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.

As expected, a few more cases have been identified in the most recent cluster of canine influenza virus (CIV) identified in Ontario. So far, there are about 20 confirmed or suspected cases. To date, we’re still only finding cases that have a link to another infected dog or facility. That’s good news. If we start getting cases of unknown origin and/or cases outside the currently affected area, I’ll be more concerned (specifically about the prospects of containing the cluster). A couple of dogs that were potentially exposed and left the area already are being tracked.

Continued diligence by pet owners and veterinarians will help contain this virus. The key is finding all the potentially infected (and infectious) dogs, testing them and keeping them quarantined until they’re no longer a risk to others.

A 28 day quarantine is recommended because of the potentially long shedding period of this virus. In the previous outbreak (as in this one), we sampled positive dogs repeatedly, and some shed the virus for over 3 weeks. So, even a 28 day quarantine doesn’t leave a lot of cushion, but the longer the quarantine period, the greater the risk of non-compliance. Getting people to keep their dogs away from other dogs for 28 days often isn’t easy to do. We like to complain about the weather in Canada, but it will probably help in this situation. It’s forecast to be few degrees above freezing with mixed precipitation over the next few days, something that may help keep dogs from congregating outdoors, buying more time to sort out the problem.

More details to follow.

While we’re still working on sorting out and containing our latest Canadian outbreak of H3N2 canine influenza, we can look to the south to see the problems this virus is still causing. Flu is still active in a variety of locations in the US. The numbers reported are presumably a marked under-estimate, since it’s based on clinical diagnostic testing. Only a fraction of sick animals tend to be tested, so many unidentified cases are probably occurring alongside the reported cases.

The latest IDEXX Laboratories’ data are displayed below:

More cases of H3N2 canine influenza have been identified in the province since the virus was re-introduction to central Ontario in the last week. That’s not surprising, since the start of any outbreak investigation is dedicated to figuring out the extent of the problem. Cases identified in the first few days or week reflect things that happened before we knew anything was going on. It’s what happens after the first week or so that’s most important. Ideally, once we know something is happening and start to intervene, new cases decrease and those that are found are found because we’ve traced them from other infected dogs. When new cases occur out of nowhere, we get concerned that we don’t truly know the extent of the issue.

So, at this point, we’re in a holding pattern, waiting for more testing and watching for more cases.

A few key points for everyone to keep in mind:

  • If you live in the affected area (Muskoka region) or visit there with your dog, be on the lookout for respiratory disease (e.g. cough, runny nose, runny eye) in your canine companion. If your dog develops signs that could be influenza, call your veterinarian first – don’t just show up at the clinic. If your dog needs to be examined, your vet will want to take precautions to make sure your dog doesn’t infect other dogs at the clinic.
  • Most dogs with flu develop fairly mild disease that resolves on its own. Some develop complications (e.g. pneumonia) that require treatment such as antibiotics. Rarely, flu can be fatal. Regardless, it’s highly transmissible and can spread quickly in the dog population
  • If you have imported a dog from Asia (or have adopted a dog that was imported in the past month), keep it isolated from other dogs for at least 28 days after arrival. If your dog has been in contact with an Asian import, keep it away from other dogs for 28 days.