Back in October/November 2020, I wrote a series of posts about what we know about SARS-CoV-2 and different animal species. It’s a dynamic field, so it’s about time I got around to updating them. We’ll start back at the beginning with one of the most susceptible domestic species: cats.  A lot of research about SARS-CoV-2 in cats in the last year has largely supported our initial observations and have helped refined what we know.

Are cats susceptible to the SARS-CoV-2 virus?

Yes, cats are clearly susceptible. No change here. We’ve known that for a while and more research has just solidified that. More on that below.

How often do cats get infected?

There are a lot of papers now about SARS-CoV-2 in cats. Some are very good. Some are interesting but low-impact single case reports, and some are rushed studies (“I want to be first, not the best”) that use small sample sizes, indistinct populations or cherry-pick interesting results from what should have been more comprehensive, bigger studies.

Overall, it’s apparent that human-to-cat transmission is common in households where people have COVID-19. A small number of studies have looked at active infection using PCR testing +/- virus isolation, which is tough to do logistically. It’s a lot of work to identify infected people, arrange to sample their pets and (typically) go to the household to do that. A study from Texas (Hamers et al. 2021) identified the virus in 3/17 (18%) of cats in infected households. The results of our Canadian study (which have been presented but not yet published) were fairly similar.

Testing for virus only tells us part of the story, because of difficulty with sampling infected cats soon enough to catch them during their short-term active shedding period. We assume that we often miss infections because we get into the household to sample too late. That’s why more studies are based on looking for antibodies in the blood of house cats as an indicator of previous infection. It’s less definitive than detecting the virus, since the performance of antibody tests can be variable, but with good tests it can really help our understanding of the situation.

When we look at antibodies to SARS-CoV-2 in cats in infected households, the apparent infection rates go up. The Texas study reported a seroprevalence (the percentage of cats with antibodies) of 44% (7/16), and the seroprevalence in our preliminary data from Canada was even higher at 67%.  Other studies have had variable results (for example,  a study from Peru found a seroprevalence of 17-30% among cats from infected households, depending on how the testing was interpreted), but the take-home message is that human-to-cat transmission of SARS-CoV-2 is pretty common.

There are also many studies that have looked at antibodies against SARS-CoV-2 in the general cat population, usually without any information about whether the cats were exposed to an infected person. These studies are fairly easy to do (for example, by testing leftover blood from samples collected for other purposes, or collecting convenience samples from cats presented to veterinary clinics or shelters), but their value is variable. Typically, these studies report low seroprevalence among cats. One study reported close to 10% prevalence, but <2% is more common (e.g. Dileepan 2021, Klaus 2021, Smith 2021, Stranieri 2021, Udom 2021, van der Leij 2021). Positives could be cats that actually had infected owners, but the information wasn’t known or collected, or false positives, due to an imperfect test. In our surveillance study of cats from shelters or spay/neuter clinics, we found there was often very limited history about the cats (e.g. cats recently acquired off Kijiji), so we can’t use the history to put the results into context.

There’s always a lag between disease occurrence and publication of reports, so it would be expected that rates of infection in cats would increase over time as the human pandemic continues and more cats become exposed.

Risk factors for infection in cats haven’t been carefully investigated yet, often because of fairly small study sizes. A Brazilian study reported that cats that slept in the bed were at higher risk of being seropositive (Calvet 2021), something we also found in our Canadian study. That’s not too surprising as things that increase close contact (direct or shared airspace) presumably increase the risk of human-to-cat transmission.

Do cats get sick from SARS-CoV-2?

They can, but most often if appears they don’t. Experimentally, clinical signs in cats have been pretty unremarkable. Most infected cats have been reported to be healthy, but it’s not always the case. There are reports of sick cats, including a paper describing a fatal infection in a cat in the UK.

In our surveillance, cats that had antibodies against the virus were more likely to have been reported as being sick at the same time as the COVID-19-infected owner, but most of the time any illness in the cats was mild (e.g. coughing, sneezing, quieter than normal). I get lots of anecdotal reports about sick cats that have been exposed to the virus, and I suspect many of them really are due to to SARS-CoV-2. When an otherwise healthy adult indoor cat with no contact with other cats develops signs of upper respiratory tract infection around the time its owner had COVID-19, there aren’t many other probable causes for the cat’s illness. However, at the same time, since infection of cats seems to be quite common, we’d expect to find incidental infection of cats that get sick or die from various other unrelated things. A small study by the US CDC (yet to be published) explored this, and the take-home message was that some cases of severe disease seemed to occur but much of the time, cats that died while infected didn’t die from the effects of SARS-CoV-2.

Similar to people, most exposed cats probably don’t get sick or get mild disease. A subset get more serious disease, and a smaller subset may even die from the infection. The relative size of those different groups is completely unknown.

Can cats infect other animals with SARS-CoV-2?

Yes. Experimentally, cats have been shown to infect other cats. That’s also been seen outside the lab, such as the high-profile outbreak in lions and tigers in the Bronx Zoo, where cat-to-cat transmission was more likely than all the big cats being individually infected by people. We also investigated one large group of infected cats, and it’s most likely there was cat-to-cat spread there too, rather than all human-to-cat infections.

Can cats infect people with SARS-CoV-2?

We still don’t know for sure if cat-to-human infection occurs. Since cats can infect other cats, we have to assume there’s some risk of them infecting people, but sorting out how much of a risk there is is a challenge. If someone got infected by a cat, it would be very difficult to determine that they got it from a cat vs a human contact, because the virus is still circulating widely in people, and contact with the infected cat would probably coincide with contact with that infected cat’s (probably infected) owner.

I think we have to assume that cat-to-human transmission is biologically possible and has probably happened. However, in the real world, it’s probably very rare given the dynamics of cat-to-human contact. If my cat gets infected, he got the virus from me, my wife or my kids. In that event, transmission from the cat to other people in the household is possible, but transmission between people is far more likely. Most cats don’t encounter a lot of different people, especially when their owners are sick. The biggest risk is likely when a cat leaves the house, such as to go to a veterinary clinic, or is surrendered to a shelter. We’ve detected infected cats in shelters, so it’s a plausible scenario, and it’s why we recommend asking about owner infection status prior to bringing animals into clinics, shelters or other places outside the home.

Do we have a SARS-CoV-2 vaccine for cats, and should we consider vaccinating cats?

My current answers are “kind of” and “no.”  There’s a SARS-CoV-2 vaccine (of unknown safety and effectiveness) licensed for use in cats in Russia.  In North America, there’s an experimental vaccine that has been used in mink and some zoo animals, and it would be the best option if we needed a vaccine. However, I don’t see a need at this point given the apparent rarity of severe disease. There’s more information on the possible utility (or not) of SARS-CoV-2 vaccines in pets in an earlier post. 

Could cats be an important reservoir of SARS-CoV-2 once it’s controlled in people?

Probably not. Cats are pretty susceptible to the virus, but they don’t shed it for long. To maintain the virus in circulation in the cat population, an infected cat would have to interact with another susceptible cat within a few days (and on and on…). Most cats don’t do that. In community cat colonies, I could see it spreading through the group, but it would likely burn out quickly as most of the cats became infected and recovered, assuming there’s some degree of immunity to re-infection (which seems to be the case) . In order to maintain a virus in a population when it’s only carried for a short period of time, you need a lot of animals and a lot of animal-to-animal contact. That’s more of a concern with some wildlife species (but that’s a story for another day).

Could cats be a source of new SARS-CoV-2 variants?

Probably not. Variants occur because of random mutations. These occur when the virus replicates. So, the risk of variant emergence is directly proportional to how much transmission (and therefore virus replication) is going on. Since we don’t expect sustained transmission in the cat population, there’s limited risk of variants emerging in there.

So, should we worry about SARS-CoV-2 in cats?

Worry, no, but we should pay attention to it.  There’s a cat health risk, and we want to avoid that by reducing contact of infected people with cats. It’s probably most important with older cats and cats with underlying diseases that may make them more susceptible to severe disease.

The risk of cats spreading the virus in a household is limited, but can’t be ignored. When you have someone isolating from the rest of the household (e.g. living in the basement), we want to make sure pets like cats are considered, so they’re not tracking the virus from the infected person to the rest of the family. It’s easy to see how someone might do a great job staying away from other people, but not think about the cat that runs back and forth between them and the rest of the family.

We also don’t want cats tracking the virus out of the household and exposing other cats or wildlife. The odds of this causing a big problem or creating a wildlife reservoir are very low, but not zero. A little prudence makes sense.  Keep cats indoors if they’re in contact with any infected people.

What should be done with cats?

This hasn’t changed from the first post….

  • Cats are people too, when it comes to SARS-CoV-2.
  • If you are infected, try to stay away from animals – all animals, human and otherwise.
  • If your cat has been exposed to SARS-CoV-2, keep it inside and away from others.

For the past year or more, we’ve been trying to track infectious upper respiratory tract disease (officially known as “canine infectious respiratory disease complex (CIRDC)” but more commonly called “kennel cough”). It’s a tough thing to do since testing is limited, the disease is always present to some degree in the dog population, and there’s no formal reporting system. Enquiries about CIRDC in different areas seem to fill my inbox in waves, but that’s probably more related to reporting (especially social media rumours) vs actual frequency of illness. This week’s been busy so far  with a dozen or so emails asking about things like “new” respiratory diseases, or specific things like canine influenza (and it’s only Monday…).

We’re still not sure what’s going on. It does seem like there’s increased CIRDC activity over a lot of North America right now, and it’s been going on to some degree for quite a while. When we think about increases in respiratory disease reports, there are a few  potential causes (as I have mentioned many times before):

Increased disease caused by the usual suspects

  • This is my main guess at this point for what’s currently going on. Common things occur commonly, and that’s particularly true for the variety of bacteria and viruses that cause CIRDC in dogs.
  • A few potential reasons for the increased disease from these pathogens can be postulated. One is there’s more dogs mixing with each other now as people start to increase activity and get together post-lockdowns, and as people prioritize safer outdoor activities (often with their dogs). Combine that with a surge in new dogs and potentially decreased vaccination (due in part to overloaded veterinary clinics and access difficulties from earlier restrictions), and it’s easy to see how we might have more disease.
  • Another potential dynamic is increased use of oral “kennel cough” vaccines, as they are easier to administer to some dogs compared to intranasal vaccines. The problem is oral vaccines only protect against one cause of CIRDC (Bordetella bronchiseptica) while intranasal vaccines protect against Bordetella and canine parainfluenza virus (CPIV). That’s important because CPIV is the most commonly diagnosed cause of CIRDC in many areas.

Increased disease caused by a new pathogen

  • We’re always on the lookout for something new, but nothing is apparent yet. With a new virus, we’d be more likely to see widespread transmission in exposed groups, since no dogs would have any immunity. We’re not really seeing that. The cases being reported are more sporadic, as we’d expect with our typical causes of CIRDC. However, we can’t rule out a new pathogen completely, and there are undoubtedly various causes of CIRDC (mainly viral) that we simply haven’t identified yet.  I don’t think it’s the explanation for the current situation, though.

Increased reporting of disease

  • This is probably part of what we’re seeing. There’s more social media use these days so word spreads quickly. One voice can be amplified disproportionately and unsubstantiated claims can be disseminated easily. Further, it feeds on itself. When there’s more buzz about sick dogs, more people that otherwise wouldn’t have said anything chime in. So, we probably hear about a greater percentage of sick dogs simply because people are talking about them when they otherwise wouldn’t have.
  • Also, as more people are at home with their dogs, we probably hear more about the typical mild cases of CIRDC, because owners pay more attention when the dog is coughing beside them all day.

What about SARS-CoV-2?

  • SARS-CoV-2 is very unlikely to be playing a role. We can never say never, since the COVID-19 pandemic is a dynamic situation and we don’t know much about recent variants in animals. However, what we know so far is that infection of dogs and cats with SARS-CoV-2 is quite common, but disease is uncommon in cats and rare in dogs.

What about canine influenza?

  • Canine flu certainly can cause large outbreaks of respiratory disease in dogs. It spreads quickly because of limited immunity in the dog population. There has been some canine flu activity in a couple places in the US in the past few months, but these seem to have burned out (or at least burned down) relatively quickly.
  • There have been social media reports of canine flu outbreaks in Ontario. As far as I know, that’s false. Canine flu is reportable in Ontario, and no such reports have been received from any lab. We haven’t seen canine flu in Ontario since we eradicated it in 2018. I’m always on the lookout for it, but I’m most concerned about flu when there’s an outbreak that has a very high attack rate, including dogs that have had intranasal kennel cough vaccine. We’re still looking but I doubt canine flu is playing a role currently.

What can people who are worried about their dogs do?

  • Reduce contacts with large numbers of unknown dogs. Just like with other respiratory pathogens, the more contacts, the greater the risk of encountering someone that’s infectious.
  • Reduce contact with sick dogs. This can be harder but it’s common sense: if a dog looks sick (e.g. coughing, runny nose, runny eyes), keep your dog away from it.
  • Keep sick dogs at home. (Duh… but you’d be surprised.)
  • Avoid things like communal water bowls in parks that are shared by multiple dogs.
  • Get your dog vaccinated (ideally intranasally) against kennel cough if it tends to encounter other dogs regularly. My dog doesn’t get this routinely since we live in the country and he has a very limited number of other dogs with which he interacts. If I was in town and/or going to dog parks or other places where he’d mix with lots of dogs of unknown status, I’d vaccinate him (especially as he’s getting older now).
  • Consider testing your dog if your dog gets sick. Testing is useful to help figure out what’s going on and maybe to help control things. However, it rarely tells us something that influences care for the individual dog (since we don’t have specific treatments). So, the cost of testing is (understandably) hard to justify for some.

We’re also still tracking cases so people with sick dogs can provide information by filling out our quick survey here:

I’ve meant to write more about SARS-CoV-2 in deer, and USDA’s recent announcement of infected deer made me get my butt in gear (warning: long post approaching).

What do we know about SARS-CoV-2 infection in deer?

We now have three different pieces of evidence:

There are two broader concerns with these findings regarding SARS-CoV-2 in white-tailed deer:

  1. Reservoir for human infection: More infected individuals (human or animal) means more potential exposures for people. If this virus is present in deer (or other wildlife) that creates more opportunities for exposure.
  2. Potential for virus mutation: This is the big concern, but linked to the reservoir concern too. As I’ve said since this pandemic started, we really want to keep this a human virus – we don’t want it to spread to other species. Yes, it’s likely present in the original reservoir host population (presumably bats), but if it gets into other species, especially those that live closer to and interact more with people, and/or  are present in larger numbers, the risk of a significant mutation occurring and spilling back into the human population increases.

Virus mutations are random events that happen all the time, but the more transmission there is, the opportunity the virus has to mutate. If there is sustained transmission in a wildlife population (or any population for that matter), it’s essentially guaranteed that new strains (variants) will develop over time. What that means in the bigger (human) picture could vary. Because they’re random, mutations can be good or bad for the virus, by making it either more or less transmissible, for example. What we’re concerned about is emergence of new variants that are more adept at infecting people and/or harder to prevent or treat, and those variants then finding their way from the animal population (in this case deer) back into people, and then spreading from person-to-person.

In the big picture, is SARS-CoV-2 in white-tailed deer a problem?

It’s hard to say. Currently, human-to-human transmission is still the problem. New mutations are going to develop in people because of widespread transmission internationally, and until we have good vaccine coverage everywhere (not just rich countries) we’ll have persistent and high risk of new variants emerging in people.

Deer probably contribute little to the risk, at least at this point.  For a deer variant to be of concern, it has to find and infect a susceptible person, and human-deer contact is fairly limited in the grand scheme of things. It’s possible, but a susceptible person is still more likely to be infected by another person than by a deer at this point.

While SARS-CoV-2 remains a human pandemic, deer are likely a niche issue. As the virus eventually gets controlled in humans (we hope), then wildlife reservoirs become more important, if they can be a source of new variants.

What do we need to do?

We need more information, as usual. We need to know lots of things like:

  • How widespread is infection in deer?
  • What’s the likelihood that an infected deer would infect a person through routine contact (e.g. hunting, handling animals or carcasses)?
  • Are variants emerging in deer?
  • Are deer infecting other wildlife?
  • Will transmission in deer be sustained, or (better for us) does this represent repeated short term transmission after introduction from people, or a rapid burn through the population?

This is one of those “let’s pay attention and get more info, but not freak out” situations. Throughout this pandemic, I’ve tried to balance increasing awareness with avoiding excessive concern or paranoia, and that applies here.

What should deer hunters do?

  • Get vaccinated.
  • Hunt with vaccinated people.
  • Use standard COVID-19 precautions around people.

Should hunters do anything specific when handling deer?

I don’t think we have enough evidence at this point to make specific recommendations for hunters handling deer. Good general hygiene is obviously important, but whether hunters should take extra precautions (e.g. mask and eye protection) is completely unclear. As we learn more, it’s possible that guidance will change.

What about venison?

There should be essentially no food safety risk when it comes to consuming venison. This virus does not survive well outside the host, so even if the animal was infected, the risk from handling meat is presumably negligible. Good hygiene practices used when handling raw meat of any kind should cover any theoretical risk.  It’s always important to cook meat properly before consuming it as well, and the virus would not survive that process either.

My usual ending for these posts is a reminder that COVID-19 is ultimately a human issue. Animal infections are a result of human activities and human contacts. The best way to reduce the risk of this virus entering animal populations is to control it in people.

Human vaccination is probably the best protection for deer.

The Canadian Food Inspection Agency (CFIA) has reported the identification of a rabid dog imported into Ontario from Iran. The dog was imported on July 1, 2021 and started showing signs of rabies on July 11. It was euthanized the next day and subsequently diagnosed with rabies caused by a canine rabies virus variant known to circulate in Iran.

  • Canine variants of the rabies virus are not present in Canada. We still have other rabies variants in wildlife (e.g. bat, skunk, raccoon, and Arctic fox variants) but canine rabies variants, the ones that causes most of the human deaths internationally, are only a risk from imported animals.  But make no mistake, all rabies virus variants are deadly and can infect any mammal.

An investigation of the case ensued and identified 24 people who potentially had contact with the rabid dog, of which 14 received rabies post-exposure prophylaxis (PEP) based on the risk of significant exposure to the dog’s saliva. Fortunately, there was no reported contact with other dogs or any other animals.

  • It’s critical that this was diagnosed and investigated expediently. It’s hard to say what the risk was to those 14 people who received PEP, but with an almost invariably fatal disease, we don’t want to leave much margin of error.
  • Overall, this incident would have cost taxpayers thousands of dollars (more likely tens of thousands of dollars). PEP is very expensive, and the personnel time required to diagnose and investigate a case like this are substantial.

This is consistent with our ongoing concerns about poor importation practices.  Our colleagues in the US may be saying “I told you so!”, as Iran is one of many countries from which importation of dogs is no longer allowed because of rabies risk.  (Although prior to the current US ban, they experienced a very similar incident in June 2021 with a rabid dog that was imported into the US from Azerbaijan).

Co-incidentally (or not, I suspect), there was also a recent news report about a group of 5 puppies from Iran being refused entry into Canada in late July. It’s a bit unclear what was wrong, but it seems like there were a few issues with the importation and that it didn’t comply with the recent changes in Canadian importation rules for commercial dogs less than 8 months of age. These puppies arrived in Montreal and were denied entry. After a short layover, they were put on a flight back to their country of origin.

This has always been a concern with increased enforcement of importation rules. Rejecting a non-compliant shipment at the border is a standard approach, but it’s much more complicated when dealing with live animals. However, there’s a reason shipments get rejected and we can’t allow people to get away with ignoring rules. I’ve always said we need a plan to properly assess, quarantine and (when possible) re-home these dogs in cases like this, with substantial fines to the importers both to dissuade them from doing it again, and to cover the costs associated with dealing with the dogs once they’re in Canada. That could help strike a balance between protection from imported diseases and imported dog welfare.

A statement by the importer of the puppies that were turned back in Montreal raises another concern that we’ve had about the business side of “dog rescues.” They said, “So, we can’t ask these people to pay $2,500 to import their puppies from Iran so we’ll have to pay that and that’ll affect our financial situation so badly that we might have to stop rescuing dogs for a while.”


If there’s a profit margin built in (which I assume has to be the case), this moves beyond being a “rescue” and clearly into the commercial dog realm, which is certainly not uncommon. Some rescues are shoestring operations that get by on donations and cost-recovery via adoption fees. They do it just to get dogs into homes. Others profit quite nicely from the business of “rescuing.”

A few days ago, I wrote about a potential H1N1 influenza outbreak in dogs in California.  As I mentioned, H1N1 influenza causing an outbreak in dogs would be noteworthy because it’s not a known canine flu strain, and an outbreak would be unexpected given how rare it is to have human-to-dog transmission of human H1N1 influenza.

One of my key questions about the preliminary report was “Is this really on outbreak of H1N1, or is it a different flu strain?

It turns out it wasn’t H1N1 after all.

Follow-up testing apparently indicated that the outbreak was caused by H3N2 canine influenza virus. That’s still noteworthy, since we haven’t see much (diagnosed) flu activity in dogs for the last year or two in the US. We assumed the virus was still lingering in the dog population and causing smaller, more local issues that weren’t diagnosed or reported.  This outbreak and an outbreak of presumed canine influenza in Florida in June 2021 are consistent with that.

Overall this is good news. I’d rather be dealing with a sporadic, endemic, known entity (for which we have a vaccine) like H3N2 canine influenza, than a potentially new flu virus in dogs.

African Swine Fever (ASF) is a devastating viral disease of swine that isn’t currently present in the US or Canada. Although the ASF virus only infects pigs, it is quite hardy and can be tracked around by humans, other animals and contaminated clothing, equipment, animal feed and uncooked pork products (like sausages).  It can also be spread by certain soft-bodied ticks belonging to the genus Ornithodoros.

Recently, ASF was found in the Dominican Republic, which is a little too close for comfort. If it reaches continental North America, it will cause massive disease and death in pigs, major disruption of the pork supply chain, and have a devastating economic impact on pork producers and result in an immediately loss of export markets for a considerable period of time.

Keeping ASF out of the US and Canada is a huge priority.  There are already a lot of regulations and restrictions on things like pork products and feed from countries that are not known to be free of ASF, as well as rules for travellers  from these countries.  As an additional precaution, the USDA has added more rules for certain dogs being imported from countries where ASF is present.

The new rules don’t apply to dogs being brought to the US as personal pets, but only to those imported for resale / adoption (which includes rescues that don’t game the system by saying all the dogs they import are personal pets, when they’re clearly not), likely because there are already additional rules for this class of dogs, which makes it easier to apply/enforce a few more.  But it would be better if they could have just said “all dogs.”

It’s still a good step.  The new requirements are basic and logical, including:

  • Shipping containers have to be free of dirt, shavings, straw and any other organic bedding materials.
  • Bedding must be disposed of at the entry point “in a way that prevents the introduction or spread of ASF” (e.g. incineration, disinfection).
  • Dogs must have a microchip.
  • Dogs must be bathed at the U.S. post-entry point within 2 calendar days of arrival. (I’m not sure why they’re given 2 days. This could easily be done quicker).

These are straightforward, feasible and minimally disruptive. The risk of a dog being the source of ASF virus entry to the US are very low, but it makes sense to take basic measures like this, since a single case of ASF in the US would have devastating effects on animal health, animal welfare and the economy.

Similar step by Canada would make sense. There’s nothing to lose, and when the outcome could be catastrophic, being proactive is the key, even with low yield activities.

I’ve had a couple of reports today about an apparent H1N1 influenza outbreak in dogs in the US. Note that I said influenza in dogs, not canine influenza – there’s a reason for that, explained below…

The situation revolves around a respiratory disease outbreak in a dog kennel in California, and PCR testing of some of the sick animals identified H1N1 influenza. Clinically, it sounds like a moderate to severe outbreak, with a reasonable number of infected dogs.

We generally see two types of influenza in dogs:

  • “Canine flu” is caused by dog-adapted strains of influenza A, and they are maintained through spread in the dog population.  The two main canine flu strains that we know about are H3N8 (which seems to have disappeared) and H3N2 (still sporadically present in the US and endemic in some parts of Asia).
  • Spillover infections in dogs with flu viruses that are primarily adapted to other species are also detected occasionally.  Most often this involves stains of influenza A that are adapted to humans, when a dog gets infected from its owner. We usually assume that these are “dead-end” infections, in that the dog doesn’t pass the virus on any further, because it’s not a canine flu virus so the infected dog likely doesn’t produce enough virus to infect others.

Back to the H1N1 in California.  We periodically see human (previous pandemic) H1N1 virus in dogs, which they catch from their owners. However, there can be different strains of the virus even within a single flu “type” like H1N1. If we look at H3N2, we have human H3N2, canine H3N2, swine H3N2, and so on. While they are all H3N2, they are adapted to a specific animal species and don’t infect others as readily. The important question in this case is, what type of H1N1 influenza is involved?  Finding a single case of human H1N1 flu in a dog wouldn’t surprise or concern me. But detecting a whole outbreak is a different story.  More information is needed, since this could range from an interesting story to a serious canine disease threat.

Here are the big questions:

Is the diagnosis confirmed/solid?

  • Is this really on outbreak of H1N1 or is it a different flu strain?
  • Is it an H1N1 outbreak, or was there an outbreak of something different and some incidental H1N1 infection was detected in the process of testing? (Unlikely since it seems like at least a few dogs were diagnosed with H1N1.)

Is this “human” H1N1 in dogs?

  • Is this outbreak due to spillover infection from humans, or is it from a different source? Presumably someone’s sequencing the virus, which will help answer that question. If it’s actually H1N1, hopefully it’s just an oddball scenario with a cluster of human H1N1 flu infections that will die out, versus an indication that we have a new canine H1N1 flu strain, or a human strain that is now more adept at infecting dogs.

Is this virus a “canine” flu virus?

  • It’s too early to say. Hopefully not. We don’t want a new flu strain in dogs for lots of reasons.  A new strain could spread easily through the dog population because no dogs would have any immunity to it. That can cause a significant amount of disease.  There would also be potential zoonotic concerns with a new strain. H3N2 and H3N8 canine flu viruses haven’t been significant zoonotic risks. They’ve stayed in dogs and haven’t spread to people, as far as we can tell. However, flu viruses like to adapt and change, and we just don’t want any more influenza viruses floating around, in terms of their potential for direct infection of people or the potential for recombination with other human flu viruses which could make more new flu strains (to which we might not have any immunity).

At this point, I’m interested and curious but not worried. Hopefully this situation is being investigated thoroughly (I assume it is).

A recent paper in the Journal of Clinical Pharmacy and Therapeutics entitled “A doggy tale: Risk of zoonotic infection with Bordetella bronchiseptica for cystic fibrosis (CF) patients from live licensed bacterial veterinary vaccines for dogs and cats” (Moore et al. 2021) discusses (as the title suggests) human health risks from commonly-used B. bronchiseptica vaccines for pets.

Bordetella bronchiseptica is just one of a few different bugs that causes “kennel cough” in dogs (more accurately called canine infectious respiratory disease complex (CIDRC)). A variety of vaccines against B. bronchiseptica are available, including both oral and intranasal formulations that contain “modified live” bacteria, and injectable formulations that contain killed bacteria. Modified live vaccines (MLVs) contain attenuated (weakened) forms of the bacterium or virus in question that are not supposed to be able to cause disease, but induce a more natural immune response. So MLVs aren’t completely innocuous, and therefore generally aren’t used in immunocompromised individuals, because of the chance that even a modified/weakened bug could cause disease in such a person.

Bordetella bronchiseptica causes disease in a number of different animal species, but seems to be a rare cause of disease in people (unlike it’s cousin, Bordetella pertussis which causes whooping cough). However, infection with B. brochiseptica can occur in people, and those with diseases like cystic fibrosis (CF) are presumably at higher risk.

The authors of the paper state that patients with CF “should avoid exposure to live veterinary bacterial vaccines and seek animal vaccination utilising non- live vaccines.

  • I agree with point #1. High-risk individuals should avoid direct exposure to live vaccines, which can occur during vaccination of the animal, as the vaccine is squirted into the dog’s mouth or nose (and sometimes splattered elsewhere). Ideally, high-risk owners should not be in the room when such a vaccine is given. That’s a very practical, very easy and probably the most effective preventive measure.
  • I’d argue against point #2. Injectable killed vaccines for B. brochiseptica are inferior to MLVs, and that has relevance to the exposure and health of a high-risk owner too.

Here is my thought process when is comes to this situation:

  • No vaccination or less effective vaccination increases the risk of disease in the pet.
  • Bordetella bronchiseptica can cause disease in high-risk people, so we don’t want the pet to be infected.
  • Disease probably also increases the risk of exposure of people to this bacterium and others (from coughing/sneezing pets).
  • Disease also increases the risk that the pet may need to be treated with antibiotics, leading to an increased risk of antibiotic resistance in other bacteria carried by the pet, and some of those bugs can also be transmitted to people.

Millions of doses of these MLVs have been given to dogs with little to no clear evidence of risk to people. The main reference to which the authors point is a report about a mild infection in a boy who was squirted directly in the eye with a vaccine. That’s a lot different in terms of exposure than having contact with a recently vaccinated dog.

The issue of residual modified live bacteria from the vaccine being present in the dog’s nose or mouth for a while after vaccination is usually raised. That’s fair, to some extent, but it ignores the big picture. Yes, there is a very minimally risk that the modified live bug might be present in the dog’s nose/mouth, but there are lots of other (and more dangerous) bacteria in the nose/mouth of every dog. The risk is basically no different from a dog that was recently vaccinated and one that has not been vaccinated, because it’s the more common bacteria found in both dogs that I’m most worried about.

The statement that vaccination “requir[es] a period of CF patient exclusion from the shedding dog,” is not supported by anything I’ve ever seen and doesn’t make sense to me given the above thought process.

Like most things, we need to consider the cost-benefit in each situation.

What’s the human health risk of using MLVs for B. brochiseptica in dogs?

  • Exceptionally low.

What’s the benefit of using MLVs for B. brochiseptica in dogs?

  • Improved animal health, and I could argue reduced human health risks from decreased exposure to sick animals (because we have to think beyond just the risk from the vaccine).

There’s also a statement in the paper that “CF pharmacists, hospital pharmacists and community pharmacists are important custodians of vaccine-related advice to people with CF, who are frequently consulted for such advice. “

  • Very true. However, I’d add the need for a One Health approach. Veterinary input is needed for a proper risk assessment, and to put the issues into context for the individual pet/pet owner. It would be nice to see papers like this written in collaboration with veterinary experts, and for pharmacists and veterinarians to engage more with each other in situations like this. Connections between pharmacists (and many other human healthcare professionals) and veterinarians tend to be pretty poor.

Game-changing research?

Something that will be walked back in the future?

Something in between?

A press release from the US Department of Agriculture (USDA) about a study looking at antibodies against SARS-CoV-2 in white-tailed deer (and an infosheet about the same study) released today makes me wonder which of these will apply. The results are potentially game-changing, but it’s so far outside of what I’d expect that we have to make sure the results are real first. Since information is currently limited to the press release and infosheet, with no specific information about the study methods or details of the results, it’s hard to draw firm conclusions.  Based on the information available though, it could be a remarkable story.

We know from experimental studies that white-tailed deer are susceptible to the SARS-CoV-2 virus. So the USDA’s Animal and Plant Health Inspection Service (APHIS) set out to analyze blood samples from free-ranging white-tailed deer for antibodies against SARS-CoV-2.  The method of testing isn’t stated, but the USDA has excellent labs.  Samples were collected from deer in four different states (Illinois, Michigan, New York, and Pennsylvania) as part of wildlife damage management activities.

According to the USDA press release, antibodies to SARS-CoV-2 were found in 33% of 481 samples collected from white-tailed dear from January 2020 through 2021. This would indicate that these animals had been exposed to the virus sometime in the past, but the testing doesn’t tell us if there was active infection in the deer populations or if the deer could have infected others. The antibody testing only gives us a historical indication of previous exposure to the virus (or, potentially, a virus that induces similar antibodies that cross-react with the test).

Only 1/241 samples collected from deer before the COVID-19 pandemic began were positive. That was presumably a false positive result (no test is perfect, so typically we’d be quite happy with less than 1% false positives).  Less than 1% positive before the pandemic and 33% positive during the pandemic after would support true infection having occurred in these deer populations.

The number raises concerns for me.  The press release states that “the finding that wild white-tailed deer have been exposed to SARS-CoV-2 is not unexpected given that white-tailed deer are susceptible to the virus, are abundant in the United States, often come into close contact with people, and that, more than 114 million Americans are estimated to have been infected with COVID-19, according to the U.S. Centers for Disease Control and Prevention (CDC).

  • All true, and good reasons to investigate exposure in deer populations. However, 33% is very high, given the limited direct contact between people and deer. Deer would have to be very susceptible and very effectively able to transmit the virus widely within the deer population for 33% to be infected.

It’s very interesting info, but more details are needed. It could be a game-changer, or a testing issue. That needs to be sorted out.  Regardless, it’s a good One Health study that’s needed to help understand the ecology of this virus and potential risks.

I remember being in a meeting years ago and hearing an estimate of the number of deaths of people from Hurricane Katrina that were linked to them staying behind because they could not evacuate their pets. People chose to ride out a devastating hurricane rather than abandon their animals – animals that weren’t part of the evacuation plans. I can’t remember the number, but it floored me.

Many people died because they wouldn’t leave their animals to die.  Additionally, it was estimated that 100,000-600,000 pets were left behind. I’m not sure there’s any reasonable estimate of how many of those survived. Certainly, many did not.

These tragic numbers are preventable, or at least can be massively reduced, but it’s not easy.

To be sure, there are many challenges with evacuating large numbers of animals – logistical challenges, animal health and welfare challenges, and public health challenges (e.g. bites from poorly behaved or stressed animals, fear of animals amongst other evacuees, risk of zoonotic disease transmission). Challenges mean we need to plan, not just ignore the issue.

Anyone, anywhere can be affected by a natural (or unnatural) disaster, so everyone should have a plan for what to do with their animals. The disaster might be a high profile, mass event like a hurricane or forest fire, or it might be an individual-level event like a house fire.

The US Centers for Disease Control and Prevention (CDC) has some good guidance for emergency preparedness for pets, including a pet disaster kit checklist.

While sometimes a disaster plan might be how to ride it out on your own, or with family or friends, or in a hotel, sometimes disasters require people to go to evacuation centres and shelters. That’s where the big challenges lie, when pets need to be evacuated as well. Balancing animal health and welfare and human health during a chaotic time, when the health of pets is far from the top of the priorty list is difficult, but it’s doable.

Planning in advance is the key. Trying to come up with a plan during a disaster rarely works well, especially when the plan is for something peripheral to the disaster (like pets).

Things that need to be considered include (but are not limited to):

  • What animal species can be taken in?
  • How are the animals transported?
  • How can the animals be housed?
  • How will they be cared for, and by whom?
  • How can the animals be identified/documented so they can stay with their owners or be re-united later if separated?
  • Is veterinary care available?
  • How are other people with allergies or fear of animals accommodated?

Why is emergency preparedness for pets important?

  • We need to ensure that people take the opportunity to safely evacuate. If they don’t, they might die unnecessarily. Additionally, people who try to ride things out may put rescuers at risk if they have to come back to do a high risk removal.
  • We need to make sure that adding animals to evacuation plans doesn’t result in unnecessary problems for evacuees and support personnel, including injuries and illness.
  • We need to remember the critical role pets may play during the stress of evacuation and the disaster itself. Removing what for some people may be their main emotional support mechanism at the time they need it most needs to be avoided.

All organizational levels need to be involved in this kind of planning, but support from the top in essential. In response to hurricane Katrina, the PETS Act (Pet Evacuation and Standards Act) was passed in the US in 2006.

This Act links the ability of states to receive federal funding for their disaster relief plans to inclusion of the needs of individuals with pets or service animals in those plans. It provides a mechanism for FEMA funding of pet-friendly emergency shelters and supporting the needs of pets in these situations.

Other countries need to take similar actions, and make sure animal needs are built into emergency preparedness plans. Funding is part of it, but it’s even more important to support the need for planning and to empower the people who want to make it work.