Finding H5N1 avian influenza in mice in the US has caused a lot of angst amongst some – some angst is warranted, but some of it is overblown. That’s not because H5N1 isn’t an issue, or that more species being involved isn’t relevant, but because there are bigger issues to address. Adding yet another species to the susceptible list isn’t a doomsday scenario, even though we’d rather that list didn’t get any longer.

The latest APHIS report involved detection of H5N1 in an additional 36 house mice in Roosevelt County, New Mexico. They’d already found 11 infected mice there earlier in May. Typical of this ongoing outbreak in the US, available details are sparse. I haven’t seen a clear statement about where these additional mice were collected. I assume they were from infected dairy farms, and that’s a pretty basic but critical piece of info. (The first 11 infected mice were reportedly from an infected poultry premise). If the new mice were from farms with infected cattle, it’s not surprising to find the virus in mice at the same location. If they were from other areas, that would be more confusing and more concerning.

How do mice get infected?

I haven’t yet seen any genomic information on the virus found in the mice; it will be helpful to know if they were infected with the dairy cow-associated H5N1 strain, or whether some of the infections might be linked to exposure to wild birds. If we go on the assumption that these mice were from dairy farms, cattle are the most likely source, because we know infected cattle shed lots of virus in their milk, which would make it easy for mice on the farm to be exposed to the virus in the environment. Even though flu virus doesn’t survive long in the environment, if there’s lots of milk loaded with lots of virus (especially in areas where mice are looking for food), mice are likely to encounter some active virus. Fecal shedding of H5N1 in cattle seems to be low, but data are pretty sparse; we need to clarify that risk more since that would be another possible means of exposure for mice (and other animals, and people). It’s obviously highly relevant since cattle produce a lot of feces, and that manure needs to be stored and/or spread somewhere.

If we think about the risks from finding H5N1 in mice, I’d consider four main areas:

1) Risk to people from H5N1 in mice

Yes, there is a risk to humans, to some degree – but we need more information, like the amount of virus the mice were shedding, and how (e.g. fecal shedding vs respiratory shedding). Some infected mammals shed a lot of virus, but others are likely dead end hosts that don’t shed enough virus to spread the infection any further.

Even if mice shed appreciable amounts of H5N1, we don’t tend to have close contact with (wild) mice, so the risk from direct exposure is presumably really low. If someone’s on a dairy farm with infected cattle, mice are very low on the risk scale. Cattle are the biggest risk. Cats are probably #2 on the list.

However, mice do get into peoples’ homes as well, and the risks from that are completely unclear. Flu virus doesn’t survive long outside the host, so it’s not like a virus like hantavirus, where mouse poop in the environment is a significant concern, but we need to know more about virus shedding.

At this point, I suspect the direct risks to people are very low, but not zero.

2) Risk to other species from H5N1 in mice

The biggest risk from this new finding might be mice acting as a bridge from wildlife / livestock to humans, through their potential to infect cats. Cats catch mice, and eating an infected mouse is presumably high risk for H5N1 transmission (just like eating an infected bird). Cats are susceptible to infection, and have close contact with both mice and people (and other domestic species), so anything that increases the risk of cats being infected is a concern.

3) Risk of mice spreading H5N1 farm-to-farm

As we start to (slowly) get more information about H5N1 on dairy farms, we’re seeing more reports of infected farms that did not bring in cattle from other infected farms. That makes us wonder about other sources of introduction, like humans tracking the virus around or spread via wild birds. Fortunately mice, like coconuts, do not migrate (yes, that’s a niche reference – see link below), so they probably pose limited risk for broad geographic spread of the virus because they’re not that mobile (unless they hitch a ride on a human conveyance of some kind…). Mice tend to have very small ranges, so it would probably be tough for them to spread H5N1 even between farms, unless the farms were very close to each other. The bigger risk would be bringing the virus from the barn into the farm house.

4) Risk of virus mutations

The more avian influenza spreads to and within mammals, the more opportunities it has to adapt to mammals. It would take a number of specific genetic steps for an avian flu virus to evolve to effectively infect and spread between mammals (including people), but the more it’s transmitted, the greater the risk that could happen. This is why we don’t want to see avian flu spreading in any mammalian species.

So, while I don’t like seeing more H5N1 infections in more mammalian species, and even though if H5N1 became endemic in mice they could be a long term reservoir, I’m still more worried about birds, cattle and cats at this point.

Back to H5N1 flu in cats

The good news is that infections in cats are still rare. The bad news is that most reported infections in cats have been very severe or fatal. Whether severe disease is the norm in cats, or whether we’ve mainly just tested really sick cats is hard to say. There have been approximately 21 cases of H5N1 influenza identified in domestic cats in the US since the outbreak in cattle was first detected. Other cases have been reported in cats in various parts of the world over the last 2+ years, including in Canada. However, those cases are probably just the tip of the iceberg. We need more surveillance, including testing of healthy and sick cats from locations where H5N1 is present. Cats on dairy farms with infected cattle are at the highest risk, but any cat with outdoor access that might encounter an infected wild bird is at some risk.

What do we need?

More surveillance and more communication. We need broader testing on affected farms, thorough epidemiological investigation of the spread on and between farms and clear (and timely) communications.

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After a recent case of H3N2 influenza was detected in a dog in Calgary (that presumably originated in the US), there’s not much to update, which is hopefully good news. Things have been quiet. On one hand, that’s a bit surprising, because flu is highly transmissible and there’s basically no pre-existing immunity in the Canadian dog population (due to lack of exposure and low vaccination rates). On the other hand, it’s possible for new disease introductions like this to die quickly if the affected dog(s) have limited contact with other dogs.

Whether introduction of flu results in no additional cases, a small cluster of cases, or a large and sustained outbreak depends on the number and types of contact the infected dog has. The more dogs it encounters when it’s infectious, the greater the risk of spread. That’s infectious diseases 101.

Over the past two weeks, since we’ve been tracking this, there have been typical reports of respiratory disease in local dogs but no new cases of canine flu. We’re prepared to do testing, but haven’t heard about any high risk situations that would warrant more testing.

Does that mean this flu outbreak has been contained?

Maybe. At the individual dog level, canine flu looks no different than other causes of infectious respiratory disease in dogs. Most dogs with respiratory bugs get “flu-like” disease that resolves on its own. Some dogs get more severe disease and/or develop secondary pneumonia, and a small percentage of those dogs may develop fatal infections. So flu can’t be ruled out by looking at just a dog’s clinical signs, and we have to temper the current “no new cases” due to the typically limited testing of dogs with respiratory disease.

However, since flu is so transmissible, case patterns mean a lot. When flu spreads into the community, I expect to see noticeable outbreaks. Yes, the virus can circulate in household dogs and maybe be missed if people aren’t reporting disease, but I’d expect it to make it into kennels, day cares and/or shelters too. There, I’d expect to see high morbidity outbreaks with a lot of sick dogs in a very short period of time. We see outbreaks in these settings regularly, but with flu, I expect pretty much every exposed dog to get sick, usually around the same time. The pattern tends to be more dramatic with flu compared to other pathogens, and we haven’t seen that pattern so far following the Calgary case (but we’re ready to test if it does pop up).

At this point, it’s so far, so good. Each day that goes by without a new case or concerning situation is good news. I wouldn’t be confident saying the virus has been eliminated for at least a few more weeks, though. We still need a bit more time and testing for that.

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Canine influenza has been identified in a dog in Calgary, Alberta. It is suspected to have been acquired from dogs that participated in a dog show in the US near the end of September. As expected, H3N2 canine flu is the cause (not H5N1 avian influenza, which has been detected in a number of poultry flocks in Alberta since September). Unfortunately, the dog died. It was a higher-risk dog for more serious disease or complications because it was a brachycephalic breed (i.e. smush-nosed breed).

The canine H3N2 influenza A strain has been present in the US since 2015, but is not known to be circulating in Canada. We had a couple of outbreaks of canine H3N2 influenza in Ontario in 2018, but we were fortunately able to eradicate it, in large part because of intensive testing and good owner compliance regarding isolating affected and exposed dogs, and likely some plain old good luck.

This virus is highly transmissible in the Canadian dog population as almost no dogs have any immunity, since most have never been exposed to the virus before and very few are vaccinated against canine flu. So, it can spread very quickly. As you’d expect, places where dogs congregate, including kennels and dog parks, are higher risk for transmission. We are getting reports of other dogs with flu-like disease in Calgary and other Alberta cities. The problem is, there are many other causes of respiratory disease in dogs, and they all can look similar to flu. So, without testing, we don’t know if we are seeing an outbreak of canine flu or just normal background canine respiratory disease activity.

How severe is influenza in dogs?

It’s like influenza in people: Most dogs have a self-limiting “flu-like illness” with fever, cough, decreased appetite and general malaise. Most will recover on their own with some TLC. Some will develop secondary bacterial pneumonia. A small percentage (1-2%) will die, with the greatest risk of death being in older dogs and brachycephalics.

Can dogs be vaccinated against canine flu?

Yes and no. Yes, there are flu vaccines for dogs. However, they have been hard to get because of production issues, and there is currently no supply available in Canada. But flu vaccines are not going to stop an outbreak regardless. It takes 2 doses and a few weeks for a dog to develop protection from a vaccine, and vaccines are not great for stopping transmission – they’re designed to reduce the severity of disease. That’s useful, especially in high risk dogs, but they’re not a good control tool for this virus.

What should people do?

Step 1: Don’t panic.

Step 2: Think about your dog’s social network. The more dogs it encounters, the higher the risk it could come in contact with the virus.

Step 3: Try to reduce your dog’s canine contacts. If I was in an area where flu was present, I’d avoid dog parks and other places where dogs can meet, until the issue is sorted out. Sometimes we have to mix dogs for specific reasons, but the more we can reduce that, the better.

Step 3b: If your dog is sick, keep it away from other dogs. Dogs with flu can be infectious for a day or so before they get sick, so we can’t rely completely on this, but any dog with potential flu (or that has been exposed to a dog with flu) should be isolated from other dogs. We’ve seen dogs that are PCR-positive for over 3 weeks after infection, so isolating them for a month is ideal. However, realistically, the risk of transmission is probably limited after 10 days. So, it becomes a matter of practicality. The longer the isolation, the better, but I’d definitely isolate for at least 10 days, as an absolute minimum.

Who should be tested?

Testing dogs is often is more useful from a population standpoint. I want to know where flu is to understand transmission and risk. It can also help with isolation recommendations. However, it rarely impacts the individual dog because rarely would be do something specific for influenza. Testing is never a bad idea, but if the dog has known contact with a dog with flu and has flu-like disease, we can be pretty confident is has the flu.

If testing is done, it needs to be done in a manner that prevents more transmission. For our outbreaks, dogs were sampled in homes and parking lots as much as possible, to limit dogs going into veterinary clinics. Clinics can handle flu cases and minimize the risk of transmission to other patients (if they know there’s a potential risk), but keeping dogs out of clinics is ideal unless they need medical care or there’s a clear need for testing (and swabbing a dog for testing can still be done outside, even at a clinic).

What’s the risk to people?

Very limited. There’s no evidence that the canine H3N2 strain of influenza can infect people. We never say never, but it’s not something we are currently concerned about. The main risk is simply from having one more influenza strain in circulation in the community, because we are most concerned about mixing of strains, where an individual gets infected with more than one flu strain at the same time, and those flu strains recombine to make a new strain. If that strain can infect people but is different enough from our seasonal human influenza viruses, then we create the risk of a new, highly transmissible human flu to which no one has any immunity. Since we are at the start of human flu season, and we are expecting a fall surge in H5N1 avian flu in wild birds, and we have endemic flu in pigs (and horses), we don’t want to add yet another flu strain to the mix. If a dog got H3N2 canine flu and also got infected with human flu (as we know they sometimes do), then the dog becomes a potential “mixing vessel.” The odds of that happening are very low, but they’re not zero, so we need to take reasonable precautions to decrease the risk.

As usual, this is a fluid situation and we’re trying to get more information. Hopefully I’ll have more updates here and on twitter/X (@weese_scott) soon.

More info about canine flu can be found in the Worms & Germs Blog infosheet on H3N2 Canine Influenza and in some of our previous Worms & Germs Blog posts on influenza.

If we know one thing about influenza A, it’s that there will always be something new with this virus.

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A recent study out of China (Meng et al. 2023) describes what seems to be a new canine flu strain. Is it a concern? It’s hard to say at this point, but having more flu strains in a species with which we have close contact is never a good thing.

This was a surveillance study of dogs in an area of China where there’s a massive amount of pet dog breeding and trading. Our familiar H3N2 canine influenza is endemic there, and avian flu strains circulate in wild birds, creating the potential for spillover of avian flu viruses into dogs and/or emergence of new strains from virus reassortment.

Researchers tested dogs from November 2018 to April 2019, and identified influenza virus in 60 of 534 dogs (11%) by PCR. Follow up testing resulted in isolation of live influenza virus from 12 dogs. Isolation of live virus requires culture techniques. We expect to get less recovery with culture compared to PCR, since PCR will detect lower viral loads and does not require the virus to still be viable by the time of testing.

Five of the flu viruses that were isolated were H3N2.

  • That’s not surprising, since H3N2 is a well established canine flu strain in China.

Interestingly, seven of the viruses were H3N6.

  • Looking at the genetic makeup of the virus, it appears to be a mix of H3N2 canine flu and an H5N6 avian flu strain that was circulating in birds in China in 2017 and 2018.
  • It was hypothesized that this was a result of a dog being co-infected with H3N2 canine flu and H5N6 avian flu, resulting in creation of this new H5N6 strain.

Does this mean there’s a new canine flu strain circulating in China?

That’s unclear. Positive samples were from dogs in one shelter at one time point, which could happen for a few reasons:

They found the first dog with this strain, and picked up transmission in the shelter that burned out, making this a one-off event.

  • It’s very unlikely they would have gotten that lucky and captured the very first emergence of this virus. Some of the in vitro characteristics of this virus suggest it should be well adapted to mammals, so full containment is probably unlikely. There’s also some genetic variation in the H3N6 isolates, which we wouldn’t expect with a single point-source exposure.

This virus is rare in dogs and there was cluster in that shelter at that time.

  • Possible, but odds are low that researchers would pick up a rare event like that. As above, the genetic variation in strains suggests that this was more likely from multiple introductions of the virus into the shelter.

H3N6 is circulating in dogs and this study detected a strain that’s been present in the region for a while.

  • This seems most likely.

The lack of clear sampling information is a big limitation in terms of interpreting the study results (e.g. were the dogs sampled on admission to the shelter? Were the positive dogs housed together? Were they sick?).  That’s very basic information that needs to be in a paper like this, but that weak journals may let slip or don’t think to query.

The main things I take away from this report are:

  • We need more surveillance to see if this strain is still present and where it is distributed. H3N6 is probably a relevant new-kid-on-the-block. It’s probably established given it was found in an area like this with massive dog breeding.
  • Changes in importation rules will reduce the risk of this virus hitting North America, but there are enough loopholes that there is still a very reasonable likelihood that it will be introduced here at some point.
  • We need to continue to watch for influenza A infection in various animal species. That includes dogs, which often fall between the cracks because it’s usually VERY hard to get support for disease surveillance in companion animals (compared to food animal). Lots of agencies want to know the results, but rarely do they want to foot the bill. It’s a significant gap in One Health surveillance.

What will we see if H3N6 flu hits Canada (or another country)?

Assuming it causes disease similar to other flu strains, we’ll see large numbers of dogs with typical flu-like disease (which will be lumped together with routine occurrences of “kennel cough”). The number of cases will be the dramatic thing, not the severity; however, with lots of cases, we’ll see more severe cases just based on percentages.

Since dogs will presumably have no existing immunity to this strain, the main thing I’m looking out for is big outbreaks. We see “kennel cough” outbreaks all the time, caused by our usual suspects like canine parainfluenza virus, Bordetella bronchiseptica and canine respiratory coronavirus. However, if/when a new flu virus hits, it will likely be much more and obvious. Rather than an outbreak that affects a lot of dogs in a group (e.g. kennel, shelter), it will affect almost all of them. Rather than a single outbreak in a town, there will be many. I suspect it will be pretty obvious pretty quickly if this virus makes it here.

Yes, I’m prone to making typos. No, this title isn’t one of them.

While we’re in the midst of an unprecedented international outbreak of H5N1 avian flu (with ongoing spillover into mammals), there’s a new kid on the block: H5N5 influenza. I think recent reports of H5N5 were glossed over by some who didn’t realize we’re talking about a different strain from the H5N1 we’ve been dealing with the last couple of years. While it’s not necessarily a game-changer, we need to pay attention to new strains like this.

The story starts with the finding of H5N5 flu in birds in Atlantic Canada, which started in January 2023. The genetic makeup of the virus indicates it’s a Eurasian lineage that’s circulating in birds in Europe. It’s suspected that it made it to Canada via migratory birds last fall.

More recently, and more concerningly, this H5N5 strain was identified in two raccoons in Charlottetown, Prince Edward Island. As far as I know, this is the first report of H5N5 in mammals. Presumably the raccoons were infected from eating infected birds, which is how we suspect most mammalian wildlife with H5N1 get infected too.

With reports of “new” diseases, we always have to consider surveillance bias. We’re looking and testing a lot more now because of H5N1, so we’re more likely to find other things (such as other strains, like this) as well. That raises the question of whether this is truly something new or just something we’ve found now because we’re looking harder. Based on the genomics of the virus (being a Eurasian lineage), it’s probably something new for this region.

Regardless, the presence of yet another avian flu strain and more spillover into mammals is a bit disconcerting, to say the least. Recent genetic study of this H5N5 virus has indicated that it’s likely also capable of long-term circulation in birds and recombination with other flu viruses, so this is a virus to watch.

That’s not to say that we’re heading into a massive H5N5 outbreak. It’s one more flu virus in the mix, one more flu virus with the potential to recombine with other (human, avian, swine, equine, canine, etc.) flu viruses, and one more flu virus that can (even in its current state) spillover into mammals. So we need to stay on alert. There are lots of influenza viruses out there: some are nasty, they are prone to changing, and sometimes that can be bad for humans or other species.

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This can be filed under “concerning but not surprising,” but H5N1 avian influenza has been identified in a dog in Ontario

It’s concerning because any spillover into mammals raises concerns about continued adaptation of this virus to spread outside birds, and because spillover infections in mammals can be severe. 

It’s not surprising because when you have millions of infected birds internationally, it’s inevitable that domestic and wild mammals will be exposed. Even if transmission is rare, when there’s a lot of exposure, transmission becomes more likely to occur and to be detected.

The case at hand is a dog from Oshawa, Ontario that died several days after being found scavenging a dead goose. Both the dog and goose were tested for H5N1 highly pathogenic avian influenza (HPAI) virus, and both were positive. Sequencing of the virus at the National Centre for Foreign Animal Diseases was performed and the virus from both the dog and goose were the same, and were consistent with the H5N1 strain that’s circulating in wild birds and domestic poultry. Further testing is being performed to confirm the cause of death in the dog. Given what we know about spillover infections into related species like foxes, it’s certainly possible that avian flu could have contributed to the dog’s death.

What should people in Ontario (or anywhere else avian flu is circulating) do?

  • Relax. That’s the first thing. This is concerning but not a doomsday scenario. We know that spillover into various mammals is happening and it will continue to happen. Also, this was a pretty high-exposure scenario where a dog had a lot of direct contact with a bird that had died of avian flu. It’s a reminder of why we’ve been emphasizing the need to try to better understand this virus since the outbreak was first identified, and to try to prevent more spillover infections from wild birds.

The next step is to just take (or continue to use) some basic common sense measures to reduce the risk of exposure.

What can be done?

  • The big thing is keeping dogs (and other domestic animals) away from wild birds.  It’s a good general rule to keep dogs away from wildlife anyway (alive or dead). That’s particularly true when there’s avian flu activity in an area.

Can dogs be vaccinated against this flu virus?

  • No, at least not at this point. Canine flu vaccines target different flu strains (canine H3N2 and H3N8) and there’s not likely any relevant cross protection. 

What’s the risk to people from infected dogs?

  • It’s probably very low but this is an unknown. Spillover infections into other species are often “dead end,” where the infected individual can’t/doesn’t infect anyone else. However, there have been some wild mammal outbreaks where limited mammal-to-mammal transmission has been a concern. When litters of wild canids have been infected, it’s hard to say if they were all exposed to the same infected birds or whether there was mammal-to-mammal spread.
  • So, it’s a big unknown. With that, it’s reasonable to take precautions to reduce contact with potentially infected mammals. However, the risk is probably quite low.

Should sick dogs be tested?

  • Testing would be considered in situations where there’s a plausible concern about H5N1 flu, based on likely exposure and the signs of illness in the dog. Lots of dogs have respiratory disease from various viral and bacterial causes and there’s no use testing every coughing dog (especially since a mildly ill coughing dog isn’t going to be a classical presentation for this viral infection). Testing for H5N1 influenza can be done through veterinarians, typically by PCR testing of oro-pharyngeal (throat), nasal and/or rectal swabs. 

What about cats?

  • Basically, replace everything above with “cat” instead of “dog.” The risks and preventive measures are pretty similar. Keeping cats indoors (when possible) to reduce their exposure to wild birds, is the main measure. That will help protect both them and their human contacts.

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As the current (and unprecedented) H5N1 avian flu outbreak continues, there’s the ongoing threat of transmission to other species. The extent of spread to mammals is hard to say since it’s hard to know how many wild mammals have been infected. However, we know that an impressive range of species has been infected. Spread to mammals is a concern because the more widely this virus spreads, the greater the chance for recombination with other flu viruses to create a “new” strain that could cause serious problems in humans or other species.

A recent news report and the corresponding WOAH report are light on details but describe H5N1 infection in a domestic cat in France from late 2022.

The cat lived on a duck farm and was euthanized after developing severe neurological disease. That’s a clinical presentation that’s not been uncommon in mammals that have been infected with H5N1 influenza during this outbreak. That doesn’t mean this virus usually causes neurological disease. It might be a matter of animals with neurological disease simply being more likely to be noticed and/or tested. H5N1 avian influenza infection was confirmed, and the virus recovered from the cat had “genetic characteristics of adaptation to mammals.”

The good news is that cats (as far as we know) don’t have their own flu virus in circulation (unlike dogs, horses, and pigs). That makes it unlikely that a cat would be infected with avian flu and another flu strain simultaneously, which would increase the potential for viral recombination. However, it’s still a concern since cats can (rarely) be infected with flu strains from other species, including human flu viruses.

Overall, the relevance here is mainly to the cat. The odds of this signalling a new problem are low, but it highlights the concerns we have about how far this virus continues to spread. It’s playing with fire.

The other consideration is the potential for cats to act as a bridge from wildlife to humans. Cats that get infected through exposure to wild birds can bring the virus into closer contact with people. It’s another good reason to keep cats indoors whenever possible, particularly if avian flu is circulating.

The ongoing H5N1 avian influenza outbreak is an unprecedented event in its size, scope and duration (but it’s not getting much press anymore these days). As infections continue to occur is birds in large numbers over a vast geographic range, we worry about spillover events into other species.

There have now been many reports of H5N1 influenza infection in a variety of wild mammals, including foxes, skunks, raccoons and most recently bears. Sporadic transmission into wild mammals that live fairly solitary lives and probably aren’t (currently) great hosts for the virus raises concern, but the broader risks are probably limited because of the low odds that rare infections would result in a relevant change in the virus or recombination with another flu virus. However, more infections create more risk, and infections of species with more animal-to-animal contact, and animal-to-human contact amplify that risk.

That’s why the recent report of H5N1 avian flu on a mink farm in Spain raises some alarm bells. Infection of a farm with tens of thousands of mink is a whole lot different than infection of the odd free-roaming fox or raccoon.

Mink in cages. Source: https://www.bbc.com/news/business-37679652

The good news is that even though the report just came out, the outbreak occurred in October, and there’s no evidence I’ve seen that this resulted in a broader issue. The bad news is that it shows what can potentially happen (and surveillance is far from good enough to say that this hasn’t caused an issue).

The report is about an outbreak on a farm in Spain that housed over 50 000 mink. Concerns were raised when the mink mortality rate increased in October, suggesting something was going on. It seemed like a pretty classic infectious disease problem, as it started in one barn and was characterized by “multiple ‘hot  spots’ within the affected barns consisting of 2–4 pens where all the animals died within a period of 1–2 days.” Mortality rates then increased in neighbouring barns, then eventually across the whole farm. Infection with SARS-CoV-2 was initially the main concern, as has been seen on mink farms in many countries now, but tests for that were negative. Eventually they confirmed H5N1 flu as the cause of illness in the mink, and sequencing of the virus showed it was the same clade (2.3.4.4b) that’s been circulating in birds in Europe.

The decision was made to cull the mink, and over the course of about a month, all of the mink were euthanized and their remains disposed.

Farm workers were tested at one point, and all 11 were negative. That was good news, but single point-in-time testing of people exposed to an infected mink farm over the course of weeks doesn’t rule out transmission. (Though it’s worth noting employees were already required to use enhanced precautions, like wearing masks, because of the concerns over SARS-CoV-2 transmission to (and from) the mink, which may have also helped limit transmission of flu.) One of the workers later developed flu-like signs but tested negative for flu virus. Because of the disease transmission concerns, a “semi-quarantine” of the people was performed to limit contact with other people for 10 days after their last contact with the farm.

The source of the outbreak isn’t known. It’s possible that it was introduced by poultry products fed to the mink, but there’s no evidence that any supply farms were infected. It’s much more likely that wild birds were the source, and infected wild birds had already been found in the area at the time of the outbreak. This highlights concerns about mink farms as a wildlife/domestic animal/human interface. It’s hard to keep wildlife away from a mink farm, which creates risk for transmission both from and to wildlife. If wild birds can infect mink, it’s equally likely that wild birds (and other wildlife) could be infected from mink, through contact with the mink farm environment. A virus that spreads to the mink can then spread to human farm workers, domestic animals on the farm, or other “visiting” wildlife. That’s not a comforting scenario.

The report concludes by stating that the mink sector is still important economically and “it is necessary to strengthen the culture of biosafety and biosecurity in this farming system and promote the implementation of ad hoc surveillance programs for influenza A viruses and other zoonotic pathogens at a global level”. I agree with the second part of this statement, but as for the first part, we need to think and risk versus reward. Are the benefits of mink farming worth the risks that come with raising large numbers of animals that are susceptible to various human viruses, in close proximity and with ongoing contact with people and wildlife? The broader societal benefits of mink farming are (to me) negligible, and the risks may be low, but they are not zero and not adequately understood.

Image from https://www.bbc.com/news/business-37679652

It’s been a busy fall for canine flu.   We’ve started tracking canine influenza cases to have a better idea of its spread and to help with risk assessment and vaccination decisions (although canine flu vaccine shortages have also been an issue).

We’ve created an interactive map of our preliminary canine flu surveillance to date.  A screen shot of the current map is shown below.

More data are hopefully coming, so the map should be more detailed in the near future. Veterinarians can use this link to quickly submit additional case information (just number of cases and location).

Our definition of a confirmed canine influenza case for the map is:

  • Laboratory-confirmed diagnosis of canine influenza OR
  • Acute respiratory disease in a dog that has had direct contact with a laboratory-confirmed case of canine influenza

More frequent map updates will likely be provided on Twitter: weese_scott

As canine flu causes another (and particularly impressive) round of outbreaks in the US, a lot of questions arise. A big one involves vaccination.

I won’t go over the whole “what is canine flu?” spiel in this post, but I’ll give a quick overview of why we care about it. It’s a highly transmissible virus that acts… well… like flu does in people. It can cause disease in dogs ranging from mild to fatal. The mortality rate is hard to estimate but it’s probably 1-2%. It was ~2% in our Canadian outbreak of canine influenza in 2018 and we had really intensive surveillance, so it’s probably a pretty accurate number. Deaths are most often reported in older dogs. Dogs with underlying heart or lung disease are presumably at higher risk for mortality too. The same might apply to brachycephalic breeds (squishy faced breeds like bulldogs) since they are more prone to respiratory complications. Like human flu, deaths in otherwise healthy, younger individuals are rare but can occur.

Flu outbreaks are a big problem, and that can be a bigger issue in dogs than people, because we don’t have the same degree of seasonal flu every year in dogs. In humans, there’s a lot more population immunity because of repeated exposure and vaccination. Most dogs in North America have neither been exposed nor infected, so they’re ripe-for-the-picking immunologically.

Obviously there’s a canine flu vaccine, since that the topic du jour…

Yes, we have a couple of canine flu vaccines. They can be for the H3N2 strain alone, or H3N2 and H3N8. H3N2 is the currently circulating canine flu strain. It’s an avian-origin strain that has become adapted to dogs and entered the US from Asia in 2015 (and repeatedly thereafter). H3N8 canine flu emerged in the early 2000s, but as far as we can tell, it hasn’t been around for a while. So, H3N2 vaccination is the key.

How good is the canine flu vaccine?

Well, it’s a flu vaccine. They’re not known for being incredibly effective, but are useful to reduce the incidence and severity of disease. I’m most motivated to have higher risk dogs (e.g. old dogs, dogs with other health problems) vaccinated to reduce the risk of them getting severe disease. It’s going to be less effective as a population control measure since it isn’t great for protection against viral shedding, but it should help some.

What dogs should be routinely vaccinated against flu?

That’s a tough call since it’s a really sporadic disease. You might not have flu within 100 km of your dog for its entire life, or you might run into an infected dog tomorrow.

My main considerations are risk of exposure and risk of severe disease.

  • Risk of exposure depends on whether the virus is in the area, how likely it is that it will be brought into the area (e.g. outbreaks nearby), how likely it is for the dog to be exposed somewhere else (e.g. the dog travels with its owner or goes to dog shows), how likely it is for the dog to be exposed to a high risk dog from somewhere else (e.g. contact with dogs imported from Asia, or dogs from other areas where flu is active) and how many dog contacts it has (the more contacts, the greater the risk, particularly if there are contacts with dogs of unknown health and travel status).
  • Risk of severe disease is the other consideration, as described above.  I’m quicker to recommend any respiratory disease vaccine in seniors, dogs with other illnesses and brachycephalics.

Thinking about those two components helps assess how useful the vaccine might be.

If flu is active in your area, vaccination is definitely worth talking about with your veterinarian.

How is canine flu vaccine given, and how often?

It’s an injectable vaccine.  It requires an initial dose and then a booster 2-4 weeks later. That booster is important and shouldn’t be missed. We don’t do that in people, but dogs need it since most don’t have pre-existing immunity from earlier exposure and vaccination. After that initial series, it’s boosted once a year.

Another potential issue is vaccine availability. It’s been a niche vaccine, but with the large number of outbreaks in the US at the moment, demand has outpaced supply. Shortages are currently an issue in many areas.

While not related to the vaccination theme of today’s post, the question of whether canine influenza poses a risk to people often comes up too.

As far as we know, currently circulating canine flu strains do not infect people. That doesn’t mean it’s impossible (the current H3N2 changed from a bird to canine flu virus) but there’s no evidence it’s a concern right now. The main concern is the potential for a recombination, where different flu viruses (e.g. human, avian, swine, canine) infect the same host and the same time, and then reassort and create a new flu virus. We don’t have evidence of this happening but it’s always a concern with flu viruses, and it’s why we try to limit the number of different flu viruses in circulation (in any species).

What am I doing about canine flu?

At this point, we don’t have any evidence of canine flu in Canada. It might occur any time, and who knows where it will pop up, but at this point, the risk of infected dogs in my area is low.

Beyond that, Ozzie and Merlin don’t’ have particularly busy social calendars. We live in the country and they don’t see other dogs here. They see a small number of family members’ dogs sporadically, but their overall dog contacts are limited.

Ozzie (pictured here) is young and probably at limited risk of severe disease.

Merlin’s 11 and has chronic lymphoid leukemia that we’ve been managing for a year. He’s pretty healthy, but presumably at higher risk of a complication.

If flu was in the area, I might vaccinate them, but their risk of exposure is still pretty low so I’m not sure I would. If they had more contacts, I’d vaccinate Merlin for sure, and probably Ozzie too. With no flu in the area and limited dog contacts, I’m not motivated to vaccinate them at the moment. For some dogs, though, vaccination is definitely worth considering.

And from a non-canine standpoint… get your own flu shot. It won’t protect you or your dog from canine flu, but it’s been a nasty human flu season, and it can definitely help with that.