I’ll start this off with “don’t freak out, overhype this, or be paranoid about your dog.”  (I’ll probably end with that too).

A recent report in Lancet (Seang et al. 2022) describes a pretty solid case of suspected monkeypox virus (MPXV) transmission from people to a dog. The dog, an otherwise healthy Italian greyhound, had close contact with two people in the household who were infected with MPX, including sleeping in their bed. Twelve days after the signs of MPX started in the  owners, the dog developed some mucocutaneous lesions (where skin meets mucous membranes, such as around the lips) as well as some pustules on the abdomen, and an ulcer of the anus.  Samples from the skin, mouth and anus were collected and were PCR positive for MPXV.  This means genetic material from the virus was present, not necessarily that the dog was infectious to others, though it’s pretty suggestive that the dog could have posed some risk (more on that below). Not surprisingly, gene sequencing of the virus from one of the owners and dog showed they had the same virus strain.

Is this surprising?

Yes and no. We’ve been saying from the start (as with SARS-CoV-2) that we need to assume that a virus can infect a range of speices until we know that it can’t. As I’ve discussed before, we have very little understanding of what species MPXV can infect. As with SARS-CoV-2, some groups have stuck with the line “we have no evidence that dogs can be infected” without acknowledging we have actually have no clear evidence either way. It’s important not to over-react, but it’s also important to be clear, honest and not dismissive of the potential risks.

Does this mean the MPX virus has changed?

Probably not. I haven’t seen any earlier studies that looked at susceptibility of dogs to MPXV, nor any surveillance of dogs in areas where the virus is endemic. It’s possible that some infection of dogs has happened under the radar at a low level in the past.

Does this mean dogs pose a risk for transmission of MPX to people or other animals?

That’s the big question. The dog in this report had PCR-positive samples from its skin lesions, mouth and anus. As we know from SARS-CoV-2, PCR-positivity doesn’t necessarily mean someone is infectious, it just means bits of genetic material from the virus are present. However, I suspect there is some risk here, as PCR-positive skin lesions in particular would seem to me to be a potential source of infectious virus (as they are the primary source of virus in infected people as well).

What do we do now?

Basically the same as we were recommending before, when we were concerned about the potential for infection in dogs and other pets but didn’t yet have the evidence.

If you have monkeypox or have been exposed to monkeypox, limit your contact with other individuals, both human and animal. This includes trying to prevent any direct contact, as well as reducing time spent in close proximity (because of potential aerosol spread) and contact with potentially contaminated items (e.g. sheets, towels, furniture).

Should someone with monkeypox get rid of their pet?

No. Consideration could be given to temporarily re-homing the pet until the person recovers, but that would only be reasonable if the pet hasn’t already been exposed to the person. Otherwise, it creates a potential transmission situation if the pet carries the virus to a new household. As with COVID-19, it’s probably best to keep the pet in the household and let the pet and owner(s) get through the situation together, in isolation.

In this case report, the owners reported being careful to prevent contact between their dog and other animals or people after they themselves developed signs of MPX. That’s good, as it helps prevent spread of the virus outside the household.  Given the time frame (the dog’s signs started 12 days after the owners’ signs), the dog was probably infected very early on in  the process when we consider the likely incubation period of such a virus in dogs.  It’s possible the dog was infected before the owners realized they were infected, or they didn’t (or couldn’t) isolate the dog sufficiently from themselves to prevent exposure.

Should someone be worried about getting monkeypox from their pet?

No. This is pretty much the same discussion as we had with SARS-CoV-2. Most of the risk is to, rather than from, the pet. If a pet has MPX, it likely got it from its owner. So, pets are unlikely to be the primary source of MPX in a household. The transmission risks are probably greatest if the pet is infected and then encounters people outside the household while it has skin lesions. That’s hopefully going to be rare, but probably of greatest concern for veterinarians.

Should I stay away from dog parks? I don’t know who’s going to be there.

That’s overkill. No, we can never guarantee any random dog doesn’t have MPX.  But really we can never guarantee much in life, and the risk posed by random, short term, outdoor contacts at a dog park are presumably exceptionally low (although contact with random dogs at dog parks does carry other infectious disease risks of course…).

What if an animal exposed to MPX needs veterinary care?

Stay tuned. We’ll have more details about recommendations for that ASAP.  The US CDC has posted some of their recommendations for veterinarians and animal health officials (but this is not necessarily the same process that will be used in other jurisdictions).

Bottom line?

Finding MPX in a dog in a household with close contact with two owners who have MPX isn’t overly surprising. It’s a bit concerning and something we definitely need to investigate more, but nothing that should cause panic.

Alberta Health Services is reporting a cluster of Salmonella infections linked to pet reptiles. In many ways, this isn’t really remarkable (unless you’re one of the people who’s infected). Reptile contact is a very well-known risk factor for acquiring Salmonella, especially in kids.

So far, 12 infections have been reported. Reported cases are always going to be an under-estimate of actual cases… perhaps by a factor of 5-10 (or greater), so more infected people are presumably out there.

There’s no link to any specific event, pet store or other common source. Cases are from homes with snakes, and infection has been linked to both snakes and feeder rodents.

  • Feeder rodents are rodents that are purchased as snake food. They’re often sold frozen, and have been the source of large Salmonella outbreaks in the past. If the link in this outbreak is to both snakes and feeder rodents, feeder rodents are presumably the root cause, since feeding snakes infected rodents can lead to infection of the snakes, and people can be infected from handling the snake or the rodent.

A big concern here is the scope of the problem. Feeder rodent-associated outbreaks can be large and widespread if the supplier is a big one that sells lots of product. Presumably the source is being investigated and hopefully addressed as best as possible.  It can be very difficult to control Salmonella in feeder rodent production facilities due to many factors.

Regardless, this is yet another reminder for reptile owners and handlers (and others) about some important basic preventive measures when it comes to Salmonella:

  • High risk people (kids less than 5 years of age, elderly individuals, pregnant women and immunocompromised individuals) should avoid reptile contact.  That also means reptiles shouldn’t be in the house, since indirect exposure to Salmonella in these situations is common.
  • Feeder rodents should be handled like you’d handle raw meat for human consumption – assume they’re contaminated, avoid cross-contamination with human food or food prep surfaces, and handle them with care.
  • Assume all reptiles are shedding Salmonella in their feces and that their enclosures are contaminated.
  • Wash your hands after contact with reptiles, feeder rodents, reptile enclosures, or anything within their enclosures.
  • If you get sick, make sure your physician knows you have contact (direct or indirect) with reptiles.

People can get pretty fired up when I talk about raw diets for pets. I’ll start off with my personal bias: I’d rather not see pets fed raw meat and raw animal-based products (e.g. pig ears and various bits-o-cow you can find in pet stores). There are clear risks to pets and owners from raw diets, including infectious and non-infectious issues. I’ll stay in my lane and focus on the infectious disease topics here.

We, and others, have shown that pets fed raw diets have high rates of shedding of certain bacteria that can cause disease.  I’ve been involved in various investigations of disease in dogs and cats (and some in owners) linked to raw diets for pets. At the same time, I’m a realist and recognize that the risk isn’t overwhelming for most people and pets, and not everyone is going to change their pet’s diet as a result of said risk.

So, I approach raw diets from the standpoint of “I’d rather not see them used, and there are almost always acceptable, lower risk commercial cooked diets available” but at the same time “The risk is probably low for most dogs and owners, but some situations are clearly higher risk.” I’d rather spend my energy focusing on situations where I think it’s a really bad idea, and try to give some guidance to people that insist on doing it. That way I can still engage people, rather than push them away with a more dogmatic approach.  That’s why we created a factsheet for pet owners about raw diets (to be honest it needs an update, but it’s still useful as many of the risks themselves haven’t changed… but more on that below).

We have to keep our eye on this issue and be alert for new information that changes the story in any direction.  Initial work on raw diets focused on Salmonella, and that’s still an issue.  However, in the past few years, my bigger concern has been antibiotic-resistant bacteria like E. coli. Dogs fed raw diets have much higher rates of shedding of multidrug-resistant Gram negative bacteria like E. coli in feces. Eating a raw diet seems to be as much of a risk factor as the dog being treated with antibiotics (probably because antibiotic treatments are short term while feeding is much longer term exposure). What this means for human or animal health isn’t clear, but raw pet food-associated infections have been identified in people and a dog carrying a resistant bacterium in its gut is likely at increased risk of developing an infection with that bacterium. For E. coli and related bugs, urinary tract infections would be among the most common issues, but a wide range of disease can potentially occur.

That’s a long introduction to the paper that prompted this post. The study in question (Mounsey et al, One Health 2022) doesn’t change the story at all, but adds more pieces of evidence.

In this study, they collected history and fecal samples from puppies at 16 weeks of age. Those samples were tested for antimicrobial-resistant E coli.

  • They ended up recruiting 223 puppies, 43 of which were being fed a raw diet.
  • 32 (74%!) of the raw-fed puppies were shedding E. coli resistant to at least one antibiotic, compared to 76/180 (42%) of the other puppies.
  • They looked at a number of other potentially contributing factors, such as where the dogs were walked, and didn’t find anything else that was associated with resistant E. coli shedding.
  • When they looked at resistance to individual antibiotics, raw diet feeding was associated with resistance to many drugs, with the strongest effect for fluoroquinolones, a drug class classified in the highest priority critically important antimicrobial group for humans.
  • When they looked more at the fluoroquinolone-resistant isolates, they found that many were strains that were found in urinary tract infections in people in the same area.

So, I’ll stick with my “I’d rather not have people feed their pets raw diets” line, with the added “I  REALLY don’t want to see those diets fed to very young pets, old pets or pets with immunodeficiencies, OR in households where someone is very young, elderly, pregnant or immunocompromised.”

If someone’s intent on feeding a raw diet, risk reduction is the key (risk elimination being impossible).

Diet selection is part of that. Some diets are treated to reduce (not eliminate) microbial contaminants, usually using high pressure pasteurization, which applies pressure to kill bacteria and parasites in the product. It’s not perfect by any means, but it’s useful in decreasing the microbial load. Sticking with companies that provide information about their quality control and risk reduction plan is good too. Some raw diet companies do a good job. Others… well, not so much.

Beyond that, it’s a lot of good ol’ common sense, hygiene and hand washing. Our raw diet factsheet has some information, and any good food safety infosheet will have a lot of tips that apply equally to handling raw diets for pets as they do to handling raw products during food preparation for people.

Hot on the heels of a recent update to dog importation rules in the US, the Canadian Food Inspection Agency (CFIA) has announced new rules for importation of commercial dogs into Canada.

The essence of the change is quite straightforward: “As of September 28, 2022, World Rabies Day, commercial dogs from countries at high-risk for dog rabies will no longer be permitted entry into Canada.”

The first key point this only affects “commercial” dogs.

There are 3 categories of dogs for the purposes of importation.

  1. Personal pets (traveling with a personal pet)
  2. Assistance dogs (travelling with a certified assistance dog)
  3. Commercial dogs (includes dogs for sale, adoption, fostering, breeding, exhibition, research, etc.)

Rescue dogs fall under the “commercial” category because they are imported for sale, adoption or fostering.

The second key point is that this affects dogs from high-risk countries for canine rabies.

There are over 100 countries considered high-risk for canine rabies on the CFIA’s list, and they include some countries from which large numbers of dogs are imported to Canada. For example, large numbers of rescue dogs are imported from China, and large numbers of dogs are imported for resale from puppy mills from Eastern Europe. So, this will impact a reasonable percentage of the massive number of dogs that are imported to Canada every year.

The driving force behind this is preventing the importation of canine rabies, and was spurred on by the importation into Ontario of two rabid dogs from Iran in the past 12 months, which resulted in extensive (and expensive) public health and animal health investigations.

How will this change be implemented?

Implementing something like this is more complex than most people think; it will take some time to get the required measures in place. Current import permits for dogs from high risk countries are still valid, but will expire on September 27, 2022. As of September 28, there will be no importation of commercial dogs – of any age – from those countries.  From what I’ve been told, no exemptions will be allowed. Dogs that show up unannounced will be sent back. That’s undesirable from a welfare standpoint, so work will have to be done with airlines to help prevent ineligible dogs from getting onto planes.

The US implemented a similar ban last year, then changed its rules recently. What’s up with Canada?

There are a lot of different parties, nuances, agendas and potential loopholes (e.g. fake personal pets) involved in something like this. Reasons for importing dogs can range from a snowbird going to Florida with their pet dog for the winter, to someone importing a few hundred French bulldogs to potentially sell on Kijiji for $6000 each. It can involve someone bringing their dog with them when they immigrate to Canada, or a rescue importing a large batch of dogs taken from a meat market.

Complex problems like this don’t usually have easy fixes. While this is only one more step in the process, it’s a step in the right direction. There will likely be a lot of blowback from certain groups, and I understand that. However, the animal and human health concerns and animal welfare issues around commercial importation are real and can be significant. There are legitimate reasons to import dogs which should be allowed, and then there are those that are worth stopping completely. There are groups that do dog importation well and safely, and those that do it horribly and end up putting animals and people at risk. There are those that do it because they care about dogs and those that do it because they care about money (and don’t give a crap about dogs), and everything in between.

This is a step in the right direction but probably (hopefully) not the final destination.

Dog importation rules in the US and Canada have changed a few times in recent years, in large part due to overdue recognition of some important long-standing issues, like the risk of importing rabid dogs. In the last several years, the US CDC has been implementing stricter rules around canine importation, culminating last summer with a temporary ban on importation of dogs from 113 countries considered high-risk for canine rabies.  These changes have had some good effects and some perhaps unsurprising negative impacts (e.g. shift of higher-risk dogs to countries like Canada with less stringent importation rules). The US CDC has now announced an extension of the ban, along with some changes to their rules for dogs from high risk countries, including reducing some restrictions to facilitate small scale importation while still trying to prevent higher risk and higher volume importation of dogs.

Which countries are considered high-risk for canine rabies?

The CDC keeps an updated list of high-risk countries for canine rabies (over 100 of them) online.  Some people are surprised by some of the countries on the list, including many countries from which large numbers of dogs have traditionally been imported by rescues (e.g. China) and some that have large puppy mill operations for the export market.

Can dogs from high-risk countries be imported into the US at all?

Yes, but with lots of restrictions. That’s fair, as it enables importation of a small number of pets for legitimate personal reasons (e.g. someone moving with their pet), but deters high volume, high risk importations.

What are the requirements for importing a dog from a high-risk country?

Under the new rules, in order to enter the US, any dog that has been in a high risk country in the previous 6 months must:

  • Appear healthy
  • Have a valid rabies certificate, with the vaccine administered at 12 weeks of age or older and at least 28 days prior to entry
  • Have a microchip, with the number listed on their rabies vaccination certificate
  • Be at least 6 months of age (this requirement helps reduce for-profit and puppy mill importation)
  • Fulfill one of the following requirements:

Option A: The dog has a US-issued rabies vaccine certificate and doesn’t require an import permit

  • The dog must enter the US at one of the 18 airports with a CDC quarantine station

Option B: The dog doesn’t have a US-issued rabies vaccination certificate but has an import permit*

  • The dog must enter the US at one of the 18 airports with a CDC quarantine station AND
  • Have a valid foreign rabies vaccination certificate AND
  • Have a valid rabies titre tested at an approved lab taken between 45 days and 1 year before arrival

*NOTE: permits will only be issued for 1-2 personal pet dogs per applicant (to help reduce mass importation).

Option C: The dog doesn’t meet the criteria for options A or B

  • The importer must make a reservation to enter via one of 4 airports that have an approved animal care facility (JFK, ATL, LAX, MIA) AND
  • The dog must have a valid foreign rabies vaccination certificate AND
  • Dogs with a valid rabies titre (see option B) must be examined by a USDA accredited veterinarian and be revaccinated at the facility, at the owner’s expense OR
  • Dogs without a valid rabies titre (see option B) must be examined, vaccinated and quarantined at a CDC-approved facility for 28 days, at the importer’s expense

Option C seems to leave the door open for large scale importation but brings in enough hassle and costs (.e. titres, revaccination, +/- quarantine) that it could still be a deterrent. Yet, if someone’s importing dogs from a puppy mill, getting them at low cost and selling them for $5000 each, those added costs might only put a dent in their profit but not necessarily be enough to dissuade them entirely. The age limit (minimum 6 months) might be the biggest deterrent for puppy mill importers, as younger puppies are always more in demand.

It’s a bit complicated at first glance, but pretty straightforward overall. A little complicated isn’t bad since that allows for consideration of some important aspects that get missed with a simple “here’s the one way to do it” approach. Making legitimate importers go through a few extra hoops isn’t overly cumbersome. If someone is importing a dog from a high risk country, it should be done with some personal motivation (e.g. it’s MY dog and I want to make sure it gets here), rather than a get-rich-quick venture through importation of a large group of puppy mill dogs, or a well-intentioned but sometimes inadequately-informed importation of rescue dogs. These rules should help facilitate valid importation of dogs from high risk countries but limit the number and thereby limit the risk.

Addendum: OMAFRA has now issued their notification, along with advisories for vets and rabbit owners.

Rabbit hemorrhagic disease has been identified in a group of pet rabbits in Lambton County, Ontario. This is a bit of a “surprising, but not surprising” scenario, as this highly contagious virus of rabbits is already present in at least 21 US states and 2 Canadian provinces (Alberta and BC), so it was largely a question of when (and how) it was going to get to Ontario.

More details will hopefully follow, but here are a few key points to keep in mind:

What’s the cause of rabbit hemorrhagic disease?

  • Rabbit hemorrhagic disease virus (RHDV). Specifically, we’re dealing with RHDV2.

What species does RHDV2 affect?

  • While many virus names don’t correspond to their true hosts (yes, monkeypox, I’m talking about you), this one does. Rabbits and hares (wild and domestic) are the hosts and the only species that are susceptible. Potential impacts on wild rabbits are of significant concern since large scale mortality events are possible.

What’s the incubation period?

  • The time from exposure to the virus to development of disease is typically 1-4 days.

What are the signs of infection?

  • The virus, as the name suggests, can cause serious hemorrhagic disease. It usually starts with non-specific signs like fever, decreased appetite and depression (which might not be noticed) and progresses to more severe signs such a difficulty breathing, neurological disease and bleeding from the nose or mouth caused by internal bleeding. Often infected rabbits are simply found dead, sometimes with evidence of bleeding.

How is the virus transmitted?

  • Transmission is from direct contact with infected bodily fluids such as saliva, nasal discharge, urine, blood, and feces. Even contact with the animal’s haircoat can be a risk since contamination of the fur with bodily fluids or feces is common. The virus is quite resilient and transmission via fomites (e.g. contaminated items like cages or even feed) is a concern. It can also be transferred by people on clothing or other items. There’s even the potential that cars can track the virus between areas on their tires. This high degree of transmissibility is why finding the virus in Ontario is in some ways “unsurprising,” because it can be moved between areas fairly easily and once established, it has the potential to spread widely.

Is RHD treatable?

  • We have no treatments that target the virus itself. Treatment is uncommonly attempted because of how severe and rapidly progressive the disease is, but consists of supportive care (e.g. intravenous fluids) to try to stabilize the rabbit while its body fights the infection.  Sometimes, attempting treatment may not even be allowed, depending on local regulations (euthanasia of exposed rabbits may be required in some jurisdictions).

Do recovered rabbits pose a risk to other rabbits?

  • Recovered rabbits can shed RHDV2 for a while. The risk is probably mainly over 4-6 weeks after recovery but longer shedding periods cannot be ruled out.

When should someone be concerned about RHD?

  • While there are a range of potential clinical signs of this disease and some are pretty non-specific, rapid death with evidence of bleeding should be the main trigger for concern. Deaths of multiple animals around the same time should similarly raise thoughts about RHD unless there is another likely cause. In a situation where the disease might be emerging, it’s best to get testing done when there’s any reasonable suspicion.

What should I do if I suspect my rabbit has RHD?

  • Call your veterinarian.  Your veterinarian should then call the Canadian Food Inspection Agency (CFIA), the organization in charge of federally reportable animal diseases. Your provincial animal health ministry will also likely be looped in quickly). A test is available to detect RHDV2.
  • Do NOT just take your rabbit to a veterinary clinic unannounced. That poses a risk for further transmission of the virus.

Also, if you suspect RHD in your rabbit or in wild rabbits in your area, do not allow your rabbit to have any outdoor access. If your rabbit lives outdoors, ensure that its enclosure is well secured and do what you can to prevent any contact with wild rabbits. If your rabbit is infected, CFIA can provide guidance for things like manure management, and ensuring that nothing that has been around the rabbits (e.g. cages) or comes from the rabbits (e.g. feces) leave the secured area.

Is there a vaccine RHDV?

  • Yes, but getting the vaccine is not as simple as making an appointment with your veterinarian, because none of the available vaccines are licensed in Canada, although they can be imported with some paperwork. Vaccination can be geared up in response to outbreaks.

Beyond vaccination, how do you prevent infection with RHDV?

  • By preventing exposure to the virus. That’s the key, but it can be easier said than done.

Some basic biosecurity measures include:

  • Preventing exposure of pet rabbits to wild rabbits (e.g. keep pet rabbits inside or have them in well protected areas where there’s no chance of close contact with wild rabbits)
  • Limiting contact of rabbits with other domestic rabbits
  • Limiting contact of rabbits with visitors that have had contact with other rabbits
  • Knowing the health status of any facility from which you get a new rabbit. Ideally, isolate any new rabbit for 30 days.
  • Controlling insects, fleas and ticks on and around pet rabbits

Is it easy to kill RHDV in the environment?

  • No, it’s a pretty hardy virus. It can survive outside the host for months, in the right conditions. Accelerated hydrogen peroxide, peroxygen compounds (Virkon) and bleach are effective disinfectants, if used right. A big component of that is making sure surfaces have been cleaned first. You can’t disinfect heavily soiled surfaces or items such as dirt floors. Surfaces need to be cleaned to minimize the amount of debris before the disinfectant is applied.

Can RHDV be spread to people?

  • No. This virus infects rabbits and hares but, as far as we know, just rabbits and hares.

Will there be more cases of RHD in Ontario?

  • That’s hard to say at this point. Hopefully the virus hasn’t spread and the source has been identified and contained. Details about that aren’t yet available. It’s hard to say if this group of rabbits is the only infected group or the only group known to be infected. Hopefully it hasn’t spread to wild rabbits. Monitoring for that and trying to ensure no spillover into wild rabbit/hare populations have to be priorities at this point.

Some additional resources on rabbit hemorrhagic disease:

USDA-APHIS Fact Sheet

CFIA Fact Sheet

I’ve done countless presentations and interviews about COVID-19 and animals, and the question of whether pets can infect people always comes up.

My general line has been “We know that human-to-pet infection with SARS-CoV-2 is pretty common. My main concern is cats, since we know they can spread the virus cat-to-cat. If they can do that, it’s logical that they could spread it cat-to-person. However, it will be tough demonstrate. If a cat is infected, it almost invariably got exposed from someone in the household, and figuring out whether it was the cat or the infected person that infected someone else in the household (or a visitor) is almost impossible. The most likely way we’ll figure that out is if we see evidence of transmission in a veterinary clinic or shelter, where there’s no linked risk of human-to-human spread.”

A paper in the upcoming edition of Emerging Infectious Diseases (Sila et al. 2022) rounds out this discussion, providing strong evidence of cat-to-veterinarian transmission.

The story involves a 32-year-old veterinarian, two people with COVID-19, and their cat.  Both owners had severe COVID-19 and were taken by ambulance on a 20-hour trip to the nearest available hospital bed. They had a cat and (I’d love to know how this came about) it rode along in the ambulance.

Upon arrival, the owners went to an isolation unit for treatment and the cat was sent to the university veterinary hospital, where it was examined by a veterinarian (and two colleagues).

The cat was healthy and the veterinarian collected nasal and rectal swabs for SARS-CoV-2 testing. In the process, the cat sneezed in her face. She was wearing an N95 mask but no eye protection.  This is a common oversight – if there’s a high risk scenario where an N95 mask is needed, eye protection is almost always indicated. As a profession, we (veterinarians) do a pretty bad job of using eye protection.

I’m not sure how concerned they were at the time. The cat wasn’t known to be SARS-CoV-2-positive, and getting sneezed on by a cat isn’t exactly a rare event for a veterinarian (neither is getting drooled on, puked on, pooped on or close encounters with pretty much any bodily fluid… occupational hazard).

However, 3 days later, the veterinarian started to feel sick. She didn’t seek medical care until the results of the cat’s test came back 2 days after that – positive. She was tested and was also positive for SARS-CoV-2.

The timing is bang-on for cat-to-human infection, unknown exposure to another infected person had to be considered, so more investigation ensued. A veterinarian in the hospital’s large animal clinic also got COVID-19 around the same time, but there was no known contact between the two veterinarians, and the small animal veterinarian didn’t report any other known contact with an infected person.

Here’s where genomics come into play. When they sequenced the virus from the two veterinarians, the two owners and the cat, they found that the large animal veterinarian had a different strain, so it was an unrelated infection.  The strains from the cat’s veterinarian, the cat and the two owners were identical. Furthermore, that strain was different from strains circulating in people in that province (remember the owners came from 900 km away).

This was the perfect storm that allowed for identification of pet-to-human transmission or SARS-CoV-2: Exposure to an animal outside the household, where the virus strain involved wasn’t common (or even present) in the background transmission in the area, timely testing of people and the animal, and an ability to sequence all the samples.

The most surprising aspect of this report for me is that they had the right conditions to find zoonotic transmission, not that it actually occurred. I’ve been pretty confident it was possible, which is why we’ve done animal surveillance and spent a lot of time developing and communicating practical but proactive guidance to veterinarians to reduce the risk of just such an event.

Cat owners shouldn’t have much to worry about. The odds of a cat bringing SARS-CoV-2 into a household are really low. However, if it gets in via a person and the cat gets infected (which can occur ~50% of the time), we have to think about the implications for other people (and pets). If a household isn’t doing anything to separate infected and uninfected people, cats probably don’t matter much since human-to-human transmission is more likely. However, if households are separating those groups, include the cat. If I have COVID-19 and move to the basement to stay away from everyone, I should keep my cat away from me too (or keep it with me and away from everyone else). It’s also a reminder that we should continue to query COVID-19 exposure status of veterinary patients, and ideally postpone elective visits for cats from households with COVID-19. Emergencies are a different story, and we can take precautions to reduce the risk, but it’s preferable to bump an elective appointment.

All this relates to cats… what about dogs?

The risk from dogs remains unclear but is probably very low. We don’t have evidence of dog-to-dog transmission, and viral loads in infected dogs are typically low. I don’t think we can say there’s zero risk, but the risk is likely much lower compared to cats.

Headline writers are probably going to screw up my day tomorrow by sensationalizing this, but a new paper in the journal Animals (Fiorito et al. 2022) describes SARS-CoV-2 infection in cattle in Italy. (It’s an MDPI journal, and I take anything published there with a big grain of salt given their low standards, but this one seems ok). It’s also similar to a pre-print from Germany abobut SARS-CoV-2 in cattle that we’ve known about for a while.

Why do I say “take a deep breath and relax”?

I’ve talked about the need to consider spillback of SARS-CoV-2 into animals since 2020. However, there are different concerns in different situations. Livestock raise some big concerns because there are a lot of them, they live in large groups in close proximity to people, and we have lots of contact with food products from them (f not the animals themselves).

We always need to consider what the results of surveillance testing really mean. Data are great, but they need to be appropriately incorporated into our understanding of a given disease and what risks might be present (or not).  So, let’s look at what this study tells us.

It’s a nice but small study of cattle from a farm where 13 of 20 workers had diagnosed or suspected COVID-19 – a great situations in which to do animal surveillance since there’s a clear risk of exposure of the animals.

Researchers collected nasal and rectal swabs, as well as milk, from 24 lactating cattle, and tested them by PCR for evidence of active infection (viral DNA).

  • All the cattle tested PCR-negative for SARS-CoV-2.

We know that PCR testing is a challenge in animal surveillance, since infected animals may only shed the virus for a short period of time. As we saw in our dog and cat SARS-CoV-2 surveillance study, it can be a challenge to sample animals at the appropriate time to catch them when they’re shedding virus. Animals can be infected but eliminate the virus by the time we hear about the exposure, arrange to get samples and get there to collect them.

Researchers also collected blood samples from the cattle on this farm, which allowed them to look for evidence of previous exposure by detecting antibodies against SARS-CoV-2. The specificity of the test (how likely a positive result is really due to SARS-CoV-2 infection) in cattle isn’t clear, but they reported positive results in 11 (46%), 14 (58%) or 13 (54%) of cattle, depending on the test used. The 54% was based on a serum neutralization test – not the standard virus neutralization test that’s been used elsewhere, but probably fairly reliable nonetheless.

So, what does this study tell us?

It suggests that human-to-cattle transmission of SARS-CoV-2 was relatively common in lactating cattle on this farm, where there was an outbreak in people. It’s too bad they only tested a small number of cattle and all of them were lactating, because lactating cattle are presumably higher risk for exposure as they have a lot of human contact a couple times a day for milking. It would have been nice to see if there was evidence of infection in other cattle and calves; seeing low rates of transmission to low risk cattle would also have provided more weight to the positive results reported in the higher risk group. Regardless, this is pretty strong evidence that people infected cattle on this farm.

Did the cattle get sick from SARS-CoV-2?

There’s no evidence the cattle had any clinical illness. Lactating dairy cattle are pretty closely monitored, so we can be pretty confident they didn’t have any overt signs of disease.

Could the cattle have infected other cattle or people?

That’s hard to say. All the cows were PCR-negative. Whether that was because of timing of sampling or very low grade infection is impossible to say based on this study. Given the low predicted susceptibility of cattle, lack of evidence of disease and zero prevalence by PCR despite high seroprevalence, it’s more likely that these cattle had very minor infections that resulted in them developing antibodies but not shedding enough virus to pose a risk for transmission. We need more studies to properly evaluate this, but nothing here suggests a major concern.

Can cattle be a reservoir for SARS-CoV-2?

For cattle to be a reservoir, they’d have to be able to infect other cattle and there would have to be ongoing transmission within the cattle population (vs a short term situation where cattle get infected and the virus burns through the group quickly). How susceptible they are, how well they can transmit the virus (if at all) and the number of cattle in contact (to be able to sustain transmission) would impact this. Most likely, if cattle were able to transmit the virus at all, it would burn through the farm relatively quickly. Dairy cattle usually number in the 10s or 100s on a given farm, not thousands (like mink or wildlife, though there are exceptions), so sustained transmission seems unlikely on most farms.

What about cow-to-human transmission of SARS-CoV-2?

We don’t know what the risk is for sure. Most likely, cattle are “dead end hosts” for this virus, whereby they get infected but can’t pass it on. If they are able to spread it, the nature of dairy farms and the number of cattle per farm mean the risk would probably be short term and only to farm personnel (who are likely at greater risk of exposure from the other infected people, not the secondarily infected cattle). However, we need to look at this more. There’s been a lot of reluctance to test food animals, so our knowledge of how the virus behaves in this species is still pretty limited.

The take home message:

Cattle are one of many species that SARS-CoV-2 seems to be able to infect.  The odds of it being relevant for cattle (or for infection of cattle to be relevant to public health) are low, but it’s worth further study.

I very commonly get emails from vets like this:

My client was diagnosed with [insert various diseases here] and their physician said they probably got it from their [insert various pets here] and as a result they want the animal [tested / treated / rehomed].

  • Sometimes the disease in question isn’t even potentially zoonotic.
  • Sometimes the concern is about a zoonotic pathogen, but the pet is an unlikely source.
  • Sometimes human-to-pet transmission is actually more likely than pet-to-human.

Very rarely does testing the pet make sense, and even more rarely does “treating” a healthy pet make sense.

That’s not to say pet-to-human infections don’t happen. They obviously do and they are important considerations. However, all too often we run into issues because someone was quick to jump to blaming the animal, and then trying to force owners (or veterinarians) to use illogical or even harmful treatments.

Why not just test the animal for the disease in question?

I don’t like to do tests that don’t make sense, because it’s a waste of time, a waste of money, and it diverts attention from the real issues. Sometimes it’s harmless, but it often leads to bad decisions.

Before I test a healthy animal (which I very rarely do apart from surveillance studies), I ask myself “What will I do with a positive or negative result?” If the answer is “I don’t know.” or if the answer is the same for both positive and negative, there’s no value in testing.

If the animal tests positive, what does that mean?

That’s hard to say.  A positive test result often leads to more questions than answers.

If an animal tests positive for the same organism as its owner, we often can’t make any conclusions about whether the pet infected the owner.  It could in fact mean any of the following:

  • The owner got it from the pet
  • The pet got it from the owner
  • They both got it from the same source
  • They have unrelated strains of the same organism

Even if the pet was the source of the person’s infection, what does testing tell us?

It’s always nice to round out the story, and confirming the source of infection helps  provide some awareness, but it doesn’t always (and I’d argue usually doesn’t) change anything.

If a person if infected by a bacterium that’s normally in/on an animal, testing the animal is useless.  Let’s say a person has a wound, and their cat licked it, and they get a Pasteurella infection. If someone tested the cat and tells me they found Pasteurella, that’s not a eureka moment, it’s a “you just spent $200 to confirm that the cat is actually a cat” moment.  Finding a bacterium that is normally found in an animal isn’t noteworthy. It’s also not actionable. I’m not going to give a cat antibiotics to eliminate Pasteurella from its mouth because:

  • It won’t work
  • It’s improper use of antibiotics
  • It’s associated with risk of adverse effects in the cat
  • The cat could bite or expose the owner to its saliva again while being medicated, which might set up another Pasteurella infection
  • It might select for resistant bacteria in the cat that pose a greater risk to the cat (or the owner) than Pasteurella

After treatment, I’m certainly not going to say “go ahead and let your cat lick your wounds” or “don’t worry about the cat biting you.” I’m going to say to avoid contact of saliva with broken skin, try to prevent bites and do good first aid if bitten. I’d say the exact same thing for any cat… tested or not, treated or not.

There are rare situations where testing the animal might make sense. However, 99% of the time it doesn’t, and I spend a fair bit of time trying to defuse situations after someone has tested an animal for something with no plan on how to interpret the results, or when a veterinarian just tested an animal based on pressure from an owner after a request from a physician.

It’s great to see physicians thinking about pet-associated infections. However, we still have a long way to go to start having good conversations (not directives) about risk and risk mitigation when it comes to zoonoses and pets.

I’ll write more about the specific bacterium (Helicobacter heilmannii) from today’s email that prompted this post soon. It’s an interesting bug that’s worth separate discussion.

While we’ve learned a lot about the susceptibility of many different animal species to SARS-CoV-2, horses have been a bit of an unknown. We’ve had concerns about potential susceptibility based on the nature of the receptor the virus uses to enter host cells, but study in horses has still been limited. A lot of that has been because people didn’t really want to know – I’ve run into a lot of roadblocks to research because people were more concerned about the implications of a positive test than the virus itself.

A couple of studies have provided a little bit of information. An Italian study didn’t find evidence of SARS-CoV-2 infection in 34 horses on two farms where there was exposure to infected people. Another study using PCR testing didn’t detect any SARS-CoV-2 in samples from 667 horses with respiratory disease, but there was no known exposure of the horses in this study to the virus – they just tested samples submitted for routine diagnostic testing of sick horses.

A recent study (Pusterla et al. 2022) has finally shown “proof of principle” with regard to infection of horses with SARS-CoV-2.  The researchers used serological testing (for antibodies) to detect recent infection in a horse. The advantage of this method is you don’t have to get respiratory swabs during the likely very narrow window that an infected horse may be shedding the virus. The downside is the potential for a false positive test, which is of particular concern when trying to interpret results for individual animals, versus an entire group.

The paper identified antibodies against SARS-CoV-2 in one of two healthy horses owned by a person who had COVID-19, caused by the Delta variant. Both horses were healthy at the time of sampling and hadn’t had any noticeable illness around the time the owner was sick. Both horses were negative on PCR tests (that look for viral nucleic acids). However, one horse tested positive on two different antibody tests, including a plaque reduction neutralization test (PRNT), which is a pretty specific test. So, I think we can be fairly confident that the horse was infected, presumably from exposure via the owner, and either had very mild disease that wasn’t noticed or had no disease whatsoever.

What does this tell us?

It confirms what I think we suspected all along: that horses have at least some albeit limited susceptibility to SARS-CoV-2. The antibody response was pretty low and short-lasting, in comparison to other susceptible species. While we have to take care interpreting results from a single horse, it’s suggestive that horses are not as susceptible as some other species but can be infected.

Does this mean the virus can’t cause disease in horses?

Not necessarily. Subclinical infections are common even in species that can get severe disease. With only 1 positive horse, we can’t say much. However, given what we have to assume is very widespread exposure of horses to people with COVID-19, and the lack of any apparent concerns about increases in respiratory disease in horses, I think we can still be confident that this is not a serious health problem for this species.

  • Maybe it never causes disease in horses.
  • Maybe it causes disease sporadically but not commonly enough that we’d notice.
  • Maybe it causes mild disease that never gets identified or isn’t serious enough that testing gets done.

Can horses infect people?

Who knows? All we know is that one horse was presumably infected. Some species can be infected and spread the virus to others. However, some species can be infected but not to the degree that they are able to infect others (known as a “dead end host”). Given what is likely a low level of susceptibility, I assume the risk posed by horses to people is very low.

What do we do now?

The same things we’ve been recommending since January 2020. If you have COVID-19, stay away from others as much as possible. “Others” includes humans AND other animals. Humans are driving this pandemic, and infections in animals are largely a by-product of that. We’d like to keep it that way by limiting exposure of infected people to animals. Some basic measures can reduce the unknown risks.