Lyme disease vaccine is a non-core vaccine, meaning it’s not needed for all dogs in all areas. It’s an effective vaccine, and I’d consider it a reasonable vaccine to give to dogs in (or visiting) higher risk areas, especially when there might be owner compliance issues with tick preventive medication. Available tick preventatives are very good, but sometimes people forget to give them on time, so vaccination is a good backup plan for those situations and in areas where the risk of exposure is particularly high.

Lyme disease vaccines are a bit unusual, in that they are primarily aimed at vaccinating the tick, not the dog (strange as that sounds). They usually target two proteins on Borrelia burgdorferi , the bacterium that causes Lyme disease. One of those is outer surface protein A (OspA), which is “expressed” on the  surface of the bacterium when it’s inside the tick. After the tick has attached to a host (like a dog) for a while, the bacterium changes to make itself more adept at infecting animals. That results in a change in the outer surface protein from OspA to OspC.

Lyme disease vaccines contain OspA, which induces the dog’s immune system to produce antibodies against that protein. When a tick starts to feed, it ingests the antibodies in the dog’s blood, which attack the bacterium before it’s ready to migrate to the dog.

Lyme disease vaccines can also contain OspC, to target the bacterium in the tick as it starts to produce that protein, and provide backup protection if the bacterium happens to evade the OspA antibodies and makes it into the body.

With typical vaccines, if an individual is exposed to the bacterium/virus for which they’ve been “primed” by the vaccine, they then get an immune response boost to generate even more antibodies. However, that doesn’t really apply to Lyme disease.  Since the dog’s antibodies flow into the tick, there’s no extra immune boost because the bacterium isn’t yet in the dog’s body (so the dog’s immune system doesn’t get exposed directly). Decreased antibody levels in the dog therefore more directly correspond with decreased protection. There will be some booster effect with exposure to OspC if the bacterium makes its way into the dog, but ideally we’d like to stop the process before it gets that far.

Lyme disease vaccines are given as an initial series of 2 doses, 2-4 weeks apart, and then an annual booster. But,  there’s concern that immunity from Lyme disease vaccines doesn’t last as long as others, so there’s less leeway for overdue dogs. It’s been recommended to re-start the 2 dose series from scratch if the dog is overdue for it’s yearly booster by more than 1 month. That’s pretty conservative, but it’s fair to assume that this vaccine’s long-term protective effect could be less predictable and solid than leptospirosis vaccines (where we accept up to 3 month delay).

Based on that, when it comes to Lyme disease vaccines, if a dog gets its:

First dose, but is late for the 2-4 week booster

  • Restart the whole series (i.e. 2 doses 2-4 weeks apart, then yearly)
  • We don’t have good guidance on what constitutes “late” or “overdue” here.  The American Animal Hospital Association vaccination guidance says within 6 weeks of the first dose is still okay, and that’s reasonable. It’s quite possible that the dog would respond well to a later booster, but we don’t have confidence in that.

First dose, 2-4 week booster, and then a yearly booster not more than 1 month late

  • Continue with the single annual boosters

First dose, 2-4 week booster, but is more than 1 month late for the yearly booster

  • Restart the whole series (i.e. 2 doses 2-4 weeks apart, then yearly)

As I mentioned above, tick prevention is still key, particularly for unvaccinated or inadequately vaccinated dogs. If vaccination has lapsed, it’s even more important to avoid ticks, do tick checks and use a good tick preventive medication (on schedule).

This is probably the vaccine about which I get the most questions when it comes to delays. Leptospirosis (aka lepto) is a regionally important and potentially life-threatening infection of dogs (and people) caused by serovars of the Leptospira bacterium. It’s generally considered a non-core vaccine, meaning it’s not needed for all dogs in all areas. However, it’s probably best considered a regionally core vaccine. If leptospirosis occurs where a dog lives or anywhere it to which that dog might travel, I consider this an essential vaccine. This disease is pretty widespread internationally, so that includes a lot of dogs.

Lepto vaccines are killed vaccines, meaning they contain bits of the dead bacterium. Killed vaccines can be effective, but typically require multiple doses given within a specific interval to maximize immunity. For lepto, we typically start with two doses of vaccine 2-4 weeks apart, and then yearly boosters. We need that initial 2-4 week booster to make sure there’s a good immune response (unlike the modified live virus (MLV) core vaccines I mentioned in Part 1). If that 2-4 week booster is missed, we can’t assume there’s much protection or ability to respond to a future single booster shot. Also, yearly booster shots are needed for lepto to maintain immunity, unlike the core vaccines that can often be given every 3 years after the initial series.

Considering all that, if a dog is late for it’s first booster or annual shot, the default is to restart the entire series. The World Small Animal Veterinary Association vaccination guidance gives some leeway for the annual booster, indicating that re-dosing within 15 months (not the labelled 12) is likely okay. Personally, I suspect we can go longer, since the vaccines are good and immune systems usually aren’t dumb. However, the farther we go off-label, the less confidence we have. While many (or maybe most) dogs are probably protected well after a year and will still respond to a single booster, as a veterinarian, I can’t tell an owner with much confidence that that’s the case. So, the default is to go back to the start so we can be sure.

Based on that, when it comes to lepto vaccines, if a dog gets its:

First dose, but is late for the 2-4 week booster

  • Restart the whole series (i.e. 2 doses 2-4 weeks apart, then yearly)

First dose, 2-4 week booster, and then a yearly booster not more than 3 months late

  • Continue with the single annual boosters

First dose, 2-4 week booster, but is more than 3 months late for the yearly booster

  • Restart the whole series (i.e. 2 doses 2-4 weeks apart, then yearly)

What if someone doesn’t want to restart the series (due to cost, logistics, not keen on vaccines, etc.)?

Odds are reasonable the dog will still respond to a single late booster, but confidence in the immunity this will generate drops the later the booster gets. There’s no way to say exactly what the risk is, so not going back to repeat that 2-4 week primary series means the owner has to accept some degree of uncertainly regarding how well protected their pet will be. Additionally, manufacturers tend to stand by their products, but they’re not likely to offer any support if a dog gets lepto when the recommended vaccine schedule isn’t followed. Those are all things that need to be discussed and considered.

I’d prioritize dogs for lepto vaccination in this order:

1a) Starting initial lepto series

1b) 2-4 week booster for dogs that received the first dose

2) Yearly booster for dogs approaching the end of the 3 month extension window

3) Yearly booster for dogs not yet near the 3 month extension window

More information about leptospirosis can be found on the Worms & Germs Resources – Pets page.

In some ways, the approach to rabies vaccine is easy. In other ways, it’s complicated. To some degree, the medicine is easy, but other considerations (like regulatory requirements) cloud the picture.

The medicine:

Rabies vaccines are highly effective. A single initial dose provides at least 1 year of protection. The first dose is supposed to be given at 12 or 16 weeks (depending on the jurisdiction – rabies vaccines in Canada are labelled for use in dogs and cats 12 weeks of age and older), with a booster one year later. Getting that first shot is critical, so the animal is protected as soon as possible against this deadly – and zoonotic – disease.

After that, we can use 1 yr or 3 yr vaccines.

  • For a 1-year vaccine product, if the animal is overdue, we’d just give another dose as soon as possible, but the yearly cycle does not change.
  • For a 3-year vaccine product, after the initial dose and the first 1-year booster, the animal can safely go 3 years between boosters.  However, if the 1-year booster is missed, then we’d have to restart that primary series to stick to the manufacturer’s instructions, meaning the late booster would only be considered good for a year. Then we’d go to every 3 years after the next dose a year later. If the animal misses any of its 3-year boosters, the same would apply, i.e it would need a booster a year later to get back on the 3-year schedule.
  • Note: As of March 2019, there is only one 1-year rabies vaccine product for cats still available in Canada, and none for dogs; all other rabies vaccines for dogs and cats in Canada are 3-year products.

That’s all pretty straightforward and by-the-book (or label, in this case).

The challenge is what constitutes “late.” Strict interpretation of the label would be that even a single day overdue would require the primary series to be repeated. Many would consider that overkill since rabies vaccines are so highly effective. However, there’s not much appetite for guessing when it comes to rabies. Once an animal is more than a couple of months overdue, it’s harder to say that the booster should count as a 3-year dose, since we’re deviating ever more from the label recommendations. So, prudence would dictate we go back to the start. If there’s concern that the provincial/state/regional authorities (especially border authorities) would use a strict interpretation and consider any lapse an indication that the vaccination series had to be restarted, then it’s safer to be more conservative and do that in your practice as well. More on that below).

From a rabies protection standpoint, I don’t worry about late vaccines (within reason) since rabies vaccines are so good, especially in an animal that has received multiple doses over the course of its life.

The “other considerations”:

What makes rabies vaccination delays complicated is most often regulatory/public health rules and interpretations thereof. In many areas, rabies vaccination is required by law; for example, in Ontario, all dogs, cats and ferrets over 12 weeks of age are legally required to be kept up-to-date on rabies vaccination, regardless of whether they have indoor or outdoor lifestyle.  I doubt there would be a fine applied in most cases for reasonable delays in vaccinating a pet due to COVID-19 restrictions over the last year (but each jurisdiction is its own…). However, the bigger issue is the response to a potential rabies exposure in such an overdue animal. When an dog or cat is exposed to a rabid (tested) or potentially rabid (untested suspicious) animal, the response depends on the pet’s rabies vaccination status. That response varies a bit by region; some default directly to the guidelines in the NASPHV Rabies Compendium, some adapt those guidelines, and others are… well, a bit unpredictable.

In Ontario, the response could range from simple observation with no strict confinement (e.g. a fully vaccinated pet that gets a booster within 7 days of the encounter) to a strict 6 month confinement (e.g. an unvaccinated pet that does not get a rabies vaccine within 7 days of the encounter). Animals with a history of lapsed vaccination are dealt with on a case-by-case basis, with things such as the time since the last dose and the number of lifetime doses being considered (among other factors). The pet could ultimately be treated as fully vaccinated or unvaccinated, depending on the details, and that can be the difference between life-and-death, as euthanasia is sometimes elected by owners in lieu of having to strictly quarantine the pet.

Understanding how your region addresses overdue vaccination is useful, to determine how strict you need to be about getting animals in for their boosters. If they’re not flexible and consider an animal’s vaccination status to be lapsed the minute they pass the 1- or 3-year mark, then we need to make sure we’re prioritizing rabies vaccinations so there are no gaps.

As an example, here’s the situation in my household:

  • My dog, Merlin, has had multiple doses of rabies vaccine and is probably effectively protected for life. Him being overdue is probably low risk, but I wouldn’t want to let it go very far. I’d booster him when feasible but not stress about it, and would keep him on the 3-year cycle. If he’s not too far overdue, I’d have a strong case to consider him completely protected if he tangles with a rabies suspect.
  • My cat, Milo, is less than a year old and has had a single dose or rabies vaccine. He’s higher priority to get boostered. If I miss the 1-year booster by much, I’d have to consider re-starting the primary series again, which means I’d give him a dose, and then another in 1 year, before switching to every three years. (That’s a picture of him… he doesn’t look very stressed about it).
  • The outdoor cats (Rumple and Alice)  have received multiple doses or rabies vaccine over their lifetimes. They’re like Merlin, but higher priority for boosters since they likely have a greater risk of exposure to rabid animals.

The take home messages on rabies vaccination delays:

  • Don’t let rabies vaccination lapse, if possible.
  • I’d prioritize pets for rabies vaccination in this order
    • Animals that may have been exposed to rabies in the last 7 days because of an encounter with a suspicious animal that couldn’t be tested for rabies (or that was tested and was confirmed to be rabid.  This is a medical urgency.
    • Animals that have never been vaccinated for rabies (or unknown if they’ve ever been vaccinated). They need a dose ASAP to make sure they’re protected and won’t have to risk a long confinement period if they’re exposed to rabies.
    • Animals that have only had one dose of rabies vaccine in their lifetime.
    • Animals that are significantly overdue for their rabies booster (more than a couple of months).
    • Other pets that are due for a rabies booster (if there’s really a need to prioritize further, focus on dogs/cats that go outside unsupervised).

I’ve been dealing with questions (and some threats) about this issue for many months:

How to handle overdue vaccines because of COVID-19 delays

It’s a complex issue that’s hard to navigate because of limited data. We know how most vaccines work when used according to the label instructions. We don’t know much about what happens when use of those vaccines differs from the label instructions.

Dr. Michelle Evason and I did a webinar for CommuniVET on this topic the other day, and it made me think a lot more about it.

The main questions are:

  • How long do vaccines actually protect an individual animal?
  • Does being overdue for a vaccine mean you have restart the primary vaccination series, or can you just give a single booster later than normal and continue with the regular vaccination schedule?

Manufacturers can’t give too much guidance because they are legally bound to the licensing (label) claims. They also don’t have much data about uses that differ from the instructions on the label, because no company is going to pay for expensive vaccine trials to test various combinations of delays and boosters once the product is licensed.

Owners want their animal protected, but they also don’t really want to come back in / pay for another vaccine, and many want to avoid giving any more vaccines than are absolutely necessary.

Veterinarians want to make sure that their patients are protected, that their owners are happy (or at least not overly unhappy), and that they can provide veterinary care during a time when that might be complicated, and when most clinics (around here at least) are completely swamped.

Our two main vaccination guidance providers (the American Animal Hospital Association and World Small Animal Veterinary Association) want to help, but are restricted by the limitations above, i.e. there’s not much hard evidence on which to base off-label recommendations.

This could become a monstrously long post, so I’ll break it down. Today’s post will cover scenarios for “core” vaccines (other than rabies). These are vaccines for diseases against which we vaccinate pretty much all dogs and cats, often using combination vaccines. Core vaccines for cats are for panleukopenia,  feline viral rhinotracheitis  (aka feline herpesvirus type 1) and calicivirus. Core vaccines for dogs are for distemper, parvovirus and canine adenovirus-2

Comments below refer to vaccines and vaccination strategies used in Canada, which are similar to many other countries, but there can be some variation in vaccines and label instructions in other jurisdictionsThe discussion will also refer primarily to modified live virus (MLV) vaccines, which are the most common type of vaccine used in dogs and cats, as they are highly effective and generally result in an excellent immune response.

1. Puppy or kitten with a delayed initial series

With MLV vaccines, a delay in the initial series is not a big deal. Core MLV vaccines are highly effective and should provide long-lasting immunity even with a single dose, but only IF the puppy/kitten didn’t have a lot of maternal (mother-derived) antibodies at the time of vaccination.

Puppies and kittens get these antibodies from their dam, which provide protection while the animal is very young and its own immune system gears up to produce its own antibodies. Unfortunately, the maternal antibodies also decrease the ability of the animal to respond to a vaccine.  We usually give a series of 3-4 doses of MLV vaccine to puppies and kittens; this is not because they need an initial dose and a series of boosters, but rather, it’s because we want to make sure they’re protected as soon as those maternal antibodies run out, and that they get long-lasting immunity. So, we start the vaccination series early, and if their immune system responds that’s great, they’re protected early. If not, they get another dose in a few weeks, and then another dose a few weeks later… By 16 weeks of age, we assume they are able to fully respond to vaccination because their maternal antibodies have disappeared (please note that puppies and kittens can be vaccinated for rabies at 12 weeks – you do not (and ideally should not) wait until 16 weeks for rabies vaccination, in order to get them protected as soon as possible – more on that in Part 2 tmrw).

So, the key is we want to get a dose of MLV vaccine into a kitten or puppy at 16 weeks of age or older. If they missed one or more shots in the series, as long as they get a dose at 16+ weeks of age (even if their very first one), they should be good to go because that’s the one that gives them lasting immunity. In some high-risk situations, such as a dog that’s going to encounter a lot of dogs or be in a high risk environment like a shelter, we’d still consider giving another dose if they got their only shot at 16-20 weeks, but that’s case-by-case.

The take home for this group: Get them vaccinated when they’re young if at all possible, but once they’re 16 weeks of age or older, they may just need a single dose.   If there are delays getting a young animal vaccinated, care must be taken to reduce the risk of exposure as maternal antibodies drop, as there is a risk the animal will be unprotected for some time. That means limiting contact with other dogs/cats and high risk environments (e.g. parks, puppy classes, kennels) until vaccinated.

2. Puppy or kitten with a delayed 6 month/one year booster

Unlike killed vaccines for which the timing of the booster is important to get the full vaccine response, boosters of MLV vaccines can be given almost any time and probably results in a similar response. After the initial puppy/kitten vaccination series with a killed vaccine, these animals are usually vaccinated again 6 months or 1 year later, only because we are less confident about long-term  (multi-year) protection from the single initial vaccine.

The risk of being a bit overdue is probably low. The MLV vaccines we use are very good and immunity is probably fairly long-lasting.  We just don’t have as much confidence in it (because we don’t have the data to back it up). I’d prioritize these boosters below a younger animal needing its 16-week vaccination, but above an older dog/cat waiting for its 3 year booster.

The take home for this group: Get them boostered when you can, but don’t worry about a delay. If there is a delay, they still likely just need the single booster they were going to get.

3. Adult dog or cat with a delayed 3 year booster

After the initial vaccination series (or single dose), and the subsequent dose 6-12 months later, we now typically give dogs and cats core booster vaccinations approximately every 3 years. Being late for the 3 year booster isn’t a big deal. These vaccines are highly effective and produce an excellent response with a single dose, regardless of vaccination history. We rarely see the core vaccine diseases in vaccinated adult dogs and cats.

If there’s a need to triage who gets in for vaccines, these animals are lowest on my priority list (but remember we’re not talking about rabies vaccination – see Part 2). They’re unlikely to get these diseases as adults, and a delay will not impact how well they respond to the next vaccine. I want to get them done, though, and the need for a rabies booster may bump them up the priority list.

The take home for this group: When it comes to just the non-rabies core vaccines, get them boostered when when you can, but don’t worry about a delay. They just need the single dose they were going to get, whenever they can get it.

MLV core vaccinations are the easiest part of the decision process. It’s basically just a matter of getting them done when possible, but not changing anything else (beyond the potential for needing fewer puppy/kitten doses).

I didn’t talk about killed vaccines (yet) but I’ll mention them quickly because the story is completely different for them. With killed vaccines, we’re much more dependent on properly timed boosters. If those aren’t given, the default is to re-start the initial series to ensure there’s a robust immune response. So, if a vaccination series is started and then delayed, the whole series may need to be re-started.

More on other vaccines soon.

There’s an interesting report that pets of people with COVID-19 in Seoul, Korea (and soon other areas) will be tested for SARS-CoV-2 for free, if the pets are showing signs of compatible illness. This comes on the heels of the (unsurprising) identification of an infected kitten in the city at the end of January, which was the first (confirmed) infection in an animal in Korea. It’s an interesting response, and it’s nice to see.


  • We get more information about human-to-pet transmission
  • We might get more information about the potential development of mutations of the virus in pets
  • Infected pets can be isolated (whether they pose a significant risk to people or other pets is still unknown at the moment, but erring on the side of caution is prudent)


  • More exposure of of testing staff to infected households in order to collect samples
  • More contact of additional people with potentially infected pets

Overall, I’d say the pros outweigh the cons, as long as there’s a good plan for safe sampling and for handling positive results.

We don’t know if a response like this is necessary, but the fact that we don’t know probably means that it is.  Once again, an Asian country is demonstrating a more proactive response to a disease risk, rather than the “show me there’s a problem, then I’ll think about acting” response we’ve seen elsewhere.

I’ve written about COVID-19 scent-detection dogs before, and I’ve done a variety of interviews on the subject, but it keeps coming up.

Can scent-detection dogs help with COVID-19 control?  The answer is (as with many things about the SARS-CoV-2 virus) less than clear.  My current answer is… maybe… in some situations… potentially.

Let’s break it down.

Can dogs detect SARS-CoV-2 using their sense of smell?  Presumably not. The virus should have no smell.

Can dogs detect SARS-CoV-2 infection using their sense of smell?  It appears that some dogs, in some situations, can actually do this.  There are a few preliminary studies of varying strengths (from laughable to pretty good) indicating that dogs can detect infected people. They aren’t smelling the virus though, they’re smelling something that an infected person’s body produces in response to virus.

What are the the dogs detecting in infected people?  We don’t know exactly what the dogs are smelling, which makes it harder to train and assess them. If we had “eau de COVID-19″ it would make training and assessment much easier.  As of yet, we don’t know the best sample for dog’s to smell (saliva vs nasopharyngeal swabs vs skin wipes vs sweat vs…?) or the best kind of patient (really sick person vs moderately sick person vs asymptomatic person…?) from which to get the samples for training.

Can a dog detect someone with COVID-19 walking by?  We don’t know. The best work has been done with samples taken directly from a person, such as sweat wipes. I haven’t seen any data about dogs detecting infected people from just sniffing around them (despite the Miami Heat trying to use dog walk-bys to screen fans for COVID-19).

Can dogs be used to tell if someone doesn’t have COVID-19, so they can be allowed to do something or go somewhere (e.g. use public transit, or attend an event like a basketball game)?

  • Maybe, but it depends on the scenario.  At best, dogs are going to be a reasonably good screening tool for COVID-19. They won’t be 100% accurate, so we can’t rely on them in critical situations.  But they could be an adjunct screening tool that’s far from perfect but still useful.

Where might scent-detection dogs be used to help with COVID-19 control?

I do NOT see scent detection dogs as a tool to say either:

  • Yes, this person is infected. They need to go home.
  • No, this person is good. Off they go.

If dogs are actually good at detecting people from a distance, then they could be used like rapid antigen tests to say either:

  • Yes, you’re good to go. But still wear your mask and do everything else because I’m not perfect.
  • Hang on a minute… something might be up. You need to go for a PCR test to find out for sure.

Even if dogs aren’t that good for rapid individual screening, they could still be useful. I think the greatest potential is identifying high risk environments. For example, they could be taken into a homeless shelter, workplace, migrant worker housing or other high risk environment, and if they detect a whiff of COVID-19, that would be the trigger to bring in targeted testing (rather than the dog trying to figure out which individual are positive).

Rapid, cheap, person-side antigen testing will probably be more useful than dog screening, but scent-detection dogs could be useful in some situations if rapid testing isn’t universally available.

First ee need to know that COVID-19 scent-detection dogs work, how well they work, and their limitations. As with a lot of things, this is an area where some people have jumped from “idea” to “application,” without all the necessary steps in between.

What we can’t do is try to use these dogs as untested tools that give people false confidence to engage in higher risk behaviours (like having them at the door of a sporting event).  They’re a potentially useful add-on, but not an excuse to do something that wouldn’t be done without them. So, if an event is going on and rules at set, sure, add dogs as an additional measure. If the dogs are being used as the argument to allow people in, allow more people in or allow them to reduce infection control measures, that’s possibly counterproductive.

I usually link blog posts to Tweets, rather than re-hash my Twitter musings (weese_scott) on the blog, but two things I posted on Twitter today may be of interest here.

COVID-19 in captive gorillas

Not surprisingly, COVID-19 has been identified in captive gorillas, in this case at the San Diego zoo.  It’s suspected that the gorillas were infected by an asymptomatically infected keeper, despite the intense precautions that have been taken to try to protect the animals since the pandemic began. It’s not at all surprising, since we assumed gorillas (and other non-human primates) that are relatively closely related to humans would be very susceptible to the SARS-CoV-2 virus, just like we are. With COVID-19 running rampant in California, it’s also completely unsurprising to have had an asymptomatically infected keeper at the zoo.

The more interesting aspect might be how the virus was actually transmitted from person to gorilla. Zoos tend to have very strict control measures in place to prevent this from happening (even when there isn’t a global pandemic), and the San Diego Zoo is an excellent facility. Figuring out how this occurred (e.g. inadequate practices, inadequate compliance) will be important to guide control measures at other facilities.

Toxoplasma gondii associated with brain cancer

Toxoplasma gondii is a protozoal parasite that has been linked to lots of issues in people, often with somewhat questionable evidence. Cats are the definitive host of this parasite, for which they get a very bad rap, but most human exposure is from the environment or food.

A recent paper has made some interesting but tenuous links between Toxoplasma infection and glioma, a type of brain cancer. It was interesting research, involving a large prospective study in which they collected blood samples from cancer-free people, and then followed them over time. After 13 years, they looked at the risk of gliomas in those who did or did not have antibodies against T. gondii prior to diagnosis (probably no real reason for picking 13 years… long enough for cancer to develop and it happened to be when they were ready to look at that).

There were some weak associations between one type of Toxoplasma antibody and development of glioma and glioblastoma. The data aren’t too convincing, but there are some similar results from elsewhere, which shows the subject needs more study.

What does this mean for cat owners?

  • Very little. Gliomas are a rare cancer, and while Toxoplasma exposure is quite common, it’s not usually from someone’s pet cat. Toxoplasmosis is a “don’t eat poop” disease, so there are lots of simple, routine things we can do to reduce the risk from pet cats (like not touching cat feces and washing your hands after cleaning the litter box).

More of my comments are posted on Twitter here:

We have more information about Toxoplamsa on the Worms & Germs Resources – Pets page.

Here’s the latest version of our pandemic guidance document for Ontario veterinary clinics, produced in collaboration with the OVMA.  Previously entitled “A guide to reopening veterinary medicine in Ontario” it has been retitled “A guide to mitigating the risk of infection in veterinary practices during the COVID-19 pandemic (04-Jan-2021)“.

Previous versions of the guidance and other related documents can be found on the Worms & Germs COVID-19 Veterinary Resources page.


Not surprisingly, COVID-19 has been identified on a mink farm in British Columbia, Canada, in the midst of Canada’s 2nd wave of the COVID-19 pandemic.

It’s important note that so far, the virus has only been found in people on the farm, not in the mink. Eight farm workers were reportedly diagnosed with COVID-19 over the weekend, so now testing of the mink is underway. With 8 infected people at the facility, it’s pretty likely that the mink are infected as well, since they are quite susceptible to the SARS-CoV-2 virus, but we’ll need to wait for the test results later this week.  If there are a few infected mink on the farm, that can become lots of infected mink pretty quickly.

This is a breaking story so more information will no doubt roll out over the next few days.

The big questions are:

Have the mink been infected with SARS-CoV-2?

  • We’ll know soon enough.

Has there been any mink-to-human transmission of SARS-CoV-2?

  • That’s a bit harder to discern, especially if all of the infected workers have had contact with each other. If the virus is detected in mink, sequence analysis and comparison of the strains in the mink versus the workers will be part of the picture.

Has/will the SARS-CoV-2 virus mutate in the mink (as was seen in Denmark)?

  • We’re still unsure about how much of a risk virus mutation is.  Mink farms have  large numbers of susceptible animals, making them good places for mutations to occur. Virus mutations are random events, so they may be good or bad. We’re worried about mutations that negatively impact control measures (like vaccination) or that could make the virus more transmissible or illness more severe IF the mutated strains spill back into people. As above, sequence analysis will be used to look for evidence of significant mutations.

Have other animals on or around the farm been infected with SARS-CoV-2?

  • Testing of any other animals on the farm (e.g. cats) and wildlife on the property will likely follow if the mink are found to be infected.

I figured I might as well hit double digits before circling back to update the earlier reviews of COVID-19 in animals. This group doesn’t get talked about much, but there are some important issues to consider with regard to non-human primates.

Not surprisingly, many non-human primates are known to be, or are likely, susceptible to SARS-CoV-2. In particular, it has been shown that the ACE2 receptor (ACE2) from apes, as well as African and Asian monkeys, is a good match for SARS-CoV-2. New World monkeys are likely not as susceptible because of some differences in their ACE2 receptors. Some lemurs are probably also susceptible.  See the Figure below from the ACE2 receptor study for more details.

My standard disclaimer is that ACE2 receptor assessment can be useful, but it doesn’t tell us the whole story. However, it’s probably fairly accurate here. Experimentally, rhesus macaques, and a few other species, have been shown to be susceptible to infection, as predicted by the shape of their ACE2 receptors.

The relevance of susceptibility is an important question. Specifically, what could it mean for the animals, and for people?

If SARS-CoV-2 got into a group of susceptible non-human primates, I’d expect a similar outcome as with introduction into a population of people. Some would be fine, some would get sick, and some would die from the infection. If the population is small and isolated, the virus would presumably burn out because it would run out of susceptible hosts in the short term and be eliminated. The more animals and the more contact they have with other groups, the greater the risk of longer-term persistence (and possibly mutation from being passed over and over again from animal to animal). My guess is this risk would mainly be sporadic and short term in specific groups.

The big concern is the potential impact on of an outbreak of SARS-CoV-2 in threatened animal populations, since an outbreak in a single group like this could be devastating for the overall population. Ebola had a huge impact on some gorilla populations – in fact Ebola virus was estimated to have killed up to one-third of critically endangered Western lowland gorillas overall, and 95% of individuals in some groups.  Transmission of human respiratory viruses such as respiratory syncytial virus, metapneumovirus and rhinovirus has also resulted in outbreaks (and deaths) in some other threatened populations of non-human primates. Clearly, if we can spread those respiratory viruses to our closest animal relatives, we can presumably do the same with SARS-CoV-2.

The risk TO people from COVID-19 in non-human primates is pretty low. The risk FROM people is pretty high. That’s why there are currently efforts to restrict contact of people with high-risk wild primate populations, including restricting field research, restricting access by tourists, increasing enforcement of boundaries (since human habitats often abut, or merge into, protected habitats), and requiring the use of masks and other preventive measures when people have to be in the vicinity of these animals. Strict infection control measures for SARS-CoV 2 are in place in some sanctuaries, such as those described by the Jane Goodall Institute.

Unfortunately there are also downsides to these precautions, including economic impacts for local communities, loss of research, difficulties with rehabilitation, and potentially increased poaching risks as there are fewer people around. However, the cost-benefit needs to be considered, and these measures are necessary to prevent potentially devastating disease outbreaks in these threatened populations.

What are the best ways to prevent disease from SARS-COV-2 in non-human primates?

  • Control COVID-19 in people
  • Reduce contacts between people and non-human primates
  • Control COVID-19 in people

Figure from