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A presumptive case of H5 avian influenza has been reported in a teenager from British Columbia. Confirmatory testing is underway. Very little additional information has been released, so it’s hard to say how surprising and concerning it is. Information vacuums like this often lead to excessive speculation, but information sharing has to be balanced with privacy of medical information, and we don’t have an automatic right to know everything about a case immediately. It also takes time to properly investigate a case, and there’s often (understandable) reluctance to release very preliminary findings where there are still a lot of unknowns. Hopefully some reliable details will be released soon as the investigation continues.

A few key things that we’d like to know include:

  • What was the source of the virus in this person? The government release indicates “The source of exposure is very likely to be an animal or bird, and is being investigated by B.C.’s chief veterinarian and public health teams.” The lack of a specific statement that this was linked to a known poultry infection has led some to questionable messaging. A ProMedMail report said “Based on the details provided, it would seem the individual did not have direct contact with infected cows or poultry” which seems to be a questionable (bordering on irresponsible) overstatement at this early point in the investigation. It might be true, but it’s way to early to raise concerns about unknown exposure routes, especially given there are active cases of H5N1 in poultry in this region.
  • What strain is the virus in the person? Presumably it’s the circulating wild bird strain (vs the strain circulating in dairy cattle in the US, or another strain from wild birds, or imported from overseas), but knowing more details about the strain and whether it has any relevant mammalian adaptations is important.
  • Have there been any additional human cases? This takes time to determine, but it’s important to know whether this was a single isolated event with no human-human transmission, part of a cluster associated with common animal contact (e.g. on a poultry farm), or whether there was any downstream human-to-human transmission. So far, no other human infections have been identified.
  • How serious was the illness in this person? The press release only indicates that the person “is receiving care at BC Children’s Hospital.” While there’s public interest in knowing how severe the infection is, that’s personal medical information, but hopefully some information will be released at some poiny. Infections in people associated with the H5N1 strain in the US have been mild, and hopefully that’s the case here too.

Ultimately, it remains to be seen if this was a rare but expected spillover to a person with known direct contact with infected birds (the most common and most reassuring scenario) or something else. The less it fits that scenario and the harder it is to explain the infection, the greater the concern.

As usual, social media has a big camp amplifying “the end is near” messaging. While it’s not good news, there’s nothing here yet that raises a lot of concern, beyond the fact that every human exposure and human infection is playing with fire, as it creates more opportunities for this virus to change and adapt to people. As I’ve said before, I’m not really concerned about the currently circulating strain of H5N1 from a human health standpoint, since it rarely causes disease in people, typically causes mild disease when it does, and is not well adapted for human-to-human spread. I’m concerned about what this virus could do if it becomes more adapted to humans, with an ability to spread effectively between people and cause more severe disease. We need to do all we can to contain it, limit spillover infections and address those that occur promptly, but we need to maintain some perspective at the same time.

Presumably more information will be released soon to help us better understand this situation.

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A lot of infectious disease events get over-hyped by the media, which makes it a bit surprising that this case has flown a bit under the radar. It’s not a sign of an impending “influenza apocalypse,” but it’s a warning sign that more may be going on lately with flu viruses than we’ve been able to observe directly.

The CDC has confirmed a case of H5 influenza infection of a person in Missouri who had no reported contact with animals of any kind. The virus has only been identified as H5 or H5Nx, which means they have not confirmed the N-type, so we can’t say if it’s the same as the H5N1 influenza that has been circulating in wild birds since 2022, or in dairy cattle in the US since spring 2024. It’s surprising that the N-type has not been determined yet, since the infection was detected over 2 weeks ago – but knowing the strains that are circulating in the US right now, I’d say it’s almost certainly H5N1. (Sometimes sample quality can impede the effectiveness of molecular diagnostics too.)

Human H5N1 infections linked to the ongoing massive multiyear avian influenza outbreak have been rare. There have been just 14 reported H5 infections in people in the US so far in 2024, despite a huge amount of potential exposure, particularly among livestock and poultry workers. All previous human infections have been linked with direct and close contact with infected animals.

Rare spillover infections like these are largely expected when there’s lots of disease in animals. The worry is the potential for the virus to change to become amenable to human-to-human spread, so finding a human infection like the one in Missouri with no direct link to animals raises a lot of concern. The source of exposure in this case has not been determined. Details are sparse, but the person was reportedly hospitalized and recovered, and H5N1 testing was done as part of ongoing surveillance.

How could a person get H5N1 without animal contact?

  • Unreported animal contact, possibly due to incomplete history taking, or poor recall or unwillingness to report contact on the part of the patient for some reason)
  • Contact with a surface contaminated by an infected animal
  • Ingestion of contaminated food products

We hope the source of infection in this case was one of those. Hopefully they queried all animal contacts, not just birds and cattle, since we’re also concerned about infection from susceptible species that can bridge bird, cattle and and human populations (particularly cats).

Otherwise, we get concerned about the last option:

  • Contact with another infected person

As has been pretty common, details have been slow in being released. More information is needed about the person’s history, including whether the person had any human contacts that were high risk for exposure (e.g. worked with infected animals), and the genome of the virus to see if it’s consistent with the circulating avian strain, the strain that jumped to dairy cattle, or something different, and whether the strain has any genetic markers that indicate it could be more adept at spreading person-to-person. Missouri hasn’t reported H5N1 in cattle, but it’s circulating in wild birds, with spillover into poultry and backyard chickens. Missouri doesn’t have a huge dairy industry, but there are still lots of dairy cattle around and it doesn’t sound like there’s been much testing (a report in July said that only 17 of the state’s approximately 16,000 dairy cattle had been tested), so we can’t rule out local dairy cattle (or unpasteurized milk) as a source either.

Hopefully this is an oddball infection that died out when the person recovered, i.e. they got infected somehow but didn’t pass it on to anyone else. However, even if that’s the case, this event demonstrates why we need to have comprehensive and nimble influenza surveillance.

  • If the infection is indirect linked to dairy cattle (by finding the dairy cattle strain in the person), it shows again that the US has to take dairy cattle infections more seriously. H5N1 in dairy cattle should be containable with short term but aggressive movement restrictions, testing and infection control measures – short term pain for long term gain. Fewer infected farms are being reported lately, which is great, but it’s still spreading across the country. The longer the outbreak lasts, the greater the chances of interspecies spillover and for the virus to adapt to a new host.
  • If the infection is somehow linked to wild birds, that’s a tougher situation, since controlling the virus in wildlife populations is challenge, to put it mildly.

This case was detected as part of surveillance program. That’s great, in that surveillance found something important and led to an action: an investigation of possible sources and a warning that there could be more. The not-so-great part is that few people with flu-like disease get tested at all, including for H5N1 influenza. If human-to-human spread is occurring, it could easily slip under the radar if there’s insufficient testing happening. That’s particularly true if most infected people only get mild disease, as they’re even less likely to get tested. We don’t know whether this was a lucky detection of a very rare situation, or a more common problem that’s been flying under the radar. Only more time and testing will tell us that.

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The Colorado Department of Public Health and Environment recently released information about 6 cats in the state diagnosed with H5N1 influenza. Some aspects of these cases are totally unsurprising, others raise a lot of questions.

Colorado has been hit hard by H5N1 in dairy cattle, with over 50 herds affected since the spring, but they’ve also taken a more proactive response than many areas. This report covers the 6 cats that have been identified (so far) in 2024.

Let’s start with the totally unsurprising.

One cat was from an infected dairy farm.

  • Duh. That one’s easy to explain.

Three were “known indoor/outdoor cats that hunted mice and/or small birds as prey and also spent time indoors with their owners.”

  • These aren’t too surprising either. When the virus is circulating in birds, species that prey on birds are likely to get exposed.
  • Genomic evaluation of the virus will help tell us if the strains in these cats are consistent with those circulating in local birds (as they should be), versus the slightly different strains circulating in cattle (hopefully not).

Now to the unexpected cases. These are the most interesting and important cases, and they illustrate some major gaps in our understanding and approach to this virus.

Two cats were indoor cats with no known exposure to H5N1.

  • These cats didn’t have contact with birds or dairy cattle.
  • Presumably they also didn’t have contact with any person known to have had H5N1 (as there are still few enough of those cases) or contact with high risk people like dairy or poultry farm workers, but that’s not explicitly stated.
  • I also presume the authorities took a good enough history to make sure “indoor” really meant “indoor,” since “indoor” is sometimes an aspiration for cats, not a lifestyle. (Veterinarians are all too familiar with “indoor” cats that have been hit by a car or gotten into a fight with some kind of wildlife.)

So how did two “indoor” cats get exposed to the H5N1 virus?

A few potential, but still unlikely, possibilities come to mind:

  • Close contact with aerosols from infected birds or bird feces through window screens?
  • Close contact with aerosols from infected mammals (e.g. other cats) through window screens?
  • Birds that snuck into the house?
  • Unidentified infected humans?
  • Contaminated material from outside tracked in on someone’s shoes or clothes?
  • Raw food? (Including possibly raw milk?)

The latter, in the form of raw diets, has been shown to be a risk factor in a few outbreaks in cats, so we can’t dismiss it. However, the odds of a raw diet containing meat from an infected bird in Colorado are really low. So, I think potential causes are still wide open at this point. Genomic analysis should help determine if the virus from these cats is most consistent with the strain in dairy cattle or circulating avian strains.

These cases also highlight something else: surveillance bias. If you don’t test, you don’t find. If testing is focused (or restricted to) cats with known high risk contacts, we can get into a self-fulfilling prophecy of “cats only get infected if they have risk factor X.” The two unexpected cases in indoor cats show that we might need to throw a wider surveillance net, both to find more infected cats and to understand how this virus is being spread.

The disease presentation is also important. Five of the six cats had “an initial complaint of lethargy and inappetence, followed by progressive respiratory signs in some and fairly consistent progressive neurologic signs in most.” It’s not clear how disease progressed in the sixth cat, or if it was perhaps found dead. Consider that if testing focuses on cats with neurological disease, we’ll bias ourselves to thinking that this virus always causes neurological disease. I’m not sure at this point whether H5N1 infection usually causes serious neurological disease or whether the cats with serious neurological disease are just the small subset that we test for H5N1. If those are the only cats we test (perhaps as a secondary test when the cat was a rabies suspect and has tested negative for that virus first), then we’re not going to understand the true picture.

We need better and broader surveillance. I get worried when the focus of testing is on a narrow population. Yes, it’s lower yield to test outside those known high risk groups, but when we have lots of knowledge gaps, we sometimes have to go on fishing expeditions.

What does this tell us?

  • If H5N1 is in birds or cattle, cats can get exposed.
  • H5N1 can cause serious neurological disease in cats. Maybe that occurs in a minority of infected cats, or maybe it occurs in most. We just don’t know yet.
  • Not all cats with H5N1 will have known exposure to infected dairy cattle or birds. We need to do more testing to figure out what’s happening.
  • Infections in cats seem to be rare, but can be fatal, so we need to pay attention.

The risk posed by cats to people and other animals is completely unclear at this time. Some earlier data suggested that cats could have pretty high viral loads in respiratory secretions, so I think we have to assume that infected cats pose some transmission risk. That doesn’t mean we should panic or not try to treat them, but we should make sure we use good infection control practices around suspected and confirmed cases.

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.