What the story with SARS-CoV-2 in horses?

This one’s easy to answer: we have no clue.

There’s been almost no investigation or research regarding this virus in horses. Horses often get left out in situations like this because they’re livestock, but not (typically) food animals, and investigation of livestock tends to focus on food animal species. Horses are often more akin to companion animals, but a smaller number of people own or have contact with horses compared to household pets. Experimental studies aren’t commonly undertaken because trials in horses are generally very expensive due to their size and upkeep.

So, what do we actually know about SARS-CoV-2 and horses?

Not much.  As I’ve mentioned in several other posts, there are studies that have looked at the composition of the ace2 receptor in different animal species. Ace2 is the part of the SARS-CoV-2 virus that it uses to attach to (and ultimately invade) the body’s cells. If the virus can’t attach to cells, it can’t infect them. The structure of this receptor varies between species, and that accounts (in part) for differences in species susceptibility. Not all studies have included horse, but one ace2 receptor study suggested that horses might be susceptible to SARS-CoV-2 – possibly even more susceptible than a few species we already know are quite susceptible, such as cats and ferrets. Another study based on ace2 receptor analysis ranked the likely susceptibility of horses to SARS-CoV-2 to be equivalent to cats (specifically domestic cats and lions, both of which we know can be infected) and camels (which we also know nothing about, beyond their being a host for another zoonotic coronavirus, Middle Eastern Respiratory Syndrome Coronavirus (MERS-CoV)).

We have to take such predictive studies with a (big) grain of salt, because the real world situation hasn’t always mirrored what was predicted.  Those studies basically tell us we should pay more attention to horses and see if there’s a problem, not that a problem is necessarily likely.

Have any horses been tested for SARS-CoV-2?

Maybe.  I haven’t tested any, and I haven’t heard of anyone who has, but it’s possible someone’s looked but not found the virus, or antibodies against it, in horses. If there was a positive, I assume it would have been reported somehow somewhere. I suspect few, if any, horses have been tested.

What should be done with horses?

Some surveillance would be good. Testing horses that have been exposed to infected people would be interesting, and tell us more about interspecies spread of the virus. There have been outbreaks of COVID-19 in grooms in racing stables, a human population that’s probably very high risk for infection, and for working while sick. They usually have close and frequent contact with horses, so testing horses from stables with outbreaks in the grooms or other staff would be a good start.

However, as for all animal species, the most important thing to do is stay away from them if you have COVID-19 or if you’ve had high-risk exposure to someone with COVID-19. It’s better to prevent a problem than have to figure out how to deal with it after it happens. If we reduce the number of infected people who have contact with horses, we reduce any potential problems.

Image source: https://dailymemphian.com/article/15734/germantown-horse-mask-ordinance

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

In our ongoing seroprevalence (antibody) testing, we’ve seen that human-to-pet transmission of SARS-CoV-2 is probably not uncommon. However, we hadn’t yet found a pet that was positive for the virus on swabs in Canada . (Antibody testing tells us if the subject was previously infected, whereas testing swabs by PCR tells us if the virus is there at the time.) The reason for that is likely the short period of time that most infected animals shed the virus, and the logistics of sampling the animal at just the right time: someone has to get infected, then get tested, then get the test result, then call us, then we have to arrange to get a sample from their pet. We’ve assumed that we’re typically getting there too late to catch the pets when they’re shedding the virus.

Anyway, we’ve (finally) identified our first SARS-CoV-2 PCR-positive dog in Canada. The timing of the sample in this case probably accounts for that, since we got into the household a bit quicker than average.

Here’s the story:

The dog is an adult dog in the Niagara region of Ontario. Four of six people in the household had COVID-19, and we detected the virus from the dog’s rectal swab. We had a borderline test result on the dog’s throat swab too, although it was a low enough level that we can’t consider it a true positive.

The other dog in the household also had a borderline result on its rectal swab. My guess is it was truly infected but at a lower level or at the start or end of infection. We’ll follow up on both dogs with antibody testing in a few weeks.  I’ll be surprised if both aren’t positive for antibodies.

Both dogs were healthy at the time of sampling and hadn’t had any obvious signs of disease. 

What does this mean to the family members?

  • Nothing (besides a unique story if they want to talk about it). The people in the household were all infected, and that was almost certainly human-to-human transmission. The dog(s) were infected by the owners and at that point didn’t pose any risk to the already-infected people.

What about other risks?

  • The potential risk from pets is if they have contact with other people or animals outside the household, such as going to parks, kennels or veterinary clinics. We don’t know if dogs often shed enough virus to be infectious to others. The Ct result (the number of PCR cycles required for the test to detect the virus) was well under the cutoff in this case, so it was clearly positive, but looking at some human data, a Ct in the same range (from nasal swabs, so maybe not a perfect comparison) was associated with a low likelihood of culturing the virus from the sample, and therefore the risk of infectivity is likely also low.
  • We’ve been going on the assumption that dogs are low risk for being infectious, and I don’t think this changes anything. However, we certainly can’t say there’s no risk from contact with an infected dog.
  • There’s also a plausible risk of transmitting virus to neighbours through the fence (something we’ve seen with canine influenza and parainfluenza). That’s why our messaging has been to consider pets part of the household in terms of COVID-19 precautions.  If people are being isolated, do the same with pets. It doesn’t matter if a dog or cat is infected if they don’t encounter anyone new.

So, from a research standpoint, we found it interesting, but it doesn’t change our messaging or mean there’s any more risk. This was the first confirmed positive for us, but it was certainly not actually the first positive dog in Canada. Lots of dogs have probably been infected before now and more will follow. We’re not testing every dog, and there is no need to do so. We don’t recommend people with COVID-19 get their pets tested outside of organized surveillance studies.

Don’t be afraid of animals in terms of COVID-19, but use common sense.

If you’re infected with COVID-19, limit your contact with anything with a pulse (not just people).

If your household is isolating because of COVID-19 exposure, make sure it includes the whole household.  (If you wouldn’t lick your neighbour through the fence, don’t let your dog do the same to the neighbour’s dog… or kid.)

It was surprising to see what things sold out early in the pandemic: toilet paper, yeast, exercise equipment…. and chicken coops.

Yes, there was a run on chicken coops.

It seems like a lot of people decided to get backyard chickens in response to all the COVID-19 restrictions.

Any human-to-animal contact has a mixture of risks and benefits (just like any human-to-human contact). Mental, social and emotional aspects of pet (including backyard chicken) contact are very important and can’t be ignored, even though they’re harder to measure than things like disease.

However, disease risk is also an important consideration, so we need to figure out how to reduce risks while maximizing the benefits of pet contact. For chickens, the big risk is Salmonella. The risk of chicken-to-human transmission is very well established, and there are outbreaks every year from activities that bring people and chickens together.

The US CDC has been reporting on a large ongoing multistate outbreak of salmonellosis linked to backyard poultry. The latest report adds 408 people to the outbreak list from the last report on July 29, 2020.

As of September 22, a total of 1346 infections have been identified.  The true number is presumably much higher, since reported infections are likely a minority of the cases that actually occur.

  • Cases have been identified in 49 states, and there are 16 separate multi-state outbreaks.
  • A third of patients for whom details were available ended up hospitalized (that’s quite high).
  • Some Salmonella strains involved were resistant to certain antibiotics, but the strains causing disease were fortunately fairly susceptible overall.
  • Some environmental testing was performed, and the outbreak strains were found in backyards and coops.
  • One death has been reported.
  • 23% of affected people were children less than 5 years of age. Standard recommendations say that this age group should be kept away from high risk pets, including poultry.

This isn’t a classical point source outbreak, where one infected site supplied infected birds to multiple distributors/sellers across a wide geographic area. Rather, multiple sources of infected birds have been identified, which reflects the fact that Salmonella is an ever-present risk with poultry. We wouldn’t expect a point source for this disease, we’d expect disease to be distributed across the broader backyard poultry population (which is what we’re seeing).

Good risk-reduction recommendations are available from groups such as the Public Health Ontario (Reducing health risks associated with backyard chickens) and US CDC (Healthy Families and Flocks).

Some things to think about if you’re considering getting backyard chickens:

  • Are there high-risk individuals in your household, or who visit you frequently?  This includes kids less than 5 years of age, adults over 65 years of age, pregnant women and those with compromised immune systems.
  • Do you have close neighbours who might be impacted by the presence of your chickens (and are any of them high risk)?
  • Can you set up your coop such that there’s no runoff to neighbouring properties or kid play areas?
  • Are you ready to put the time, effort and cost into doing it right?
  • Do you think you’ll enjoy them, or are you just looking something different to do?  (If the latter, how about considering something else that might carry less risk, or risks you can better control?)
  • Is it legal to have backyard chickens where you live?

Backyard chickens aren’t inherently bad. There’s risk and there’s reward. We’re a low risk household and I wouldn’t mind having some myself, but there are two main barriers in our case: One is coyotes and foxes, since we are over-run with them (and they decimated my rare breed sheep flock). The other is I’d probably have to sneak them in without telling Heather and then live with the repercussions… probably not a good plan.

We’ll have some more research info about backyard chickens here soon.

Image from https://ottawacitizen.com/news/local-news/chickens-are-the-new-toilet-paper-people-flock-to-backyard-chickens-gardens-amidst-pandemic

Round two of my COVID-19 in animals summaries: Dogs

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

Yes, but not very… maybe.  It depends what you mean by “susceptible.”

Nice and clear, eh?

There’s a difference between being infected and getting sick. Dogs can be infected by the SARS-CoV-2 virus (which is the virus that causes COVID-19 in people), but they don’t seem to be as susceptible as cats, and it’s debatable whether dogs get sick (more on that below).

Infection in dogs has been shown in a few different experimental studies, and through identification of infected pet dogs that were exposed to people with COVID-19.  In one small study, SARS-CoV-2 was detected by PCR in experimentally infected dogs, but the researchers could not isolate any “live” virus from the animals, suggesting the virus was present at a low level and the dogs were probably not infectious. The dogs remained healthy, but some developed antibodies against SARS-CoV-2, supporting the idea that they were truly infected and their immune systems responded accordingly. They did not pass to virus to other dogs with which they were co-housed. In the end, some or all of the exposed dogs got infected, but none got sick and they didn’t infect any other dogs.

Another experimental study yielded similar results, in that dogs were infected and mounted an antibody response, but didn’t get sick and were probably not infectious.

How often do dogs get infected with SARS-CoV-2?

We don’t know. Surveillance has been limited, so the scope of human-to-dog transmission isn’t clear. In Hong Kong, early in the pandemic, they quarantined pets of COVID-19 patients who could not care for them (e.g. owner lived alone and had to be hospitalized), and the pets were all tested at the quarantine facility. Hong Kong authorities identified SARS-CoV-2 in nasal, oral and/or rectal swabs from  2/15 dogs that were quarantined following exposure to their infected owners. Neither of the positive dogs had signs of infection, both developed antibodies to the virus, and gene sequencing of showed that the virus from the dogs was the same as that of their respective owners. Of particular note was they were able to isolate live virus from one of the dogs, which suggests the dog could have been infectious to others, at least briefly.

Additional data has been limited, in large part because it’s a logistical challenge to sample dogs in households with infected people during their isolation period. One small study in Spain didn’t detect SARS-CoV-2 in any of the 12 exposed dogs tested.  An investigation of pets from a cluster of infected and exposed veterinary students in France also failed to identify the virus in 12 other dogs, although it wasn’t clear how many of the dogs were actually exposed to an infected person.  A study from Italy reported no detection of the virus in 64 dogs from households with previous human COVID-19 infections, including 3 dogs that had respiratory disease.

Our Canadian study didn’t initially find the SARS-CoV-2 virus in any of 18 dogs (more to come on the expanded version).

There are still numerous reports of individual infected dogs from different countries. In the US, approximately 23 dogs have tested positive for the virus so far. That’s not a lot in the context of the dog population, but remember that not many dogs have been tested. Furthermore, testing has focused on looking for the virus by PCR. That will underestimate infections, because based on what we’ve seen so far there’s only a short window of time when you can get a positive PCR result from an infected dog. Dogs seem to only shed the virus for a few days after infection, so sampling dogs in infected households (after the people are no longer infectious and it’s safe to do so) runs the risk of a lot of false negatives simply based on the timing of sampling.

Studies looking at antibodies in dogs (and other animals) will be more informative, if the tests are accurate.  Antibodies are an indicator of past infection, and they tend to hang around significantly longer than the virus itself.  So unlike PCR-based surveillance, we don’t have to get into the household right away during the time of human illness – we can test dogs later to see if they were infected.

Not a lot has been reported yet on antibody testing (also called serology) in dogs. A study in Italy found antibodies to SARS-CoV-2 in 3.4% of dogs; 6/47 (14%) dogs from known-positive households, 1/7 (14%) dogs from households of suspected cases, and 2/133 (1.5%) dogs from other households. Whether the 1.5% prevalence in other dogs is from dogs that were infected by owners that were never diagnosed, or it represents the false positive rate of the test isn’t clear. A French study found antibodies in 2/13 (15%) exposed dogs and 0/22 dogs from households with no known cases of COVID-19.  Those results are similar to our preliminary 20% (2/10) prevalence in dogs from positive households in Canada so far. Obviously, we need to test a lot more dogs to get better estimates, and the study is ongoing.

Do dogs get sick from SARS-CoV-2?

That’s still unclear. I’d say that evidence is still far from convincing. There are a few poorly documented reports of sick dogs, but the question largely unanswered in those cases is “were they sick from infection with SARS-CoV-2, or were they sick with something else and coindicdentally happened to have been infected by this virus at the same time?” My guess is that disease is rare in dogs, but not impossible, especially in animals that may have other comorbidities that make them more prone to severe disease from many other pathogens as well.

Can dogs infect other animals or people with SARS-CoV-2?

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

Overall, I’d say the risk of transmission of SARS-CoV-2 from dogs is very low. I don’t think we can say it’s zero, but I think it’s unlikely that a dog would pose a realistic risk.  That said, why chance it? If a dog is infected or at risk of being infected (i.e. living in a household with an infected person), it should be kept away from other people and pets. Dogs interact nose-to-nose and nose-to-bum a lot, and we have a lot of contact with their faces. We’ve seen transmission of other respiratory viruses between neighbouring dogs through fence-line contact, so keeping exposed dogs under control and away from others is reasonable and practical.

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

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

Could dogs be a bridge to transmit SARS-CoV-2 to wildlife?

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

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

Worry, no. But, we should pay attention.

What should be done with dogs?

Do the same things recommended for cats:

  • If you are infected, try to stay away from animals – all animals, human and otherwise.
  • If your dog has been exposed, keep it inside and away from others.

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


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

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

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

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

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

How often do cats get infected?

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

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

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

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

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

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

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

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

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

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

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

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

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

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

From where did Alaskapox come?

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Image below from Amoroso et al. Clin Infect Dis 2020

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

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

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

Why we need to boost community knowledge in rabies endemic countries

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

This is just one example of barriers that are present.

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

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

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

Various educational opportunities are highlighted by this case.

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

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

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