Round two of my COVID in animals summaries….

Are dogs susceptible to this virus?

  • Yes…but…not very…maybe.
  •  Depends what you mean by ‘susceptible’.
  •  Nice and clear, eh?

There’s a difference between being infected and being sick. Yes, dogs can become infected. However, they don’t seem to be as susceptible as cats and it’s debatable whether they get sick (more on that below).

Regardless, it’s clear that the virus can infect dogs. This has been shown in experimental studies and through identification of infected pet dogs. A few different experimental studies have been performed, with similar overall results. In one small study, SARS-CoV-2 (the virus that causes COVID-19) was detected by PCR in experimentally infected dogs, but they could not isolate the virus (suggesting the virus was present at a low level and the dogs were probably not infectious). The dogs remained healthy but some developed antibodies against SARS-CoV-2, supporting the idea that they were truly infected. They did not pass to virus to dogs with which they were co-housed. So, some or all of the exposed dogs got infected (the virus replicated in them for a while) but none got sick and they were probably not able to infect others.

Another experimental study yielded similar results….dogs could be infected and mount an antibody response, but didn’t get sick and were probably not infectious.

How often do dogs get infected?

We don’t know. Surveillance has been limited so the scope of human-dog transmission isn’t clear. The most organized approach to this was in Hong Kong, early in the pandemic. There, they offered to take pets from COVID-positive households into quarantine and test them. They identified the virus in nasal, oral and rectal swabs from  2/15 dogs that were quarantined initially. Neither had signs of infection, both developed antibodies to the virus and gene sequencing of the viruses from the dogs showed that they had the same viruses as their respective owners. Of particular note was the ability to isolate live virus from the dog. That suggests the dog could have been infectious.

Other study has been limited, in large part because it’s a logistical challenge to sample dogs in households with infected people during their isolation period. One small study in Spain didn’t detect the virus in 12 exposed dogs. An investigation of pets from a cluster of infected and exposed vet students didn’t find the virus in any of 12 tested dogs, although it wasn’t clear how many were actually exposed to an infected person.

Our initial study didn’t find it in any of 18 dogs (more to come on the expanded version).

However, there are numerous reports of individual infected dogs from different countries. In the US, ~23 infected dogs have been reported so far. That’s not a lot in the context of the dog population. But, not many dogs have been tested. Further, testing has focused on looking for the virus by PCR. That will underestimate infections because there’s a short window of time when you can get a positive PCR result from an infected dog. Dogs seem to only shed the virus for a few days after infection, so sampling dogs in infected households runs the risk of a lot of false negatives simply based on the timing of sampling.

Studies looking at antibodies will be more informative (if the tests are accurate) since detection of antibodies indicates infection in the past. Unlike our PCR-based surveillance, we don’t have to get into the household right at the time of human illness. We can test dogs later to see if they were infected.

Not a lot has been reported yet. A study in Italy found antibodies in 3.4% of dogs; 1/7 (14%) of dogs from known positive households and 2/133 (1.5%) of dogs from other households. Whether the 1.5% prevalence in other dogs is from dogs that were infected by owners that were never diagnosed or represents the false positive rate of the test isn’t clear. A French study found antibodies in 2/13 (15%) of exposed dogs and 0/22 dogs from households without known COVID-19. Those results are similar to our 20% (2/10) prevalence in positive households here so far. Obviously, we need to test a lot more dogs to get better info…that’s still underway.

Do dogs get sick?

That’s still unclear. I’d say that evidence is still far from convincing. There are a few poorly documented reports of sick dogs, but the question that has been largely unanswered with those is “did they have COVID-19 or were they sick with something else and also happened to have been infected by this virus?”. My guess is that disease is rare but not impossible.

Can dogs infect other animals or people?

Probably not, but that’s unclear too. Dogs are likely much lower risk that cats. The fact that virus was isolated from a dog raises concern, since if there was live virus in the dog’s nose, you have to assume there was some risk of exposure to in-contact individuals. Whether it was enough to actually infect someone is completely unknown. Lack of transmission in experimental models isn’t a guarantee (artificial environment, very small numbers) but provides more support of limited risk.

Overall, I’d say the risk is very low. I don’t think we can say it’s zero but I think it’s unlikely that a dog would pose a realistic risk.

That said, why chance it? If a dog is infected or at risk of being infected (living in a positive household) it should be kept away from other people and dogs. Dogs interact nose-to-nose and nose-to-bum a lot, and we have a lot of contact with their faces. We’ve seen other respiratory viruses transmission between neighbouring dogs through fence-line contact, so keeping exposed dogs under control and away from others is reasonable.

Could dogs be an important reservoir of the virus once it’s controlled in people?

No. Dogs are not susceptible enough to the virus. For dogs to be a reservoir, they’d have to be able to keep spreading it dog-to-dog. That’s not going to happen because of the low susceptibility and short shedding time. You’d need a very large number of dogs in regular close contact to even begin to get a risk. That’s not realistic here.

Could dogs be a bridge to wildlife?

Probably not…or at least it’s much less likely than cats. Their low susceptibility, short period of infection, limited (if any) infectivity and limited direct contact with wildlife mean the odds of them being infected by their owners then infecting wildlife are pretty negligible.

So, we shouldn’t worry about COVID in dogs?

Worry, no.

But, we should pay attention.

What should be done with dogs?

Same as for cats…(see the cat synopsis for more details)

  • If you are infected, try to stay away from animals…all animals…human and otherwise.
  • If your dog has been exposed, keep it inside and away from others.
  • Ultimately, dogs are part of the family so if your family is being isolated, the dog should be part of that.


Relax. This is almost exclusively a human virus. With a modicum of common sense, the risk posed from pets approaches zero.

I’ve let the blog slip over the past week so it’s catch-up time. (I’ve been busier on Twitter – @weese_scott if anyone wants to follow that).

I want to get back to some COVID-19 discussion, and rather than a multi-species update, I figured I’d back up and focus on an overview of one species at a time. We’ll start with cats (so this will be longer than a typical blog post).

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

Yes, cats are clearly susceptible. This has been shown in multiple experimental studies and infected cats have been found in the “real world,” infected by their owners.

How often do cats get infected?

That’s a good question, but we don’t have a good answer because surveillance has been limited. One of the earliest studies from Wuhan, China, raised concern about this because they found anti-SARS-CoV-2 antibodies in 14.7% of cats from that city, even though they did not target cats with known exposure to infected people. Finding antibodies indicates that the cats were previously infected. In contrast, another study of cats in Wuhan didn’t find any cats with antibodies.

The most relevant studies are those looking at cats living in households with people who had COVID-19, in which the rates of infection appear to be pretty high. A study from Hong Kong identified SARS-CoV-2 by PCR in 12% of cats from COVID-19-positive households.

Studies looking for the virus by PCR will under-estimate the number of infected cats, because there appears to be only a short window of time that cats will shed the virus. This is illustrated in the figure below from a small experimental study, which shows the shedding time for experimentally infected cats and cats infected by those cats.

The logistics of sampling cats right around the time their owners are infected are challenging, so looking for antibodies against the virus can tell us more, because antibodies stick around for longer after infection.

Our (small, so far) study found antibodies in ~50% of cats living in households with infected people. A pre-print of a study from France had somewhat similar results, finding antibodies in 24-59% of cats from positive households (depending on how the tests were interpreted).

So, my assumption is that cats living with people with COVID-19 are quite commonly infected. Whether it’s 5%, 15% or 50% we don’t know yet, but I think human-to-cat transmission in households is likely pretty common.

Figure from Halfmann et al. N Engl J Med 2020 (

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 pre-print describing what appeared to be a fatal infection with SARS-CoV-2 in a cat from the UK. More work needs to be done in this area. 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, it’s pretty suggestive since there aren’t many other probable causes for the cat’s illness.

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, with the outbreak in lions and tigers in the Bronx Zoo (where cat-to-cat transmission was more likely than all the big cats being infected by people). How often this occurs in households will be hard to figure out, because if multiple pets are infected in a household, it’s pretty much impossible to say whether the pets spread it between each other or whether people infected them all.

Can cats infect people with SARS-CoV-2? (Yes, people are animals too, but I assume you know what I mean.)

We don’t know. Since cats can infect other cats, we have to assume there’s some risk of them infecting people. However, sorting out how much of a risk is a challenge.

Why haven’t we figured out cat-to-human transmission yet?

If a pet cat gets infected with SARS-CoV-2, it almost certainly got it from its owner(s). Your average pet cat mainly or only has contact with its owners, especially when an owner has COVID-19 and visitors hopefully are not around. If I get COVID-19 and infect my cat, and then the rest of my family gets sick, did I infect them or did the cat? Most likely, it was me, and it would be essentially impossible to differentiate.

For a cat to spread SARS-CoV-2 to someone outside the household, it would have to leave the household during the short window when it’s actually shedding the virus. That can happen (e.g. veterinary visit, indoor-outdoor cat), but fewer veterinary visits would occur when the owner is sick due to the human-to-human transmission concerns. Even then, if the cat infected someone at the vet clinic, a link to the cat would be hard to find, especially if the cat was not showing any signs of illness. If the cat was sick, it might be considered as a potential source, but with rampant human-to-human transmission, that’s not enough proof. What we’d need is for the cat and person to both be tested and have whole genome sequencing performed on the virus from both, to show it’s the exact same virus (even then we can’t be 100% certain, since cat and person could have been infected by the same source (e.g. another person), but with identical virus in both, it would be a pretty solid conclusion). Since there’s limited testing of cats and little likelihood that samples from both owner and cat would be sequenced, the odds of identifying a cat as the source of a human infection are low.

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

Probably not. Cats are pretty susceptible but they don’t shed the virus 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. 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).

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.

What should be done with cats?

  • 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.

Ultimately, cats are part of the family – so if your family is being isolated, the cat needs to be a part of that.

Naming a new virus or disease after a location is now generally frowned upon because of the potential stigma it can create, so we’ll see if the name “Alaskapox” actually sticks to this relatively new poxvirus that was first reported in 2015 in a person in Alaska, and has now been reported for a second time in August 2020.

The first case was in a woman in Fairbanks, Alaska, who went to a physician because of a suspected spider bite. She also had fatigue, fever, malaise and some tender lymph nodes. She had some small skin lesions, including a couple of vesicles (i.e. little fluid-filled bumps). As is often the case, the key role was played by an astute or curious primary care practitioner, who in this case decided to collect a sample from a vesicle and submit it for viral testing. That’s how the “Alaskapox” virus was first detected. None of the patient’s human contacts were sick or had similar skin lesions, apart from a social contact who reported a transient rash within a week of an earlier contact with the patient. Neither that person nor any of her other contacts (including family members) developed antibodies to the virus, supporting the conclusion that the index patient was the only infected person. The patient reported contact with rodents (which are hosts for many poxviruses), but the virus wasn’t identified in any rodents that were trapped in the area.

A genetic analysis of the Alaskapox virus showed it’s a member of the Orthopoxvirus genus, which includes a wide range of poxviruses such as smallpox, monkeypox and cowpox. Some poxviruses are very host-specific, meaning they only infect one species, like smallpox which infects only people. Some are more promiscuous, living in a reservoir species but spilling over into other species, as we see with coxpox and monkeypox that infect both animals and people.

That was the end of the story until another case of Alaskapox was identified in August 2020. It was pretty similar story to the first case: a person in Fairbanks went to their doctor because of a strange skin lesion, along with fatigue and fever, and Alaskapox was once again identified. As before, there was no apparent transmission to human contacts, and her infection resolved by itself after about a month. The patient didn’t report any direct contact with rodents this time, but said her cats captured and killed small rodents and that she’d spent time outside.

Why has this virus only been found in the past few years?

Emerging disease always “emerg” for one of a few reasons:

  • The disease was already there but was not previously identified, because no one looked for it or testing methods weren’t good enough to detect it. With mild disease, lack of curiosity or lack of access to testing, it’s easy to overlook something like this.
  • OR the disease has been around but controlled, so it’s rarely evident. With this virus, it’s possible that smallpox vaccination was cross-protective and historically kept it under control. Now that smallpox vaccination isn’t being done (since smallpox has been eradicated), Alaskapox virus might have more opportunity to cause disease.
  • OR the disease is truly something new and we’re actually detecting the first few occurrences in real time.

From where did Alaskapox come?

That’s still unclear. Since the majority of emerging infectious diseases are zoonotic, it’s a safe bet to assume the source was an animal of some kind. The very limited information that’s available seems to indicate that it’s not highly (or at all) transmissible between people, since contacts of the infected patients were not infected. Also, genetically the virus seems to have recombined (i.e. swapped DNA) with ectromelia virus (a mouse poxvirus) at some point in the past. All these factors suggest that an animal, most likely a rodent, is the reservoir, and that people are sporadically infected from direct or indirect contact with infected rodents.

In the grand scheme of emerging diseases, a rodent-associated virus that causes rare and mild infection in people isn’t a big deal. However, it’s a reminder of the many unknown threats that are lurking in the animal kingdom, and the need to continue to study emerging diseases.

In human medicine, a needlestick is a big deal. That’s not surprising because of concerns about transmission of bloodborne pathogens like hepatitis B and HIV.

In contrast, in veterinary medicine needlesticks are (unfortunately) largely considered “regular” events that aren’t really a big deal.  Most of the time perhaps they’re not. They hurt, but serious consequences are rare.  However, “rare” is not the same as “non-existent” – and if you’re the one that gets the “rare” complication, then it’s a very big deal to you.

While most needlesticks associated with animals and veterinary procedures/medications just hurt, sometimes bad things happen, such as:

  • Infection from bacteria from the patient’s skin or the person’s own skin (especially if the needlestick involves a joint, tendon sheath or other sensitive structure)
  • Allergic reaction to medication on or in the needle
  • Known effects of the drug  on or in the needle (e.g. exposure to a sedative)
  • Adverse effects of the drug in people (e.g. people have died from inadvertent injection of the cattle antibiotic tilmicosin)

A recent case report in Clinical Infectious Diseases (Amoroso et al. 2020) describes another potential issue: transmission of a patient’s infection to a veterinarian.  This same scenario, involving the same pathogen, has been previously described (Ramsey JAVMA 1994). I mention this risk when I talk about needlestick issues, but this new case report is a good reminder.  Here’s the summary:

  • The veterinarian was performing a fine needle aspirate on a mass from a dog that was ultimately diagnosed with blastomycosis (a fungal infection caused by Blastomyces dermatitidis). This procedure involves sticking a needle into the mass to try to extract some cells for testing. In the process, she stuck her finger by accident. Three weeks later, she went to her doctor because the finger was swollen and painful. She had surgery to open up the infected finger joint and testing revealed Blastomyces dermatitidis. Presumably the vet had informed her physician about the dog’s diagnosis, but surprisingly, that’s not always the case in occupational or animal-associated exposures. Sometimes important information like this isn’t passed on. The veterinarian was treated with an antifungal and fortunately the infection resolved.

I try not to be alarmist when it comes to emerging diseases, but we can’t be dismissive either. There wasn’t much attention paid to needlesticks in human medicine until people started to get sick (and die) from the consequences (especially infections). You don’t know about an emerging disease until it’s emerged. Infection control is inherently reactionary. Actions are most often taken in response to a known problem, rather than a potential issue.

One of my mantras is “don’t be a case report.” I can’t completely prevent that, but by reducing the risk of a needlestick injury, I can reduce the risk of me being the “first reported case of ______ acquired by a needlestick from an animal.”

Unlike many infection control activities, needlestick injury risk reduction is straightforward and doesn’t really take much time or effort. It includes things like:

  • Never recap a needle
  • Never leave an uncapped needle on a surface
  • Never pass an uncapped needle to someone else
  • Always dispose of needles immediately into an approved sharps container
  • Never leave needles in lab coats or other laundry (yes, this still happens and people get stuck… and understandably pissed off)
  • Consider using safety devices that include sharps injury protection mechanisms like retracting needles or sheathes that are pushed over the needle

I’ve done all of the “never” list above, except maybe the laundry one. As a busy medicine resident, in particular, I was pretty cavalier and got stuck many times, usually because we were rushing with an emergency, but also because I gave it little thought. There was never a culture of needlestick injury prevention, or even event reporting (even when a patient broke a bunch of my ribs).

Like a lot of things in infection control, the science is easy. Behaviour change and culture change are the bigger challenges.  Sometimes taking a few seconds of time and having some basic awareness is all that’s needed.

Image below from Amoroso et al. Clin Infect Dis 2020

Rabies is a disease that’s met with an interesting mix of inherent fear and dismissiveness in most developed countries, where canine rabies has been eradicated. It’s also a disease that’s often poorly understood in areas where it causes large numbers of deaths. As an almost completely preventable disease (with proper post-exposure treatment), and one for which we have highly effective vaccines (for people and animals), barriers to accessing these critical prevention tools need to be assessed.

Like a lot of things in infectious diseases, the science is (relatively) easy.  Application of the science is another story.

As we recognize World Rabies Day, here’s a post from Dr. Philip Mshelbwala, a colleague and collaborator from Nigeria who is currently studying rabies at the University of Queensland.

Why we need to boost community knowledge in rabies endemic countries

Over 59, 000 people die due to rabies each year, the vast majority in Africa and Asia, where the domestic dog is the major culprit. The World Health Organization (WHO) and other partner organizations have targeted the year 2030 for elimination of dog-mediated rabies. In order to achieve this aim, people in endemic countries need to know how to recognise the disease and report it to appropriate authorities for effective action as well as discourage practices that may hamper its control. 

This is just one example of barriers that are present.

In June, a dog was presented to a private veterinary hospital in Umuahia, Abia State, Nigeria as a suspected case of rabies. The dog was bitten by a stray dog on the foreleg some weeks back. The dog had been vaccinated against typical canine diseases but not rabies.  It had a clearly identified risk factor for rabies and had clinical signs consistent with rabies… anorexia, drooling, loss of tongue tone… but the owner treated it initially with coconut water as a local cure for suspected poisoning.  As the dog deteriorated, veterinary care was sought and the veterinarian immediately suspected rabies. The owner was informed and the dog was taken home.

The veterinarian contacted the state epidemiologist and senior colleagues for guidance. However, by the time the owner was reached the next day, the dog had been slaughtered and eaten. Testing could not be performed but rabies was most likely.

This case highlights one of the many challenges of rabies control in developing countries.  The mere attack by a stray dog should have pointed his attention to rabies in an endemic area, leading to prompt isolation of the dog and investigation of the need for post-exposure treatment of human contacts. Too often, case reports like this are prompted after a human death, such as a bite to children in the household or someone caring for the sick dog. Fortunately, that was not the case here, but that was more related to luck rather than any measures taken to prevent rabies in the exposed household.

Various educational opportunities are highlighted by this case.

The owner of the dog went to the cost and effort of getting their dog vaccinated but failed to have it vaccinated against rabies. Most dog owners in Nigeria are aware of common canine diseases like parvoviral enteritis,  because it commonly affects dogs at their early stage of life, with a high mortality rate.  Unfortunately, with less knowledge of rabies (despite the ever-present threat in the area), rabies vaccination was not elected. Education of owners about the rabies, including the need for vaccination, remains an important need. An ability to access rabies vaccination is also needed, another issue in some areas because of availability or cost barriers. Education about dog bite avoidance and when to seek medical care is also needed. Parallel education of human and veterinary healthcare providers to ensure appropriate responses to rabies exposures or questions is also critical.

Many opportunities were missed in this case, including many aspects of disease prevention, diagnosis, human healthcare and education. Testing of the dog would have allowed for a definitive diagnosis, and if positive, would have prompted contact tracing and post-exposure vaccination (provided there was adequate access to supplies and healthcare… another issue in some developing regions). Diagnosis also helps increase awareness, potentially leading to different behaviours and more vaccination.  For Nigeria to eliminate rabies, the  general public need to be empowered  with good knowledge about rabies and how to prevent it. 

2030 is an optimistic date for elimination of dog-mediated rabies in people. Is it still realistic now that we’re well into 2020? Probably not. Does that mean we should give up? No. Whether it’s 2030, 2040 or some other date, elimination of canine rabies is an important goal and one that is achievable with the right support.

Here’s a quick update on some recent feline studies on SARS-CoV-2. Some come with the increasingly common disclaimer that they are pre-prints, meaning the studies haven’t yet undergone peer review by other scientists in the field.

Cats in Hong Kong (Barrs et al. Emerg Infect Dis 2020)

This study has undergone peer review, and provides a nice description of Hong Kong’s efforts early in the pandemic. They had the most comprehensive response to potential animal exposure, and this information is available as a result of their approach to quarantine and test pets of infected people early in the pandemic, when alternate housing was not available.

They tested 50 cats from households with COVID-19 patients, or where owners had close contact with an infected person. They detected SARS-CoV-2 by PCR in 6 (12%) of the cats. They sequenced the viral isolates from a person and a cat in one household, and they were (unsurprisingly) identical, supporting the conclusion that one infected the other (presumably human-to-cat).

Dogs and cats in France (Fritz et al. 2020)

This pre-print describes a study of dogs and cats from COVID-19-positive households in France. They used a battery of antibody tests to detect previous exposure to the virus (as compared to PCR testing, which aims to detect active infection by finding pieces of the actual virus). They ran 4 tests: a neutralizing assay and 3 tests looking for IgG against three different viral proteins.

  • If a positive is considered an animal that was positive on either the neutralization assay OR all 3 IgG tests, 8 of 34 (24%) cats and 2 of 13 (15%) dogs were positive.
  • If a positive is considered an animal that was positive on ANY one of the tests, the numbers jump to 59% in cats and 39% in dogs.
  • Only 1 of 16 cats and 0 of 22 dogs from non-COVID-19 households were positive using the first criterion (whether that means the one household had undetected COVID-19 in a person, that the cat was exposed outside the house, or the result was a false positive isn’t possible to discern). Using the second criterion there were 6 (15%) positive animals in this group. That’s high for a negative control group, but substantially less than from the COVID-19 households.

The seroprevalence is high, but consistent with what we have found so far with our serological studies of dogs and cats in Canada  (4/8 cats, 2/10 dogs), supporting fairly common human-to-pet transmission.

Another cat experimental study (Gaudreault et al. 2020)

Another pre-print, this one doesn’t add much to what we already know, but beefs up our overall knowledge. They took 6 cats (4-5 months old) and exposed them to the SARS-CoV-2 virus through the nose or mouth. They then added naive cats one day later to look for cat-to-cat transmission. All pretty standard.  Cats stayed clinically healthy but there was evidence of infection via detection of the virus in tissues and some signs of inflammation in the airways. Transmission to the other cats occurred within 2 days.

So, it’s similar to what we’ve already heard: cats can be infected, they don’t usually get noticeably sick, but they can infect other cats.

Cats: A Case Report (Hosie et al. 2020)

This is a pre-print case report of two cats with SARS-CoV-2 infection in the UK.

The first case was a 4-month-old kitten whose owner had COVID-19. A couple of weeks after the onset of the owner’s illness, the kitten was taken to a veterinarian with severe respiratory disease.  The kitten’s condition deteriorated and it was euthanized. There were signs of severe respiratory disease on radiographs, and necropsy results were consistent with severe viral pneumonia. SARS-CoV-2 was identified in the lung, and no other potential causes were identified.

They researchers then tested 387 swabs that were submitted to the University of Glasgow diagnostic lab for respiratory pathogen testing. One of these was positive for SARS-CoV-2. This was from a 6-year-old cat with mild respiratory and ocular disease. It was also positive for feline herpesvirus, a common cause of those signs in many cats. However, one of the cat’s owners had signs consistent with COVID-19 at the time the cat was sick. Most likely, SARS-CoV-2 infection was an incidental finding here.

Taken together, these reports are consistent with our current messaging:

  • Cats are susceptible to the SARS-CoV-2 virus.
  • Most often, infections are likely subclinical (i.e. cats stay healthy).
  • Just like in people, some cats can get sick, including (rarely) fatal illness.
  • Cats can spread the virus cat-to-cat, so we have to consider cat-to-human transmission a possibility (however uncommon).
  • Most cats that get infected are directly infected by their owners.

I’ve written before about COVID-19 scent-detection dogs. I get lots of questions about them, and there are now several groups working in this area. There’s been a mix of information to date, ranging from encouraging to some pretty bad preliminary studies released on pre-print websites and other places. A dog’s nose is a wonderful thing (except when my dog sticks his in places I don’t want it to go), and dogs have been shown to be able to detect a wide range of different scents with great sensitivity.

The first question is: Will dogs be able to detect people with COVID-19?

If the answer is yes, then the bigger question is, will it be a practical way to detect people with COVID-19?

We may get more answers now that dogs are being used in a Finnish airport to sniff out COVID-19.  Ten dogs have been trained to detect people with COVID-19 based on smelling wipes collected from individuals. News reports include claims of close to 100% accuracy… I’d love to see good data on that, as I suspect it’s not 100% effective in the field. However, even if the dogs are moderately effective, they could be a useful tool when combined with other measures (e.g. rapid confirmatory testing of people that dogs flag as potentially infected).

My big questions at this point is, how effective is it really?

  • We need to consider both sensitivity (how good dogs are at detecting infected people) and specificity (how good they are at only detecting infected people).
  • For a screening test, we want a test that is highly sensitive, meaning it detects most infected people, even if it has some false positives (i.e. people who are mistakenly identified as positive but aren’t actually infected). That works if the false positive rate isn’t massive and if there is a convenient way to follow up to confirm who’s really positive. If we have a quick follow up test of another kind, the initial false positives are a bit of a hassle but not a big deal and easy enough to weed out, so we could tolerate some loss of specificity.
  • False negatives on the other hand (i.e. people who are infected but go undetected by the test) are a bigger concern.
  • So, knowing the sensitivity and specificity of these COVID019 detection dogs in a field situation (where there are lots of people of different types, with different stages of infection and with different smells) is key. Hopefully that’s being studied well.

Another question I have is, what’s the management plan for dogs that stick their noses in wipes from people with COVID-19?

  • Dogs have limited susceptibility to SARS-CoV-2, but limited and zero aren’t the same.
  • Will the dogs be screened in case they get infected in the process?
  • And (an oddball question perhaps) if a dog gets infected, does it lose the ability to detect infection in people? would the dog then smell the scent associated with the virus all the time?

There will be more to come, I assume.

The UCLA Fielding School of Public Health, Department of Epidemiology, is seeking volunteers to participate in their Veterinary and Zoonotic Surveillance for SARS-CoV-2 (COVID-19) and Other Coronaviruses Study.  Their goals are to assess potential exposures to SARS-CoV-2 and other zoonotic pathogens among veterinary and animal healthcare workers, as well as clinical symptoms, mental health, and attitudes and practices associated with the pandemic response. To be eligible to participate, you must work with or around animals, for example: in a veterinary clinic/hospital, with a mobile veterinary clinic, at an animal shelter, animal rehabilitation facility, animal control facility, zoo or aquarium, in an animal research lab, or animal husbandry operation.

Click here for more information and to enroll in the study.

An abstract in the upcoming ECCVID Conference (ESCMID conference on coronavirus disease) has some of our very preliminary Canadian dog/cat surveillance data (Beinzle, Marom and Weese, SARS-CoV-2 infection in pets). A press release went out about it from the conference that’s been picked up by various news agencies, resulting in some articles about the study that are a bit alarmist.  As is typical with zoonotic diseases, we’re trying to walk the fine line between raising awareness and preventing people from over-reacting.

Before I get to the details, I’ll give the overall synopsis of our results to date to provide some very important perspective first:

  • Transmission of SARS-CoV-2 to pets probably isn’t uncommon. That’s not big news. We know cats, in particular, are susceptible to infection. With limited surveillance, a reasonable number of infected pets have been identified. I’ve been saying for a while that transmission to pets was likely occurring under the radar, but it’s not likely a big deal – it’s something to watch and figure out over time, but not to freak out about.
  • Pets in households with human COVID-19 cases are unlikely to be shedding the virus at any given time. While they can be infected, the window that they’ll shed the virus is likely pretty short. That’s why we have a hard time finding positive animals through PCR testing (looking for the virus) vs antibodies (looking for evidence of previous infection).
  • Relax. The messages are the same: treat pets like other members of the family when it comes to control measures for this virus. If the people in the household are isolating, the pets should too. If someone is staying away from people because they might have COVID-19, they should stay away from animals too.
  • The health impact of SARS-CoV-2 infection in pets is still unclear. I suspect cats are somewhat similar to people (with fewer infections). Most don’t get sick. Most that get sick get mild flu-like disease. A small percentage may get more seriously ill. It’s still a bit of a guess but I think it’s reasonable.

OK… now here are the details of our preliminary Canadian study results.

We looked at two things: testing for the virus itself, and testing for antibodies in pets.

  • We looked for viral RNA using PCR on swabs of the nose, mouth and rectum of pets in contact with people infected with COVID-19. We did this by going into the homes of these people and sampling the pets around the time of human illness. Of the 36 animals tested, 18 dogs, 16 cats and 1 ferret were negative. We got inconclusive results from one cat, and based on the timing of the owners’ and cat’s illness, we suspect it was sampled late in infection (so not shedding enough virus to give a definitive positive result).
  • We also tested pets for antibodies against the SARS-CoV-2 virus. Antibodies indicate previous infection.  We’re still early in the process on this phase of the research, but antibodies were present in 4/8 (50%) cats and 2/10 (20%) dogs. Samples from animals from 2019 (pre-COVID) were all negative, including cats with feline coronavirus infection (so we know the antibody test does not cross-react). All of the seropositive cats were reported to have been sick around the time of the owners’ illness. Take that with a grain of salt because it’s retrospective, but it’s interesting.

The 50% and 20%  seropositive results are high, but maybe not too surprising, and I don’t really focus on the specific percentages because the sample size is small. The key is antibodies are not uncommon in these animals, which supports that cats seem to be fairly susceptible to infection. Our numbers are currently higher than the few other recent studies, but not out of line. A study from Wuhan, China showed 14.7% of cats sampled in early 2020 were seropositive. That study included testing of stray cats, not just cats from known positive households like we did. It’s possible that some were pet cats that had been released or were indoor-outdoor cats, but they weren’t all known to have been exposed. Another study reported antibodies in 3.4% of dogs and 3.9% of cats in Italy. This involved sampling of healthy pets in veterinary clinics, rather than targeting positive households. So, our study population was a lot higher risk, and therefore a higher prevalence of antibodies in our sample makes sense.

The relatively good state of COVID-19 in our area over the summer hurt the study (but I’m not complaining) since we didn’t have many human cases in the area with pets we could test. As we ramp up in the second wave, we’ll unfortunately be in a better position to get more samples. We’re also working on a few ways to get more blood samples from pets of people who had COVID-19 earlier in the year. We’ll hopefully have more robust results soon.

A group of us wrote a Letter to the Editor of Lancet in response to a recent One Health paper. Not surprisingly, it wasn’t published, but  we think it’s an important message, so here it is:

A Call to Action for a One Health approach in COVID-19 and Beyond

While we echo Amuasi and colleagues’ call for a One Health COVID-19 Research Coalition1, we urge the scientific community to genuinely embrace a cross-disciplinary approach. Oblivion to One Health principles has characterized the response to the evolving pandemic. Once human-to-human transmission emerged as the cause of the pandemic, broader One Health aspects were ignored. The initial assessment put forth by some high-profile agencies was antithetical to the concept of One Health2, focusing on “no evidence” of the potential for SARS-CoV-2 transmission to animals or of risk of further interspecies spread, despite a lack of investigation. While subsequent research forced a change in message, dismissing involvement of animals in zoonotic diseases, until such is proven, is detrimental on all fronts. Almost all recent infectious disease outbreaks have been of zoonotic origin, and a logical, proactive approach to identify and address all ramifications is essential. Additionally, human-induced environmental drivers of infectious disease emergence are fundamental triggers of zoonoses. Although environmental changes such as habitat destruction, urbanization and agricultural intensification were highlighted as ongoing factors driving zoonotic disease emergence, efforts to improve ecosystem health and resiliency continue to be absent from broader discussions in the current response and future pandemic prevention.3

It is essential that One Health concepts, not simply discussions, are integrated into political, environmental and social actions. A One Health approach built on strong cross-disciplinary collaborations must be the default approach to prevention and control of emerging diseases, rather than an afterthought that is reserved until there is definitive proof of need.


Scott Weese, Dorothee Bienzle, Katie M. Clow, Heather M. Murphy, and Kari E. Dunfield

Departments of Pathobiology (JSW, DB) and Population Medicine (KMC), Ontario Veterinary College, University of Guelph, Guelph, ON, Canada

School of Environmental Sciences (KED), Ontario Agricultural College, University of Guelph, Guelph, ON, Canada

College of Public Health (HMM), Temple University, Philadelphia, PA, USA

  1. Amuasi JH, Walzer C, Heymann D, et al. Calling for a COVID-19 One Health Research Coalition. Lancet 2020; 395: 1543
  2. Centers for Disease Control and Prevention. Covid 19 and Animals [Internet]. Atlanta, GA: Centres for Disease Control and Prevention; 2020 [updated 2020 April 30; cited 2020 May 17]. Available from:
  3. Allen T, Murray KA, Zambrana-Torellio C, et al. Global hotspots and correlates of emerging zoonotic diseases. Nat Commun 2017; 8: 1124.