I get asked about this topic a lot. Early in the pandemic, I wrote a post about options for caring for pets of people with COVID-19.  Some things have changed a bit now that we know more know about SARS-CoV-2 in animals and the associated zoonotic risks, and we have a vaccine for people.

One example of a commonly encountered scenario is: A dog owner is being hospitalized because of COVID-19 and a friend or family member has been asked to take care of the pet.

What are the risks to the caretaker of the dog?

  • We don’t know. I’d consider it very low but I can’t say it’s zero.
  • Person-to-dog transmission of SARS-CoV-2 is fairly common in households where the owner has COVID-19, based on our and other groups’ surveillance efforts. However, dogs are not really a great host for this virus and infections are probably fairly low grade and transient, and therefore low risk for further transmission.
  • Dog-to-dog transmission of SARS-CoV-2 hasn’t been seen experimentally, but the studies to date have been fairly small so we can’t read too much into that.  Nonetheless, it’s clear that dogs are lower risk than cats for passing the virus on to other individuals. Yet, live virus has been grown from canine respiratory secretions, suggesting there is at least some plausible risk.

What can or should be done in this situation?  There are two key considerations:

1. Should the person in question agree to look after the animal at all?

  • This requires consideration of the risk status of everyone in the household (e.g.  is anyone at high risk of serious disease if they get infected?), vaccination status of everyone in the household, whether other pets are present, how well the dog can be contained in the household, and whether the household members are willing to accept a small degree of risk.
  • The best case scenario is to send the dog to a pet-free household where everyone is vaccinated and where they can keep the dog away from other people or animals (e.g. they have a fenced yard). Asking someone else to look after a pet like this was harder earlier in the pandemic, but now that we have highly effective vaccines, it’s easier.  Asking if someone from a fully vaccinated household will take the job is reasonable.

2. How should the dog be managed?

  • That also depends on the risk status of the household. In a vaccinated household, I’d say it can be “business as usual” in the house, but restricted outside. By that, I mean I’d do nothing different with the human-dog interactions in the household, but when the dog goes outside it should be under control (e.g. on a leash, or in a fenced yard) so the dog doesn’t interact with other people or dogs from outside the household.
  • If there are unvaccinated people in the household, it’s tougher. I still consider the risk of transmission from a dog to be very low, but I can’t say it’s zero. So, it would be prudent to keep the dog away from unvaccinated individuals as much as possible for the first 14 days (7 days is probably reasonable if it’s a major issue, but 14 days is ideal).  That doesn’t mean locking the dog in the bathroom and never going near it, but rather avoiding contact with respiratory secretions, not having the dog in the same small airspace for prolonged periods of time (e.g. not sleeping in the bedroom), and focusing on good hand hygiene.

The main issue is we just don’t know the risk. It’s definitely very low and could be zero, but I don’t think we can say it’s zero at this point. Vaccines are a game changer for these scenarios.

Okay, but what if the pet in question is a cat instead of a dog?

That changes the risk a bit, but not really the overall approach. Cats are more susceptible to SARS-CoV-2 and cat-to-cat transmission can occur, so there’s also more concern about the potential for cat-to-human transmission.  That means the issues above all apply to cats as well, but are probably heightened.

My focus here would be on finding a vaccinated household to look after the cat, if possible.  If not, it’s a matter of restricting contact with anyone who isn’t vaccinated. The good thing about cats is they are (for the most part) easier to contain than dogs.  They can be kept in a large cage or kennel if necessary, or they can be confined more easily to certain areas of the house, and cats don’t need to go outside. So, if someone who’s unvaccinated has to take in a cat, it’s easier to limit contact. The concepts above still apply, with a goal of minimizing the closeness and duration of contact during the first 7-14 days after the cat is removed from the person who was infected with COVID-19.

We have a lot of different concerns about SARS-CoV-2 on mink farms. Mink are really susceptible to this virus, and human-to-mink transmission isn’t uncommon, so if we continue to farm mink, we will continue to expose mink to SARS-CoV-2 as long as the virus is still circulating in people.

Two of the biggest concerns relate to the potential for infection of mink to make things worse in the “big picture:”

  1. Development of mutations of the virus in mink that lead to new variants of concern (VOCs) that spread back to people
  2. Spread of the virus to other animal species

For this post, I’ll focus on concern #2.

We want to keep COVID-19 a human-only disease as much as possible. If it gets established in animal populations, especially wildlife, that changes the game in terms of disease control. I doubt we’re going to eradicate this virus entirely regardless, but if it establishes animal reservoirs, there’s no chance whatsoever.

Furthermore, if SARS-CoV-2 gets established in animals (of any species), we may have to deal with greater risk of VOCs. VOCs are already worsening and dragging out this pandemic, and with more transmission (in animals or people), there will be more VOCs. Mutations are a normal event when viruses replicate. The more a virus spreads, the more mutations occur, and the greater the chance that a mutation that impacts transmissibility, virulence or vaccine evasion emerges.

For a virus to establish an animal reservoir that poses a risk to people, a few things need to happen:

  • Animals have to be exposed, directly or indirectly, to infected people.
  • The animal species has to be susceptible to the virus, and able to transmit it between individuals.
  • The species must live in large enough groups for sustained transmission within the population.
  • There has to be a mechanism to spread the virus back to people from the animals

That might seem like a tough list to fulfill, but it’s not impossible (and it’s what has happened with some other zoonotic viruses).

Therefore, we want to keep this virus away from animals, particularly wildlife.  This is where we come back to mink.

A recent paper in Transboundary and Emerging Diseases (van Aart et al. 2021) reports on surveillance for SARS-CoV-2 in dogs and cats on mink farms in the Netherlands, where SARS-CoV-2 was identified in over half of the mink farms in the country.

  • 13 farm dogs and 101 (mostly feral) cats (69 adults and 32 kittens) on 10 farms were tested.
  • SARS-CoV-2 was detected by PCR in 3 (4.4%) adult cats and 1 (7.7%) dog.
  • Since PCR testing just tells you a single point-in-time result, antibody testing was used to identify prior infection. Antibodies to the virus were found in 18% of adult cats, 0% of kittens and 2 (15%) dogs.
  • When PCR and serological test results are combined, 19.4% of adult cats and 15% of dogs had evidence of infection with SARS-CoV-2.

That’s pretty impressive.  There’s no guarantee that all the dogs and cats were exposed to the virus by mink vs an infected farm worker, but mink-to-cat transmission seems reasonable since these were mostly feral cats that would not have interacted closely with people. The source of infection of in the dogs is harder to tease out since they presumably had closer contact with farm personnel.

Interestingly, none of the nine domestic cats that were tested were positive, despite having infected owners. Infection was only found in the feral cats. Whether all the cats were infected by the mink or there was some subsequent cat-to-cat transmission (a likely scenario) is also impossible to discern.

Mink-to-cat infection would have been through indirect exposure, because the cats generally wouldn’t have direct contact with the mink in their cages.  This raises concerns that other species could have been similarly infected through indirect contact with the mink, including small mammals like mice, or from direct/indirect contact with an infected cat (e.g. mouse surviving an encounter with an infected cat).

These concerns are why there is wildlife surveillance conducted around many infected mink farms. That type of work has also found SARS-CoV-2 in “wild” (or more likely “previously escaped” free-ranging) mink.

What’s the relevance of all this?  It’s hard to say.

However, it supports plausible concerns about animal-to-animal transmission of SARS-CoV-2 and the need to reduce exposure to animals.  Vaccination of mink is a consideration, and I’ve written about that recently. Ultimately, the best way to reduce the risks associated with the virus in animals is to control this disease in people.

Overall, this shows the importance of the “One Health” approach and a need to be proactive to identify and hopefully prevent problems, rather than our typical reactionary approach whereby we wait for definitive proof of an animal-related issue before putting any real effort into addressing the risk.

As we start seeing a light at the end of the (long) tunnel, we have to think about how and when to restart various activities. One particular activity that I get a lot of emails about is pet therapy/visitation programs. These are great programs, where animals (usually, and ideally, dogs) are taken into facilities to interact with residents or patients. They’re not for everyone, but have been shown to have physical and mental health benefits.  Not surprisingly, they were largely stopped during COVID-19 pandemic, but many are now gearing up again.

What’s the risk of animal visitation programs?

People.

The main issue isn’t the animals (at least when it comes to dogs), it’s the human component. Human visitors pose much more risk than most pets, since people are more likely to be infected with the SARS-CoV-2 virus and an infected person poses a greater risk of spreading the virus than an infected pet. That’s particularly true with dogs, who are not uncommonly infected by their owners but who are low (or maybe almost no) risk for transmitting it back to people.  Also, if the animal happens to be infected, it’s quite possible the owner is too.

So, there is some risk from these programs, but the main (if not exclusive) risk is from an infected handler.

When can these programs restart?

The focus should really be on deciding:

  • when COVID-19 is controlled enough in humans the area
  • when resident/patient vaccination rates are high enough
  • when animal handler vaccination rates are high enough
  • what basic practices to identify high risk handlers (e.g. those with respiratory disease) need to be in place.

Should vaccination be mandatory for pet therapy program participants?

(Bracing for the next wave of anti-vaxxer “love” letters as I say this…)

In my opinion, yes, vaccination should be mandatory for the people (not the animals).  A reasonable exemption for people that TRULY CANNOT be vaccinated is reasonable, but the bar has to be high so that “cannot” and “don’t wanna” are differentiated.

Mandating vaccination of handlers would be a logical measure for a voluntary activity that involves close contact with a disproportionate percentage of high-risk participants.  Also, there’s a need to make sure handlers received both doses of vaccine, as concerns about the delta variant increase.

The other approach could be to have a phased re-introduction, e.g. fully (2-dose) vaccinated people can start first, with follow up assessment of when people who are not vaccinated can start as well. That way the policy isn’t saying unvaccinated people can’t participate, it just says they can’t yet. That’s not an unusual approach now as people start to think about re-opening in other areas and how vaccination comes into play for that.

How to we reduce the risk in the event an infected person (or animal) ends up visiting?

Good ol’ infection control and common sense. There are very good guidelines for healthcare visitation programs that apply to most animal visitation settings, and those are the core of risk reduction.  A little basic hygiene and common sense go a long way.

I’ve written before about animal vaccines against SARS-CoV-2 with regard to mink, but with Russia having recently licensed its Carnivac-Cov vaccine for use in several species (namely dogs, cats, foxes and mink) and Zoetis developing a vaccine in the US for mink, there’s continued interest in the subject, so I’ll revisit it.

I’m glad companies are working on SARS-CoV-2 vaccines for animals. It’s good to be prepared and have the work done in case it’s needed in a particular situation. Whether there’s much use for these vaccines in most animals at this time is hard to say.

When I think about SARS-CoV-2 vaccines for animals, there are three main reasons we would use them:

1. Prevention of severe disease

This is the main goal of most vaccines. However, dogs and cats don’t seem to get very sick, very often, from this virus.

  • I’m still on the fence as to whether this virus really causes significant disease in dogs at all. We have some data that suggests infection is associated with risk of very mild disease but overall, it’s still not entirely clear. However, it is clear that they rarely, if ever, get seriously ill.
  • Cats are commonly infected with SARS-CoV-2, but even cats rarely develop severe illness. There’s evidence that they can, so we can’t dismiss it. However, our research and others suggests that a large percentage of cats from households where people have COVID-19 get infected. So, we have probably had millions of infected cats worldwide since the start of the pandemic. If this was causing severe disease in a reasonable percentage of cats, I think we’d have clear signs of that by now. Since serious illness can occur in a small minority of cases, vaccination could help, but in the grand scheme of things, given the low risk of severe disease, it’s hard to say that the potential benefits justify the cost and potential adverse events.  (We don’t know about any specific adverse effects of vaccination in animals to date. I’m not talking about VITT or the misinformation about mRNA vaccine adverse events in humans. I’m talking about the typical adverse events that we can see in animals with any vaccine.) I’d rather focus on better rabies vaccine coverage and other good preventive medicine things than trying to get cats vaccinated against SARS-CoV-2. I’m not opposed to it. I just think the value is probably limited.
  • Mink are different. They are clearly susceptible to infection and it can cause serious illness and even death. The two points below probably are more important when considering vaccination of mink, but there could be mink health benefits from vaccination.

I’d be most interested in vaccination of endangered species with suspected high susceptibility that have human contact, particularly wild felids (e.g. lions, tigers) and non-human primates (e.g. great apes). Vaccination of captive animals (zoos), animals in rehab facilities and animals in areas where there’s close contact with human populations (mainly applicable to primates) might be worthwhile because of the potential implications of infection in endangered populations.

2. Prevention of transmission from animals to people

Dogs pose little risk to people, if any, in terms of transmission of SARS-CoV-2. Dog-to-dog transmission has not been seen experimentally, and infected dogs seem to have pretty low viral loads, so I doubt there’s much risk. Cats pose more risk to people. Cat-to-cat transmission does happen, so we have to assume cat-to-human transmission can occur too.  But human-to-cat transmission is still far more common. Because most infected cats probably catch the virus from their owners in the first place, they are probably “dead-end” hosts in households and rarely play a role in transmission. Cats get infected from family members, who have also infected each other, and everyone burns off the virus together. I think the greatest risk of cat-to-human transmission is when infected cats leave the house, particularly to go to a veterinary clinic or shelter. However, the risk associated with that can be significantly reduced using basic infection control practices..

The risk of animal-to-human transmission is probably highest with mink, as mink-to-human transmission clearly occurs. Vaccination of mink could be an important way to control mink-to-human transmission (but preventing human-to-mink transmission is most important).

3. Prevention of viral mutation

This is an important aspect for species that might serve as reservoirs and source of new variants. Virus variants emerge because of random mutations in the viral genome, and mutations happen when the virus replicates. So, the more the virus replicates and the more individuals are infected, the greater chance of a “bad” mutation occurring. For dogs and cats, this isn’t really a big concern. We don’t have massive numbers of dogs or cats together where widespread sustained transmission  is of great concern. Yes, a mutation could happen within a single infected dog or cat, but it’s really unlikely (and even then, it’s only relevant if that dog/cat then can pass it on to a person.)

The greatest risk of significant viral mutation in any animal species to date appears to be in mink.  We know that the virus can mutate in mink populations AND spread back to people. When you house thousands of a highly susceptible animals close together and introduce the virus from an infected person, that’s the recipe for widespread transmission and massive viral replication that’s needed for “bad”mutations to result in the emergence of a significant variant. Vaccination of mink farm workers helps reduce the risk of mink getting infected and from passing the virus back to people, but there’s still some degree of risk.

 

Overall, I can’t see a need at this point for vaccination of dogs and cats against SARS-CoV-2. The cost-benefit comparison of vaccination of those species doesn’t seem convincing.  Vaccination of high-risk (e.g. endangered) susceptible animals like large cats and non-human primates might make more sense, such as in zoos, rehab facilities and other places where there’s some degree of human contact with these species.

Mink are a different story. If we’re going to continue to farm mink, vaccination is a reasonable consideration.

The final disclaimer here is that all this is based on what we know about current virus variants. New variants always have the potential to reset our knowledge to some degree.  Variants that can infect a wider range of animal species, cause more serious disease in animals or be more transmissible from animals to humans might impact the current risks and make vaccination of other species more beneficial.  That’s why I’m glad we have some information about vaccines for animals now. I don’t think we need them currently for most species, but it’s good to be prepared should things change.

Ivermectin is a commonly used anti-parasitic in animals, and it’s also used in people to treat some parasitic diseases. Additionally, it’s still widely discussed in some internet circles for treatment or prevention of COVID-19. That’s based on mainly anecdotes, some in vitro study, and very poor quality “clinical trials”.

It’s led to stories of people using or even hoarding veterinary ivermectin products. I’ve had lots of questions from the general public and veterinarians as a result (including stories of people buying more heartworm meds for their dog  than they’d ever need).

Bad idea. Here are some reasons why:

  1. There no evidence that it works. An in vitro study showed ivermectin inhibited SARS-CoV-2, but only at massive doses, well beyond what would be safe for use in people.
  2. Anecdotes aren’t data.
    • I don’t dismiss clinical observation, as it is the starting point of many important discoveries. However, a lot of things I have thought I observed or initially appeared to “work” didn’t pan out to be true over time.
    • Observations should lead us to take specific steps to figure out if something is real.  They help raise questions, not answer them.
  3. Other factors may be involved that make the drug appear effective in some siutations, but those factors don’t apply broadly.
    • One potential reason ivermectin may seem to work in some areas is because it’s an anti-parasitic. Strongyloides stercoralis is a human respiratory parasite that is common in some countries. People get infected and the parasite can lay dormant in the body, but when they are immunosuppressed, it can be re-activated.
    • Dexamethasone is a common and effective treatment in people with moderate to severe signs of COVID-19.  It reduces inflammation, but also impacts the function of the immune system (since that’s what triggers inflammation).
    • If someone is infected with dormant Strongyloides stercoralis, dexamethasone treatment for COVID-19 might lead to re-activation of the parasite, and that would complicate respiratory disease.
    • I don’t dismiss that potential, but it would mean that ivermectin might be effective in people with dormant Strongyloides stercoralis infection that are also receiving dexamethasone.
    • That’s a lot different than “ivermectin works against SARS-CoV-2 and everyone, everywhere, who is infected should be on it.”  They should not.
  4. Ivermectin isn’t a very commonly used drug in people, but it is important for treatment of certain parasitic infections.
    • Diversion of the relatively small amount of human ivermectin products towards unnecessary use compromises the care of people that really need it. (I realize that isn’t associated with “don’t steal Fido’s stash” but it’s still an important point.)
  5. Your dog’s heartworm preventative is a low dose treatment.
    • To get the levels used in the aforementioned in vitro study, a person would require a dose of  about 3500 ug/kg. Heartworm prevention in dogs is dosed at about 6 ug/kg.
    • So, my dog Merlin gets one 272 ug chewable a month. To get 3500 ug/kg, I’d need 965 tablets per dose. If I had a small dog, I’d need even more of his supply.
    • If I wanted to self-treat for Strongyloides stercoralis (not sure why I would, but let’s pretend), I’d need 52 of my dog’s chewables – per day.
  6. Ivermectin also comes in more concentrated oral, injectable (don’t even think about it) and pour-on (topical) forms. While I have good confidence in mainstream veterinary pharmaceutical companies, I still don’t want people taking a product that is only intended for (studied in and approved for) use in animals.

Ivermectin is one of many so-called “miracle cures” that we’ve seen pushed on the internet. Like most others, there’s limited substance to the stories behind it. There’s no magic bullet for COVID-19. I’d love it if ivermectin was one, as it’s a drug we know how to use and how to produce. Production could be ramped up and it’s relatively cheap. While conspiracy theories abound, no one has come up with any plausible explanation why an effective drug would be suppressed. Dexamethasone is cheap, widely used and widely produced, and it’s standard of care for some patients. That’s because it works. Ivermectin fits all of those except the “works for COVID-19” which is the most important one.

I’ve taken a look back at some posts from the start of the COVID-19 pandemic, to see how my thoughts have evolved, what I got right and what I screwed up. We have a lot of COVID-19 posts (starting from when we called it “novel coronavirus” or “Wuhan coronavirus” before the SARS-CoV-2 terminology existed). Here are some highlights and “grading” of my comments from a selection of posts

January 20, 2020 “New coronavirus: Companion animal concerns?”: Very early on I said While this virus still seems to be less transmissible and less virulent than its relative, the SARS coronavirus, it’s pretty early to have a lot of confidence in that.

  • Grade B: It turns out SARS-CoV-2 is not less transmissible than the first SARS virus, but I guess I covered myself by saying it was early to have much confidence.

For containment measures for SARS, this new coronavirus or any other new disease, we need to assume that multiple species can be affected until proven otherwise, and we need to act accordingly. That doesn’t necessarily need to be complex. It might just be making sure animal contact questions are asked along with human contact questions, that quarantine protocols consider what to do with exposed animals, and that quarantined individuals are kept away from animals. 

  • Grade A: This turned out to be a fairly accurate statement, but fortunately risks from animals seem to be pretty limited (let’s hope this statement holds up). This is also around the time I sent some (essentially ignored) emails to try to get some consideration of animal aspects in any human exposure response planning here in Ontario.

January 23, 2020 “Novel coronavirus in China… Hold off on blaming snakes”:  In a post talking about how snakes might be the source of SARS-CoV-2, I wasn’t convinced and said I’m sure we’ll see much more genetic analysis of this virus by many different groups, but I suspect it will keep coming back to bats as the source. 

  • Grade A:  A final answer is still needed but this seems correct.

February 5, 2020 “Novel coronavirus and animals”: In talking about whether there’s actually a problem with companion animals, I said we need to focus on ensuring exposed animals are quarantined, using good old fashioned infection control like hand washing, keeping fear at bay and applying logic to the problem.

  • Grade B+: I’ll dock myself some marks on this one since it was focused on dogs. To be fair, the post was about concerns regarding over-reaction and euthanasia or abandonment of dogs, but it didn’t get into the bigger risks we now know are present with other species.

February 14, 2020 “More on COVID-19 (novel coronavirus) in animals”: I said We still have no evidence that this virus affects domestic animals, but since we also still have no real evidence that it doesn’t, it’s best to continue to take reasonable precautions to reduce the risk of exposure of animals to infected people, and to properly manage pets of people who are infected. “

  • Grade A+: Especially since it was at the same time groups like the US CDC were actively pushing back against there being any risk to/from animals.

February 18, 2020 “COVID-19 and potential animal hosts”: This post talked about a study that predicts species susceptibility based on ACE2 receptors. The potential susceptibility of cats is obviously a concern given their commonness as pets and the close interaction many people have with their cats. Pigs could be an even worse issue. If pigs could be infected and shed the virus, and it got into the commercial pig population, it would potentially be an even worse issue.  As with SARS, mice and rats are likely resistant to infection – that’s good from the standpoint of them not being reservoirs in the wild, but it also means they can’t be used for experimental study (as these are the most common lab animal species).

  • Grade C+: I think I over-estimated how useful these studies would be. They were interesting, but some species predicted to be high risk (e.g. pigs) aren’t, and some that were predicted to be lower risk (e.g. cat) most certainly as susceptible to SARS-CoV-2.  I also missed a couple of points. It seems like infection of pigs isn’t a concern but I think I missed some of the main potential concerns, as I wasn’t thinking about them as sources of virus mutants or wildlife exposure.

February 28, 2020 “COVID-19 in a dog”: A post about the first SARS-CoV-2 positive dog: Overall, my concerns are still more about cats. Dogs will probably get investigated more because there are more pet dogs than cats in most regions, and people tend to seek healthcare for the dogs (or alternative caretakers if the owner is indisposed due to illness) quicker than for their cats. 

  • Grade A: That turned out to be true.

March 27, 2020 “Human-to-cat COVID-19 transmission: Belgium”: I said If you’re worried about getting COVID-19, worry about your human contacts, not your pets. Keep pets away from high risk people, but otherwise, your risk is from exposure to people, not your pet

  • Grade A: I haven’t really changed that line in the past year.

March 29, 2020 “Social distancing WITHIN veterinary clinics”: I said Masks can reduce the risk of transmission if someone is unknowingly shedding the virus . Masks aren’t perfect but there can be some benefit. Whether it’s a good use of masks is questionable. Putting on masks for occasional close contact procedures (and ideally reusing that mask for the whole shift) isn’t unreasonable, but whether it’s really worth the mask use is hard to say.

  • Grade D: My line on masking was influenced by influenza data and concerns about mask availability, and I underestimated the usefulness of routine masking. I also focused on it being needed for known close contact situations, not more broadly. Those were the standard recommendations at that time but I still get a “D” for this one.

March 30, 2020 “COVID-19 and ferrets”: Here, I discussed concerns about ferrets.

  • Grade C:  We haven’t seen much SARS-CoV-2 activity in ferrets. Maybe that’s just because they aren’t common pets and don’t get taken to a veterinarian as often. Where I missed the boat was thinking about related species. Mink were not on my radar at all… (see below.)

April 24, 2020 “Pets and COVID-19 fears”: A commentary sent in partnership with the Ontario Veterinary Medical Association to veterinarians to balance awareness and paranoia when talking to pet owners about SARS-CoV-2.

  • Grade A: I’m not sure I’d change anything a year later.

April 26, 2020 “COVID-19 in mink: The Netherlands”: I said We’ll put this in the “interesting but not really surprising” file.

  • Grade C-: Fair statement, but while I talked about the concerns, I don’t think I really appreciated how susceptible mink would be and the issues that would develop from that.

April 28, 2020 “COVID-19 modelling and the impact of releasing cats”: This was a commentary about a crap-tastic paper about releasing infected cats and the potential impact on virus tranmission. Little did I realize this was one of many future “studies” based on little substance, little common sense and a complete abandonment of any principles of peer review. Academic opportunism has abounded in the past year and a bit, with some people putting out utterly useless papers, reviews and commentaries, and sometimes causing harm.

  • No grade… just a rant.

May 28, 2020 “Veterinary clinic staff cohorting”: I said One concept that we’ve recommended for COVID-19 control in veterinary clinics is staff cohorting.

  • Grade D: This turned out to be too impractical in most situations. It might have been useful if this was a short lived problem, but obviously that hasn’t been the case. I dropped this idea pretty quickly.

In the same post Routine cloth mask use whenever a 6-foot gap can’t be maintained between people is emerging as a key infection control tool. Cloth masks are far from perfect, but they can do a good job containing most infectious droplets, which are probably the main source of exposure.

  • Grade C: We now know the focus on the 6-foot distancing as a risk/no risk cutoff isn’t valid. Emphasizing mask use was good, but focusing on known close contact situations wasn’t.

I’d give a higher grade for the rest of the post. Most of it was actually pretty good, but these are some glaring issues.

I’ll pause here to avoid this post getting even longer. Overall, I think we had some pretty good thoughts about animals from the start. I missed the ball on a couple of key things:

  • Importance of masking: I mentioned masking above, but I didn’t realize how much of a core lifestyle component this would be.
  • Duration of the pandemic: I was expecting the pandemic to hit hard in the spring of 2020 based on modelling, so I wasn’t surprised at what we encountered then. However, I didn’t expect the pandemic to drag on this long. I was truly thinking we just needed to hit it hard in the spring of 2020 to return to normalcy in the fall or winter.

As spring approaches, a pressing question has come to the minds of many kids: “Can the Easter bunny get COVID-19?” or “Can Easter bunny eggs spread COVID-19?

Fortunately, the answer is no. Easter bunnies are safe from this virus and kids don’t have to worry about whatever the Easter bunny leaves behind.

Based on what we know to date, “regular” rabbits aren’t very susceptible to the SARS-CoV-2 virus.  Some types of rabbits can be infected with SARS-CoV-2 experimentally, but they don’t seem to get sick and they only shed low levels of virus. So, even a regular rabbit that was infected probably poses little to no risk.  (Don’t worry kids, no one’s going to try that with the Easter bunny.)

Furthermore, as we all know, the Easter bunnies have inherent magical properties that protect them from various problems (e.g. nosy household dogs). Their elusive nature (have you actually ever seen an Easter bunny depositing its wares?) and strategic placement of gifts in empty rooms mean the Easter bunny is following our “3 Cs approach to COVID-19 control,” that is avoiding closed spaces, close contact and crowded settings. And maybe the Easter bunny wears a mask too? We’ll probably never know for sure…

Don’t be afraid of the Easter bunny.

Don’t worry about what the Easter bunny leaves behind

No, you don’t need to disinfect Easter eggs.

The biggest risk from the Easter bunny is when the family dog finds all that chocolate first (yes, I am speaking from personal experience). That has nothing to do with COVID-19.

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).