Search results for: influenza

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TLDR: Nope.

These days I commonly get the question ”Does vaccination of dogs with available canine influenza vaccines protect them from H5N1 avian flu?” While we don’t have any hard data on this, we still have a pretty good idea of the answer.

One of the challenges with flu vaccination (in any species, including humans) is the lack of good cross protection between strains (e.g. H3N2 vs H1N1 vs H5N1). In general, we assume there’s little to no cross-protection, and organizations such as CDC, Public Health Agency of Canada and WHO have stated that seasonal flu vaccines don’t offer any protection to people against H5N1 flu. 

That said, theoretically there there may be a bit of protection, though it’s hard to have confidence in that based on data from older lab animal studies. One study (Rockman et al. J Virol 2013) showed that ferrets vaccinated with human seasonal flu vaccine had partial protection against challenge with H5N1 flu. They determined that this was from the H1N1 component of the vaccine, and was predominantly from the neuraminidase (N) part (H5N1 and H1N1 have the same N1). While we typically pay more attention to the H component for vaccination, the similarity in N may be useful. That means there may be some protection of people from H5N1 flu if they’re vaccinated for seasonal flu, but not a lot, and we have to be careful extrapolating too much from older studies using different types of H5N1 in lab animal models. 

Canine flu vaccines target H3N2 canine flu, plus or minus H3N8 canine flu strain. (Realistically we only care about H3N2 now, since H3N8 appears to have disappeared as of a few years ago.) Those are quite different from H5N1 avian flu in flu terms.  Since there’s no overlap in the Hs or Ns, we wouldn’t expect to even have that small theoretical cross-protection benefit. If we had an H1N1 canine flu strain, maybe there’d be some protection, but (thankfully!) we don’t.

Does canine flu vaccination help protect against flu recombination? 

Recombination (mixing) of different flu strains in the same host (human or animal) to create a new, more problematic strain is certainly a concern. We don’t want someone to be infected with seasonal flu and H5N1 flu at the same time, as that creates the potential for a new flu strain to emerge that has the hallmarks of a human flu (readily infected people, effective human-to-human transmission) but has picked up enough H5N1 bits that we don’t have protection from previous exposure or vaccination and may can cause more severe disease. So even though seasonal flu vaccines in people don’t protect against H5N1 flu, there is still benefit from reducing the human seasonal flu burden, as it in turn reduces the risk that a person will be infected with multiple flu strains at the same time, which reduces the chances of recombination.

Does the same principle apply to vaccination of dogs against canine flu? It’s a stretch. There could be some potential benefits for canine health, but probably not much benefit for public health. Canine flu is much rarer than seasonal flu is in people, so there’s less potential benefit simply because there’s less disease to prevent. There’s also less baseline protection against canine flu in dogs because it’s rare and therefore vaccination is uncommon. So from a disease transmission standpoint for dogs, a new flu strain against which they don’t have immunity isn’t that different from the current H3N2 canine flu strain, since most dogs don’t have immunity to that either.

However, there could potentially be a difference in terms of disease severity. Fatal H5N1 infections have occurred in many mammals and at least one dog, and we don’t want an H3N2/H5N1 recombinant virus that spreads nicely dog-to-dog and is more likely to cause severe disease.  The odds of that happening are extremely low, but not zero.

Also bear in mind that canine flu vaccines aim to reduce the severity of disease more than prevent infection altogether. That still might be useful, as a mildly affected dog with some degree of immunity might have a lower H3N2 viral burden, but it’s hard to say how much that would really help protect against recombination of flu viruses, even if we had more widespread vaccination in the dog population. Probably not too much.

Public health benefits would be less of a reason to promote vaccination of dogs against canine flu stains. Canine H3N2 flu poses little risk of infection of people, so a hybrid of canine H3N2 and H5N1 wouldn’t be expected to be more transmissible to people (even though it would potentially add some mammalian adaptations to an H5N1-related virus, which is definitely not the direction we want the virus to go). For dogs to be a flu “mixing vessel” of public health concern, a human flu strain would need to be involved. While dogs can occasionally be infected with human flu strains, the odds of a dog having H3N2, human seasonal flu and H5N1 at the same time are pretty low. Even then, whether or not the dog was vaccinated against H3N2 wouldn’t really affect the risk, since we’d be primarily concerned about the human flu and the H5N1 flu mixing in the dog, not whether or not H3N2 joins the party.

Should we change how we approach canine flu vaccination?

I’d mostly stick with our current approach, which is based on assessment of the risk of exposure of the dog to canine flu, and the risk of serious consequences should the dog get flu (e.g. elderly, brachycephalic, underlying heart or respiratory disease). Since there are some plausible dog health concerns about H3N2/H5N1 recombinants, I’d drop my threshold for vaccination in dogs that also have a higher risk of exposure to wild birds (or dairy farms in the US). Dogs that have a reasonable risk of exposure to both types of flu virus (canine and avian) would be higher on my list to vaccinate, but that’s a very small subset (currently), and the benefits of vaccination beyond H3N2 protection are probably very limited.

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Issues with raw diets and H5N1 influenza risk in cats (and dogs) have gotten a lot of attention in the last week or two. Like most emerging disease situations, it’s still fluid, and we’re learning more as time goes on, but we know enough at this point to at least make some basic assessments and recommendations. Here’s my current take on it.

What are the concerns with H5N1 influenza and raw diets for pets?

The unprecedented pandemic of H5N1 highly pathogenic avian influenza (HPAI) has ongoing for more than 2 years. Massive numbers of wild birds have been affected around the world. Spillover into domestic animals is an ever-present risk where this virus is circulating in wild birds, with domestic poultry being the most severely affected. Millions of domestic poultry have died or been depopulated due to infection, and spillover infections have also occurred in mammals, including many cats and at least one dog.

Recently, H5N1 influenza infection has been linked to consumption of contaminated raw meat diets in at least two cats. It’s been well established for some time that ingestion of infected birds can lead to H5N1 influenza infection in cats, based on earlier studies and field observations. It is therefore unsurprising that infections could occur if infected poultry makes its way into raw diets fed to cats, and unfortunately the infection in cats is often fatal.  The risk to dogs is less clear, but infection was reported in one dog that died shortly after close contact (chewing on) an infected bird. Dogs may be less susceptible to H5N1 influenza than cats, but they are still susceptible and infection can have dire consequences, so the same concepts apply to both species.

What types of raw diets for pets pose a risk of H5N1 influenza infection?

Poultry-based diets are the main concern, including chicken, turkey and duck, as all poultry are highly susceptible to H5N1 influenza. However, the virus is now also widespread in dairy cattle in the US, particularly in certain states (like California at the moment). Work done by the Food Safety and Inspection Service (FSIS) in the US has found no evidence of virus in retail beef samples and only very low levels of virus in samples from 1 of 185 cull dairy cows tested (the positive cow did not enter the food chain). More investigation is needed, but it is likely that viral loads in muscle of infected cattle are far less than those in poultry. Risks from beef are presumably low, but the potential for the virus to be present in meat from infected dairy cattle cannot be dismissed.

Does use of “human grade” meat in raw diets eliminate the risk?

Human grade meat does not mean pathogen-free – it only means that the meat would have been allowed for sale for human consumption based on more rigourous requirements for the animals, facilities, processing and handling. These presumably reduce, but do not eliminate,  the risk of H5N1 infected animals entering the pet food chain.  

Does high-pressure pasteurization of raw diets eliminate H5N1 influenza virus?

High pressure pasteurization (HPP) of food products uses high pressure (rather than high heat, as in cooking) to reduce contamination with bacteria and viruses. Many commercial raw diets for pets are high pressure pasteurized (which is good). The pressures achieved during this process should inactivate influenza virus, but there are no standard methods for HPP. The effectiveness of HPP depends on the pressure, temperature, and composition of the food matrix. It is unclear whether manufacturers have developed and validated the method for their wide range of diets and pathogen risks. Recalls of high-pressure pasteurized raw diets because of Salmonella contamination have been regular occurrences, and a recent infection in a cat was linked to such a diet. High pressure pasteurization should be considered a risk reduction step, not a risk elimination step.

Are frozen or freeze-dried raw diets lower risk for H5N1 influenza?

Freezing and freeze drying are effective preservation methods for viruses, so its unlikely that these methods substantially reduce the risk of viral contamination in raw diets. Ultralow freezing is used for longterm preservation of viruses, but shorter-term survival is also possible at temperatures achieved using normal freezers (-20C). A study of the survivability of H7N9 influenza on raw chicken meat (Dai et al. Lancet 2022) reported that viral infectivity was maintained for 9 days at -20C, 4 days at 4C and 4 days at 25C. This was a rather small study, so it is possible that somewhat longer survival could occur in some situations. In nature, long term (e.g. overwintering) survival of influenza virus in ice has been suspected.

While the survival kinetics of this virus with freezing are not clear, it should be assumed that the virus could survive frozen for at least a week, and possibly much longer. Freezing should not be assumed to be a risk mitigation measure for viral contamination of raw diets.

Freeze drying is a highly effective virus preservation method. Survival of virus in freeze dried food has not been assessed, but in the absence of specific evidence, it is reasonable to assume that influenza virus would survive for long periods of time in such diets.

My cat is doing well on a raw diet and I don’t want to change. What can I do?

Raw diets can be cooked so that the cat receives a diet with the same ingredients but without the risk from H5N1 influenza (and other pathogens). There is no evidence that cooking reduces the health benefits of a diet. Cooking the food to an internal temperature of 165F/74C will inactivate influenza virus and other pathogens such as Salmonella.  

My cat has eaten a raw diet that’s been recalled diet. What should I do?

You should observe your cat closely and contact your veterinarian in you are concerned or your cat develops any signs of illness. Antiviral prophylaxis could be considered in particularly high-risk situations where it is likely that the cat has eaten contaminated food. This may not be the case for all recalled diets and would depend on the nature of the recall. Early signs of H5N1 influenza in cats are not well established, but often seem to be vague signs such as lethargy, malaise and decreased appetite. Rapid progression to severe disease can occur so veterinary care should be sought as soon as possible.

My cat has eaten a raw diet that’s not been recalled. What should I do?

Unless there is evidence that the diet has been implicated in disease, the odds of a problem developing are low. However, it would still be ideal to transition the cat to a cooked diet, whether that’s a commercial wet or dry diet, a home-cooked diet or cooking the cat’s current raw diet. Monitoring of your cat for illness, as above, is still indicated, as always.

What are risks to people from contact with contaminated raw diets?

The risk to people from H5N1 influenza from handling contaminated raw diets is likely quite low but not zero. Exposure could happen from inadvertent ingestion of the virus from contaminated surfaces (e.g. food prep surfaces, refrigerator, food bowls). That would likely be low level exposure, but the infectious dose of the virus is not known so it could still be relevant. There are similar risks with these diets from pathogens such as Salmonella, so good food handling practices are always warranted. These include avoiding cross-contamination with human foods and kitchen surfaces, careful cleaning and disinfection of in contact surfaces, dishes and utensils, and thorough handwashing (or use of an alcohol-based hand sanitizer) after contact with the raw diet or food bowls.

The greatest risk to people would be from exposure to a cat (or less likely a dog) infected with H5N1 influenza. An infected animal might be shedding enough virus to infect people, although the risk of this is still unclear. Any cat or dog with suspected influenza should be handled sparingly, and with use of good infection control measures, including a mask (ideally an N95 respirator) and eye protection.  

Closing thoughts

My opinions on raw diets have been pretty clear all along. I don’t think there’s any evidence that raw diets have any health benefits over an appropriate cooked diet, but raw diets come with numerous infectious disease risks. I’ve seen enough dogs and cats (and sometimes owners) sickened from raw diets to be confident in that. At the same time, I’m a realist and know that some people will continue to feed pets raw diets regardless. That’s why we have a infosheet about raw diets that includes ways to reduce the infectious disease risks for those who choose to feed them to their pets.

The current situation doesn’t really change anything for me. I’m still opposed to raw diets for pets, and this simply adds yet another layer of risk to pets and people that consume/feed them.

If someone is adamant that they are going to feed their pet a raw diet, here’s what I currently recommend:

  • Avoid diets that contain poultry (including duck)
  • Use a diet treated with high pressure pasteurization (realizing it reduces risk, but does not eliminate it)
  • Take care to avoid cross contamination of human food, and use good food handling and hygiene practices (always)
  • If your pet has been fed raw meat and gets sick, make sure your veterinarian knows about the diet so they can consider whether that might be relevant
  • Pay attention to the news and recalls so that you can stop feeding a diet if there are any known issues (but realize that we don’t typically know about any issues until one or more animals gets really sick or dies from the diet)
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Hot on the heels of the recent death of a cat in Oregon due to H5N1 influenza infection linked to a raw diet (that some raw diet proponents are trying to deflect or downplay), we have confirmation of a very similar case in California. Los Angeles County Public Health has issued a notice to avoid feeding Monarch Raw Pet Food “due to detection of H5 bird flu in product samples.” (note the plural). H5N1 was confirmed in one cat that was fed this diet and is suspected in four other cats from the same household.

The diet type was not reported, but the company’s website indicates “Our pet food is made of human grade USDA free-range poultry that is raised in the San Joaquin Valley.” Free range poultry are at increased risk of H5N1 infection from wild birds. Nonetheless, it would be interesting to know how infected poultry made it into the food chain (even the pet food chain), since H5N1 influenza usually causes widespread illness and death in domestic poultry, so it’s pretty obvious when it hits a poultry farm (and sick birds cannot be sent to slaughter).

The status of the infected cat wasn’t reported, but H5N1 infection in cats is often fatal based on what we know to date. Hopefully the cat had a milder infection, but I assume it was at least worse than a routine upper respiratory tract infection, since testing is usually limited to pets that are pretty sick.

The good news is that food-associated H5N1 influenza risks are totally avoidable… just don’t feed pets raw diets. The cost:benefit calculus is pretty easy since this virus kills cats and there are no health benefits of raw diets. More information about raw meat-based diets for pets (beyond the risk of H5N1 flu) can be found in the Worms & Germs / OAHN Raw Meat Diets infosheet, available on the Worms & Germs Resources – Pets page.

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The Oregon Department of Health has issued a warning to pet owners about contaminated raw pet food after H5N1 avian influenza virus was detected in turkey-based raw (and frozen raw) pet food from Morasch Meats. Testing was performed after the death of an indoor cat from H5N1 flu in Washington County, Oregon. The virus from the cat and from the pet food were a genetic match, making a solid link between the two. The pet food company is voluntarily recalling some of their Northwest Naturals diets.

This highlights (yet another) risk posed by poultry-based raw pet food at the moment in areas like the US where H5N1 flu is actively circulating. There could also potentially be risk of H5N1 contamination of raw pet food made with beef, if the meat came from infected US dairy cattle. Risks could also extend to other raw pet food formulations if there is cross-contamination from these higher-risk ingredients.

There are no health benefits to raw diets beyond a properly formulated cooked (be it commerical or homemade) diet. H5N1 flu is now yet another potential threat to animals fed raw diets. The risk may extend to owners as well, through exposure to virus from handling food, and potentially from infected pets (especially cats, but we still don’t know the level of cat-to-human transmission risk).

We have seen foodborne H5N1 influenza infection in cats in multiple situations, often resulting in fatal disease. Foodborne disease probably helps explain some of the earlier reports of H5N1 in indoor cats, and in that respect it’s good to have an idea of how all these infections are occurring. The more infections we can’t explain, the more we worry about serious issues like unknown human (owner) infections with subsequent human-to-cat transmission. I’d much rather be able to attribute cases to straightforward food-associated transmission than have to explore other transmission pathways, or think that there may be silent human-associated spread.

The mitigation approach here is simple: just avoid raw pet food diets (especially poultry-based diets).

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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.