There is still lots of confusion about what use of different types of masks is supposed to do in different situations. As I’ve said before, it comes down to thinking about who the mask is meant to protect – the user, or people around the user. This dictates what type of mask should be used.

Cloth masks

  • These masks protect others from the user’s respiratory droplets – the little liquid particles that we expel when talking, breathing, coughing or doing similar things.  Exposure to such droplets is the biggest risk for transmission of SARS-CoV-2. Cloth masks help contain droplets. While they will help protect the user to some degree, they are mainly to protect others FROM the user.

Surgical masks

  • These are meant to protect others FROM the person wearing the mask (same as cloth masks).

N95 masks/respirators

  • These masks can help protect both the user and those around the user. IF they are properly fitted to create a seal around the mouth and nose (unfortunately many people don’t realize these masks need to be fit-tested to be effective), then they will help protect the user.  However, the user also needs to protect the eyes – it makes little sense to cover some mucous membranes on your face (nose and mouth) and leave two others just above those wide open and unshielded.
  • N95 respirators can also protect others FROM the wearer, since they are good filtering masks, IF they don’t have an exhalation valve.

What is an exhalation valve?

An exhalation valve makes it easier to breathe by allowing air to leave the mask without passing through a filter. That’s fine if the mask is being worn to protect the user, who inhales filtered air and is presumably not exhaling infectious droplets.  However, if the person is infected and there is virus in the expelled air, an N95 with an exhalation valve will not protect others FROM the user. Since most community mask usage is designed to protect others from people expelling infectious droplets, in situations where mask use by everyone is mandated to reduce the risk of exposing others, N95 masks with exhalation valves should not be used.

Cats are susceptible to SARS-CoV-2. That’s been shown experimentally and in a limited number of documented natural infections. However, there’s still a lot we need to know to better understand the feline and human health implications of this virus. While limitations of experimental studies always have to be considered (since they’re based on an artificial situation), they can answer some questions a lot quicker than field studies.

A new correspondence in the New England Journal of Medicine (Halfmann et al. 2020) provides a bit more information about this virus in cats, largely supporting what’s been reported before . I found it pretty surprising to see this report in a prominent human medical journal, since it only involves cats.  I also found it surprising how superficial the information was. I guess they were trying to squeeze everything into a letter to the editor, but they sacrificed providing good information for publication in a high profile journal. They did provide more details are in the supplementary appendix file, but there are still lots of gaps.

The study looked at experimental infection with SARS-CoV-2 in three cats:

  • The day after the three cats were inoculated with the virus, another cat was co-housed with each of them.
    • There is no mention of what, if anything, they did to make sure there was no viable virus on the haircoat of the infected cats after experimental inoculation.
  • Nasal and rectal swabs were collected daily to test for the virus.
  • By day 3, virus was recovered from all inoculated cats.
    • There is no mention if the virus was found on the nasal swabs, rectal swabs or both.
    • It appears that the infected cats were healthy, although how they were monitored isn’t clear beyond saying they didn’t lose weight or have abnormal body temperatures.  However, their graph shows 2 of 3 infected cats had a 1C temperature jump by 24 hours post-infection, and one of the co-housed cats seemed to spike a fever on day 7.
  • Virus was ultimately detected in all three cats co-housed with the inoculated cats.
  • Virus was detectable for several days in all cats (see graph below).
  • All cats developed antibodies to the virus, further confirming they were truly infected.

My take home messages from this study aren’t really anything we didn’t know before, but it’s still useful confirmation:

  • Cats can be infected with SARS-CoV-2.
  • Infected cats don’t necessarily get sick.
  • Cats can spread the virus to other cats.

Since cats can spread the virus to other cats, the logical question is whether they can spread it to people. It’s logical to assume that they could, so it makes sense to take some basic precautions around exposed cats (like we’ve been saying for months). This is nothing new or scary, just a reminder to keep using some common sense preventive measures.

As the authors state, earlier reports, “coupled with our data showing the ease of transmission between domestic cats, [show] there is a public health need to recognize and further investigate the potential chain of human–cat–human transmission.”

Well said.

We’ve spent a lot of timing working on various recommendations for managing COVID-19 risks in veterinary practice. They’re mainly focused on the most biohazardous species with which veterinary personnel work on a daily basis: humans. While we’re still sorting through animal-related issues, the main emphasis is reducing exposure risk from people, and a recent assessment from the UK’s Office of National Statistics shows why. They have an interesting interactive map that characterizes the risk for a range of occupations, based on the frequency and closeness of contact they have with other people in general, and the potential exposure to infected people specifically.


  • Not surprisingly, healthcare practitioners top the list, particularly dental nurses.
  • Where veterinarians and veterinary technicians rank might surprise some (take a guess then check out the link to the interactive map here).  This shows why we’re working so hard on this, and why some short- and long-term changes in behaviours and veterinary practice are needed to help protect everyone’s health.
  • It’s designed as an assessment of generic disease exposure, not just COVID-19, so the vets and vet techs get higher on the ranking than they would be on a strictly COVID-19 exposure risk assessment, but it highlights the amount of close contact that vets have with a large number of people on a daily basis. More contacts means more risk. Reducing those contacts reduces the risk

Pretty soon, I’ll stop writing about single reports of cats identified as infected with SARS-CoV-2. These cases aren’t surprising,  and sporadic case reports don’t provide much new information. However, I’ll give a quick rundown of the latest case of an infected cat from Spain. It’s only reported in news articles, as far as I can find, so we have to be a bit wary of the info.

As expected, the cat lived in a household with COVID-19-infected people. The cat developed respiratory difficulties, and was ultimately euthanized. Low levels of SARS-CoV-2 were found in its nasal passages and an abdominal lymph node. But the cat also had hypertrophic cardiomyopathy, a potentially serious heart disease that can cause death.

This case raises concern about a severe SARS-CoV-2 infection in the cat, which would be different from the milder cases that have been previously reported. However, the cat’s underlying health issues could have accounted for its death, so it’s more likely that the cat had an incidental infection rather than a fatal SARS-CoV-2 infection.

Regardless, my assumption has been that we’re bound to see the odd case of serious disease in cats. I get some calls about suspicious cases, but we haven’t been able to test too many of them. Most infected cats probably don’t get sick at all or develop mild signs of illness (like people), but it’s reasonable to expect that a subset of infected cats (especially those with underlying health problems) could get more serious disease, but that’s likely rare. However, most cats exposed to infected people likely don’t even get infected.

As per all my other discussions, the key here is that if you social distance pets (as we do people), then the risk that a pet would bring this virus into the household is very low.

We’re nowhere near the end of this pandemic, and one concern we have is opening things up too quickly and losing the benefits of all the sacrifices that have been made to “flatten the curve.” As restrictions get lifted, we’re not going straight from “now” to “normal.”  We’ll have to continue with good physical distancing practices for the foreseeable future.

With that in mind, a new document has been released, in collaboration with the OVMA, outlining preparation for veterinary medicine when the “urgent care only” directive in Ontario gets lifted. It’s meant to help us be prepared for the next phase, so that we can provide more veterinary services while still minimizing the risk of COVID-19 transmission.

That’s a difficult balance to find.

The document is written for the Ontario context, but the overall concepts would likely apply pretty much anywhere. We’re going to have to change how we practice for a while, and some changes may be permanent. The better we can be prepared, the more responsible and effective we can be.

As always, guidance may change based on how the pandemic evolves, government guidance, experiences and new ideas, but this is a good place to start.

You can find the Guide to reopening veterinary medicine in Ontario as well as many of the other resources we’ve posted since March on the Worms & Germs COVID-19 Veterinary Resources page.

A recent report from the Canadian Wildlife Health Cooperative (CWHC) describes an outbreak of tularemia in muskrats in Long Point, Ontario. Tularemia is a potentially nasty disease caused by the bacterium Francisella tularensis. While not many people have contact with muskrats or live in Long Point, it’s still noteworthy.

 The investigation was  initiated following a report of at least 35 sick or dead muskrats in the area. Necropsies were done on some of the rodents, and they were found to have enlarged lymph nodes and lesions in their spleens and livers. Testing at the National Microbiology Laboratory identified Francisella tularensis.  This was done at the national lab because F. tularensis is a containment level 3 pathogen requiring enhanced biosafety practices – so it’s not a bacterium which regular labs handle.

This isn’t a new finding, since we know this bacterium is present in Ontario, but it’s rare. Francisella tularensis is sporadically found in various animals and rarely in people (there’s been one reported human case in Ontario so far in 2020). It’s a reportable disease in animals and people because of the potential severity of infection, and because it’s a potential bioterrorism agent.

Back to the muskrats… tularemia is a rare finding in wildlife. That doesn’t mean it doesn’t cause disease, since sporadic disease in wildlife rarely gets investigated. It’s most commonly associated with rabbits, and human and domestic animal infections can be associated with rabbit or rodent contact. The fact that this occurred as an outbreak with a significant number of animals affected over a short period of time is interesting, and it’s also concerning from human and animal health standpoints. The bacterium can be spread in a variety of ways, including direct contact, inhalation (e.g. running over an infected animal with a lawnmower and aerosolizing the bug and then breathing it in… gross but true) and via some insects (e.g. ticks, deer flies).

Tularemia avoidance measures are pretty basic:

  • Avoid contact with wildlife, live or dead.
  • People handling dead wildlife, especially those handling them closely such as trappers, should use good routine hygiene and infection control practices.
  • Avoid ticks. For pets, that involves use of a good tick preventive. For the rest of us, well… we don’t have a chewable tick preventive but we can do other things to reduce the risk of tick exposure, including (and most importantly) doing “tick checks” if you’ve been outside in an area where ticks are likely to be lurking.
  • Keep your pets under control, especially if they are prone to chasing wildlife or snacking on dead animals (also gross but true).

The CWHC warning is pretty similar to my comments: “During an outbreak situation, it is presumed that bacterial levels would be higher in the surrounding environment, so caution is warranted for anyone who is traversing through the area or wading into the water in the Crown Marsh area of Long Point. There is also a danger to off-leash dogs as they can become infected and develop similar symptoms to humans, especially if they consume infected meat. It is recommended that dogs are kept on leash and monitored closely while in this area. It is recommended that people do not handle wildlife found dead unless they are wearing protective gloves (or a similar protective barrier) to prevent direct contact of the animal with the skin. Anyone who handles dead wildlife (even while wearing the appropriate protective gear) should wash their hands thoroughly to minimize the chances of exposure.

A related topic that applies to animals and people is talking to healthcare providers about travel. The risk for various diseases differs geographically. A disease might not be on a physician’s or veterinarian’s list of considerations if they don’t know about travel. So, physicians and veterinarians need to query travel history, and everyone needs to remember that travel means going somewhere else, regardless where it is (even if they haven’t left the province).

Here’s a scenario that highlights that:

Me: Have you traveled with your dog lately?

Owner: No.

Me: Do you have a cottage?

Owner: Yes, it’s a beautiful place a couple of hours from here. We go there every weekend in the summer.

Me: So, you travel with your dog every weekend in the summer?

Owner: Well, that’s not travel, it’s going to the cottage.

Me: Ok, now let’s talk about the different things I need to consider now that I know your dog travels.

That’s not an unusual situation. Understanding where people and animals have been is important when thinking about infectious disease risks. Veterinarians and owners need to clearly communicate to identify potential problems.

An update to the Canadian COVID-19 in animals FAQ for veterinarians (30-Apr-2020) has been released.

Like pretty much any other document during this dynamic situation, it gets outdated as soon as we finish it (the original version was released more than a month ago), but it’s a good outline of what we know and what we suspect at this time (or at least as of April 30).


A few quick updates and comments.

Are pugs a high risk breed for SARS-CoV-2?

This question has come up a few times since the report of an infected pug in North Carolina. It has been suggested by some people in news articles that pugs are higher risk for getting infected. Like other brachycephalic (squishy faced) breeds, some pugs are at increased risk of respiratory disease in general. They are also at increased risk of complications if they get a respiratory infection of any kind. But they should otherwise not be at increased risk of getting infected with this particular virus compared to any other similarly exposed dog.

So, pug owners should relax (some have apparently already asked about getting rid of their dogs). If you own a pug, it is probably at increased risk of complications if it gets infected with SARS-CoV-2 (or any other respiratory virus), but it should not be at increased risk of getting infected in the first place, and the odds of any dog getting infected are very low.

Update on two positive cats in New York

Antibodies to SARS-CoV2 were detected in the blood of both cats from New York that tested positive by PCR in late April . This is not unexpected, but it is one more indication that they were truly infected.

Infected cat in France

In a study of cats owned by people with COVID-19 in France, one cat was identified as positive by PCR.  There’s no mention of how many cats were tested (yet). The positive cat had mild respiratory and gastrointestinal disease, and only its rectal swab (not the throat swab) was positive.

This result isn’t surprising either, as it’s likely that a reasonably large number of human-cat infections have occurred. As has been typical so far, the cat had mild disease. I’ve had some anecdotal reports that suggest some cats can get more serious disease but we need to properly investigate those. This report is just one more piece of evidence indicating that human-animal transmission of this virus is occurring. Human and animal health implications of this are probably limited but it’s an area we need to keep studying.

How to practice veterinary medicine in a COVID-19 world is causing a lot of angst. Questions about dental procedures often top the list. Rightly so, since those are perhaps the highest risk type of procedure for SARS-CoV-2 exposure from animals. Dentistry involves close contact with the face and respiratory secretions, and the potential generation of aerosols.

Routine procedures of all kinds have largely been postponed in most areas because of the need to restrict in-clinic care to urgent cases due to potential COVID-19 risks. As we learn more about the likelihood of human-to-pet transmission (our surveillance study is moving along nicely now) and the dynamics of transmission in people, it will get easier to make informed decisions about how to control the risks. Ultimately, patient-side testing might be a useful approach, but it’s hard to say whether that’s going to be needed or even an option, and that doesn’t help us right now.

In times of uncertainly, I’d always rather be over-prepared, within reason. That means erring on the side of protection, rather than being a case report. We have very little data to work with, so we have to base our recommendations on common sense and reasonable guesses. As with pretty much all of our other advice, things may change.  But, since I get asked about this so often, here are my thoughts and considerations around SARS-CoV-2 and veterinary dental procedures. (Remember I’m an internist, not a dentist! Dental colleagues should feel free to chime in and correct my blatant non-dentist errors and provide their thoughts.)

Is the patient at high risk for SARS-CoV-2 exposure?

Querying the pet’s likely exposure risk is a good first step. The potential presence of asymptomatic (human) infections in household contacts means that a lack of known exposure it not 100% protective, but if the pet does come from a household where COVID-19 is present, we know there’s some degree of increased risk. My concerns are also greater with cats vs dogs, since cats are likely at greater risk of infection, and infected cats maybe would have more virus present in respiratory secretions compared to infected dogs.

How long should a patient be considered high risk?

This is yet another area where we have very limited information. However, based on what we do know, it’s reasonable to estimate that the risk of a pet shedding the virus would be very low by 14 days after its last potential exposure. That means 14 days after the last infected person in the household is deemed non-infectious (often 10-14 days after the start of their illness) .

Does the patient have signs suggestive of SARS-CoV-2 infection?

Any acute unexplained onset of respiratory or GI disease in an exposed animal needs to be considered high risk. Lots of things can cause these problems but if there’s plausible exposure, we need to be wary of SARS-CoV-2. That would mean the risk to veterinary personnel would be even higher, and the threshold of urgency for doing any procedure would have to be quite high.

Can the patient be managed by telemedicine and medication?

No, we can’t extract a tooth over the phone. However, some patients might be manageable in the short term (a couple weeks) with analgesics and/or antibiotics (that’s the recommended approach in human dentistry in some regions). We don’t want to throw those drugs around unnecessarily (the demise of antimicrobial stewardship is a concern in human medicine with the focus on COVID-19), but there may be some cases in which we can delay the definitive treatment long enough that the patient is no longer a high risk to staff.

The patient is high risk and the procedure has to be done. How can we reduce the risk?

The first question is probably “should I handle the case?” If a clinic or clinician are not adequately equipped with PPE and are not comfortable handling the case, referral to a colleague or specialist who is is reasonable.

If the case will proceed, here are some considerations for reducing the risk of SARS-CoV-2 exposure:

  • Minimize aerosol generating procedures. This might involve use of older techniques and manual instruments over instruments (e.g. burrs) that will aerosolize respiratory secretions. Think about every step, whether it’s needed and how it can be done the most efficiently.
  • Consider staging the procedure. If the urgent aspect of the patient’s problem can be managed quicker and/or with less use of aerosol-generating techniques, consider taking care of that part to control pain and limit disease, with a plan to finish the job later. Yes, that requires another anesthesia and more cost, but if the best way to fix things involves lots of aerosol generation and that can be delayed, it may reduce the risks.
  • Wear proper PPE. For an animal from a high-risk household, that means a gown, gloves, N95 respirator and eye protection. A surgical mask plus a face shield is probably an acceptable alternative to the respirator and eye protection, unless the animal has signs consistent with SARS-CoV-2 infection. However, the lower the level of PPE available, the more I’d want to limit the procedure and reduce aerosolization.
  • Consider where the procedure will be performed. It’s ideally done in a closed area where aerosols are confined, and where potentially contaminated surfaces are easy to identify and disinfect. Movement into and out of the room should be minimized to limit airflow disruption. The area should be as free of other items as possible, so that there are fewer potentially contaminated surfaces to address when the procedure is done.
  • Limit people in the area to essential personnel only. Make sure no other patients are in the aerosolization zone.

Hopefully we’ll learn more about the risks and the best ways to control them, and hopefully the risks are actually exceptionally low. We need to balance practicality, patient care and occupational health, and we’re trying to do that largely blindfolded at this time. A little common sense and basic infection control knowledge can go a long way, though.

While COVID-19 is almost exclusively a human disease, it’s clear there can be spillover into animals. That’s probably of greatest concern in pets, because of the amount of contact we have with them and the susceptibility of some pet species (especially cats and ferrets). However, while we have less contact with other types of animals, there might still be important implications. We don’t know the range of species that can be affected and the potential animal health impacts in each species. We also don’t want this virus establishing itself in wild animals.  Ultimately, we want to keep this a “human problem” by preventing movement into animal populations, for the sake of animals and ourselves.

A few different issues with different species are highlighted below.


Since this virus almost certainly originated in a bat, there’s concern about it moving back to bats. While the bats species we have in North America are quite different from the suspected source bat species (i.e. Chinese horseshoe bat), we’d rather prevent our native bats from being exposed rather than hope that they’re just not effective hosts. Normal research and surveillance activities that put people into bat environments are being curtailed in many areas to reduce the risk that we’ll expose bats. We have no idea what the risk is, but it’s better to be prudent than to have to do damage control.


The outbreak of COVID-19 in lions and tigers at the Bronx Zoo raised concerns about risks to wild tiger populations. While there’s less human contact with those animals, they often live in fairly (surprisingly) close proximity to people, and there can (normally) be a lot of people visiting parks and reserves. The risk of infection is probably low, but we want to avoid any health hazards in threatened or endangered populations if we can.

A recent ProMed mail post discussed COVID-19 in a tiger at Pench Tiger Reserve in India. It’s unclear whether the tiger actually had COVID-19.  It seems that park staff were concerned because of the reports of COVID-19 at the Bronx Zoo and that their response (i.e. quarantine of staff, banning visitors from the park) was out of abundance of caution rather than an actual diagnosis. Regardless, it’s something that needs to be considered in areas where people can get close to wild cats.


Gorillas are closely related to humans and probably quite susceptible to this virus. The last thing wild gorilla populations need is COVID-19 spreading through them. This is resulting in park closures to protect the animals, with potentially major impacts to local economies (and the parks that protect the animals). Enforcement will be the challenge. Measures are already in place to protect animals from exposure to human respiratory viruses in many parks, and they’re often flouted.