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.

Headline:  “Are Dogs Spreading SARS-CoV-2?  Study Finds Living With a Dog Increases Risk of Contracting COVID-19

NO, it did NOT!

Even though the paper said that, it’s not what they actually found.  Unfortunately, a lot of people are reading that headline, or worse, they’re reading “…yada yada… dogs spreading SARS-CoV-2… yada yada.

What did the study really find?

Let’s break down some important aspects of the paper on which this headline is based.  The study, entitled “The spread of SARS-CoV-2 in Spain: Hygiene habits, sociodemographic profile, mobility patterns and comorbidities“(Rodriguez-Barranco et al. Enviro Res 2021), reported that people who walked their pets were 78% more likely to have reported having had or maybe had COVID-19.

  • They didn’t investigate that any further, and it’s not clear what “walked their pets” entailed (e.g. walking a dog once outside the house vs walking a dog on a regular basis).
  • The question, strangely, asks about walking “pets” not “dogs.” It’s reasonable to assume that the pets were at least mostly dogs, but they didn’t actually specify that.
  • How the authors analyzed the data is also unclear. The answer options for the pet-walking question were yes / no / I don’t have a pet. However, for analysis, they combined pet owners who didn’t walk their pets and non-pet owners (further demonstrating that they did not look at the risk of living with a pet).
  • They said that 6.9% of people who walked their pet had been infected, vs 4.2% of those who did not take their pet for a walk, despite the fact that most of the latter group actually didn’t own a pet at all.

So what they really looked at was leaving the house with a pet (vs living with a pet), and that raises some serious questions about how clearly they thought about the results. The focus should be on the “going for a walk” component, since that’s what they actually studied. Unfortunately, they didn’t also ask if people went for walks without pets.

Some of the other study results also raise more questions than answers:

  • They reported that people who used home delivery for food were almost twice as likely to have had COVID-19. Does that mean they were getting infected by delivery people and would have been safer shopping? Presumably not.  My concern is that there was some reason that people were more likely to order food, and that was also a risk factor for COVID-19. For example, if they knew they had been exposed or were in some other high risk situation, that might lead people to avoid stores and also be at higher risk of being infected.
  • Another big issue is the fact that people with COVID-19 were presumably more likely to order delivery after being diagnosed. The survey doesn’t ask what they did BEFORE getting infected (if they had COVID-19), just what they did during Spain’s period of restrictions. So, finding increased risk from home delivery might actually be because people who were more likely to use home delivery were otherwise higher risk or already had COVID-19.

Another concern is who they surveyed. The study population is critical for any study like this. You need to understand the study population to understand the results and any potential bias. You can get really misleading information or not understand your results if you don’t understand the group of people that provided them and how they compare to the general population.

Why is the study population so important? Here’s an over-the-top example to illustrate:  Let’s say a study said “pet owners were significantly more likely to say their dog was an important part of the family compared to cat owners,” but the study only enrolled people through websites like www.ilovemydog.com and www.mycatisademonicpsychopath.org – you can see how we might end up with a biased understanding of the situation.

In the discussion of the Spanish study, the authors mention that most respondents were graduate or post-graduate students, which is a pretty specific group. We have to consider how well they represent the general population. The farther away they are from average, the less confidence we have in extrapolating results to anyone other than graduate and post-graduate students.  I’m not saying there’s a problem using this study population. What I’m saying is we just don’t have enough information to know what it means. That’s one of the (many) things I’d flag reviewing a paper like this.

Survey response rate (and response bias) is also an issue, but I deleted my detailed comments on that since this post is already getting quite long (and probably a bit dry).

The way the authors wrapped things up is a big issue for me.

In the discussion they say, “These results point to living with dogs as a strong risk factor for COVID-19 infection.” Their concluding statement was, “The results of this study demonstrate that living with dogs… have been the main routes of transmission of SARS-CoV-2 during the most restrictive period of confinement in Spain.”

Neither of those is true.

Pet ownership was not associated with increased risk of COVID-19. Their statistical analysis of pet ownership did not identify any risk. Walking a pet was a potential risk factor, not owning or living with a pet. There’s a long paragraph in the discussion talking about risk from dogs, despite the fact the paper didn’t actually look at that, and they did not find a risk from pet ownership.

So, what does this study tell us about pets and risk of COVID-19?

It’s hard to say… probably nothing.

This study raises some interesting questions but doesn’t provide many answers. It certainly doesn’t provide answers about risks associated with pets. A more rigourous peer review could have helped catch and address some of those issues.

The study does NOT show pet ownership was a risk factor for COVID-19.

  • If the pet walking risk factor is real, I suspect the critical factor is more “walking” than “pet.”

I’ll stick with the same messaging I’ve had for months about animals and COVID-19:

  • If you have or might have COVID-19, stay away from animals (human and non-human).
  • If your pets have been exposed to someone with COVID-19, keep them away from others (just like you would if you or your kids were exposed).
  • Relax.

I’ve spent a lot more talking about mink in the past few months than I ever thought I would. In regard to SARS-CoV-2 (the virus that causes COVID-19 in people), mink and ferrets (their close relatives) are a fascinating story, but I’ll try to be brief about it. Mink have become important because of the widespread outbreaks of SARS-CoV-2 on mink farms in some countries, and ferrets are important because they’re household pets and appear to be equally susceptible to the virus.  What we know about these two species within the mustelid family is quite different. We have good experimental data for ferrets and very little field data. For mink, it’s the opposite.

What’s the story with mink and SARS-CoV-2?

I think it’s fair to say this caught us off guard. At the start of the COVID-19 pandemic, no one was talking about risks to/from mink farms. Yet, mink are highly susceptible to the SARS-CoV-2 virus. There have been widespread outbreaks on mink farms in some countries, first in the Netherlands but now in several countries in Europe, as well as in the US. In the vast majority of cases, it is suspected that the mink were initially infected by a person, and then the virus spread further from animal-to-animal.  Some affected farms have had few health issues while others have reported considerable illness and increased mortality in their animals, which has led to widespread culling of mink in some countries to try to contain the spread of the virus.

There are a few additional concerns with these outbreaks beyond the health of the animals themselves. One is zoonotic transmission back to people, as apparent mink-to-human transmission has been reported in one Dutch study. Infection of feral cats on mink farms has also been identified, which raises concern about the cats (or escaped mink) potentially infecting wildlife in the surrounding area.  Work on this issue is ongoing.

So, mink can be infected, the virus is effectively spread between mink, mink can potentially infect people in contact them, and mink may be a source of exposure for other animals. All of those are concerning.

How about ferrets and SARS-CoV-2? Are they as susceptible as mink?

Whether ferrets are “as susceptible” as mink is hard to say; however, they are clearly susceptible to infection, can get sick, and can shed enough virus to infect other ferrets, as has been demonstrated in multiple experimental studies. Notably, ferrets can be infected with fairly low doses of SARS-CoV-2.

One thing that raised some concern and confusion was a report that ferrets could spread the virus “via the air.” While the study showed that ferrets were able to transmit the virus to other ferrets in cages 10 cm away, the results weren’r actually indicative of true airborne spread (a bit of a loaded term). Rather, it was likely droplet spread over a short distance. A more recent study raised a bit more concern, as it  reported transmission of the virus between ferrets over more than 1 metre. In this study, airflow was high and was directed from the infected to uninfected ferrets, so while the virus traveled at least 1 metre under those conditions, we have to be careful when assessing what that means. I think it supports the fact that this virus can move in the air for short distances, but a lot of factors influence how far it goes and the risks associated with aerosol transmission. We’re learning more and more than ventilation and environmental conditions are important for human-to-human transmission as well.

How sick can ferrets get from SARS-CoV-2?

At the start, I was expecting ferrets to be susceptible to severe disease because ferrets can also get quite sick, and sometimes die, after infection with the original SARS virus. The SARS-CoV-2 doesn’t seem quite as hard on them, but experimental data are variable. Some studies have reported infections with limited or no obvious signs of disease (Shi et al.Schlottau et al., Kim et al.)  However, at least one study reported more serious disease from SARS-CoV-2 in ferrets, sometimes requiring euthanasia. The difference in results might be related to the dose of virus, with higher doses used in the experimental study where more serious disease was observed.

If ferrets are susceptible to SARS-CoV-2, why aren’t there reports of infected pet ferrets?

Good question. That probably relates to limited testing. In our Canadian SARS-CoV-2 surveillance study, we’ve only been able to test one ferret. I haven’t seen much other surveillance data in this species. There’s one pre-print study looking at human-to-ferret transmission in a household where there were two infected people and 29 ferrets, but they didn’t find any evidence of transmission to ferrets. However, it’s hard to conclude much from a study of one household. Testing of the ferrets started 16 days after the onset of the first person’s illness and 13 days after the onset of the second person’s illness. It’s a challenge getting samples from the animals early in the disease of the people, so we probably under-estimate transmission with studies like this (ours included). The same study looked for antibodies in the ferrets too, but it was antibodies from oral swabs that were submitted for virus testing, and I’m not sure anyone knows how sensitive that technique is. So, there was no evidence of human-to-ferret transmission, but it was only one household and the testing had some significant limitations. Study of more ferrets in more households is needed. The lack of reports of infected ferrets may also be a function of there being fewer pet ferrets compared to dogs/cats, and correspondingly less testing for that reason as well.  Ferrets seem to be more susceptible than dogs and cats in experimental studies.

Can ferrets infect people with SARS-CoV-2?

We don’t know.  Given their susceptibility to the virus, the experimental study data and evidence of potential transmission of SARS-CoV-2 from mink to people, I think we have to assume that an infected ferret might pose some degree of risk to people as well. However, if a ferret is infected, it almost certainly got it from a human household contact, and that person poses much more risk to others in the household than the ferret does. The main risk is if the ferret leaves the household (e.g. to see a veterinarian) during the period when people in the household are infected, as it may take the virus along for the ride and could then potentially spread it to others.

What should be done with mink and ferrets?

  • Anyone with COVID-19 should absolutely not go near a mink farm (or anyone who works on a mink farm). That’s the big one.

The same general approach that we recommend for dogs and cats applies to ferrets:

  • If you have COVID-19, try to limit or avoid contact with your ferret.
  • If your ferret has been exposed to someone with COVID-19, keep it away from other people or animals.
  • If your ferret has been exposed to someone with COVID-19 and is sick, let your vet know.  Discuss what to do over the phone, at least initially, rather than showing up to the veterinary clinic with your ferret.

Next up for animal reviews: Horses

Image source: https://www.cbc.ca/news/canada/newfoundland-labrador/covid-outbreaks-mink-farms-canadian-breeders-prepare-1.5769815

Moving on from cats and dogs, let’s talk about one of our major livestock species, pigs.

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

  • Kind of, but not really. There are conflicting experimental data that show no or very little susceptibility to the virus.

Why did we talk a lot about pigs and SARS-CoV-2 initially?

At the start of the pandemic, we were worried about the potential for this virus to infect pigs because of their ace2 receptor, which is used by SARS-CoV-2 to invade pigs’ cells. If the virus can’t enter an animal’s cells, it can’t infect them. Different animals have slightly different ace2 receptors on their cells. The pig ace2 receptor is quite similar to the one people have,  suggesting there could be similar susceptibility to SARS-CoV-2. Looking at ace2 receptors has been interesting, but we’ve also seen the limitations of this method, with some purportedly low-risk species being susceptible and some purportedly high-risk species being resistant. Ace2 is only a part of the picture, so while it’s worth considering, it really doesn’t answer the question of whether there’s a concern with pigs.

Trying to grow the virus in a laboratory in cell lines from a particular animal species can provide some additional information on potential susceptibility. In one study, SARS-CoV-2 was grown in 2 of 3 pig cell types, but did not damage the cells. In another study, the virus was grown in pig cell lines and caused some cell damage.  These all raised concerns about the virus’ ability to infect pigs, but there are limitations to what in vitro studies can tell us. To get the real story, we need to look at real pigs.

So, forget about pig cells – are actual pigs susceptible to SARS-CoV-2?

In three separate studies (Shi et al.,  Schlottau et al., Meekins et al.), pigs were experimentally inoculated with SARS-CoV-2 and mixed with naive pigs. Nothing remarkable happened. None of the pigs got sick and all samples collected were negative for the virus. Antibodies against the virus weren’t found in any animal. All of these results indicated that the pigs were not infected, and there was a collective sigh of relief as it appeared that concerns about pigs were unnecessary.

In another study, pigs were exposed to the virus via the nose, trachea and injection. All the pigs stayed healthy and the virus wasn’t detected in any samples, but antibodies against the virus were found after pigs were injected with the virus. Exposure by injection doesn’t tell us much about natural infection, and the other results are consistent with no natural susceptibility.

However, leave it to Canadians to be disruptive – an experimental study conducted by the CFIA found slightly different results in pigs.  It didn’t raise major concerns, but it suggested things are not not quite as clearcut. In that study, 16 pigs were exposed to a higher dose of the virus than in previous studies.  Once again, nothing remarkable happened. Some developed mild discharge from the eyes for a few days. One had a slight cough and was mildly depressed for a few days. However, low levels of virus were detected from respiratory samples by PCR from two of the sixteen pigs, although live virus could not be isolated. The virus was also isolated from a lymph node of one pig, and antibodies were detected in the blood of two pigs, supporting some level of true infection. Two pigs were added to the exposed pigs 10 days after inoculation, and they did not get infected. Overall, 5 of the 16 pigs (~30%) had some evidence of mild infection. So, this study showed some degree of susceptibility, but with infrequent mild disease and no evidence that pigs are infected to the degree that they would be able to pass on the virus to other animals or people.

Have any pigs outside of the lab been infected with SARS-CoV-2?

There are no reports of infected pigs to date, but I’m also not aware of any testing of pigs on farms. Field data are always useful because experimental studies don’t tell the full story of what happens in the “real world.” Some data about pigs exposed to infected farmers would be useful to have, to round out the story, but it would probably be low yield research since it’s quite unlikely anything would be found.

What should be done with pigs?

The same general recommendations apply as for other animal species. While the risks are low, we can’t say they are zero. If we keep infected people away from animals, we don’t need to worry about human-to-animal transmission, and any subsequent animal health or animal-to-human transmission issues. While the odds of someone infecting a pig are very low, it’s best to avoid exposing pigs to infected people whenever possible. That may not be an option on small farms run by one person or a family, but the more we can keep infected people away from animals, the better.  In short, better to be safe than sorry.

Next up for animal reviews: probably mustelids (mink and ferrets).

Image source: https://theconversation.com/could-chinas-strategic-pork-reserve-be-a-model-for-the-us-139949

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

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

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

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

How often do cats get infected?

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

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

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

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

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

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

Figure from Halfmann et al. N Engl J Med 2020 (https://www.nejm.org/doi/full/10.1056/nejmc2013400).

Do cats get sick from SARS-CoV-2?

They can, but most often if appears they don’t. Experimentally, clinical signs in cats have been pretty unremarkable. Most infected cats have been reported to be healthy, but it’s not always the case. There are reports of sick cats, including a pre-print describing what appeared to be a fatal infection with SARS-CoV-2 in a cat from the UK. More work needs to be done in this area. I get lots of anecdotal reports about sick cats that have been exposed to the virus, and I suspect many of them really are due to to SARS-CoV-2. When an otherwise healthy adult indoor cat with no contact with other cats develops signs of upper respiratory tract infection around the time its owner had COVID-19, it’s pretty suggestive since there aren’t many other probable causes for the cat’s illness.

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

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

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

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

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

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

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

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

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

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

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

  • Worry, no.  But we should pay attention to it.
  • There’s a cat health risk, and we want to avoid that by reducing contact of infected people with cats. It’s probably most important with older cats and cats with underlying diseases that may make them more susceptible to severe disease.
  • The risk of cats spreading the virus in a household is limited, but can’t be ignored. When you have someone isolating from the rest of the household (e.g. living in the basement), we want to make sure pets like cats are considered, so they’re not tracking the virus from the infected person to the rest of the family. It’s easy to see how someone might do a great job staying away from other people, but not think about the cat that runs back and forth between them and the rest of the family.
  • We also don’t want cats tracking the virus out of the household and exposing other cats or wildlife. The odds of this causing a big problem or creating a wildlife reservoir are very low, but not zero. A little prudence makes sense.

What should be done with cats?

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

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

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

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

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

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

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

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

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

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

As things continue to gradually open up (more gradually in some areas than others), myriad questions of “can we do…” or “how do we do…” come up. One that I’m getting increasingly is about pet visitation or pet therapy programs. These programs can be very valuable to patients in hospitals and residents in long-term care homes and other settings; however, they always come with some degree of risk from interaction with the animal, and the handler.

Currently, most places have these kinds of visits on hold, which is reasonable in this phase of the COVID-19 pandemic. Fewer people coming in means fewer potential sources of infection. However, some programs are restarting, so thought needs to go into doing this safely.

What are the risks?

While we often try to get people to think about the various pathogens that pets (particular dogs in this case) can leave behind or pick up in these settings, right now the main risk with pet visitation programs is SARS-CoV-2 from the human handlers. This virus likes people a lot better than dogs – the COVID-19 pandemic is being propagated almost exclusively through human-to-human transmission. While there is some potential for dogs to be infected or for them to act as fomites (i.e. tracking virus around on their haircoats), the far greater susceptibility of people means that dogs are probably the lower-risk component of visitation teams.

Routine prevention measures:

  • Standard pet therapy program measures, as outlined in the 2015 SHEA guidelines on animals in healthcare facilities, are still key, with particular emphasis on making sure:
  • Handlers self-screen and are healthy before entering a facility.
  • Everyone involved pays close attention to hand hygiene. Patients should use hand sanitizer before and after animal contact. Handlers should use hand sanitizer before and after every visitation, regardless of whether they touched the person or any part of the person’s environment.

Added COVID-19 measures:

  • Ensure the patient has no signs of COVID-19 and is not being isolated. (Yes, that sounds like common sense, but you’d be amazed how often things like that get missed.)
  • Ensure the handler and animal have not had exposure to an infected person in the past 14 days.
  • Have everyone involved (that is to say the people, not the dogs) wear a mask.
  • Remember the 3 C’s to avoid: closed spaces, crowded spaces, close contact. (I also talk about a fourth C, “continuous,” with regard to time.)
  • Limit person-to-person contact. Handlers should stay as far back from patients as possible.
  • Have the visit outside in an open space, when possible.
  • Keep the visits relatively short – 15 minutes is typically used as the time when risk goes up.
  • Have handlers use a tracking app, like Canada’s COVID Alert app. Anyone involved with pet therapy in a region with an app like this should use it. It might help pick up exposure in a facility, but more importantly, it helps identify other community exposures, so exposed people know when they’ve been exposed and can suspend their visitation activities.
  • Stick to one facility. Some visitation teams typically visit multiple facilities. That’s probably best avoided, especially now. Teams should focus on one facility, to reduce the risk of cross-transmission.
  • Consider limiting visits to one person per team per day, especially as programs restart and while there’s less risk tolerance. Limiting a visit to a single patient each time reduces the risk of encountering or spreading the virus between patients.

How to respond to an outbreak or exposure

  • The key here is being able to identify exposed individuals quickly and easily. One recommendation we’ve had since our very first guidelines on pet therapy is keeping track of who gets visited when, and by whom. This has been very hard to get implemented, but it’s especially critical now. Tracking can be as simple as having handlers write down the date and the rooms/patients they visited, and leave the log with the facility as they depart.
  • An additional component of this tracking should be recording the duration of the visit, since the time spent with the infected person plays a role in determining whether exposure was likely.  With basic practices like hand hygiene, mask use, and distancing, it’s unlikely a handler would be considered exposed if they visited an infected patient for a short time. However, some visits could end up stretching beyond that typical 15 minute limit, and some could end up involving direct contact between the handler and patient. If the handler fits the criteria for exposure, the response would depend on the local public health directives for exposed people (e.g. self-monitoring vs isolation). However, given the severe implications of COVID-19 in most populations where pet therapy is used, handlers with any plausible degree of exposure should suspend visitation for 14 days. If a dog had direct contact with an infected person, then I’d isolate the dog for 14 days as well, to be safe.
  • Handlers also need to have an established means of communication with the facility and must be able to report illness. If a handler develops COVID-19 (probably acquired in the community, not during visitation), the person needs to be able to contact the facility as soon as possible, so they can then determine if any of the patients/residents might have been exposed, based on the timing of illness and visitation.

None of this is rocket science, or expensive. It’s use of basic infection control practices and good communication. Unfortunately, those are often lacking.

The risk from a well-run pet visitation program following these precautions is low, but not zero. There’s never going to be risk-free pet visitation. The key is limiting the risk as much as possible, while maximizing the benefits. The implications of tracking SARS-CoV-2 to, within or between facilities (especially long-term care homes) can be huge, so serious thought needs to go into when and how to restart these programs.

I’ve been slow posting in the past few days, so here are a few quick recaps from the animal/COVID-19 world.

Higher quality debunking of crappy dog-SARS-CoV-2 paper

Back in April, a paper (Xia 2020) was released that suggested dogs could be the source of SARS-CoV-2.  Most of us considered it crap at the time (read more about it in our previous post), and most people moved on pretty quickly, but it still left some fear and poor messaging in its wake. Now, a proper dismissal of this paper (in the same journal) has been published.  I won’t get into the details, but it basically says “Everything that was written in that paper… yeah, not so much.”

More formally, here’s what they concluded: “In summary, the proposition of Xia (2020) that dogs are a likely pre-human host for SARS-CoV-2 is not justified by available evidence. Xia (2020) did not demonstrate that the low CpG frequency in the SARS- CoV-2 genome was driven by a unique selective environment in dog digestive tracts. The SARS-CoV-2 is also less virulent than other human betacoronaviruses (SARS-CoV-1 and MERS-CoV), contradicting his assertion that CpG-deficient viruses are more virulent. Furthermore, closely related betacoronaviruses from bats and pangolins have CpG-deficiencies similar to SARS-CoV-2. Dogs are not more plausible than most other potential host species, and based on current data, far less plausible than bats or pangolins. Still, we are missing ~20-70 years of the recent evolutionary history of the lineage leading to SARS-CoV-2, and we must broadly survey a wide range of wild and domestic species to uncover the origin of SARS-like coronaviruses.

More SARS-CoV-2 in mink

Mink are really susceptible to this virus, and human-to-mink transmission seems to occur quite easy.  In the Netherlands, SARS-CoV-2 has infected mink on at least 24 farms, with widespread disease in mink and even some plausible mink-to-human transmission. There was a plan to end the mink industry in the Netherlands by 2024, and this crisis appears to be speeding things up as mink on affected farms are culled.

In Denmark, multiple farms have also been affected. They’re taking a different approach there, now choosing not to cull affected mink farms, but putting strict measures in place to control any outbreaks and monitoring closely for more.

In Canada, so far, so good. Since infection with SARS-CoV-2 in mink was first reported, there’s been an emphasis on biosecurity measures to avoid infecting mink, and relatively low disease rates in people in Canada (at the moment) mean the risk is currently fairly low. However, it’s still a concern. An additional worry is mink farms becoming a source the virus that could spread to wildlife. Feral cats have been infected on at least one affected mink farm in the Netherlands. Spread to wild mink (which are present throughout Canada and the US) is an even bigger concern given how susceptible this species is. We don’t want to create a wildlife reservoir of SARS-CoV-2, either through spread from farms to wild animals or from escape of farmed mink.

Human-to-pets transmission is still a thing

Reports of cases of human-to-pet transmission of SARS-CoV-2 continue to trickle in, and probably represent a small fraction of cases that actually occur. I’m sticking to my promise not to report each new case if there’s not really anything new about it. Infections in pets are still uncommonly reported, but a lot of cases are likely not detected because there’s limited testing. The animal and public health risks of these cases are probably very limited regardless, especially in places where there’s rampant human-to-human transmission. But, we’d still like to contain exposed animals to prevent them from playing any relevant role.

Still no signs of infection in livestock

So far, so good on the livestock front. Fortunately, major livestock species do not seem to be overly (or at all) susceptible to SARS-CoV-2. We still need to pay attention to this though, and I think the message “If you might be infected, stay away from animals” remains important, regardless of the species. However, the risk of significant issues from livestock seems pretty limited right now.

Still looking for the animal origin of SARS-CoV-2

This is still a huge question. It seems a little late, but the World Health Organization has sent a team to China to further investigate the animal origin of the virus. Kind of.  They’ve sent two people there to discuss a larger investigation.  It might be a challenge to find the animal source but we still have to try. We need to know if this virus is still lurking somewhere in the wild, and where. We also need to understand how and why this outbreak happened, to help prevent it from happening again (with this virus or one of many other potentially nasty bugs that are no doubt also lurking in the wild).

The USDA has issued announced the first confirmed case of SARS-CoV-2 infection in dog in the US. The affected dog was a German Shepherd from New York state, and unsurprisingly its owner had COVID-19. Interestingly, this dog did have signs of respiratory disease,  a finding that hasn’t been reported in dogs to date. It tested positive for the virus by PCR, and also had antibodies against SARS-CoV-2. Another dog in the household was healthy, but also had antibodies, indicating it had been infected too.

This case is noteworthy for a couple of reasons:

  • The positive dog was sick, though that still doesn’t necessarily mean the illness was due to the infection with SARS-CoV-2. The dog could have had other underlying disease due to some other cause.  Hopefully more information will come to clarify that. However, if this dog was sick because of SARS-CoV-2 infection, it would run contrary to the evidence to date that indicates dogs can be infected but don’t (typically) get sick.
  • Both dogs in the household were infected, even though only one got sick and tested positive by PCR.  The assumption has been that human-to-dog transmission is uncommon, and that still might be the case, but finding transmission to multiple dogs in a household is interesting.

Overall, it doesn’t really change our main talking points, but it highlights the need for more study.

A few quick updates on some recent SARS-CoV-2-related stories.

North Carolina dog: Positive result not confirmed

This case, a pug in North Carolina that had an oral swab that supposedly tested positive for SARS-CoV-2 as part of a Duke University household surveillance study, was reported a few weeks ago.  It was strange that there was no confirmation of the test result since then. Now we know why.  It appears the original test result was actually “inconclusive” (i.e. not strong enough to be truly considered positive). Follow up PCR testing was negative. That in itself doesn’t mean the dog wasn’t infected, since it could have been a short term infection that wasn’t sampled during peak shedding. However, no antibodies were detected in the dog. That indicates the immune system didn’t recognize the presence of the virus. It’s not completely definitive, but supports this not being a true infection.  Perhaps transient contamination of the dog’s mouth with virus from its infected owners could have caused the original inconclusive test result.

Hydroxychloroquine/chloroquine study debate

This topic is a bit outside the animal health-related area, but is still interesting (and relates to some of my recent Twitter ranting about the state of scientific publication). The high profile Lancet paper that reported increased deaths associated with hydoxychloroquine use in COVID-19 patients, and led to WHO suspending that arm of its study, has been challenged because of numerous concerns about data and data availability. It doesn’t mean the results are necessarily wrong, but questions about the data mean that things need to be clarified, which the authors have apparently been reluctant to do so far. An open  letter to the journal outlines various problems with the report and has a large and reputable list of signatories.

Tiger SARS-CoV-2 whole genome sequencing

There’s not really anything notable here in the big picture, but anyone with an inclination towards whole genome sequencing data might be interested in the sequence results from the virus isolated from one of the Bronx Zoo tigers.

SARS-CoV-2 in a cat in Russia

Just one more report of a cat with SARS-CoV-2 infection, presumably from its infected owner. Not surprising.