As the unprecedented outbreak of H5N1 avian influenza continues in North America, there are numerous concerns about where the outbreak is heading and threats to other species, including domestic and wild mammals, and people (the latter being just another “domestic mammal”).  My inbox is filled with questions about different concerns and scenarios. The one I’ll address today is about risks to veterinary clinics that treat backyard poultry.

Backyard poultry are increasingly common in many areas.  Since they are typically kept outdoors and not managed with anywhere near the same degree of biosecurity as most commercial poultry, they are at high risk of exposure to avian flu when it’s circulating in wild birds in the area, as it is right now.

The good news about the current H5N1 influenza outbreak:

This H5N1 strain is not well adapted to infect humans, or mammals in general. It lacks some of the genetic material that makes other flu virus more transmissible to and between people. Only a couple of human infections with this strain have been reported, including one person infected with H5N1 in the US in whom the only symptom was fatigue. Transmission to other non-avian species is probably rare too, but all we can say is “probably” because of limited testing of wildlife. Spillover has occurred, including the recent cases of H5N1 influenza in fox kits in Ontario. Whether these infections are really rare events or just rarely diagnosed isn’t clear and remains a big question. Still, it’s safe to say that, at this point, spillover risks are limited.

(Some of) the concerning parts about the current H5N1 influenza outbreak:

It’s still a flu virus, and flu viruses change. The circulating strain can evolve and reassort (swap genes with other flu viruses) anytime. We have plenty of other flu viruses circulating in North America, including seasonal human flu and flu in other species such as pigs, horses and (in the US) dogs. There are also other avian flu strains around here and there. The more flu viruses in circulation, the greater risk of them getting together to reassort and make a new strain, potentially with more affinity for people.

So, back to veterinary clinics treating backyard poultry:

Like all domestic animals, backyard poultry sometimes need veterinary care, and this often falls to small animal or mixed animal veterinary clinics, since there are only a small number of specialist poultry veterinarians in Ontario (and many do not treat backyard birds, for several reasons including biosecurity risks). Unlike most livestock, backyard poultry that need veterinary care may be taken to the clinic (in contrast to most livestock where the veterinarian visits the farm). This creates a few concerns that need to be taken into consideration by the clinic when it comes to avian influenza.

Risk of transmission to people

  • Fortunately, as noted above, transmission to people is rare, at least at this point. Rare doesn’t mean it can’t happen, but the odds of clinically significant bird-to-human infection seems to be very low. It’s not likely someone handling an infected bird will get sick, but it’s possible.
  • We also need to think about the potential impact of people who have human flu getting exposed to birds that might have avian flu. If one infects the other (and therefore has an infection with two different flu viruses), that’s the recipe for re-assortment to create a new strain. We might be getting into excessively theoretical issues here (I doubt it, though), but hopefully the “stay home if you’re sick” message is getting across.  Unfortunately we know that’s not always the case, and people who are infected with influenza don’t always have symptoms.

A comment I made today to someone was “There’s some degree of risk but in the absence of sick birds, the zoonotic risk isn’t likely any greater than that posed by your average new puppy (e.g. Campylobacter).” I think that’s a fair statement, but at the same time, one of my goals in life is not to become a case report describing a rare/new infectious disease, so I still want to take care.

Risk of transmission to mammals

  • The issues with risk to other mammals are similar to humans (in the end we’re just another mammal, afterall). The risk of transmission is low but not zero. I wouldn’t get too concerned about it, but I’d still rather not create the chance for rare bird-to-mammal transmission in the clinic, especially since we can largely prevent it with some basic infection control measures (see below).

Risk of transmission to other birds

  • This is probably my main concern. There could be transmission to other backyard poultry (not too likely, since there usually aren’t multiple backyard chickens at a clinic at the same time) or transmission to other pet birds. Susceptibility amongst different bird species varies, but we’re seeing lots of wild birds dying from this virus. We don’t want to see it spread in a clinic to someone’s pet bird (or worse, to someone’s aviary). That creates risk of illness and death for the bird(s), and more human exposure to the virus.

So, what do we do?  We do what we do every day: We assess and manage risk.

We can never 100% eliminate risk of infectious disease in a clinic setting, especially flu. However, we can use some basic, common sense measures to reduce risk of avian flu transmission.

Risk assessment

Since healthy looking birds can be infected, there’s no way to guarantee that a given bird isn’t shedding avian flu virus. However, we can identify situations where the risk is higher and increase the infection control measures that are used. Higher risk situations include:

  • The bird is sick with signs that are compatible with avian flu infection (including neurological disease)
  • Other birds in the group are sick
  • Other birds in the group have died
  • Avian flu has been found in wildlife in the area, and the bird has outdoor access

Physical separation

If we can keep poultry away from people and animals as much as possible, we greatly reduce the risk of pathogen transmission. That can be done a few ways:

  • Admitting birds directly to isolation or another separate, contained space (versus hanging around in the waiting room)
  • Examining birds outside so they never set foot in the clinic
  • Housing hospitalized birds in isolation or a separate area

Limiting contact

Minimizing the number of people who handle the birds in the clinic to the one or two who might be required for examination and procedures reduces transmission points.

Appointment scheduling

It’s not always possible to have poultry come into the clinic at a time when no other birds are present if there’s a high bird caseload or for emergencies, but it’s something that should be done whenever possible.

PPE and hand hygiene

Routine infection control practices can go a long way, and are used based on the assumption that any patient might be harbouring something infectious.  Things like wearing proper protective outwear (basic lab coat) and hand hygiene help a lot. Protective measures can be increased if there’s more risk (see above) to include a disposable gown, mask and eye protection.


Accurate rapid tests for avian flu would be very useful and are available in some other jurisdictions. However, we have not had success getting approval to import the tests for screening birds in places like clinics and wildlife rehab facilities. Rapid tests (as we learned from COVID-19) are not perfect and can never rule out flu. However, they could be a useful screening measure, as a positive would indicate a need to use stricter precautions, and to get confirmatory testing done while providing more surveillance info. There was reluctance to use rapid tests for COVID-19 initially, but they ended up being a very useful tool. Currently, the only testing available for avian flu is PCR testing through diagnostic labs, which doesn’t help us from a clinic control standpoint since the turnaround time can be a few days.

The current H5N1 avian flu outbreak is definitely something to be concerned about. It’s having major impacts on domestic and wild birds. We want to control it to reduce the impact on those population and reduce the risk of this developing into something more. However, vet erinary clinics should be able to treat poultry without much risk, if some basic infection control measures are used.

Photo credit:

H5N1 influenza was recently found in two wild fox kits in St. Marys, Ontario. It’s a pretty noteworthy event given the scope of the current H5N1 highly pathogenic avian influenza (HPAI) outbreak across Canada, and the fact this is the first identification of H5N1 influenza in wild mammals in Ontario. The fox kits were submitted by a wildlife rehabilitation centre; these centres are great sources of information about emerging wildlife diseases as they are on the front lines and often bear the brunt of such issues. One of the fox kits was found dead and the other had severe neurological disease and died shortly after admission. Influenza virus was found in their brain tissue and was likely the cause of death. Further characterization of the virus identified it as an H5N1 strain of influenza A, more specifically of the A/goose/Guangdong/1996 (Gs/GD) lineage.

Is this surprising?

Not really. We don’t recognize much spillover of flu viruses into wild canids, but when you consider how widespread this virus currently is, it’s not a shock that spillover would happen. (It’s maybe more of a shock that we’d actually find it.)

We know that foxes, like other canids, are susceptible to various flu viruses. In an experimental study (Reperant et al. 2008), researchers were able to infect foxes by feeding them carcasses of infected birds, though the infected foxes were only mildly sick, at most. In a more recent study (Rijks et al. 2021) found two naturally infected red fox kits in the Netherlands. Those foxes also had neurological disease, like the one Ontario fox kit and as is often seen with severe infections in certain types of birds. In April 2022, avian influenza was also reported in a fox found dead in Japan; the strain was not reported in this case, but is likely related to the H5N1 strains circulating around the globe in migratory wild birds.

Why foxes and not other canids?

It’s not clear (to me, at least) whether foxes are predisposed to infection with influenza, or whether it’s a matter of there being more foxes than other canids in affected areas that get tested. I suspect it’s a numbers and surveillance bias rather than foxes being predisposed or particularly susceptible to infection.

Have more wild mammals been infected in Ontario than these two fox kits?

It’s hard to say, but it’s likely. These were only identified because they happened to be presented to a rehab facility AND they were submitted for testing. That doesn’t happen with most sick or dead wild animals. So, we don’t know if this was a very lucky identification of a very rare event, or a result of something bigger happening in the wildlife population of which we are as of yet unaware.

Let’s back up a bit… What do we know about influenza in canids in general?

There are two main situations to consider when it comes to influenza in canids: 1) infection with flu strains that are adapted to canids (including domestic dogs, foxes, coyotes, wolves, etc.) and 2) spillover infection with other non-adapated flu strains in canids.

“Canine flu” strains are influenza A strains that effectively circulate in the dog population. Currently the most common canine flu strain is an H3N2 that’s endemic in Asia and causes sporadic outbreaks in the US, often associated with imported dogs.  Canine H3N2 influenza was introduced into Canada this way back in 2018, but as far as we know was rapidly eliminated.  That’s not the strain we’re dealing with here (at least at this time).

Dogs (and other canids) can also get “spillover” infections of influenza from other species. For example, human-to-dog transmission of seasonal human influenza strains can occur. It’s probably more common than we realize, because dogs don’t usually get very sick and testing is uncommon, but it still seems to be a pretty uncommon event. Spillover of equine H3N8 influenza has also been reported.

Most of the time, spillover events are sporadic and a dead end for the virus, as the animal gets infected but doesn’t effectively spread a strain that isn’t adapted to that host, so it dies out in that individual. However, that’s not guaranteed in every case. Canine H3N8 is believed to have originated in horses, with subsequent adaptation to dogs to become a true canine flu virus.

Why do we care about H5N1 influenza in a couple of foxes?

From a dog health standpoint, spillover events are not a big deal because they are rare and don’t typically cause severe disease. However, the foxes in this report died, so we can’t assume all infections will be benign.

The main big-picture concern with spillover infections is the potential for emergence of a new flu variant, through adaptation of that strain to the new species, or (more critically) recombination of influenza viruses within the new host, which can happen when two different flu viruses infected an individual at the same time and swap genes. If the new variant that emerges is still able to infect a particular species (like humans) and is highly transmissible, yet different enough from the original virus that we have little immunity from previous infections or vaccination, it’s a recipe for a new pandemic virus. Dogs are unlikely to be the source of a new strain, but the more flu viruses that can infect them, the greater the risk. Since dogs can be infected by strains of human flu, dog flu and spillover of avian flu, there’s a theoretical chance that a dog could be infected with two different flu viruses at the same time. That’s why we want to control and eliminate flu viruses in dogs (and other species) as much as possible. Realistically, the recombination risk is probably greater in other species (including people), but we’d rather not roll the dice unnecessarily.

How did the fox kits get infected?

Presumably it was from eating an infected bird, especially since we know that can occur based on the previous experimental study. Whether these kits both got infected from the same infected bird, whether one got infected and then infected the other, or whether both were infected by a littermate or their vixen is impossible to say. I guess we also can’t rule out they got it from another mammal that acquired it from a bird, but then we’d be talking about a spillover from a spillover, which is quite a stretch.

What should the average dog owner do about influenza in dogs during the current outbreak in birds?

Step 1: Relax. Yes, this virus currently wreaking havoc in wild birds and domestic poultry around the globe can presumably infect domestic dogs. So can lots of other viruses (including many that are more serious, and yet we don’t panic about them either). Don’t ignore the issue, but let’s keep things in perspective.

Step 2: Use some common sense measures to reduce the risk of dogs being exposed to influenza-infected birds.

Step 3: Use some common sense measures to reduce the risk of dogs being exposed to influenza from other species.

Here are some examples of easy and practical measures:

  • Keep dogs away from sick and dead birds.
  • If avian flu is reported in your region, stay away from areas where infected birds have been found and keep your dog under control so it can’t wander off and snack on a recently dead bird.
  • Remove bird feeders to reduce congregation of birds, reduce the potential for bird-to-dog contact, and reduce exposure of dogs (and other animals, including people) to potentially influenza-contaminated bird poop.

Likely the most important thing the average person can do to reduce the risk of their dog getting a spillover influenza infection is for that person to get a flu shot, to reduce the risk of getting infected themselves and exposing their dog to flu.

Is there a flu vaccine for dogs?

Yes, but it won’t help us here. Flu vaccines aren’t great at providing cross protection against other strains. The canine vaccines are for H3N2 and/or H3N8, not the strain we’re currently dealing with in wildlife.

After a couple of years of very little apparent canine influenza activity in the US, the virus seems to have come back with a vengeance in some parts of California. Canine H3N2 influenza came to  North America from Asia in approximately 2015 and caused outbreaks in many areas, but then seemed to slip into the background. Sporadic outbreaks have been identified in recent years, but were mainly small clusters in individual facilities like kennels.

A recent, prolonged outbreak of H3N2 influenza in dogs in southern California has highlighted the importance of this virus again. The best tracking and reporting of the outbreak has been provided by the County of Los Angeles Public Health:

“Between July and October 2021, approximately 800 confirmed and suspect cases of CIV [canine influenza virus] H3N2 in dogs in LA County have been reported to Veterinary Public Health.  Sadly, 7 deaths in dogs have been associated with this outbreak.  Of the cases reported, most were associated with attending boarding kennels or dog daycare settings.  There are a number of cases that have never visited a boarding or daycare facility, but were exposed while on walks in their neighborhood, at dog parks, groomers, or at veterinary clinics.  This virus has spread rapidly among dogs throughout LA County, affecting many congregate facilities.  Based on interviews with these facilities, many additional cases have not yet been reported to VPH.  We suspect that this outbreak likely involves more than 1000 cases of CIV H3N2 in LA County dogs.  Dogs that appear to have ‘kennel cough’ have a high likelihood of having CIV H3N2.  To date, this is the largest outbreak of CIV H3N2 ever reported in LA County.  To stop the spread of this outbreak, pet owners and veterinarians are strongly encouraged to vaccinate dogs against CIV H3N2 and isolate sick pets at home for 28 days from the first day of illness.  Pets exposed to confirmed or suspected cases should be kept on a home quarantine and observed for clinical signs for 14 days.”

The 7 deaths puts the mortality rate at approximately 1%, which is pretty consistent with what we’ve seen before with this virus in community settings. I’d guess that 20-40% of the affected dogs have received antibiotics and other treatments due to more serious disease (and some overuse of antibiotics, which unfortunately is still common with respiratory disease in dogs, as it is in people).

As is typical with canine influenza (and canine infectious respiratory disease complex (CIRDC), in general) we only have a partial picture of what’s going on. Testing is sporadic and  various other respiratory viruses and bacteria that cause similar disease are always circulating in the dog population.

When canine flu was found in Canada in 2018, we aggressively tested and traced in-contact dogs, and the virus was successfully eradicated in Ontario.  That’s not a realistic goal in this case. LA County has a great veterinary public health team, but you have to be able to intervene early to have any chance of stopping a highly transmissible virus like flu in its tracks.   Once it’s widespread in the general dog population, it becomes impractical to properly trace and test all in-contact dogs for every case (especially when there is rarely much or any financial support to do so). So, containment through education and vaccination is the focus. Presumably, this outbreak will burn out in the area eventually. Whether it will be tracked to other areas outside California is a big question.  We’re still watching for new introductions of canine influenza in Canada. We were able to control the first introductions of H3N2 canine flu in 2018, but I’m not naive enough to think that luck wasn’t a big component of that.

Since respiratory disease is common in dogs, particularly of late, and because we only test a minority of coughing dogs, we need to be aware of higher risk situations. I pay the most attention to:

  • Large clusters of cases, especially in well vaccinated populations
  • Outbreaks that affect virtually all exposed dogs
  • Outbreaks where there’s a known or possible initial exposure to a dog from a high risk region (e.g. Asia, and now parts of the US where the virus is active).

In situations like those, prompt testing, along with good infection control practices, are what we need to identify and contain the problem as much as possible.

I’ve had a couple of reports today about an apparent H1N1 influenza outbreak in dogs in the US. Note that I said influenza in dogs, not canine influenza – there’s a reason for that, explained below…

The situation revolves around a respiratory disease outbreak in a dog kennel in California, and PCR testing of some of the sick animals identified H1N1 influenza. Clinically, it sounds like a moderate to severe outbreak, with a reasonable number of infected dogs.

We generally see two types of influenza in dogs:

  • “Canine flu” is caused by dog-adapted strains of influenza A, and they are maintained through spread in the dog population.  The two main canine flu strains that we know about are H3N8 (which seems to have disappeared) and H3N2 (still sporadically present in the US and endemic in some parts of Asia).
  • Spillover infections in dogs with flu viruses that are primarily adapted to other species are also detected occasionally.  Most often this involves stains of influenza A that are adapted to humans, when a dog gets infected from its owner. We usually assume that these are “dead-end” infections, in that the dog doesn’t pass the virus on any further, because it’s not a canine flu virus so the infected dog likely doesn’t produce enough virus to infect others.

Back to the H1N1 in California.  We periodically see human (previous pandemic) H1N1 virus in dogs, which they catch from their owners. However, there can be different strains of the virus even within a single flu “type” like H1N1. If we look at H3N2, we have human H3N2, canine H3N2, swine H3N2, and so on. While they are all H3N2, they are adapted to a specific animal species and don’t infect others as readily. The important question in this case is, what type of H1N1 influenza is involved?  Finding a single case of human H1N1 flu in a dog wouldn’t surprise or concern me. But detecting a whole outbreak is a different story.  More information is needed, since this could range from an interesting story to a serious canine disease threat.

Here are the big questions:

Is the diagnosis confirmed/solid?

  • Is this really on outbreak of H1N1 or is it a different flu strain?
  • Is it an H1N1 outbreak, or was there an outbreak of something different and some incidental H1N1 infection was detected in the process of testing? (Unlikely since it seems like at least a few dogs were diagnosed with H1N1.)

Is this “human” H1N1 in dogs?

  • Is this outbreak due to spillover infection from humans, or is it from a different source? Presumably someone’s sequencing the virus, which will help answer that question. If it’s actually H1N1, hopefully it’s just an oddball scenario with a cluster of human H1N1 flu infections that will die out, versus an indication that we have a new canine H1N1 flu strain, or a human strain that is now more adept at infecting dogs.

Is this virus a “canine” flu virus?

  • It’s too early to say. Hopefully not. We don’t want a new flu strain in dogs for lots of reasons.  A new strain could spread easily through the dog population because no dogs would have any immunity to it. That can cause a significant amount of disease.  There would also be potential zoonotic concerns with a new strain. H3N2 and H3N8 canine flu viruses haven’t been significant zoonotic risks. They’ve stayed in dogs and haven’t spread to people, as far as we can tell. However, flu viruses like to adapt and change, and we just don’t want any more influenza viruses floating around, in terms of their potential for direct infection of people or the potential for recombination with other human flu viruses which could make more new flu strains (to which we might not have any immunity).

At this point, I’m interested and curious but not worried. Hopefully this situation is being investigated thoroughly (I assume it is).

Canine influenza is back in the news in the US, with close to 50 dogs infected with canine influenza at a dog rescue in Florida.  The outbreak has been going on for over two weeks already.  This is a “surprising but not surprising” scenario to me.

It’s a bit surprising because canine flu activity seems to have been really low to non-existent in the US lately. While there’s no formal surveillance program, I haven’t seen reports of it and haven’t heard any other chatter about diagnoses.

It’s more towards unsurprising though. We were able to eradicate canine influenza (as far as we can tell) in Ontario, Canada, when it hit here in 2018, but that took a lot of surveillance and effort, and we intervened very quickly after introduction of the virus. With widespread disease in the US over the years after multiple introductions from Asia and no broad control plan, it was expected that canine flu would continue to spread on this continent – sometimes insidiously, sometimes dramatically. Since the virus is so transmissible and vaccine coverage is low, it can spread quickly, but disease can also burn out in a particular area if infected dogs don’t continue to meet susceptible dogs.

While we weren’t seeing reports of infections, it seemed optimistic to assume it had completely disappeared, and even if it did, importation of dogs from areas where the virus is endemic poses ongoing risk of reintroduction and spread.

It would be nice to know a few things about the reported outbreak in Florida:

  • How solid is the diagnosis? The reports say “canine influenza” but sometimes people get confused and default to saying “flu” for any respiratory disease, or don’t realize there’s a difference between canine influenza and parainfluenza (a very common respiratory virus in dogs worldwide).
  • Assuming this really is canine influenza virus, what strain is it? Is it our expected H3N2 canine flu strain, or could it be something new? (which would also have huge implications from a vaccination standpoint)
  • How did the outbreak start? The rescue says a dog “from the area” brought it into the facility, but where did that dog likely get infected? Unknown-origin infections suggest there could be more transmission going on than we realize.

If this is H3N2 canine influenza (which is the most likely strain), that leads to questions about vaccination. We have an H3N2 canine vaccine in Canada and the US. (We also have a vaccine that covers H3N8 in dogs, but that strain hasn’t been seen in years.) Canine flu vaccines are like human flu vaccines – they’re designed to reduce the likelihood and severity of disease, but they’re far from perfect and may not do a lot for preventing transmission overall. However, they are still useful.

When I think about use of influenza vaccines in dogs, I consider two main factors:

  1. Likelihood of exposure: Dogs in the area of this rescue would obviously be at increased risk of exposure to the virus. Dogs that have contact with imported dogs (e.g. dogs in a rescue that periodically imports dogs) and dogs that travel to areas where the virus is, or may be, present, would also be at increased risk of exposure.  This dogs are more likely to benefit from vaccination.
  2. Likelihood of severe disease: My 8-year-old otherwise healthy Labrador is unlikely to have a severe outcome if he’s infected with influenza virus. If he was a bit older, had respiratory or heart disease, had other debilitating issues or was a brachycephalic breed (like a bulldog), the odds of him having a severe (or even fatal) outcome from infection would presumably be much higher. Vaccination is therefore more important in dogs in these groups. All the deaths we saw here in Ontario from canine flu back in 2018 were in senior dogs. However, severe disease can still occur in younger dogs. So, vaccination is more important in higher risk dogs, but that doesn’t mean it’s not useful in others.

We’ll have to see how this story plays out, hopefully more information will follow.

While it was pretty well documented on the Worms & Germs Blog as it was underway, the full story regarding Ontario’s 2018 canine influenza outbreak(s) has now been published in the latest edition of Emerging Infectious Diseases. You can use the link above to access the full report, but here are some highlights.

  • There were 104 confirmed cases. In most outbreaks, we talk about how that’s likely the minority of true cases. However, here, it probably accounts for the vast majority of cases, given the amount of contact tracing and testing that was performed.
  • Transmission occurred in many ways, including while boarding, at a groomer, pack walking, day care, between neighbouring dogs and at a veterinary clinic.
  • High attack rates were common. In an area where flu is not normally present, when it hits, large numbers of dogs can be affected quickly. Large clusters of disease, or situations where most or all dogs in a group develop respiratory disease around the same time, is a trigger for me to test for canine flu. That’s true even if there’s no initial link to imported dogs. One of our large clusters was first identified because of a high attack rate of respiratory disease in a good kennel. The link to imported dogs was only found later.
  • Outbreaks were the result of multiple introductions of H3N2 canine influenza virus into Canada through dogs imported from Asia (China and South Korea).
  • Two dogs died from complications of influenza. Both were older dogs, which isn’t surprising as older individuals are at greater risk of death from influenza, whether they’re dogs with canine flu or people with human flu. One other death was suspected but not confirmed.
  • Some dogs shed the virus for a long period of time. We were able to collect serial samples from a reasonable number of dogs and some shed for at least 20 days, despite looking healthy after just a few days of illness.

The good news is that canine flu was eradicated. Good, old fashioned infection control was the key.  Some astute primary care veterinarians and responsible dog owners who were willing to quarantine infected dogs or facilities (e.g. kennels, groomers) for 28 days played a critical role.

While we were able to eradicate the virus in 2018, we’re under no illusion that it won’t come back. The large number of dogs imported from Asia and the lack of any quarantine or testing requirements for influenza means another outbreak is likely inevitable. However, we’ve shown that even with the introduction of a new virus to a population of dogs with no pre-existing immunity, it can be contained. It takes time, effort and money (and probably no small amount of luck), but it’s possible and worth the effort.

The map below shows the various clusters of H3N2 canine influenza identified in Ontario in 2018.

Canine influenza is (once again) causing big problems in some parts of the western US. Following reports of influenza outbreaks in animal shelters in Oakland, California, it’s apparent that it has spread within California shelters and to an Oregon shelter. It is also affecting pet dogs in various cities in California.

It’s not surprising that these problems have surfaced again. H3N2 canine flu has been present in the US since it was first introduced from Asia in 2015, and continual re-introductions are probably occurring from importation of dogs from endemic areas. That’s how we got it in Canada, but we were able to contain and eradicate it Ontario (twice).

Here are a few key points for people in affected areas OR who are travelling with dogs to those areas OR moving dogs from those areas.

  • Canine influenza looks like any other type of “kennel cough.” There’s nothing clinically that says a dog’s illness is “flu” vs “not flu.” Dogs with respiratory disease that have been in affected areas should be considered flu suspects.
  • If your dog has a fever, cough, runny nose or eyes, or any other signs of respiratory disease, keep it away from other dogs. Dogs can shed H3N2 for a few weeks, so keeping any flu cases isolated from other dogs for at least 28 days is the goal.
  • If your dog has signs of respiratory disease, definitely don’t take it to a kennel or other place where there are lots of other dogs. That’s how we end up with rapid widespread transmission.  When the flu virus gets into a place like a shelter or kennel, it spreads quickly. Often, most or all dogs get infected. Some might not look sick, but they can still be infectious.
  • If you think your dog might have flu, call your vet. Don’t just show up at the clinic. If your dog needs to be seen by a vet, calling in advance can let them make plans to reduce the risk of exposure of other dogs at the clinic.

Vaccination against H3N2 can be useful but cannot be relied on as the primary means of infection control. It’s like any influenza vaccination (including the ones used in people) – it’s not going to totally prevent most individuals from getting infected. It’s designed to reduce the incidence and severity of disease. For me, its role is to reduce the likelihood that an infected dog will get seriously ill or die. That’s certainly useful, but vaccination is not a way to prevent flu from getting into a kennel or shelter, or spreading once it’s there.

While canine flu is highly contagious, it can be contained, with effort. We were able to contain it when it hit Ontario a couple times in 2018, with a lot of testing, communication, quarantine and probably a healthy dose of luck, to be honest. Sometimes, people take an “oh well, it’s here and there’s nothing we can do” approach. There’s almost always something that can be done -usually good ol’ basic infection control measures will go a long way.

I’m once again prepared to call Ontario (and Canada) canine influenza-free… for now, at least. The latest cluster, associated with another importation of the virus from China, seems to have been contained.

The last new positive case was identified October 30, with the likely date of exposure being October 23. We are now beyond the 28-day shedding window that we use for H3N2 canine flu, plus some extra time tacked on to give us time to identify new cases that might have been exposed near the end of the last dog’s shedding period.

The apparent abrupt halt in new positive cases, within two weeks of the first case, once again shows how this highly contagious virus can be contained with quick identification (astute primary care vets), quick response (testing, contact tracing and communication) and responsible ownership (complying with requests to keep infected dogs away from other dogs).

Will canine flu come back?

  • Probably. It’s widespread in Asia and parts of the US. We import a lot of dogs from those areas.

Can we reduce the risk?

  • Yes. Quarantine and testing of new dogs after they have been imported from high risk areas is a fairly straightforward measure that is used too uncommonly.

What else about imported dogs?

  • We need to figure out more about the risks associated with importing dogs and how we can contain those risks. While I’d like to see importations decrease, I’m not naive enough to think that’s going to happen anytime soon, and at this point, I’d rather work with importers to reduce the risk. More on that soon.

I’ve been behind on posts so here’s a quick update: things seem to be going well in the latest Canadian H3N2 canine influenza outbreak. Here’s the rundown:

  • After eradicating the last outbreak in the spring, cases were identified again in mid-October, associated with more importation of dogs from Asia.
  • The last new positive dog was identified October 30th.
  • All infected dogs that have been identified in the latest cluster have  close ties to the index site and have been from one area. One of these dogs left the region but has (hopefully) been kept quarantined for 28 days (as have the rest of the infected dogs).
  • Most of the infected dogs that we have been able to follow serially (i.e. test multiple times) are no longer shedding the virus.

We can’t call this over yet, since our last new case was October 30. Dogs can shed the virus for a few weeks after infection (even if they look healthy). Currently, we use 28 days as the potential shedding period. So, we’re looking at ~November 26 as the end of the window for the last known case. I tack on a week or so to give us time to find any cases that might have been infected at end of that period. Odds are quite low at this point that there will be more transmission from this outbreak, but we need a bit more time and testing to be sure. By early December, we can hopefully declare this over.

This is hopefully another example of our ability to eradicate this highly infectious virus with astute primary care veterinarians, quick testing, good communication and responsible owners who will quarantine infected animals. I’m always wary of speaking to soon (or jinxing it), but it’s important to know this approach can be successful. It’s not often done (explaining why flu continues to spread in some regions) but with some effort, diseases like this can be contained.

At the same time, the effort required and the potential for such a virus to spread beyond our control can’t be ignored. That’s why we need to be careful when importing dogs from areas where canine influenza is widespread.

Things have been quiet over the past few days. That’s good news (but always makes me a bit antsy, because I want to be sure it’s because there are no new cases vs we’re just not finding them). Documented infections have been confined to one region, with the exception of a dog that travelled out of the area, and which is (hopefully) being kept under quarantine for 28 days at its new location. We’re still testing and getting negative results, and veterinarians in the area are still looking out for potentially infected dogs, so hopefully the situation is being contained. The next week or so will tell us more, as we continue to test and as initially infected dogs start to eliminate the virus.

At a minimum, we want to go 35 days or so after the last new infection before we say we might be in the clear again. Since some dogs can shed the virus for over 3 weeks, I use 28 days as the upper end of the shedding period. I then tack on an additional week, since it takes some time for a newly exposed dog to get sick and be tested. So, if our last known dog was infected Oct 23 (to pick a random but reasonable date), it could shed until Nov 20. Add on a week, and we get to Nov 27. If there are no new cases by then and we still have excellent surveillance by vets and dog owners, we would suspect that the virus has again been contained. If we find any new cases, the clock restarts each time. (I hesitate to write about containment at this point because it sounds like I’m inviting bad luck, but I get a lot of questions about this).

To contain the current cluster of canine influenza we need:

  • Continued diligence by veterinarians and dog owners
  • Continued testing of exposed dogs and any other suspected cases
  • Compliance with quarantine recommendations so infected dogs don’t pass on the flu to other dogs

So far, so good, but time will tell.