause unintended negative consequences. We’ve seen all those outcomes in the past.

Why? The short answer is, it’s complicated.


Too often, the approach to AMU in animals is focused more on sound bites than science and practical measures that will actually achieve anything positive. That’s partly because of the complexity of the larger problem, partly because of big data gaps, and partly because of a lack of understanding of key issues within the problem.

I don’t want to take the lazy way out and just say “read the paper if you want more details” but I recommend you do if you want to understand the area more. It’s far too complex to summarize neatly in a blog post, but here are a few key points to consider as a start:

  • “Antimicrobial use” encompasses a wide range of uses, including treatment, metaphylaxis, prevention and, in some countries still, growth promotion. The issues differ between those, but even within each category, there can be lots of variation leading to different issues. For example, it’s common to hear “Antimicrobials shouldn’t be used for prophylaxis in animals.” However, prophylaxis is very broad, including things such as medication of thousands of healthy animals at once based on historical use more than data, or a single dose of antibiotics in an animal undergoing a high-risk surgical procedure (where infection is a reasonable concern and would result in a longer therapeutic course). We want to reduce prophylaxis as much as possible but there are some situations where it’s needed for animal health and welfare reasons. There are also situations where use is unnecessary, done based on fear or habit versus evidence, or used in lieu of good management practices. We definitely want to curtail use in those cases.
  • Ideally, we’d have all antimicrobial use in animals driven directly by a veterinarian. That works in areas where there is good access to veterinary care, but it doesn’t work everywhere, at least not at this point. We need to improve veterinary access and animal health systems in parallel with efforts to reduce AMU and bring all AMU under the auspices of a trained veterinarian (or allied health professional). “Stop over the counter access to antimicrobials” makes sense in many places, but in some, it would significantly compromise animal health and welfare. It’s even a challenge in some parts of Canada that are under serviced in terms of access to veterinarians.

There are many similar components that sound simple at first, but get much more complex when you delve into them. Failure to understand that complexity dooms approaches to address the issue of AMR.

At the same time, there are lots of potential interventions, some of which are amenable to an international instrument like a treaty. We can’t solve this problem with a treaty, since there’s no single thing that can eliminate the scourge of AMR. However, the way we will solve the problem is through myriad interventions by myriad groups, each providing a small piece of the greater prevention puzzle. An international instrument can be a key part of that by driving some changes and by emphasizing that this is an issue that needs to be addressed across the globe.

If you’ve managed to make it this far through this post, maybe that’s a good indicator you’d be interested in reading the article or the full special edition. Enjoy.

I doubt you’ll be shocked to hear that the normal host of Staphylococcus felis is cats. It’s a bacterium that can often be found in healthy cats and periodically causes disease in cats (e.g. urinary tract infections). Overall, though, it’s a pretty innocuous bug. Human health risks related to S. felis haven’t been well investigated, but it’s been reasonable to assume there’s a potential (but low) risk of infection in people.

Some supportive evidence of this is provided in a recent case report about suspected transmission of S. felis from a cat to its owner in the form of a wound infection (Sips et al, J Med Microbiol 2023).

The case involves a 58-year-old woman who had back surgery. Two weeks after surgery, she delevloped a mild surgical site infection, with some drainage from the incision and mild redness. She was otherwise fine. They did a routine culture of the wound that identified Staphylococcus felis that was susceptible to all of the antibiotics tested. She received some wound care and was sent home with antibiotics.

While Staphylococcus spp. are leading causes of surgical site and wound infections, S. felis isn’t one we’d expect to find here. It’s a coagulase-negative species, part of a large group of staph that typically only cause infections in higher-risk situations. Coagulase-negative staph can also be found as contaminants in cultures when samples pick up bacteria that just happen to be present on the skin, but aren’t actually part of the problem. So, it’s not definitive that S. felis was the cause of the wound infection in this case, but it’s pretty likely.

When they got the culture results, medical staff queried animal exposure and it turned out that the patient had three cats.

Too often, case reports in medical journals stop here. They say “the infection happened in a person… this bacterium is usually found in animals… the person lives with an animal… they must have gotten it from the animal. Eureka, my job is done, let’s write a paper.” In many cases the link is probably real, but no always, so we need to investigate such things properly.

Fortunately, this case report highlights a great investigation of the situation.

After the owner was diagnosed, they tested her three (healthy) cats. Not surprisingly, all three cats had positive oral swabs for S. felis, and there were mixed results from axillary (armpit) and perineum (bum region) samples as well.

But they didn’t stop there. They looked at the genetic sequences of the bacteria and found that the three cats harboured different strains of S. felis. One cat had the same strain as the owner, so that animal was presumably the source of the wound infection. The others were innocent bystanders, even though they harboured the same bacterial species.

What does this change?

Not much, but it’s a good reminder that infections from various bacteria that are present on/in healthy animals can happen, and that proper investigation is required to truly understand any transmission links.

Staphylococcus felis infections haven’t been reported before in people, but I’d guess they have occurred. Until recently, most identification of bacteria in diagnostic labs was done with biochemical tests. Often, testing would stop at “coagulase-negative Staphylococcus spp” on the assumption that the bug was probably not overly relevant and/or it didn’t really matter which one of those different coag-negative staph it was for treatment purposes. In recent years, more advanced testing has become standard, so we now get more specific identification of bacteria that otherwise might have been missed or generically reported. As a result, my guess is that previous incidents of such infections were just not identified. Regardless, it’s still fair to assume this is a rare event.

There’s no mention of what happened to the cats. Hopefully, nothing. I wouldn’t treat the cats in a case like this because we have no evidence it helps. It’s hard to eliminate a bacterium from its normal ecological niche, and treatment might cause more problems, such as selecting for resistant bacteria that could pose a bigger risk to the owner. Staphylococcus felis is just one of many bacteria present in these cats that can potentially cause disease, and even if was eliminated, the risk posed by the cats wouldn’t drop by much. In these types of situations, I focus on basic hygiene and infection control, and owner awareness about risks.