Back in March 2024, I wrote a post about a systematic review of the efficacy of antibiotics and probiotics and the associated treatment guidelines for acute diarrhea in dogs from the European Network for Optimization of Veterinary Antimicrobial Treatment (ENOVAT). Now, we have an ENOVAT/WSAVA infographic to put all that into a (hopefully) quick reference for veterinarians.

While we’ve historically used antimicrobials like metronidazole by rote to “treat” acute diarrhea in dogs, a lot of dogs were probably getting better despite what we were doing rather than because of it. Antimicrobials are needed in dogs with severe disease, but that’s to target systemic infection in those cases, not necessarily what’s going on in the intestine.

It’s pretty straightforward, as the infographic shows:

  • Dogs with mild diarrhea: no antimicrobials needed, just basic supportive care like a GI diet.
  • Dogs with moderate diarrhea: fluid therapy first, and if that resolves the systemic signs then no antimicrobials required. If signs persist that might be attributable to sepsis, then it’s considered severe and systemic antimicrobials are warranted.
  • Dogs with severe diarrhea and systemic illness: systemic antimicrobials are warranted.

The standard disclaimer is that guidelines are meant to cover most cases, but there can be nuances to individual cases that indicate the need for a different approach. That’s fine, but we still want to try to use an evidence-based approach as much as we can to determine the default treatment.

Of all the guidelines with which I’ve been involved, this one is by far the hardest to get people (including veterinarians and pet owners) to accept, since we are so conditioned to treating diarrhea with antibiotics. We do it because we’re risk averse, because it’s habit, and because we are conditioned to want to do something – even when there’s no evidence that the something is useful. A large percentage of the metronidazole that is used in dogs is psychotherapeutic… for the pet owners and veterinarians, because it makes the people feel better, but not the dog. In fact, those antimicrobials might actually make the dog feel worse.

We’ve made big strides in veterinary antimicrobial treatment guidelines in recent years, and this is one more step in the right direction, but we still have a long way to go.

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H5N1 influenza has been widespread is US dairy cattle for close to a year, so you might wonder why a recent report of H5N1 in dairy cattle in Nevada is garnering extra attention. Well, it all comes down to the strain. TLDR:

H5N1 influenza isn’t one specific virus. There are already numerous known subtypes and new ones continue to emerge. The “dairy strain” that’s spread among US dairy cattle is called clade 2.3.4.4b, genotype B3.13. 

Finding the B3.13 strain in cattle in Nevada wouldn’t have been surprising, but multiple herds in Nevada tested positive for a stain of H5N1, subtype D1.1. This “new kid on the block” is a recombination of one of the H5N1 strains that moved from Asia to North America in late 2021 and early 2022 and a low pathogenicity avian flu strain that was already present in birds in North America. It was first identified in September 2024 and has now emerged as a dominant strain in wild birds (and spillovers into poultry). 

The first detection of the D1.1 strain in Nevada cattle was from samples collected January 6 and 7, 2025, so (as is typical) we’re playing catch-up. It will be important to see if these farms are linked, and whether there are other affected farms. It will also be important to see if shedding patterns (lots of virus in milk, little in respiratory secretions) and virulence in cats on these farms (lots of dead cats) are similar to B3.13. Obviously the risk to humans must also be tracked(more on that below). 

This is a noteworthy event because it represents a new spillover into cattle from wild birds. Infection of a single cow wouldn’t be too remarkable, since rare spillovers to mammals are expected given how widespread the virus is in birds. However, infection in multiple cattle on multiple farms suggests either effective bird-to-cow transmission on multiple different premises, or another single bird-to-cow spillover that has subsequently been spread cow-to-cow and farm-to-farm like B3.13.

Another concern is the potential for more severe disease in people. Human infections with D1.1 have been previously identified in people who were depopulating infected poultry farms. They had mild disease, like most of the human H5N1 flu spillover infections in the North America to date. But D1.1 is the strain that was involved in a fatal H5N1 flu infection in a person in Louisiana, and that caused very severe disease in a teen from BC. On one hand, we can say any H5N1 strain can cause severe disease under the right circumstances and maybe those were just rare events. On the other hand, those two severe infections show that we can’t sit back and just say but human infections are always mild. When something spreads widely, rare events become more common, so we can’t ignore them. It also raises concerns about what could happen if this strain becomes better able to spread human-to-human. A more transmissible strain that can cause severe disease in people is the big concern.

Highlighting these concerns, a human infection has already been linked to these Nevada dairy cattle. Fortunately, the person had mild disease (conjunctivitis), akin to what’s been seen in dairy workers with B3.13 infections. Still, it shows that this strain also poses a risk to people who work with infected animals. 

There’s also a concern about evolution of this virus in cattle, even over this short timeframe. The Nevada cattle D1.1 strain has already acquired one mutation (PB2 D701N) that makes it more able to infect mammalian cells. Lots of things still have to happen to make this a mammal-adapted virus, and even more for it to become an effective human pathogen, but this is a potential step in that process. Spillover into farm workers raises the stakes further, since any new infection of a person increases the likelihood of human adaptation or, worse, recombination with a human flu virus in someone coinfected with two flu strains at the same time (e.g. H5N1 and a human seasonal flu). A recent CNN article has a nice description of some of the issues related to the H and N changes in these H5N1 subtypes.

More information about the effects of this “new” strain on cattle is also needed. It’s reported that the cows were not obviously sick when the positive results were first obtained as part of a state screening program, but that disease subsequently occurred. That might suggest that disease is mild and only found when someone is really looking for it, or that they just picked up these infected farms very early with their surveillance program. The US recently started a national Milk Testing Strategy surveillance program, which should help detect problems earlier. We’ll also need more information about the spread of this strain within farms and whether it’s spreading between farms (and if so, how). 

The sky is not falling, despite some social media reports, but it’s another concerning development. The more this virus infects mammals and spreads between mammals, the more risk to humans and domestic animals. Surveillance is a key part of our response but there also needs to be a concerted effort to limit mammal-to-mammal transmission and exposure of people to infected animals. 

From a Canadian context, this highlights a few things too. We can’t just focus on preventing H5N1 flu in dairy cattle through movement of cattle from the US. If D1.1 can move from birds to cattle in Nevada, it can do it anywhere.

We have to maintain a robust milk surveillance program to identify early incursions of this virus. We also have to be ready, able and willing to act decisively if/when H5N1 flu is identified in dairy cattle in Canada. That doesn’t mean culling cattle, but it does mean using strict controls to prevent farm-to-farm spread, and reduce the risks to humans on farms.

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Earlier today I wrote about a New York Times story about some interesting H5N1 flu transmission data from the US CDC that was posted briefly on Wednesday and was then quickly removed from the CDC website. The information suggested they’d identified cat-to-human and human-to-cat transmission of H5N1 flu in two separate households, both of which would be noteworthy events. A bit more information about the cases has since come to light, from outside official channels (the lack of transparency regarding these findings is a separate story).

Household 1

  • Cat 1 got sick, died, and tested positive for H5N1 influenza.
  • Cat 2 got sick 4 days after Cat 1 got sick. That’s pretty consistent timing for cat-to-cat transmission, but it appears Cat 2 was not tested for flu.
  • Cat 3 was tested for flu and was negative. Sorting out the testing for this cat is important, including when the cat was tested and what samples were collected, as this can impact how likely a the result is to be a true negative or a false negative.
  • An adolescent got sick 6 days after Cat 1 got sick / 2 days after Cat 2 got sick. The adolescent tested negative for H5N1 flu 6 days after the onset of illness. It’s not clear if there was testing for other diseases (I’d guess either that was not done or results were negative).
  • An adult dairy farm worker was in the household. That person was healthy and was not tested. There’s no mention of whether the cattle on the farm where the person worked were known to be infected with H5N1 flu (but I wonder if a farm exposure history is why Cat 1 was tested initially).

We still need more details to assess this further. The timing of disease in the cats and the adolescent certainly fit with H5N1 flu transmission within the household. The negative tests decrease the concern a bit, but sample quality and especially timing of testing can make a significant difference. False negative tests can occur when we sample too late in disease if the virus has been eliminated by the time we test (even if the individual has not fully recovered yet). That’s a particular concern for a virus like H5N1 flu (in its current form) that’s not well adapted to humans and other mammals (hopefully it stays that way); I’d expect longer viral shedding with a well-adapted virus. So in this case sampling later in the disease course doesn’t rule out H5N1 flu entirely. If the adolescent had flu-like disease and tested negative for other potential causes (e.g. SARS-CoV-2, human seasonal flu), then I’d still be concerned about H5N1 flu.

Based on the limited information available so far, I’d consider this to be potential but as yet unconfirmed H5N1 flu transmission from cat-to-cat and cat-to-human.

Knowing the strain of H5N1 flu in the cat will help too. If it’s the dairy strain but the cat had no direct contact with an affected farm (e.g. indoor only cat on a farm, or an off-farm cat owned by a farm worker), that would suggest that the cat got infected from its owner, either because the person had and asymptomatic / unrecognized infection or they tracked the virus home on their clothes. Hopefully they’ll do some sequencing, and serological testing too. Antibodies against H5N1 in either the cats or the people could tell us if infection occurred in the past, even if they weren’t sick. Positive serology in the remaining cats or the kids would be strongly supportive of household transmission.

Household 2

  • Cat 1 got sick, died a day later and tested positive for H5N1 influenza.
  • Cat 2 was healthy and tested negative for H5N1 influenza on the same day as Cat 1.
  • The owner was a dairy farm worker who got sick 2 days before Cat 1, but it appears the person was not tested (at least not for H5N1 influenza).
  • The household was lost to follow up 3 days later.

We can’t rule out transmission from Cat 1 to Cat 2 in this case because the time frame for both the initial test and the monitoring period were too short to say for sure that Cat 2 did not get infected, but there’s nothing to indicate cat-to-cat transmission here either.

The timing of illness in Cat 1 could fit with human-to-cat transmission, because people can be infectious before they start to feel sick, and/or have only mild signs of illness at the start that they don’t recognize as being flu-related. Only 2 days between the owner and the cat getting sick is on the short side, but still within the range we might anticipate for flu transmission with very close contact in a household.

Knowing the cats’ lifestyles and other risk factors is important too. If Cat 1 was indoor only and not fed raw meat or milk, the owner is the logical source of the virus. If sequencing shows the cat was infected with the dairy strain of H5N1 and the cat didn’t have access to dairy cattle or their environment, that would be a very solid link too. With the person being sick first, it’s strongly suggestive of human-to cat transmission, but the smoking gun (testing the person before the cat and finding the same strain in the cat and person) is missing.

What does this all tell us?

We still need more details. Presumably most or all of this information is known to someone involved in the investigation. Getting the information out is important to help others identify risks and keep messaging balanced, in order to avoid panic but also help prevent additional infections. Cat-to-human transmission concerns can raise a lot of fear (and potentially bad consequences for cats). Human-to-anything transmission would be really noteworthy, so we need to know if it was almost certainly occurred, maybe occurred or almost certainly didn’t occur.

I’ve already been working under the assumption that cats with H5N1 influenza can be infectious to others, and this doesn’t change that. It gives a little more support to the concern (and weight to the recommendations to help avoid it) but doesn’t answer the question completely. It definitely does not make me less concerned.

As usual with emerging diseases like this, we need more surveillance, including the details.

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Cat-to-human or human-to-cat transmission of H5N1 influenza would be concerning but not too surprising.

Suppression of information by the US government would be concerning but not surprising given what’s going on at the moment.

But, did those occur?

The sharp eyes at the New York Times have raised concerns, because they spotted a CDC report that mentioned potential cat-to-human and human-to-cat transmission of H5N1 flu that was available online briefly on February 5, but then removed. 

Why was the CDC report removed? 

It could be because:

  • they found that the information was inaccurate
  • the story was incomplete and they wanted to get more details
  • the info is coming soon but needed additional sign-off by someone internally or an external collaborator
  • they were told not to release it

Each of those potential reasons causes a different level of concern, but the net result is that there might be some really important information that’s not being made available.

The New York Times article says the CDC report mentioned (likely/potential/confirmed?) transmission of H5N1 flu between cats and people in two households:

  • In one household there was potential transmission from a cat to another cat and a child.
  • In another household, a dairy worker got sick, then their cat got sick a couple of days later and died, raising the question of whether the cat was infected by the person.

I’ve assumed cats would be able to transmit H5N1 flu based on the amount of virus that has been found in respiratory samples from some cats using PCR. Cat-to-cat transmission would be quite likely given how closely some cats interact (e.g. playing / fighting, mutual grooming, sleeping together). Cat-to-human transmission seems possible for similar reasons. If an infected cat is shedding a reasonable amounts of virus in its respiratory secretions, I’d assume there’s some risk to any people who are in close contact, especially those who may have close contact with the cat’s face (e.g. owner of an infected house cat, veterinary personnel). In the case of potential human-to-cat transmission, we don’t really know if cats may be more susceptible to current H5N1 flu strains than people, or whether cats are just more likely to get serious disease when they are infected.

The nature of the evidence and investigation is important to know. 

Sometimes, it’s pretty clear how things were transmitted, based on things like a lack of other potential sources of infection and timing. Other times, it can be very messy. For example, in the second scenario, if the cat was an indoor cat (that didn’t sneak outside), didn’t live on a farm and was not fed raw meat or milk, human-to-cat transmission is by far the most logical source. Transmission by fomites (e.g. clothing worn on the farm) would have to be investigated too.

As I said at the start, cat-to-human and human-to-cat transmission would be concerning but unsurprising. “Concerning” may be a bit of an understatement, as it’s a potentially big deal. If a person can infect a cat, then it’s reasonable to assume that person was shedding a reasonable amount of virus (presumably in respiratory secretions) and therefore could have also infected another person. Human-to-human transmission is a very big concern, because if the H5N1 virus evolves to spread effectively person-to-person, and the general population has no immunity to this virus from previous exposure or vaccination, it could result in rapid widespread transmission (similar to SARS-CoV-2). There are still many gradations in transmission risk, and this one (disappearing) report by no means indicates we’re on the brink of a new flu pandemic, but it would be one more step along the way.

If H5N1 flu ever gets good at human-to-human transmission, cats will ultimately be only a minor risk to people in the grand scheme (even though we know they’re quite susceptible), because we’d be at greater risk of transmission from other people. However, if human-to-human transmission does not occur or remains rare, cats can be a bridge to humans from sources like wildlife, poultry and dairy cows, by bringing the virus into the household. A lot more people have close contact with indoor-outdoor cats than with other major sources of H5N1 flu.

From a personal standpoint, as someone who goes out and samples animals during emerging infectious disease events and who provides guidance to veterinarians, shelters and other groups about management of H5N1 flu suspects, I want more information about this risk ASAP, and it needs to be good, reliable information. I realize that there are inevitably necessary channels and approvals for sensitive information, but these should (hopefully) only cause minor delays in getting the information to those who need it most. The information doesn’t need to be polished, but it should be as close to real time as possible.

Emerging infectious diseases must be managed with active and transparent approaches. Too often, that’s not the case (and the initial US response to H5N1 in dairy cattle showed issues that were present even before the current administration).

Hopefully we’ll get more information about this soon. Hopefully these are rare events that don’t indicate an increased risk of mammal-to-mammal transmission. But, as I’ve said before, hope is not an effective infection control strategy.

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Addendum: The Oregon Veterinary Medical Association has indicated in a release that the cat discussed below was euthanized because of the severity of disease. That’s more consistent with the severe disease that’s usually reported but I think the discussion below still applies since this seems to have been an initial primary respiratory disease presentation. It probably still shows that there can be a primary presentation that overlaps with more common presentations so we need to consider H5N1 beyond severe neuro or sudden death cases.

I’m not commenting on every new report of an H5N1 influenza spillover infection in a domestic animal because it’s not really news anymore, but that doesn’t mean they’re not concerning. Spillover infections definitely are a concern with this virus, and we expect these spillovers to continue as long as this virus is circulating in wild birds (or in large numbers of dairy cattle, as it is the the US).

Nonetheless, a recent case of H5N1 influenza in another cat in Oregon highlights something important, because it’s different from previous cases. Most reported cases of H5N1 flu in cats to date have been of severe disease, usually with neurological signs, but it’s been unclear whether this is because infected cats typically get severe neurological disease or whether we’ve only been testing the cats with severe disease. It remains unknown how often infected cats get milder disease, and that’s a really important testing consideration, for both clinical patients and surveillance testing.

Respiratory disease in very common in cats, especially outdoor cats. Knowing whether flu should be a consideration in your average cat with an upper respiratory tract infection is important for determining how they are managed in a clinic (to avoid transmission to staff and other patients) and how they should be managed at home (to avoid transmission to family members and other animals in ad around the home). 

In contrast to previously described severe cases in cats, the recent case of H5N1 in a cat from Oregon was described as having a much more typical respiratory tract infection. “A veterinarian examined the cat after it exhibited symptoms including a fever, runny nose and eyes, lethargy, difficulty breathing and loss of appetite.” Although difficulty breathing isn’t typical for a run-of-the-mill upper respiratory tract infection in a cat, it is consistent with pneumonia, which can occur secondary to any viral infection. The news report is light on clinical details, but if this case was actually was more akin to a typical pneumonia that we might see in cat secondary to other more common bugs, it (long with a few other milder cases where cats have recovered) suggests that we need to vastly expand the cats we should consider potential H5N1 flu suspects. It means we need to focus on more than just the severely ill cats with respiratory and neurological disease. At the same time, it’s tough to say how wide a net we should cast, given the commonness of mild upper respiratory tract disease in cats.

At this point, the key is flagging risk factors for exposure in these animals, including outdoor access, contact with farms and being fed raw poultry diets. In combination with respiratory tract or neurological disease, we should consider the cat an H5N1 flu suspect unless another cause is evident. 

A challenge with this is that cats with outdoor access are also the main risk group for any typical feline upper respiratory tract infection, so including them greatly expands the pool of suspects and can make practical management harder. Nonetheless, at least for now, we should probably still be flagging any outdoor or indoor-outdoor cat presenting with respiratory disease beyond the routine upper respiratory disease complex as a potential flu suspect, with corresponding considerations for testing and infection control.

Should we consider any outdoor/raw fed cat with any signs of respiratory disease a flu suspect? Maybe. It’s certainly possible that H5N1 can also cause typical flu-like disease/upper respiratory infection. I’d recommend not completely discounting it in any case, but paying particular attention the more severe the disease is, and the greater the cat’s risk of exposure.  

As with most emerging diseases, this is a fluid situation and it’s tough to figure out where to draw the line in order to balance protection and practicality. As we learn more, that line will likely move, so we must keep an eye on new developments and take reasonable measures in the interim. Personally, I always prefer to err on the side of testing more and being more aggressive at the start, and then de-escalating when we know more, but there’s also a practical limit to how far we can go with that. 

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As H5N1 avian influenza continues to spread in wild birds and spills over into domestic birds and mammals of many kinds, we’re becoming more aware of the risks to domestic mammals and there are more questions about test selection and interpretation. Fortunately, testing for H5N1 influenza is relatively straightforward.

  • For cats and dogs, the recommended samples for testing are typically oropharyngeal swabs, plus or minus nasal swabs (plus or minus other tissue samples of the animal is deceased. 

What tests are currently being run by veterinary diagnostic labs?

PCR is the most accessible and useful test; diagnostic labs basically offer two types of influenza PCR: matrix / pan-influenza A PCR, and strain-specific PCRs (see below). Different commercial labs offer different tests or combinations of these tests, and the tests offered may also vary by species (i.e. what’s routinely done for dogs can be different from cats). Test offerings may also change over time as labs adapt to the ever-changing situation with flu in different populations. If influenza is a consideration in your patient, check with your lab regarding which tests they will run (particularly if you are submitting samples for a respiratory PCR panel) and how to interpret the results, including whether or not the test will detect H5N1 flu if that’s a concern.

Influenza A matrix PCR (aka pan-influenza A PCR)

This test will detect RNA from any / all influenza A viruses. A positive test confirms that flu virus is present, but not the strain (and not that the virus present is necessarily viable). Knowing the strain is important to understand how the animal might have been exposed and transmission risk. It’s a good first screening step, but if it’s positive we need more testing. If a cat was positive, it could mean it has a human seasonal flu strain (people sometimes infect their cats, and ’tis the season), or it could have H5N1 influenza, or another flu strain (e.g. a low pathogenicity flu strain which can cats sometimes get from wild birds, or potentially a swine flu virus if they have contact with pigs). Really rarely, but importantly, an animal could be infected with a combination of different flu viruses. Our concerns about and responses to these different scenarios are really different, so it’s important information to get. 

Strain-specific influenza PCR

These tests target specific influenza strains in different species, like canine H3N2, canine H3N8, avian H7N2 (found sometimes in cats) and human H1N1 (which can spill over sometimes into dogs and cats). It’s important to be aware that these are strain-specific tests, so an animal that just has H5N1 influenza will test negative on the H3N2 test, for example.

H5N1-specific influenza PCR 

As the name suggests, this test is specifically for H5N1 influenza, and we can be more confident in the result if that’s the strain for which we’re looking. The downside is that it won’t detect co-infections with multiple flu strains. The odds of a dog having H3N2 canine flu or H1N1 human flu and H5N1 avian flu at the same time are REALLY low, but that would be a REALLY concerning situation, so it would be nice to know. It’s more relevant when there’s higher non-H5N1 flu activity in the area as well, since that would mean there’s a greater chance of a hidden co-infection.

In order to provide the best possible information without over-testing every sample, labs will sometimes perform different tests in sequence: 

Run matrix PCR; if positive, then test for H5N1

This adds a step, but it’s usually a quick one, and we find out whether the animal has a flu virus and if so, whether its H5N1. The same issue with not identifying co-infections applies here, because there’s no testing for other flu strains.

Run matrix PCR, then test for non-H5N1 strains; if negative, then test for H5N1 

This works too. It adds a bit of extra time/work, and the more steps that are required, the greater the chance of a test error, but it gets to the same result pretty quickly and gives us a specific H5N1 result. The main theoretical issue is that we could still miss a coinfection (in this case because the H5N1 test isn’t run if any of the other strains are detected). 

Run matrix PCR, then test for non-H5N1 strains; if negative, then refer to another lab for H5N1 testing

This slows things down more and adds in some uncertainty as it requires sending the sample out for follow-up testing, which is another step where human error could affect things. It also misses co-infections.

Run matrix PCR, then test for non-H5N1 strains, then test for H5N1; if negative, stop and call it a generic influenza A positive

This isn’t ideal but still tells us a lot. In most cases nowadays, if the sample is matrix positive and negative for all the other main flu strains, it’s probably H5N1 flu, but pets can get spillover infection of other strains that aren’t included in strain-specific tests. If they stop here, it’s functionally okay but not ideal. I’d want to try to get followup testing of any matrix positive, type-specific negative samples (and would treat them as H5N1 positive until proven otherwise).

Any of these combinations would be okay for testing an animal in which there’s suspicion of H5N1 flu exposure / infection, but I’d rather have a quick H5N1-specific result in these cases, and I’d want to make sure that the lab will forward any positive sample for further genomic testing, so we can better understand the situation with H5N1 flu. 

Take home message

  • Talk to your lab to know what they can (and can’t) do in terms of testing for H5N1 flu, and follow up testing.
  • We can’t just stop at “flu positive.” Any such result needs to be scrutinized to make sure we know the strain (or strains) involved.

The FDA has issued a directive to pet food producers to ensure that their food safety plans address H5N1 influenza contamination issues. It’s in response to multiple cases of H5N1 avian influenza in domestic and wild cats fed contaminated raw diets containing poultry. Infection was fatal in many of these cats, and this also puts humans at risk of exposure from both the infected cats and handling the contaminated diets. The severity of disease in cats and the potential public health concerns with H5N1 flu in animals means action is needed to reduce the risk of infections. The FDA notice is directed at any manufacturers that use raw poultry or beef ingredients, but is most relevant for manufacturers of raw diets, since cooking during canned or dry diet production will kill influenza virus before it reaches the consumer or pet. Here’s what the first part of the notice says:

  • “The U.S. Food and Drug Administration has determined that it is necessary for manufacturers of cat and dog foods who are covered by the FDA Food Safety Modernization Act Preventive Controls for Animal Food (PCAF) rule and using uncooked or unpasteurized materials derived from poultry or cattle (e.g., uncooked meat, unpasteurized milk or unpasteurized eggs) to reanalyze their food safety plans to include Highly Pathogenic Avian Influenza virus (specifically H5N1) as a known or reasonably foreseeable hazard. Furthermore, the FDA is issuing this update to ensure that cat and dog food manufacturers are aware of information about the new H5N1 hazard associated with their pet food products, which is an additional reason that manufacturers must conduct a reanalysis of their food safety plans.”

Manufacturers covered under rule mentioned in the notice have a standard requirement to reassess their food safety plan when the FDA determines there’s a need to respond to a new hazard, as they have here.  The notice also encourages producers to minimize H5N1 transmission through practices such as “… seeking ingredients from flocks or herds that are healthy, and taking processing steps, such as heat treatment, that are capable of inactivating viruses.” 

Will the FDA notice achieve much?

That’s a tough question. It won’t likely have an immediate direct impact, as it’s reliant on the companies taking effective action themselves. It’s a directive to consider changing their food safety plans, not a directive to actually do something specific to mitigate risk. Presumably, that’s because there are limits to what the FDA can require; getting into very granular actions (e.g. “you have to do this specific thing”) is likely beyond what the FDA can or would do in a situation like this. The impact will vary between manufacturers, but even if it won’t make everyone do something useful, it should help.

The good, more mainstream raw diet manufacturers are already likely taking the necessary steps to prevent H5N1 flu contamination in their products. Most of these companies use high pressure pasteurization (HPP), which is a useful risk reduction step (although it’s not guaranteed to eliminate risk of all pathogens). I assume the first cases of H5N1 in cats from raw diets already sparked a review of what they are doing and what they can do to reduce the risk of using contaminated meat in the first place.

The all-too-common dodgy raw diet producers usually ignore (or deny-and-deflect) infectious disease issues with their products, and some have been doing the same with H5N1 flu. They will likely continue to do so. Their “reanalysis” might be akin to “yep, we thought about it and we’re good. Go away.”

As is typical, the manufacturers in the middle might be the group where this could have the most potential impact. They may not know much about the issue or understand how serious it is. They also may be at a loss about what they can and should do to mitigate the risk. They probably don’t have much expertise in house to be proactive about emerging issues, and a notice like this helps to ensure it’s on their radar, emphasize the importance, raise some liability concerns (that might be the biggest driver of action for some – getting sued is a big motivator), force at least some consideration of the problem, and point them in the right direction in terms of what to do. It might also be another nudge to introduce better overall practices like high pressure pasteurization and better supply management. 

What else can be done to reduce the risk of pets getting H5N1 flu from raw diets?

It would be nice to have more consumer-facing education about the risks and how to reduce them to help help consumers protect themselves. It could also help drive better manufacturing practices, if educated consumers start spending their pet food dollars on products produced in safer ways. 

What can people do about the risk of H5N1 flu if they are adamant they want to feed a raw diet to their pet(s)?

  • Avoid poultry-based diets (and probably also beef in the US).
  • Use diets that are high-pressure pasteurized, and ask companies about if how the effectiveness of their HPP method is tested (not all HPP is equally effective).
  • Ask companies about their food safety plan and what pathogens they consider in their plan.
  • Use good food handling practices in the home to avoid cross-contamination of human food and other surfaces.
  • Report any illnesses in pets (or people) that might be linked to the diet.

For more general information about food safety and raw diets, check out the Worms & Germs and OAHN Raw Meat Diets infosheet, available on the Worms & Germs Resources – Pets page.

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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.

My post earlier this week about culling considerations for control of disease outbreaks in animals generated some good discussion and ideas (and a surprisingly small number of “you’re an idiot” emails). Although that post was focused primarily on culling in response to influenza outbreaks, we can also think about it little more broadly and how it would apply to other disease outbreaks.  Australia has a really nice related guidance document that I hadn’t seen before, and it was great to receive it from a couple of people: Risk based assessment of disease control options for rare and valuable animals. It’s a good read for anyone interested in the topic. 

So, I’ve expanded the assessment table I created with a few more rows, with some more explanation below:

Likelihood animals/group have been exposed

If most of the group has been exposed, that’s bad. If it’s possible or likely that there’s only been limited exposure, containment is more feasible. 

For example, if a farm brought in a new animal and kept it isolated after arrival (a good but underused routine infection control measure), or it was kept with a small, separate group, then the rest of the farm/group might not have any realistic risk of exposure if that new animal turns out to be a disease carrier. It takes work to sort out what the risk is depending on how long the new animal has been there, the quality of the infection control practices, management issues and physical proximity to the other animals, but it can be done (and may well be worth the work in some cases).

Rapid and effective vaccination

Vaccination is often “too little, too late” for a facility-level outbreak. However, some vaccines (usually modified live vaccines) can produce very rapid and effective protection. Vaccination of this kind could also be considered for adjacent facilities to help avoid the need for culling (in some situations culling may be applied to all susceptible animals within a certain radius of an affected property, not just on the one property). If layered onto a situation where there hasn’t likely been widespread exposure of other animals on the farm or adjacent farms, rapid and effective vaccination of these other animals makes managing the outbreak without a call a more reasonable and feasible option.

Effective post-exposure prophylaxis

Although not very common, there are some situations where we might have an effective post-exposure treatment that can prevent infection in exposed animals. If we can do that (without causing more risk or damage), then it decreases the likelihood that culling is necessary.

International trade and regulatory restrictions

As I said before, I hate to see us acting based on regulations that might not be up-to-date, logical or fit the situation. However, I’m practical enough to know that doesn’t always matter. While we want to make sure regulations are practical and reasonable (and updating regulations is typically a very slow process), it doesn’t change the fact that they can be important. Trade issues can be even more important if there’s a potential loss of a multi-million or multi-billion dollar export market because of the presence of a disease.

Immunity after infection

This factor is perhaps a bit more obscure, but it’s worth considering. It comes down to how likely it is that the pathogen can be effectively, rapidly and safely contained and eliminated. If infected animals have solid post-infection immunity, the disease will typically burn through a group and die out as the number of susceptible animals decreases. If animals don’t have good post-infection immunity, they can get infected again (and again, and again), which can lead to ongoing cycling of the infection in a group. That makes it much harder to contain. 

Testing options

Accurate, rapid and accessible testing for the pathogen in question is important. Without it, we’re flying blind: we have less confidence in our understanding of the disease status of individuals, which makes it harder to implement control measures and determine when an animal or facility is no longer a risk. 

Is the species known or reasonable suspected to be able to transmit the pathogen?

This overlaps with some of the rows in the first version of the culling assessment table (i.e. transmission risk to humans/domestic animals/wildlife). However, it probably deserves its own row since since it’s a key factor and “transmission risk” covers a broader range of considerations. Being infected is not always the same as being infectious. It’s possible for animals to be infected but to pose little or no risk of transmitting the pathogen. If they are infected but are unlikely to be shedding the pathogen, the risk they pose to others is very low, as is the value of culling such animals.

Risk to people involved in culling

Culling may mean a lot of people having a lot of contact with infected animals, which is a significant risk, especially if it’s a zoonotic disease. Culling can be done with lots of infection control measures to mitigate the risk, but there’s always still some degree of risk to consider. With some animals there may also be physical risks/dangers to people, depending on the mechanism used for culling, which also ties into the last factor on this list.

Humane aspects of culling

Culling needs to be done effectively and humanely. That’s always a controversial topic, but it needs to be part of the equation. Human health risks will always win out over animal health (and usually welfare) concerns, but we need to make sure both sides are fairly assessed. The flip side of this is also humane aspects of not culling, i.e. what is the likelihood of animal suffering with highly infectious and very severe / fatal diseases (like highly pathogenic avian influenza in poultry) if the animals are not culled.

There are probably other things we could add to the list so the table might get even bigger. That makes it messier, but it’s important to consider all the different (and sometimes competing) factors to make sure we make the best decisions. 

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The recent situation has raised more discussion about the role of mass culling in response to H5N1 influenza infection in domestic / captive birds. After H5N1 flu was identified on an ostrich farm in British Columbia, the CFIA ordered all 400 birds to be culled, but the owner is trying to find options to preserve her herd. 

It’s a tough decision, and views on the matter vary drastically depending on perspective and mandate (e.g. animal owner versus public health versus protecting trade and treaty obligations and and broader animal health across the country). So it gets messy.

I have not been involved in any discussions about this particular situation, so this post is more of a generic discussion of when, where, how and why culling can be used for disease control.

  • On one hand, culling can be necessary to eliminate a pressing and poorly controllable threat in order to protect other people and animals.
  • On the other hand, culling can (at times) be an overly heavy hammer that’s used to simply remove concerns altogether. Killing affected animals is a very definitive (and irreversible) response to a disease concern, but question is whether it actually achieves much in terms of reducing risk, depending on the specific situation.

There are a lot of issues to consider when determining the best response to an infectious disease in animals. There’s no magic rule that says “if X happens, then the best thing to do is always Y.” There are lots of grey areas, nuances and case-by-case variations, which makes it a big challenge from a regulatory standpoint, because regulations and policies are usually designed to be as black and white as possible (“do this, or do that” full stop). That’s good for clarity, but it runs the risk of inappropriate or unnecessary responses in cases that fall in the grey.

While lots of factors come into play, in general, culling makes more sense when there’s an imminent and substantial risk to human or animal populations from the affected animals that’s too hard to contain by any other means. In the case of H5N1 influenza, culling is easier to justify in poultry where those infected birds would not likely ever end up going into the food chain anyway (due to illness and mortality from the disease), so keeping them alive would just put the people handling them at risk (as well as potentially birds on nearby or linked properties) for little net benefit to the birds.

As H5N1 influenza is now well-established in wild birds in Canada and internationally, there’s less argument for culling from the standpoint of controlling disease. Previously, if we had rare incursions of highly pathogenic flu, culling would make more sense as it would quickly eliminate a large infected group of birds when there’s limited or no known infection in birds outside of that group. Here, we can’t say that. Now if we have H5N1 in a group of domestic birds, we still likely have lots of H5N1 circulating in wild birds in the area. If an individual group of birds is a drop in the bucket now that H5N1 is widely distributed, culling probably has little benefit to the larger population. There’s still some impact, but it’s probably low, and if it’s a small group, transmission isn’t sustained and there are some basic infection control measures in place, the risk that they will infect other birds or mammals is low.

Human health risk is a major consideration, but the risk is only for a short period of time with a group of domestic birds, because H5N1 influenza would be expected to burn through the population quickly and then be gone. If they can limit contact with the birds and use good infection control practices for necessary contacts, the risk is lowered further. However, it’s “lowered” not “eliminated.”

The value (economic, conservation, emotional) of the birds or animals is also part an important factor. The conservation aspect is particular important when it comes to rehabilitation facilities or zoos have infected animals, where culling could have important impacts on some uncommon species. The same doesn’t apply to ostriches or many other poultry and non-poultry species, but economic and emotional values might.

Ultimately, whether or not to cull birds on an infected premises is a cost-benefit decision where we can’t really quantify the costs or benefits well. The easiest thing from a risk aversion standpoint is to cull, but that’s not necessarily always the best thing from a broader standpoint.

I sketched this out for a synopsis of considerations for culling. The more answers end up in the red, the greater the value of culling:

Here are my answers for commercial chickens:

Here are my answers for ostriches:

How about for dairy cattle?

Cattle infected with H5N1 influenza probably pose at least as much (or likely more) risk to domestic animals and people as poultry. I’d score them similarly or sometimes a bit more to the right compared to chickens and ostriches, apart from the value row. The economic value of a dairy cow is much higher than a chicken, and I doubt culling would be on the table just because of that. Economics are likely going to be a major driver of any decision of this kind.

Does that mean we should or shouldn’t cull the ostriches? That’s beyond my pay grade, but I think these are some of the things we need to seriously consider when making those decisions.