While we’ve learned a lot about the susceptibility of many different animal species to SARS-CoV-2, horses have been a bit of an unknown. We’ve had concerns about potential susceptibility based on the nature of the receptor the virus uses to enter host cells, but study in horses has still been limited. A lot of that has been because people didn’t really want to know – I’ve run into a lot of roadblocks to research because people were more concerned about the implications of a positive test than the virus itself.

A couple of studies have provided a little bit of information. An Italian study didn’t find evidence of SARS-CoV-2 infection in 34 horses on two farms where there was exposure to infected people. Another study using PCR testing didn’t detect any SARS-CoV-2 in samples from 667 horses with respiratory disease, but there was no known exposure of the horses in this study to the virus – they just tested samples submitted for routine diagnostic testing of sick horses.

A recent study (Pusterla et al. 2022) has finally shown “proof of principle” with regard to infection of horses with SARS-CoV-2.  The researchers used serological testing (for antibodies) to detect recent infection in a horse. The advantage of this method is you don’t have to get respiratory swabs during the likely very narrow window that an infected horse may be shedding the virus. The downside is the potential for a false positive test, which is of particular concern when trying to interpret results for individual animals, versus an entire group.

The paper identified antibodies against SARS-CoV-2 in one of two healthy horses owned by a person who had COVID-19, caused by the Delta variant. Both horses were healthy at the time of sampling and hadn’t had any noticeable illness around the time the owner was sick. Both horses were negative on PCR tests (that look for viral nucleic acids). However, one horse tested positive on two different antibody tests, including a plaque reduction neutralization test (PRNT), which is a pretty specific test. So, I think we can be fairly confident that the horse was infected, presumably from exposure via the owner, and either had very mild disease that wasn’t noticed or had no disease whatsoever.

What does this tell us?

It confirms what I think we suspected all along: that horses have at least some albeit limited susceptibility to SARS-CoV-2. The antibody response was pretty low and short-lasting, in comparison to other susceptible species. While we have to take care interpreting results from a single horse, it’s suggestive that horses are not as susceptible as some other species but can be infected.

Does this mean the virus can’t cause disease in horses?

Not necessarily. Subclinical infections are common even in species that can get severe disease. With only 1 positive horse, we can’t say much. However, given what we have to assume is very widespread exposure of horses to people with COVID-19, and the lack of any apparent concerns about increases in respiratory disease in horses, I think we can still be confident that this is not a serious health problem for this species.

  • Maybe it never causes disease in horses.
  • Maybe it causes disease sporadically but not commonly enough that we’d notice.
  • Maybe it causes mild disease that never gets identified or isn’t serious enough that testing gets done.

Can horses infect people?

Who knows? All we know is that one horse was presumably infected. Some species can be infected and spread the virus to others. However, some species can be infected but not to the degree that they are able to infect others (known as a “dead end host”). Given what is likely a low level of susceptibility, I assume the risk posed by horses to people is very low.

What do we do now?

The same things we’ve been recommending since January 2020. If you have COVID-19, stay away from others as much as possible. “Others” includes humans AND other animals. Humans are driving this pandemic, and infections in animals are largely a by-product of that. We’d like to keep it that way by limiting exposure of infected people to animals. Some basic measures can reduce the unknown risks.

As the current international monkeypox outbreak in people continues, more consideration is being given to the potential impact on, and subsequently from, animals. Animals are the reservoirs for this virus, although there are lots of gaps in our knowledge of the species monkeypox virus can infect.

The current cases outside of Africa are being spread from human-to-human. Controlling this in people will therefore hopefully contain the outbreak. However, we have to consider the risk of spillback into animals (particularly wild animals) and the potential to establish animal reservoirs of the virus outside of Africa. Based on what we know, the primary concern would be infection of rodents, but we don’t know enough to say which species are of “no” concern when it comes to monkeypox.

Best case scenario:

  • This is a weird outbreak caused by a lot of human-to-human transmission, but it will be contained and die out with the current surveillance and control measures.

Worst case scenario:

  • Monkeypox is spread from infected people to new animal species outside of Africa, and an animal reservoir is created in countries where the virus has not been present previously. The virus could then be maintained in animals in these countries long term, with periodic spread back to people.

The best case scenario is most likely here, and that’s what we’re hoping for. However, it’s pretty dumb and dangerous to use a hope-based approach to infection control, so we still need to assess the risks of spread to (and then from) animals, and take reasonable precautions to control the risks as needed. In the interim, we should use some common sense measures to reduce the risk of human-to-animal spread. It’s better to use easy control measures early (even if they ultimately are found to be unnecessary) than to look back 6 months from now and say “crap… doing some things a few months ago would have really made a difference.”

Risk assessments are regularly done for emerging threats. I was involved in a couple of Canadian rapid risk assessments for SARS-CoV-2 in animals, and those provided useful information and discussion. The UK has just released their own qualitative assessment of the risk to the UK human population of monkeypox infection in a canine, feline, mustelid, lagomorth or rodent UK pet.  More concisely, I’d call it their “rapid assessment of the risk of spillback of monkeypox into selected domestic species.”

The assessment looks at what are likely the highest risk pet animal groups (rodents and rabbits (lagomorphs) and ferrets (mustelids)) and the most common pets (dogs/cats), but it doesn’t cover all species.  Of note, it doesn’t address pigs (commercial or pet) and there are questions about susceptibility of that species. However, it’s a pretty logical approach overall, particularly when it needs to be done rapidly.  A lot of the assessment and recommnedations are just good, common sense, and use of the precautionary principle in a controlled manner that doesn’t over-react.

Here are some highlights from the assessment:

As the numbers of affected households in the UK related to the current outbreak are rapidly increasing, this warrants a more thorough assessment of the risk posed by mammalian pets exposed to monkeypox virus to people with whom they may come into contact.

  • Absolutely. We need to assess this as the outbreak continues and not rely on the somewhat limited data we have from past studies and outbreaks.

For the purposes of the assessment, it is presumed the pet is present in the contaminated household of a confirmed human monkeypox case. The risk posed is therefore to the non-infected human contacts or in-contact peridomestic or wild rodents. It is concluded that the highest risk is posed by the presence of pet rodents, more so than lagomorphs, canids, felids and mustelids.

It is unlikely (but cannot be ruled out) that an infected rodent pet could spread infection to peridomestic or wild rodents. As rodents may not show clinical signs of infection, and the incubation period is unknown, testing to detect the presence of antibodies as well as virus would provide more confidence in ruling out infection.

The evidence of susceptibility for non-rodent pets is poor or incomplete, and therefore a precautionary risk management process should be considered.

  • This is a really important statement. Too often (and COVID-19 showed us this yet again), the early response by some groups is to say “there’s no evidence of a concern” and therefore no action required.  However, with an emerging disease, you sometimes have to act before there’s time to collect the evidence. By the time you know definitely that there can be spread to/from animals, it might be too late to control or prevent it.

Based on current evidence, for pet rodents in households where there are infected people, temporary removal from the household for a limited quarantine period (21 days) and testing to exclude infection is recommended, particularly where there are infected human contacts who have had close direct and prolonged contact with the animal or its bedding and/or litter.

  • I disagree with this one. It’s good that the risk is being taken seriously. It’s good to consider testing (but we don’t know the sensitivity of testing, so it can’t be used to declare an animal uninfected). But does removing the animal help? It’s great that they clearly said “temporary removal,” so there’s no ambiguity that this might mean people should surrender or euthanize exposed animals. However, I wonder if removal of the pet really helps in a household where there’s been an infected person present, where the animal can be caged and where basic infection control practices aren’t hard to use during a quarantine period.
  • Furthermore, does moving the animal create risk somewhere else, where there was no risk before? We had the same questions when SARS-CoV-2 emerged and we quickly settled on keeping pets in their infected households as the best solution.
  • Making sure there’s no potential exposure of pet rodents to wild rodents is important, and if there’s a rodent infestation of the house, I’d be more inclined to want to get pet rodents out, to reduce the risk of human-to-pet-to-wild rodent transmission.  But taking care of the rodent infestation itself would also be critical to avoid direct human-to-wild rodent transmission.

Are effective control measures in place to mitigate against these routes of introduction? Outcome: yes – humans; no – rodents and non-rodent mammalian animals.

  • This gets into the human control approaches that include smallpox vaccination, as well as lack of control measures in the UK for rodents imported from the EU that might introduce the virus.  So it’s true, but “no” isn’t necessarily what I’d say, since there’s always something we can to do mitigate risk. We have easy measure to reduce the risk, and those focus on restricting contact between infected people and their pets.

Do environmental conditions in the UK support the natural reservoirs or vectors of disease? Outcome: yes. Quality of evidence: satisfactory.

  • This is a nice section. It’s long so I won’t copy it here but if you’re interested, check out the link for a good review of species susceptibility info.

I’ve wondered what countries were going to do a rapid risk assessment about spillback (I’ve also asked whether we’re going to do one here in Canada). The good news is that the vast majority of the content from the UK’s report would apply here and elsewhere. We have some differences in the types of wildlife that are present in Canada, but the overall risks, control measures and messages are the same.

Here’s my own assessment:

  • the likelihood of spillback into an animal somewhere is moderately high if the outbreak continues for a while. Lots of people infected means lots of pets exposed, and transmission to a susceptible species certainly wouldn’t be shocking.
  • the likelihood of infection of wild animals is low.
  • the likelihood of establishment of monkeypox virus in a wildlife reservoir in currently non-endemic areas is very low.

But, “very low” isn’t zero, and I’ve definitely been wrong before. So, a bit of basic infection control and common sense can go a long way while we’re collecting more information.

Local transmission of monkeypox wasn’t on my 2022 bingo card, but I guess we’re learning to expect the unexpected. I commonly talk about monkeypox when discussing zoonotic diseases, especially those associated with importation of animals, as this was highlighted by an outbreak of monkeypox in the US associated with imported rodents from Africa in 2003.  However, in the past the focus has always been on zoonotic (animal-to-human) spread. The current situation is making us think about some other issues, and spillback of monkeypox virus into animals from people.

What is monkeypox?

Monkeypox is a potentially nasty disease caused by the monkeypox virus. The virus is in the same family as smallpox, but is nowhere near as transmissible or severe. It’s mainly found in tropical rainforest areas of Central and West Africa.

What is the reservoir of the virus?

You might say “duh… it’s monkeys” but it’s not. It’s another misleadingly named virus, like chickenpox (which doesn’t come from chickens, and isn’t even a poxvirus) or cowpox (the reservoir of which is actually rodents).  We don’t actually know for certain what species is the natural reservoir of monkeypox virus, but it’s likely one or more small mammals in Africa. It was named “monkeypox” because the disease was first reported in monkeys, but monkeys aren’t the true reservoir, they are just (like us) susceptible to infection.

What animal species are susceptible to monkeypox?

We know that a number of species are susceptible through natural or experimental studies. These include:

  • People (obviously)
  • Various non-human primates
  • Prairie dogs
  • Ground squirrels
  • Various rodents (including some pet species, such as rats, although susceptibility of rats seem to vary even by rat species, with some being highly susceptible and others resistant)
  • African hedgehogs

There’s also potentially susceptibility of other species, such as:

  • Rabbits.  There’s some mixed information, with very young rabbits clearly being susceptible and more variable susceptibility in older rabbits. It’s possible that older rabbits are not really susceptible to natural exposure, just artificial exposure like intravenous injection of the virus.
  • Pigs.  Pigs are on various lists of susceptible species, but I haven’t found much detailed information about this yet.

Not much is known about other large mammals either. There’s one report that suggests potential infection of monkeypox from a gazelle, and that gazelles with pox-like lesions were common in one area. However, the evidence is pretty limited.

Guinea pigs and golden hamsters seem pretty resistant to infection.

So, potentially susceptible species include a few domestic species and could include some wild rodents. Missing from the list are common pets such as dogs and cats, and other livestock such as cattle and horses.  A challenge here is differentiating “not susceptible” from “not known to be susceptible”. It’s probably a mix of both – we have species that are truly not susceptible but we also have species that haven’t been studied enough to really know. We also have to interpret older experimental studies with caution because of evolution of the virus. We can probably have confidence in limited or no susceptibility of many common domestic species that are present in areas of Africa where the virus is endemic, since it’s likely there would have been reports of infections in dogs, cattle or goats if they were highly susceptible.

So, realistically, the main concerns are probably with rodents, maybe ferrets, rabbits and potentially pigs.

Can people infect animals with monkeypox?

We don’t know. All the focus to date has been on transmission of the virus in the other direction. Monkeypox virus can be transmitted by droplets and direct contact, but it’s not highly transmissible, so close and prolonged contact is likely required. We have that kind of contact with pets, so we have to assume there’s some risk of exposure. Whether that’s enough to cause infection is the big question. I suspect the risk is low but not zero.

How do we answer some of these questions?

I’d love to look at spillback risks from infected people to their pets. I’ve been working the phones (email actually) to see if anything is being done or whether we can set up some surveillance. It’s not straightforward, as we need access to testing, a way to identify exposed animals, and various approvals. I got my first email about a potential animal exposure today and that’s presumably going to increase.

Hopefully we’ll get some information and not repeat the typical pattern where animal transmission risks get thrown out the window when the focus is on human infections. Spillback into domestic animals here is probably quite unlikely, but it would be nice to have some actual data to understand the risk and what/if control measures need to be used. With emerging infectious diseases, it’s best to over-react (within reason) at the start than to try to play catch up later on.

What can be done to reduce the risk of transmission to animals?

The most important thing is to control the disease in people, at least in the context of what’s going on in North America and Europe, where the issue is now human-to-human spread, versus infection from a wildlife reservoir.

If someone has monkeypox or is concerned they might have monkeypox, using basic control measures make sense including reducing direct contact with animals. Distancing and masking will help reduce droplet spread. Keeping pets out of the bedroom at night makes sense too, given the long contact time in a small airspace. I don’t think drastic measures are needed, just some easy, basic infection control practices that are not overly disruptive but likely reduce any risk that might be present.

What should veterinarians do if an owner calls saying they have monkeypox and are worried about their pet(s)?

At this point, I’d tell owners to stay isolated with their animals, and reduce contact with their animals within the household, to reduce any uncertain risks (but not freak out or do anything drastic). I’d tell them the risks are low for most pet species, but since we don’t know too much, it’s best to take some precautions. I wouldn’t want them to take the animal to a clinic unless it’s sick. That all sounds eerily like the myriad COVID-19 discussions, doesn’t it? It goes to show that infection control is a lot of basics that we just need to do right.

Image: Electron microscopic image of the mokeypox virion (source: CDC Public Health Image Library 22664)

As the unprecedented outbreak of H5N1 avian influenza continues in North America, there are numerous concerns about where the outbreak is heading and threats to other species, including domestic and wild mammals, and people (the latter being just another “domestic mammal”).  My inbox is filled with questions about different concerns and scenarios. The one I’ll address today is about risks to veterinary clinics that treat backyard poultry.

Backyard poultry are increasingly common in many areas.  Since they are typically kept outdoors and not managed with anywhere near the same degree of biosecurity as most commercial poultry, they are at high risk of exposure to avian flu when it’s circulating in wild birds in the area, as it is right now.

The good news about the current H5N1 influenza outbreak:

This H5N1 strain is not well adapted to infect humans, or mammals in general. It lacks some of the genetic material that makes other flu virus more transmissible to and between people. Only a couple of human infections with this strain have been reported, including one person infected with H5N1 in the US in whom the only symptom was fatigue. Transmission to other non-avian species is probably rare too, but all we can say is “probably” because of limited testing of wildlife. Spillover has occurred, including the recent cases of H5N1 influenza in fox kits in Ontario. Whether these infections are really rare events or just rarely diagnosed isn’t clear and remains a big question. Still, it’s safe to say that, at this point, spillover risks are limited.

(Some of) the concerning parts about the current H5N1 influenza outbreak:

It’s still a flu virus, and flu viruses change. The circulating strain can evolve and reassort (swap genes with other flu viruses) anytime. We have plenty of other flu viruses circulating in North America, including seasonal human flu and flu in other species such as pigs, horses and (in the US) dogs. There are also other avian flu strains around here and there. The more flu viruses in circulation, the greater risk of them getting together to reassort and make a new strain, potentially with more affinity for people.

So, back to veterinary clinics treating backyard poultry:

Like all domestic animals, backyard poultry sometimes need veterinary care, and this often falls to small animal or mixed animal veterinary clinics, since there are only a small number of specialist poultry veterinarians in Ontario (and many do not treat backyard birds, for several reasons including biosecurity risks). Unlike most livestock, backyard poultry that need veterinary care may be taken to the clinic (in contrast to most livestock where the veterinarian visits the farm). This creates a few concerns that need to be taken into consideration by the clinic when it comes to avian influenza.

Risk of transmission to people

  • Fortunately, as noted above, transmission to people is rare, at least at this point. Rare doesn’t mean it can’t happen, but the odds of clinically significant bird-to-human infection seems to be very low. It’s not likely someone handling an infected bird will get sick, but it’s possible.
  • We also need to think about the potential impact of people who have human flu getting exposed to birds that might have avian flu. If one infects the other (and therefore has an infection with two different flu viruses), that’s the recipe for re-assortment to create a new strain. We might be getting into excessively theoretical issues here (I doubt it, though), but hopefully the “stay home if you’re sick” message is getting across.  Unfortunately we know that’s not always the case, and people who are infected with influenza don’t always have symptoms.

A comment I made today to someone was “There’s some degree of risk but in the absence of sick birds, the zoonotic risk isn’t likely any greater than that posed by your average new puppy (e.g. Campylobacter).” I think that’s a fair statement, but at the same time, one of my goals in life is not to become a case report describing a rare/new infectious disease, so I still want to take care.

Risk of transmission to mammals

  • The issues with risk to other mammals are similar to humans (in the end we’re just another mammal, afterall). The risk of transmission is low but not zero. I wouldn’t get too concerned about it, but I’d still rather not create the chance for rare bird-to-mammal transmission in the clinic, especially since we can largely prevent it with some basic infection control measures (see below).

Risk of transmission to other birds

  • This is probably my main concern. There could be transmission to other backyard poultry (not too likely, since there usually aren’t multiple backyard chickens at a clinic at the same time) or transmission to other pet birds. Susceptibility amongst different bird species varies, but we’re seeing lots of wild birds dying from this virus. We don’t want to see it spread in a clinic to someone’s pet bird (or worse, to someone’s aviary). That creates risk of illness and death for the bird(s), and more human exposure to the virus.

So, what do we do?  We do what we do every day: We assess and manage risk.

We can never 100% eliminate risk of infectious disease in a clinic setting, especially flu. However, we can use some basic, common sense measures to reduce risk of avian flu transmission.

Risk assessment

Since healthy looking birds can be infected, there’s no way to guarantee that a given bird isn’t shedding avian flu virus. However, we can identify situations where the risk is higher and increase the infection control measures that are used. Higher risk situations include:

  • The bird is sick with signs that are compatible with avian flu infection (including neurological disease)
  • Other birds in the group are sick
  • Other birds in the group have died
  • Avian flu has been found in wildlife in the area, and the bird has outdoor access

Physical separation

If we can keep poultry away from people and animals as much as possible, we greatly reduce the risk of pathogen transmission. That can be done a few ways:

  • Admitting birds directly to isolation or another separate, contained space (versus hanging around in the waiting room)
  • Examining birds outside so they never set foot in the clinic
  • Housing hospitalized birds in isolation or a separate area

Limiting contact

Minimizing the number of people who handle the birds in the clinic to the one or two who might be required for examination and procedures reduces transmission points.

Appointment scheduling

It’s not always possible to have poultry come into the clinic at a time when no other birds are present if there’s a high bird caseload or for emergencies, but it’s something that should be done whenever possible.

PPE and hand hygiene

Routine infection control practices can go a long way, and are used based on the assumption that any patient might be harbouring something infectious.  Things like wearing proper protective outwear (basic lab coat) and hand hygiene help a lot. Protective measures can be increased if there’s more risk (see above) to include a disposable gown, mask and eye protection.


Accurate rapid tests for avian flu would be very useful and are available in some other jurisdictions. However, we have not had success getting approval to import the tests for screening birds in places like clinics and wildlife rehab facilities. Rapid tests (as we learned from COVID-19) are not perfect and can never rule out flu. However, they could be a useful screening measure, as a positive would indicate a need to use stricter precautions, and to get confirmatory testing done while providing more surveillance info. There was reluctance to use rapid tests for COVID-19 initially, but they ended up being a very useful tool. Currently, the only testing available for avian flu is PCR testing through diagnostic labs, which doesn’t help us from a clinic control standpoint since the turnaround time can be a few days.

The current H5N1 avian flu outbreak is definitely something to be concerned about. It’s having major impacts on domestic and wild birds. We want to control it to reduce the impact on those population and reduce the risk of this developing into something more. However, vet erinary clinics should be able to treat poultry without much risk, if some basic infection control measures are used.

Photo credit: https://www.insauga.com/backyard-chickens-may-come-home-to-roost-in-ajax/

A recent publication in the Journal of Veterinary Diagnostic Investigation (Haydock et al. 2022) describes an interesting but unfortunate case of tuberculosis in a dog. Published reports of rare cases like this are often of limited value, but sometimes they highlight important broader issues, and I think this one fits that category.

The patient was four-year-old mixed breed dog that was presented to the Ontario Veterinary College because she had some liver and lung masses, and fluid in her chest. She had a very extensive workup, including lots of bloodwork, radiographs, a CT scan, ultrasounds, bronchoalveolar lavage, and even exploratory surgery to get samples of the masses for testing. I was involved because an infectious cause seemed likely, but a specific cause wasn’t readily apparent despite a pretty vast array of infectious disease tests.

There’s another twist to this story based on the origin of the dog: she was living in Toronto, but had been adopted through a rescue 18-24 months earlier, originally having come from a remote community in northern Quebec. Whether it’s a dog from another country or from another region of Canada, we have to think about what different infectious diseases might be involved when we see dogs from other places. That can be a challenge since we often don’t have good data on disease risks in different areas. There were a few things we considered in this case, but nothing really fit.

As things progressed, it seemed there was a good chance the dog had a Mycobacterium species infection. Mycobacterium is a genus of bacteria that includes a lot of different species, including the causes of human (M. tuberculosis) and bovine (M. bovis) tuberculosis, along with a big group of environmental species that rarely cause disease. We divide Mycobacterium into two main groups, tuberculous mycobacteria (including M. tuberculosis and M. bovis) and non-tuberculous mycobacteria (NTM, which includes the important M. avium complex, or MAC).

At that point, I suspected the dog was infected with MAC, a fairly ubiquitous group of environmental mycobacteria that can sometimes cause severe disseminated infection.

  • I was partly correct, but that wasn’t much consolation when we got PCR results saying it indeed was mycobacterial – but it was M. tuberculosis, the cause of human TB.

I think the first thing I said in response to the result was “I suspect there’s an issue with the test. We’ve seen cross-reaction before in samples from that lab for that test. It’s probably a non-tuberculous Mycobacterium since that’s more common and the disease fits.”

  • But it turns out, that was not the case.

It was subsequently confirmed as M. tuberculosis by culture. Whole genome sequencing and MIRU-VNTU profiling showed it was a near exact match with a TB isolate from a person from Quebec, providing more support that the dog was infected before being moved to Ontario.

So, we had a diagnosis. Unfortunately, the dog deteriorated and was euthanized shortly before we got the TB result.

However, that led to a whole new issue: human exposure to TB from the dog. This dog had obviously had close contact with its owners for close to 2 years, and was cared for by numerous veterinary personnel at the referring veterinary clinic and at OVC, including some high-risk procedures (e.g. intubation for surgery, close contact in ICU). We don’t know a lot about dog-to-human transmission of TB, but there was certainly potential risk since the dog had lung lesions and could therefore have had viable M. tuberculosis in its respiratory secretions.

Public health units in both Guelph (where we are) and Toronto (where the dog lived) were informed, and coordinated contact tracing, using definitions for exposure we created for this situation (see table below). A lot of investigation and testing was required, but fortunately in the end there was no evidence anyone was infected by the dog.

TB has been reported in dogs before, but it originates from humans in these cases. Concern has been raised about importation of TB-infected dogs from areas where the disease is common in people, and this scenario both supports that risk and highlights how “importation” should really be thought of as “dog movement,” since there can be risks with dogs from other areas of the country, even if they haven’t crossed an international border.

Dogs don’t seem to be very good hosts for M. tuberculosis, but we don’t have great data about how often human-to-dog transmission occurs, in part because testing of dogs is a challenge. Typical human tests for TB (e.g. tuberculin skin test) do not work well in dogs, so there’s no quick and easy way to screen dogs who have been exposed to people with TB. Presumably, human-to-dog transmission occur sporadically but usually doesn’t result in severe disease in dogs. Transmission from dogs back to people is hard to evaluate, since most infected dogs come from infected households, so figuring out who infected who is a challenge. Scenarios like this, where an infected dog came into the household where there were no other known sources of exposure can help us figure these things out, but aren’t commonly encountered. The fact that no one got infected from this dog is encouraging, but it’s a pretty small sample size from which to draw conclusions.

This report doesn’t mean we need to think that every dog with strange disease has TB. This is a rare case. However, it should be taken as a reminder that strange things do happen, and that the origin of a dog needs to be considered when thinking about infectious diseases. We’re getting better at asking if dogs were imported. However, it’s not the act of changing countries that increases risk. It’s traveling between different risk areas, or between communities with different disease risks, even if they’re within Canada. We need to pay more attention to dog origin and dog movement (including people who take their dog on vacation), not just whether the dog was “imported.”

Image: Medical illustration of Mycobacterium tuberculosis (source: CDC Public Health Image Library 23254)

H5N1 influenza was recently found in two wild fox kits in St. Marys, Ontario. It’s a pretty noteworthy event given the scope of the current H5N1 highly pathogenic avian influenza (HPAI) outbreak across Canada, and the fact this is the first identification of H5N1 influenza in wild mammals in Ontario. The fox kits were submitted by a wildlife rehabilitation centre; these centres are great sources of information about emerging wildlife diseases as they are on the front lines and often bear the brunt of such issues. One of the fox kits was found dead and the other had severe neurological disease and died shortly after admission. Influenza virus was found in their brain tissue and was likely the cause of death. Further characterization of the virus identified it as an H5N1 strain of influenza A, more specifically of the A/goose/Guangdong/1996 (Gs/GD) lineage.

Is this surprising?

Not really. We don’t recognize much spillover of flu viruses into wild canids, but when you consider how widespread this virus currently is, it’s not a shock that spillover would happen. (It’s maybe more of a shock that we’d actually find it.)

We know that foxes, like other canids, are susceptible to various flu viruses. In an experimental study (Reperant et al. 2008), researchers were able to infect foxes by feeding them carcasses of infected birds, though the infected foxes were only mildly sick, at most. In a more recent study (Rijks et al. 2021) found two naturally infected red fox kits in the Netherlands. Those foxes also had neurological disease, like the one Ontario fox kit and as is often seen with severe infections in certain types of birds. In April 2022, avian influenza was also reported in a fox found dead in Japan; the strain was not reported in this case, but is likely related to the H5N1 strains circulating around the globe in migratory wild birds.

Why foxes and not other canids?

It’s not clear (to me, at least) whether foxes are predisposed to infection with influenza, or whether it’s a matter of there being more foxes than other canids in affected areas that get tested. I suspect it’s a numbers and surveillance bias rather than foxes being predisposed or particularly susceptible to infection.

Have more wild mammals been infected in Ontario than these two fox kits?

It’s hard to say, but it’s likely. These were only identified because they happened to be presented to a rehab facility AND they were submitted for testing. That doesn’t happen with most sick or dead wild animals. So, we don’t know if this was a very lucky identification of a very rare event, or a result of something bigger happening in the wildlife population of which we are as of yet unaware.

Let’s back up a bit… What do we know about influenza in canids in general?

There are two main situations to consider when it comes to influenza in canids: 1) infection with flu strains that are adapted to canids (including domestic dogs, foxes, coyotes, wolves, etc.) and 2) spillover infection with other non-adapated flu strains in canids.

“Canine flu” strains are influenza A strains that effectively circulate in the dog population. Currently the most common canine flu strain is an H3N2 that’s endemic in Asia and causes sporadic outbreaks in the US, often associated with imported dogs.  Canine H3N2 influenza was introduced into Canada this way back in 2018, but as far as we know was rapidly eliminated.  That’s not the strain we’re dealing with here (at least at this time).

Dogs (and other canids) can also get “spillover” infections of influenza from other species. For example, human-to-dog transmission of seasonal human influenza strains can occur. It’s probably more common than we realize, because dogs don’t usually get very sick and testing is uncommon, but it still seems to be a pretty uncommon event. Spillover of equine H3N8 influenza has also been reported.

Most of the time, spillover events are sporadic and a dead end for the virus, as the animal gets infected but doesn’t effectively spread a strain that isn’t adapted to that host, so it dies out in that individual. However, that’s not guaranteed in every case. Canine H3N8 is believed to have originated in horses, with subsequent adaptation to dogs to become a true canine flu virus.

Why do we care about H5N1 influenza in a couple of foxes?

From a dog health standpoint, spillover events are not a big deal because they are rare and don’t typically cause severe disease. However, the foxes in this report died, so we can’t assume all infections will be benign.

The main big-picture concern with spillover infections is the potential for emergence of a new flu variant, through adaptation of that strain to the new species, or (more critically) recombination of influenza viruses within the new host, which can happen when two different flu viruses infected an individual at the same time and swap genes. If the new variant that emerges is still able to infect a particular species (like humans) and is highly transmissible, yet different enough from the original virus that we have little immunity from previous infections or vaccination, it’s a recipe for a new pandemic virus. Dogs are unlikely to be the source of a new strain, but the more flu viruses that can infect them, the greater the risk. Since dogs can be infected by strains of human flu, dog flu and spillover of avian flu, there’s a theoretical chance that a dog could be infected with two different flu viruses at the same time. That’s why we want to control and eliminate flu viruses in dogs (and other species) as much as possible. Realistically, the recombination risk is probably greater in other species (including people), but we’d rather not roll the dice unnecessarily.

How did the fox kits get infected?

Presumably it was from eating an infected bird, especially since we know that can occur based on the previous experimental study. Whether these kits both got infected from the same infected bird, whether one got infected and then infected the other, or whether both were infected by a littermate or their vixen is impossible to say. I guess we also can’t rule out they got it from another mammal that acquired it from a bird, but then we’d be talking about a spillover from a spillover, which is quite a stretch.

What should the average dog owner do about influenza in dogs during the current outbreak in birds?

Step 1: Relax. Yes, this virus currently wreaking havoc in wild birds and domestic poultry around the globe can presumably infect domestic dogs. So can lots of other viruses (including many that are more serious, and yet we don’t panic about them either). Don’t ignore the issue, but let’s keep things in perspective.

Step 2: Use some common sense measures to reduce the risk of dogs being exposed to influenza-infected birds.

Step 3: Use some common sense measures to reduce the risk of dogs being exposed to influenza from other species.

Here are some examples of easy and practical measures:

  • Keep dogs away from sick and dead birds.
  • If avian flu is reported in your region, stay away from areas where infected birds have been found and keep your dog under control so it can’t wander off and snack on a recently dead bird.
  • Remove bird feeders to reduce congregation of birds, reduce the potential for bird-to-dog contact, and reduce exposure of dogs (and other animals, including people) to potentially influenza-contaminated bird poop.

Likely the most important thing the average person can do to reduce the risk of their dog getting a spillover influenza infection is for that person to get a flu shot, to reduce the risk of getting infected themselves and exposing their dog to flu.

Is there a flu vaccine for dogs?

Yes, but it won’t help us here. Flu vaccines aren’t great at providing cross protection against other strains. The canine vaccines are for H3N2 and/or H3N8, not the strain we’re currently dealing with in wildlife.

A recent commentary in the Journal of Clinical Pharmacy and Therapeutics by Moore et al. entitled “A doggy tale: Risk of zoonotic infection with Bordetella bronchiseptica for cystic fibrosis (CF) patients from live licenced bacterial veterinary vaccines for cats and dogs” discusses concerns about using the most common “kennel cough” vaccines in animals owned by people with CF.

Bordetella bronchiseptica is just one of the causes of “kennel cough” (or using our current terminology, canine infectious respiratory disease complex (CIRDC)). It’s a highly transmissible bacterium that can cause disease in dogs and cats, but is also found in some healthy animals.

We have two main types of vaccine for this B. bronchiseptica: injectable vaccines with a killed form of  the bacterium, and oral / intranasal vaccines with a modified live form of the bacterium.

  • Modified live vaccines use bacteria or viruses that have been attenuated to cause no or very mild disease, but still maintain the ability to cause a low grade, transient infection.
  • These vaccines can be highly effective, because they induce an immune response that’s the same as when the “wild type” circulating strain of the pathogen that causes diseases is encountered, but without the same risk of illness.  They are much more protective than the injectable, killed vaccines.  If I want a pet to be protected against B. bronchiseptica, I absolutely want to use a modified live vaccine.
  • However, while the vaccine strains are attenuated, they’re not completely harmless.  The concern is that they could cause disease in individuals (human or animal) who have compromised immune systems. That’s why we typically avoid giving this type of vaccine to individuals with significant immunodeficiencies.

The published commentary focuses on the use of modified live vaccines in pets whose owners have CF, who are at particularly high risk for certain respiratory infections. Infections with Bordetella bronchiseptica have been reported in people with CF, so there’s good reason to consider the risks. However, like most things, we need to think about the risks and the benefits, and it’s often not as clearcut as it might seem at first glance.

Concerns about vaccinating pets

The issue is exposure of the owner to an attenuated form of a bacterium that can (uncommonly) cause disease in people.

Is this really a significant concern?

  • That’s debatable. Attenuated B. bronchiseptica in the vaccine is a much less virulent form of a bacterium that even in its normal, unattenuated state rarely infects people. Add “less virulent” to an already minimal-risk bacterium and you get a very low risk situation, but it’s not no risk, which is why we’re talking about it.

What evidence of risk do we have?

  • Not much. There’s one report that suggests a B. bronchispetica vaccine caused disease in a boy, but he was squirted in the face with the vaccine, so it’s different than exposure to a vaccinated animal. Furthermore, they never tested to see if the boy was actually infected with the vaccine strain (or even Bordetella bronchiseptica). They simply attributed his respiratory disease that occurred shortly after the exposure to the vaccine (reasonable but presumptive).
  • Another report described B. bronchiseptica infection in a transplant patient. Their dog had been vaccinated with a modified live vaccine, but they didn’t do any testing to see if the person was infected with the vaccine strain or not. So it’s suggestive, at best.

That’s not meant to dismiss the risk. We want to avoid infections, but we need to keep things in perspective. Millions of dogs are vaccinated with these modified live vaccines every year. Huge numbers of high risk people have contact with these dogs. Large numbers of high-risk veterinary personnel also get exposed (often at high levels) routinely. Yet, there’s very little evidence of anyone getting infected. Little isn’t zero, but we rarely have zero risk situations when dealing with zoonotic diseases of any kind.

Concerns about NOT vaccinating pets

This part doesn’t often get discussed, but we have to consider the downsides of not vaccinating, and there are a few:

  • The obvious concern is that the animal will be more likely to get infected withe the “wild type” disease-causing bacterium. Human infections with wild type strains are rare but presumably much (much!) more likely than with the attenuated vaccine strain. I’d be much more worried about a person with CF being exposed to a sick dog with wild type B. bronchiseptica, than to a dog that was just vaccinated with the attenuated strain.
  • A sick pet may increase exposure of the owner to various other bacteria from coughing, sneezing and nasal discharge. The mouth and nose harbour myriad bacteria, many of which can cause disease (and do so much more commonly than B. bronchiseptica). An animal that is coughing, sneezing or depositing nasal discharge everywhere presumably greatly increases the risk of exposure of people to this array of bacteria.
  • A sick pet may be more likely to be treated with antibiotics, which are often used (often unnecessarily, but that’s a different issue) to treat kennel cough. Antibiotic use is a known risk factor for dogs and cats acquiring and shedding antibiotic-resistant bacteria, some of which cause disease in people, and can be very difficult to treat.

Overall, whether or not to vaccinate a pet is a cost-benefit decision, but we have limited data on the true costs and benefits when it comes to modified live B. bronchiseptica vaccines. My main considerations when deciding whether to recommend a kennel cough vaccine are focused on the dog/cat: what’s their risk of exposure, and what are the potential implications of infection for the animal. A high-risk owner doesn’t mean I shy away from modified live kennel cough vaccines. In some ways, it pushes me towards wanting to use them, because my concerns with the pet getting sick because it’s inadequately vaccinated and then exposing the owner to something are greater.  We can take some basic measures to reduce the risks associated with vaccination procedure itself. The commentary rightly talks about the potential importance of Bordetella transmission from pets to CF patients, but if anything, I take that as more of a reason to vaccinate, to reduce the risk of this happening.

Risk reduction measures are pretty straightforward. The main concern is avoiding human exposure to large numbers of live bacteria from the vaccine.

  • Keep the owner out of the room when vaccinating to prevent inadvertent exposure to the vaccine itself, including when the animals (often) sneezes right after it’s given.
  • Consider wiping residual vaccine off the pet’s face after vaccination.
  • Tell the owner to avoid close contact with the pet’s face, and to avoid allowing the pet to lick the owner for at least a day (but really I recommend both these measured most of the time for high risk owners regardless).

It’s great to see the human medical folks putting some thought put into pet related disease issues. Too often, these issues are not on the radar at all. However, zoonotic disease issues related to pets in high risk households are often complex and nuanced, and that is often not recognized or considered.

The concluding statement of the commentary is great, and to me is the most important recommendation they make:

“Patients should make their veterinarian aware of their CF status, so that a safe and efficacious vaccine strategy is formulated, both mitigating the potential infection risks from live components of the vaccine, but simultaneously offering maximum immunological protection to the animal.”

That’s the key. People need to engage their veterinarian about risks in their households, and veterinarians need to be part of the team that manages risk to all members of the household.

Photo credit: Dr. Kate Armstrong (from Weese & Evason, Infectious Diseases of the Dog and Cat, A Color Handbook)

As the world tries to (prematurely) transition back to some semblance of normalcy (or at least what used to be “normal”), it’s a challenge to figure out what changes to make, and when. There will never be agreement between everybody. Some want full reversion to “normal” now, some want third-wave-level restrictions until further notice… like most things, there’s presumably a sweet spot in the middle.

I won’t try to address that particularly contentious area (I get enough hate mail as it is). Instead I’ll stick to a discussion about animal shelters, based on some talks I’ve given lately and requests for information, as shelter personnel and management struggle with what to do.

Some people might think “Why do shelters in particular warrant discussion? Animals shelters can be treated like any retail operation since they have staff, members of the public who come into the building, and they don’t provide care for high risk (human) individuals.

That’s all true.  But…

Animal shelters are an essential service, and impacts to that essential service can be harmful in more ways than one.  When thinking about control of SARS-CoV-2 in an animal shelter, there are 4 main issues to consider:

  • Preventing infection of animals (from people or other animals)
  • Preventing infection of people FROM animals
  • Preventing infection of visitors/adopters
  • Preventing infection of staff

AND there is one more important goal that also needs to be remembered:

  • Protection of the shelter itself and its operations.

Preventing infection of animals

Human-to-dog/cat transmission of SARS-CoV-2 is common, but rarely does it cause a significant problem for the dog/cat. So, while we’d like to minimize such transmission and we should take basic precautions to reduce transmission, the overall impact of infection in animals on the animals themselves is probably very limited and not a driving factor.

Preventing infection of people FROM animals

The risk of dog/cat-to-human transmission is low but not zero. This risk has not been well documented, even though it presumably it occurs, but we need to put it into context. It’s more of a concern when there’s less risk of human-to-human transmission. When there’s rampant community transmission of SARS-CoV-2 between people, the potential impact of animal-to-human transmission is limited. An animal shelter worker is much more likely to get infected outside of the shelter, even if there are infected animals in the shelter.

Preventing infection of visitors/adopters

The relative risk of SARS-CoV-2 transmission posed by adopted animals is really low, and, as noted above, if an adopter has abundant risk of exposure from people, the added risk from the animal is minimal. If someone is taking strict measures to isolate from people, the relative risk from the animal goes up a bit. We focus mostly on risk from animals from known COVID-19-positive households, since the incidence of active infection in dogs and cats coming into shelters without a history of recent exposure to an infected person is very low. The main risk to adopters (in terms of the adoption process) is human-to-human contact, and shelters can take measures to limit that (e.g. do as much interaction remotely/virtually as possible) and mitigate risk from required visits (e.g. ventilation, masks, distancing, making sure sick people don’t come in).

Preventing infection of staff (human-to-human)

This is the big one. Staff can be exposed to SARS-CoV-2 by other staff and by visitors. The more COVID-19 there is in the community, the greater the risk.  That’s the same for any other workplace where staff and customers mingle, and we know outbreaks occurs in those settings. The impact is the issue. We can’t shift animal care to remote for a couple of weeks while an outbreak among staff is underway. People need to attend to the animals. Staffing issues are a major concern in a wide range of industries, but many of those can handle things through shifting to remote activities or pausing some activities.  Shelters can’t.

The more people who get sick in a shelter, the more animal care can be compromised.

  • That can lead to suboptimal general care and impacts on preventive medicine or veterinary care for animals in the shelter.
  • It can probably increase the risk of outbreaks of other diseases in the animals through reduced monitoring and infection prevention practices.
  • It can also lead to pausing or slowing adoptions if staff can’t maintain those operations. That creates more risk and cost for the shelter, and also causes capacity issues.
  • Severe staffing shortages could also lead to an inability to take in new animals, which could lead to abandonment or euthanasia of animals.

Since shelters often have many personnel, including the large number of volunteers that are often involved, the odds of someone coming into the shelter with COVID-19 are high. If lots of people are coming in (especially in an unstructured manner) to look at animals, the risk goes up even more.

What do we do to balance being proactive and practical, reducing disease risk while maintaining as much normalcy as possible in shelter operations?

Good question.  To be honest, we’re making it up as we go (because we have to), and there’s no one-size-fits-all solution.

However, there are some basic practices and concepts that certainly apply and need to be considered carefully in any situation:

  • Maximize vaccination of staff (and that means 3 doses, not 2).
  • Maintain basic non-pharmaceutical interventions such as masks.
  • Monitor and improve ventilation.
  • Continue to have a strict “if you’re sick, stay home” policy.

Managing visitors/adopters is also important, including measures such as:

  • Minimize the number of visitors in the shelter.  Do as much remotely as possible. Discussions about animals and adoption protocols can be done online or by phone.
  • Minimize the number of people in the shelter in general or in any specific area of the shelter at one time.  Keep access to the shelter by appointment only, so that there are no crowded periods. Keep people spaced out
  • Maximize the use of outdoor spaces for interviews and animal visits.
  • Require visitors to wear masks.

Some adopters won’t like it, but it’s a case of “your facility, your rules.” If someone won’t use these very basic precautions (during a pandemic that’s still in full swing), it may be a red flag about how well they will follow any other requirements associated with adoption as well.

An recent news article from Thailand entitled Superbugs lurk in local food systems came to my inbox the other day. There’s nothing really new in it, but it has some talking points that are commonly used (and sometimes misused) when we discuss and debate antimicrobial use (AMU) and antimicrobial resistance (AMR) in food animals.

Here I’ll break down these various statements, not really to defend, support or criticize them, but hopefully to show some of the complexities and challenges around these issues (the article quotes are in italics).

Antibiotics are the silent props of the factory farm system, preventing stressed, confined animals from otherwise getting sick due to the dismal conditions they live in.

  • I don’t like it when articles start with “factory farm.” It shifts the focus from AMU/AMR to the ethics of large scale food animal production systems. That’s not to say there aren’t (sometimes major) issues there, but we need to separate those out. Some huge farms do a great job with AMU (and welfare). Some small farms are horrible with both. Certainly, large farms can have more challenges, and bad practices can have disproportionate impacts when they involve so many animals. However, “big = bad” and “small = good” isn’t accurate. There’s likely a sweet spot in the middle, where farms are big enough to have the expertise and finances to improve animal health and animal management, incorporate optimal disease prevention strategies and have a good antimicrobial stewardship program, but small enough to limit some of the other concerns that often come with large-scale production. These factors also vary a lot by animal species.
  • Like most things around AMR in livestock, over-simplification and buzz words can make us lose focus.

Around 131 000 tons of antibiotics each year are used in farming globally, comprising 3/4 of the antibiotics produced in the world, and the amount is expected to rise to 300 000 tons in 2030, according to an academic article entitled “Reducing antimicrobial use in food animals” published in the journal Science in 2017

  • There’s no doubt massive amounts of antibiotics are used in animals, mainly in food animals. The relative use of various drug classes in food animals and humans tends to quite different, and we’re trying to foster less use of “critically important’” antimicrobials in animals.
  • Looking at the mass (tons) of antimicrobials used is (relatively) easy, but oversimplifies things and can therefore be misleading. Explaining this alone could be a whole series of blog posts, so I’ll just add a few comments for now. Not all drugs are equally potent. If I change from using a drug that is dosed at 20 mg/kg two times a day to one that is used at 2 mg/kg once a day, I’ve dropped from 40 mg/kg/d to 2 mg/kg/d.  If I look at tons of drug used, that would look like a huge improvement, and a farm could do that quite easily in some situations. But, if in the process they switch from a lower-tier drug (e.g. a penicillin) to a “highest priority critically important” antibiotic, that would be a huge mistake that can cause a lot of harm, even though it looks good from a tonnage perspective.
  • There are also some drugs that are used in animals that have no relevance in humans – they are not used in people and there’s no cross resistance with antibiotics that are used in people. They are largely irrelevant from an AMR standpoint (at least in terms of human health) but can skew the tonnage data for AMU in animals.
  • We need better metrics for measuring AMU and more thought and analysis than just looking at a single number. The easy sound-bite approach to data collection and dissemination isn’t really helpful.

There is now abundant research showing how this overuse of antibiotics in farming is a leading cause of “superbugs”, and that these superbugs are infecting workers and spreading into the food supply chain and our environment.

  • “A” is an important word here. Most AMR issues in humans relate to AMU in humans. At conferences, I’ve occasionally asked the audience “what percentage of AMR in people is likely attributable to AMR in animals?” I’ve gotten responses from 1-96%. It’s probably actually fairly low, but there are nonetheless some important issues there and AMU in animals is absolutely a contributor to AMR in people. How much of a contributor…? We don’t know.
  • So, AMU in farm animals is an important factor when it comes to AMR. However, it’s not an issue of addressing AMU in just farm animals. We need to address AMU in all sectors, including people. Failing to do that means we’ll never address the problem adequately.

Indeed, more than 100 Thais die every day because of superbugs. Yet even though the mortality rate is higher than COVID-19, there is almost a complete lack of awareness about this public health threat.

  • A great statement. AMR has been called the “silent pandemic.” It was well established before COVID-19, and it isn’t going away soon. Yet, people pay relatively little attention to it. Governments have less motivation to properly fund work on AMR and AMU, whether that’s research or stewardship initiatives. Canada has a framework for a national action plan for AMR that was released in 2017 and has been sitting on a desk for 5 years. We have a plan (that’s getting outdated) but no funding or action. So, we don’t have a plan, really.

Antibiotics are typically used at factory farms to either treat sick animals, promote their growth, or prevent disease. Fortunately, the use of antibiotics for growth promotion in several countries, including Thailand, has been bannedThe abuse of antibiotics in farming in Thailand is mostly to prevent stressed animals from getting sick due to farms’ poor welfare and management. The drugs are typically mixed with food and water and given across group herds. 

  • It varies by region, but there is definitely a large component of this in animal agriculture. Antibiotics can be used as a crutch to compensate for poor management, especially if antibiotics are cheaper and easier than good management or changes to things like animal housing.
  • As indicated, antibiotics aren’t used for growth promotion in many countries now. But, we need to increase that number. That’s relatively low hanging fruit. It just needs action at the national level in countries where antimicrobials are still used like this, and support for farmers to improve their practices so they don’t feel a need to use antimicrobials as growth promoters.

The root cause of the issue is the poor welfare in which farmed animals are kept in factory farms, and this must be addressed. Improvement in this area will support United Nations Sustainable Development Goal to ensure access by all to safe food. 

  • This is may be the most important statement in the article (although I’d remove the factory farm comment). As a member of the Global Leader’s Group on AMR, I bring this up repeatedly. We need to improve animal health systems to reduce the need for antimicrobials in animals, and to improve how they are used, when they are needed. Similarly, we need improvements in human health systems to optimize AMU in people. Healthier people and healthier animals need fewer antimicrobials.

Pig factory farms in Thailand are discharging huge quantities of pig waste (manure and urine), containing significant quantities of antibiotic-resistant genes and superbugs, into public waterways and the wider environment. 

  • AMR is a classic One Health issue, impacting human, animal and environmental health. Environmental impacts are often ignored, in part because they’re harder to see and understand. However, it’s impossible to argue that AMU in animals (and humans) doesn’t have profound environmental impacts. Some of those can come back to bite us too, as the environment can be a source of new resistant bacteria or resistance genes.

These findings by World Animal Protection also raise questions as to why superbugs from banned antibiotics can still be found in the environment near factory farms four years into the implementation of the national plan. 

  • Whether it’s in the environment, animals or people, changes in antibiotic use don’t instantly result in changes in resistance. It can take a long time to see changes, sometimes decades. We still see widespread chloramphenicol resistance in bacteria in livestock in Canada, despite the fact that this drug has been banned in food animals for decades. There’s no easy or quick fix for AMR. That’s why we need to focus on prevention and act now.

A ban on the preventive use of antibiotics in factory farms by increasing animal welfare standards would drastically reduce the presence of superbugs in our environment, but also guarantee safe meat for all. 

  • As with many things, a bit more nuance is needed. Bans aren’t the way out of the AMR problem. Reductions are (ideally massive reductions). Banning certain drugs and practices is reasonable. However, even well-raised animals (and people) sometimes need antibiotics. Sometimes, short courses of preventive treatment using lower-tier drugs are better for both health and AMR than needing to treat sick (or sicker) animals with other drugs, maybe for longer periods of time.
  • A lot of preventive use is unnecessary. Sometimes it’s done because of poor management. Sometimes it’s done because of inadequate education. Often it’s done because of historical reasons (“I’m doing this because that’s the way we’ve always done it and I’m afraid to make a change.”). Reducing AMU requires addressing all these factors, with improved health, improved education, access to better decision support mechanisms and addressing the social science components of AMU that are too often neglected.

This is a huge topic, and this long blog post can’t even start to do it justice. However, hopefully it raises awareness of some of the issues and highlights some of the complexities of the situation.

Everyone has a role to play in controlling AMR. It’s not just prescribers, farmers and regulators. It’s everyone involved in the chain of drug production to prescription to use to disposal. That’s pretty much everyone. The average person may think there’s little they can do, but there are lots of little things we can all do:

  • don’t press for antibiotics (for people or animals)
  • use antibiotics properly when prescribed
  • improve health of people, animals and the planet through other means (even small things)
  • call for change (give governments a reason to act)

That sounds a bit daunting, but for most people, it’s just little things, and lots of people doing little things can have a big impact.

Concerns about the animal aspects of the COVID-19 pandemic continue to come in waves. Most of the time they are ignored or dismissed, but there are also periodic flurries of attention and (often over-) reaction.  Lately, questions about vaccination of animals against SARS-CoV-2 follow have been on the rise.

Should domestic and wild animals be vaccinated against SARS-CoV-2?

  • Yes, no and maybe… but mainly no.  To properly assess this question, we need to step back and think about what vaccines can potentially do.

There are 4 main areas I think about when considering whether vaccination may be useful in any given species:

  • Prevention of disease:
    • This is really “prevention of severe disease.” If a species doesn’t get very sick and just has mild, transient illness, there’s little value in vaccinating from an animal health standpoint.
  • Prevention of transmission of the disease to people:
    • Transmission of SARS-CoV-2 from animals to humans has been documented or suspected in very few species. Most transmission is human-to-animal, and animals are most often dead end hosts (e.g. if my cat gets infected, he got it from someone in my household and is unlikely to spread the virus to any other humans).
  • Prevention of transmission to other animals:
    • Can the animal spread SARS-CoV-2 to other animals of the same species? Or be a bridge, spreading the virus to other domestic animals or wildlife?
  • Prevention of establishment of an animal reservoir where new variants could emerge:
    • This is the big concern with certain animal species (e.g. deer, mink) that are both highly susceptible and have a large population with frequent, close contact between animals, which allows for for potential long term, continued transmission of SARS-CoV-2.

Not many species check many (or any) of those boxes when it comes to vaccination against SARS-CoV-2.

The other thing to consider is what vaccines for animals may or may not actually be able to do. We have very little information about the very limited vaccines for animals that are currently out there. These vaccines are based on older technology than our human mRNA vaccines, and the older tech hasn’t been known to be able to produce highly effective coronavirus vaccines in the past. Vaccine science is improving, and I’m not trying to bash the animal vaccines or the companies (I’m grateful they’re working on them),  but I’m trying to be realistic.

Vaccines can have a range of effects, depending on their efficacy:

  • Reduction of severe disease
  • Reduction of disease
  • Reduction of infection (with or without disease)
  • Prevention of infection (sterilizing immunity)

We don’t know how effective animal vaccines are in different species.  Based on what we know about the more technologically advanced human vaccines, reduction of severe disease is likely a much more realistic target than reduction or prevention of infection (which would reduce the risk of transmission).

Another issue is the level of vaccine coverage that would be needed in a given species. For example, if we want to use vaccination as a tool to reduce establishment of the virus in wildlife, we need a vaccine that significantly reduces infection and transmission AND we need to vaccinate a large percentage of the population AND keep vaccinating animals over time, since population turnover is high in many wildlife species.

We also don’t know how long immunity persists in different species, or how it might hold up against different variants of SARS-CoV-2 (which we wonder about it humans as well…).

Once we start thinking about all these factors, I think it shows that the utility of vaccination in animals currently is going to be limited to a few niche situations.

Dogs / cats

  • Dogs and cats commonly get infected, but rarely get seriously ill. They are rarely going to be the source of infection for people (they are usually infected by their owners).
  • Dogs and cats don’t live in large groups where virus transmission can be sustained long term, such that it could create a reservoir and become a source of virus variants.
  • Indoor-outdoor cats are more of a risk as a bridge between infected households and other people or animals, but the odds of them playing a significant role in transmission are fairly low AND any effect on this would require a vaccine that prevents infection and virus shedding (unlikely).  The far easier and more effective solution is to keep cats from infected households indoors until the risk period for transmission has passed.
  • I’m glad we have vaccines ready in case something changes and we get a strain that causes more serious disease in dogs or cats, but I can’t see a use for vaccination in these species now.


  • Mink check a few of the boxes for vaccination, as a species that is susceptible, gets sick, is housed in large populations (i.e. farmed mink), that has generated new variants in the past, and can spread the virus to people  and other species.
  • Vaccination of all mink on a farm is also possible.
  • Vaccination is probably a more effective tool for mink health than public health, given the questions above about whether vaccines actually reduce or prevent infection, and therefore transmission. If vaccination just reduces disease but still allows for transmission between and from mink, then it might not be useful or might even be counterproductive for public health purposes.

Zoo animals

  • Here’s where there’s the most potential for benefits from vaccination against SARS-CoV-2 in animals. Some zoo species are highly susceptible and can die from infection with this virus. These animals can be valuable emotionally and economically, and from a conservation standpoint. So, more zoos are vaccinating their non-human primates (e.g. apes) and big cats. Some are also vaccinating their mustelids (i.e. species related to mink; some, like the black footed ferret, are highly endangered) and cervids (i.e. species related to deer, since we know white-tailed deer are quite susceptible and can spread the virus).

Wild deer (specifically white-tailed deer)

  • Deer check a few of the boxes for vaccination, as they are highly susceptible and may be able to maintain circulation of the virus in area where they have a high population density, potentially leading to new “deer” variants.
  • However, we would need a vaccine that significantly reduces infection and therefore the risk transmission (and I’m not very confident we have that).  Deer don’t appear to get significantly ill themselves (thus far), so vaccination isn’t directly helpful to the deer.
  • To be useful, it would also require vaccination of a LOT of animals. For example, if we need to vaccinate 80% of the wild deer population… well, good luck finding a way to do that.
  • Furthermore, lots of new deer are born every year so vaccination campaigns would have to be continued until SARS-CoV-2 is out of circulation in deer and people.  That doesn’t seem very practical to me. Rabies vaccination of some wildlife species is used in some areas (including Ontario) and it’s highly effective. However, it uses a highly effective vaccine that can be delivered through baits that can eventually cover a pretty high percentage of the target population, and it does have to be repeated at least annually until the virus is eradicated from an area.  It also takes a lot of effort and coordination.  It would be very tough to do the same for SARS-CoV-2 vaccination in deer.

We’re not going to vaccinate our way out of animal issues with this virus. We need to control SARS-CoV-2 in humans to have any hope of controlling SARS-CoV-2 in animals. Vaccine research is important so that we have vaccines available should opportunities for their use be identified, and continued vaccine development may get us to the point where we have a highly effective vaccine that stops transmission. However, without that, the potential impact of vaccination of most animals is limited.