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

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

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

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

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

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

As a journal associate editor and reviewer, I’ve seen lots of papers about SARS-CoV-2 in animals. Some have been great, ground breaking papers. Many have been small, weak studies rushed out to be “first,” with inadequate depth and lacking critical assessment. Some have been a complete disaster. The latter two groups are a concern beyond just being bad science. Shortcuts can lead to bad conclusions when things aren’t studied properly.

A recent study (Hoppe et al, Infection 2023) highlights the need for proper study to avoid bad conclusions. It describes SARS-CoV-2 infection in a household where both people and a dog were identified as infected.

A human (the father) was the first identified case, and the rest of the family subsequently got COVID-19 as well. The source of the father’s infection was unclear, but he noted that his dog had been sick (i.e. coughing, lethargic) starting 11 days before the onset of his own illness. The dog had been taken to a veterinarian and tested negative for some routine respiratory pathogens, but false negatives are very common with these tests based on timing of sampling and our inability to test for all causes of respiratory disease.

After the owner was diagnosed with COVID-19, the dog was tested for SARS-CoV-2. Samples were taken 18 days after the onset of the dog’s respiratory disease, and all 3 samples from the dog were positive for SARS-CoV-2 at that time.

Timeframe figure of SARS-CoV-2 infection in a dog and 4 family members, with the dog’s infection preceding human infections.

It was suggested that the time frame was consistent with dog-to-human SARS-CoV-2 transmission. I’d say that’s a bit of a stretch based on what we know about infection of dogs, but it’s not impossible. Dogs seem to be commonly infected from their owners, but seem to be pretty resistant to clinical infection and don’t seem to be great hosts for the virus. Virus shedding in dogs tends to be low and of short duration. With a fairly short incubation period in people, the dog would have had to have been infectious for well over a week to be responsible for the father’s infection, and that’s unlikely. The dog also would have had to have been PCR-positive for 18 days after the onset of disease, which I’d consider really unlikely.

However, “unlikely” doesn’t mean “impossible,” so more study was needed. Presumably, at this point, they thought the dog was the source of the family’s infection and were waiting for sequencing results to confirm that.

(Un)surprisingly, the sequencing results didn’t implicate the dog.

There were enough differences in the viral sequences between the dog and owner that the viruses were classified as two different lineages (B.1.1.29 and B.1.1.163, respectively). They concluded the infections were independent, since the series of mutations that would have to happen between the dog and person were “so unlikely, that secondary zoonotic transmission can virtually be excluded.”

It’s pretty clear that the dog was infected. The dog was PCR-positive and antibodies to SARS-CoV-2 were later detected in the dog’s blood.

It’s also pretty clear that the dog wasn’t the source of human infection. The dog’s infection was actually unrelated.

Then how did the dog get infected?

That’s an interesting and unresolved question, since the pet had little outside contact given restrictions that were in place at the time.

  • Maybe he picked it up from unreported contact outside the household.
  • Maybe a person in the household had an undiagnosed (potentially asymptomatic infection) with the strain that infected the dog.
  • Maybe the dog picked up the virus while visiting the veterinary clinic.

It’s impossible to say. That highlights a challenge. Confirming interspecies transmission of a virus that’s widespread in humans is very difficult, and often a really unique set of circumstances need to be present (as was for the cat-human transmission of SARS-CoV-2 that occurred in a Thai veterinarian).

This is a good example of the need to investigate interspecies transmission but the need to do it right. 

Dog image from: http://www.quickmeme.com/meme/3oyz00

Figure from Hoppe et al, Infection 2023.

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

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

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

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

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

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

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

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

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

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

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

Canada has a long-standing requirement for rabies vaccination of most categories of dogs and cats being imported from countries not considered free of non-bat rabies.  While this requirement helps protect dogs and cats from rabies infection should they be exposed to endemic wildlife rabies that is present in Canada, it does little to prevent rabies in animals that were exposed to the virus prior to vaccination and importation.  Two cases (July 2021 and January 2022) of rabies in dogs recently imported into Ontario, along with ongoing pressure from public health agencies for more regulatory control of canine importation, lead to the Canadian Food Inspection Agency (CFIA) prohibiting the importation of all commercial dogs from countries considered high-risk for canine rabies, effective September 28, 2022 (World Rabies Day).

Many members of the public and organizations involved in canine importation do not understand the rabies disease process, risk periods for virus shedding, and how and when rabies vaccination is or is not effective at preventing infection.  Providing an explanation of these nuances in a format that can be relatively easily understood by members of the public is key to garnering support for and compliance with current and future canine import requirements regarding rabies, which helps support both animal health and public health efforts to reduce the risks from this deadly disease.  The companion animal Ontario Animal Health Network (OAHN) therefore undertook a project to produce the short whiteboard video below on this topic (which I think is pretty awesome, but I’m a bit biased!). Check it out on the OAHN website or directly on YouTube for links to additional rabies resources for pet owners and veterinarians.

I’ve written (ranted?) about this before – namely the misuse of antimicrobials intended for treatment of aquarium fish in other species. Usually such posts are followed by a deluge of nasty emails along with a bunch of curious requests for links to fish antibiotic sellers (8% kickback available!).

Another sponsorship request came in this morning, prompting this rant. I guess it was a poorly programmed bot, or someone who didn’t carefully read even the title, let alone the content of my previous posts.

Picture of a bottle of 'fish ciprofloxacin'

In some ways, this issues is small potatoes in the grand scheme of the “silent pandemic” of antimicrobial resistance (AMR), something that impacts millions of people and costs billions of dollars every year, but it flies largely under the radar. However, even small potatoes need to be addressed when we’re dealing with a problem like AMR. Everyone has a role to play.

Why is diversion of fish antibiotics an issue?

Anytime an antibiotic is used, in any species (including humans) there are risks: adverse effects, treatment failure, emergence of resistance, etc. So, when antibiotics are used, we need to make sure we maximize the benefits and minimize the risks/costs. The more antibiotics are used without medical (human/veterinary) advice and control, the more risks and the fewer benefits there are.

What are “fish antibiotics?”

They’re the same antibiotics we use in people and other animals, but with “fish” slapped on the label. They’re marketed that way to try to keep them under the regulatory radar (even though it’s still illegal in some countries where they are sold this way). If you look at websites that sell fish antibiotics, you’ll often find the same drugs and same formations (even the same tablet sizes and shapes) as are used in other species. Websites are smart enough now not to explicitly say you can use them on yourself or in other species, but that’s pretty well known so they don’t have to, and product reviews show other people what’s being done.

Do many people actually use fish antibiotics on themselves?

It’s hard to say. One study of internet reviews reported that 2.4% of reviews suggested they were purchased for use in people (see screenshot below). That’s presumably an underestimate, since most people who buy fish antibiotics to use on themselves or their kids likely don’t write that in a review. A larger percentage probably bought them for use in their dogs or cats.

Is the ability to buy and divert fish antibiotics actually causing harm?

Who knows? However, there are a number of potential issues.

Adverse effects: Antibiotics are not innocuous. There’s always some risk of adverse effects. Some situations and some drugs pose higher risk, which is just part of the reason to always get medical advice before taking antibiotics.

Product safety: Who knows what’s actually in these products? A 500 mg ciprofloxacin tablet for fish might contain 500 mg of ciprofloxacin. However, I suspect it often doesn’t. It could contain more or less (both potentially being an issue) or contain contaminants. I’m not going to have much confidence in quality control for a product that’s being produced for dodgy or illegal sale.

Inadequate/ineffective treatment: Some reviews I’ve seen talk about use for things where there’s not much hope of the antibiotic working. People using it themselves have to know the right drug, the right dose and the right duration. I doubt that’s common.

Resistance: Anytime an antibiotic is used, there’s pressure to select for antibiotic resistant bacteria. At the individual level, it’s a small risk, but the more it’s done, the more that risk becomes relevant at a population level.

It’s easy to say “just stop it,” but we need to consider why this happens in the first place.

A general principle of antibiotic stewardship and good medicine is that antibiotics should be available only by prescription (human or animal). That helps makes sure they are used when needed, not used when not needed and used properly (right drug, dose, duration and any other necessary treatments).

Some people are looking for a cheaper option, even though they can afford to see a doctor or take their pet to a veterinarian, and purchase the proper product. However, what’s the true cost savings if the antibiotic they buy online isn’t necessary, is the wrong drug, is harmful or isn’t used properly?

Some people truly can’t afford the proper product. Access to treatment needs to be a right, not a privilege.

Lack of access to healthcare is a big issue. At the core of antibiotic stewardship is a need to improve human and animal health systems in general. Whether it’s because they can’t afford healthcare, don’t have access to a doctor or veterinarian in their area, have tenuous employment where they can’t get time to go see a doctor or veterinarian, some people truly have significant barriers to getting antibiotics through the proper pathways. We need to improve those pathways so people can get antibiotics when needed (for themselves and their pets) and get proper preventative healthcare to avoid needing antibiotics in the first place.

Education is another issue. If someone can buy something that is labelled the same and looks the same as a product licensed for people or other pets, it’s easy to see why they’d think it’s fine. We need more general education about antibiotics, antibiotic use and antibiotic resistance so people are more aware of the risks associated with misuse of these products.

So, what can be done about diversion of fish antibiotics?

When there are companies based in countries where it’s illegal to market products like this, it’s simply an enforcement issue. Selling over the counter fish antibiotics is illegal in the US (and in Canada) and many of the companies selling these products list US addresses. So, it’s a matter of someone deciding to crack down on these kinds of sales. That doesn’t address the broader issue of black market drugs being imported into North America, but it’s at least a start.

Even some “main stream” companies are involved in these scenarios, probably inadvertently, but it’s something they need to scrutenize. For example, I looked at Walmart’s PetRx website and there are reviews that indicate diversion of pet medications. I’m not sure how rigourous some of the US online veterinary pharmacies are with their verification of prescriptions and “vetting” of purchases, but some effort to minimize diversion would be good. At a minimum, removing reviews that show others are misusing these products (which might encourage others to do the same) is a no-brainer.

Undoubtedly, small improvements in antibiotic use in human healthcare, veterinary medicine and food production would have much more of an impact than completely eliminating diversion of fish antibiotics. However, the scourge of AMR is a complex, multifactorial problem. There will never be a simple, single solution. We need a toolbox of many different interventions that on their own only contribute a little, but put together and over time will have a larger impact. Low hanging fruit like this needs to be part of that.

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

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

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

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

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

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

We have different  approaches to rabies in dogs and cats versus humans. The ultimate goal is still the same: preventing this almost invariably fatal infection. However, between humans and animals there are differences in who we target for vaccination, frequency of vaccination, utility of rabies antibody titres, and how we respond to potential rabies exposures, to name a few.

There are good discussion points for all of those, but today I’ll focus on how we deal with rabies antibody titres.

What is a rabies titre?

A rabies titre is a test that measures the amount of anti-rabies antibodies in a person or an animal’s blood. In general, antibodies indicate whether an individual’s immune system has responded to either infection or vaccination; in the case of rabies, because infection is almost always fatal, a titre usually indicates response to a vaccine.  The higher the titre, the more antibodies are present, which usually means a stronger response.  We can periodically recheck an individual’s titre to see how long those antibodies persist over time.

However, interpreting the test results can be a challenge.

While we have reasonable cutoffs for what titre we think indicates a good response to a rabies vaccine, we don’t truly know what is a “protective titre” –  because that would involve testing titres and then seeing which individuals get rabies after being exposed. That’s not the type of research that’s ever going to be done in people (and rarely even in animals, due to risk, ethics and expense, among other things).

Rabies titre monitoring in people

Traditionally, it has been recommended that individuals at higher risk of rabies exposure (like veterinarians and animal control personnel) have their rabies titre checked every 2 years, and that they get a booster vaccine if their titre is below the recommended cut-off (although compliance with that is pretty low).  However, in 2022 the US CDC’s Advisory Committee on Immunization Practices (APIC) updated their recommendations for the prevention of human rabies.  Under the new guidelines, veterinarians fall under category 3 “people who interact with, or are at higher risk to interact, with mammals other than bats that could be rabid, for a period longer than three years after they receive PrEP” (PrEP stand for pre-exposure prophylaxis, which simply means pre-exposure vaccination). The recommendation for individuals in this group is to either have their titre checked 1-3 years after their initial 2-dose vaccination series (with a booster if the titre is low) or get a one-time booster 3 weeks to 3 years after their initial vaccination series. Routine repeat testing every two years is no longer recommended, presumably because they’ve found over time that the vast majority of people who respond to the vaccine initially will have a very good titre for a long time (because human rabies vaccines are very good vaccines).

Rabies titre testing in dogs and cats

We approach titre testing in pets differently and more cautiously than in humans. While not cheap, we can measure rabies titres in dogs and cats and we have a cutoff for what is considered “acceptable” in terms of demonstrating response to previous vaccination.  However, as discussed above, an acceptable titre is not a guarantee of protection against infection if an animal is exposed to rabies.  (Also, while there are some excellent rabies vaccines available for pets, there are a lot more rabies vaccine products for pets than there are for people, and they are not all of equal quality.)

The best way to ensure pets are protected is to use a high-quality vaccine, and vaccinate them according to the manufacturer’s instructions, because research has been done to demonstrate  that this will actually protect the pet from (experimental) infection with rabies.

Many jurisdictions where rabies is being controlled require pets (or at least dogs) to be currently vaccinated against rabies, which typically means  vaccination every 1-3 years depending on the vaccine product used. Titres are not typically considered equivalent to vaccine status, and usually have no influence on what is done in response to rabies exposure in a pet (e.g. if a dog is overdue for its rabies vaccine, it doesn’t matter what its rabies titre is, it is managed the same as any other exposed overdue pet, which often means a long quarantine period (months) at a minimum).

Why do we continually revaccinated dogs/cats against rabies, instead of periodically measuring rabies titres like we do in people?

Part of the reason for this seemingly very cautious approach to protecting pets from rabies prior to exposure is that we don’t have proven post-exposure prophylaxis for dogs and cats like we do in people. If a person reports exposure to rabies, we know how to administer post-exposure prophylaxis such that we can provide virtually 100% protection from infection, whether the person is vaccinated (easier) or unvaccinated (harder, but still extremely effective).  We expect that vaccinated individuals would be able to report most potential exposures and get post-exposure prophylaxis.  Pre-exposure vaccination helps reduce the risk associated with any unknown or inadequately addressed rabies exposures that may occur because these individuals are in higher-risk positions, but even a person with an adequate rabies titre should still receive post-exposure prophylaxis to be confident that infections will be prevented.

For dogs and cats, revaccination after an exposure is still highly recommended / required, whether the animal is currently vaccinated or not, just as post-exposure vaccination is recommended in exposed people. We have more confidence in being able to protect a vaccinated vs unvaccinated animal this way, so vaccinated animals usually have lower or sometimes no requirements for quarantine as long as they’re revaccinated in time.  Unfortunately though, we have no proven post-exposure treatment in pets, so we can’t be as confident in the protection provided as we can be in people.

We also have less confidence in identifying rabies exposures in animals (because pets can get into all sorts of trouble when we’re not looking!).  Therefore, we’re therefore more reliant on vaccination as the main line of defense against rabies in pets. If we had proven post-exposure regimens for dogs and cats, and we had a way to be very confident that we’d identify all exposures, using an identical approach to that for humans would make sense. Since we don’t, and since rabies is almost invariably fatal (and since one infected pet can potentially expose lots of other animals and people), the default is to err on the side of vaccination.

Rabies vaccines are relatively cheap (much cheaper than titres), very safe and effective.  The downsides associated with regular revaccination are outweighed by the potential downsides of taking a titre-based approach when we have little data, no proven post-exposure regimens and limited confidence in identifying all potential exposures in pets.

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

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

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

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

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

How good is the canine flu vaccine?

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

What dogs should be routinely vaccinated against flu?

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

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

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

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

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

How is canine flu vaccine given, and how often?

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

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

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

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

What am I doing about canine flu?

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

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

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

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

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

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

How do I link all those? It’s not as big of a stretch as you might think, but it’s definitely getting into some theoretical components.

Dogs are unique from a Lyme disease perspective in that healthy individuals are very commonly tested.

Hundreds of thousands of dogs get tested every year for heartworm, and common heartworm tests also test for antibodies against Borrelia burgdorferi, the bacterium that causes Lyme disease. Seropositivity rates vary a lot by geography and lifestyle, but rates of up to 10% are not uncommon in some areas. The vast majority of those dogs don’t have Lyme disease. They were exposed to the bacterium at some point from an infected tick, mounted an immune response that produced detectable antibodies, and nothing untoward happened to the dog. A minority of exposed dogs ever go on to developing Lyme disease.

The upside: We get lots of surveillance data with all this routine testing.

The downside: There’s often a pressure to “do something” when there’s a positive result, even though doing nothing is usually the best approach.

I think things are improving, but a large number of healthy dogs are still treated unnecessarily with antibiotics (mainly doxycycline) because of positive routine antibody tests.

There are several concerns with that, but the potential for emergence of antibiotic resistance is one of the main ones.  Sometimes, people think that means a higher risk of resistance of Borrelia burgdorferi to antibiotics.  However, I’m concerned about emergence of resistance in the myriad other bacteria that are present in and on the dog, such as staphylococci and E. coli.

The risk of emergence of doxycycline resistance in Borrelia from unnecessary treatment of dogs is basically zero. It’s not because Borrelia can’t become resistant. Presumably it can, but it comes down to some basic ecology. There are a few basic things that need to occur for resistance to be an issue:

  • The bacterium has to be present.
  • A resistant strain has to emerge.
  • That resistant strain has to be spread to other individuals (directly or indirectly).

In dogs that are not actively infected (but still antibody-positive), resistance in Borrelia can’t emerge because the bacterium is not there.

In dogs that are actually actively infected, it’s theoretically possible that resistance could emerge during treatment. However, that would be the end of it because dogs are “dead end hosts” that don’t spread the bacterium any further. Emergence of resistance in reservoirs of the bacteria (in this case rodents, particularly white-footed mice) would be a concern, because then ticks could spread the resistant strain to many dogs (or people).

The main risk of emergence of doxycycline resistance in Borrelia burgdorferi is more likely heavy use of tetracycline in livestock, especially pigs.  Tetracycline is closely related to doxycycline, and the bacterial resistance mechanisms to the two drugs overlap. So, tetracycline exposure is a risk for emergence of doxycycline resistance, in general.

Livestock aren’t reservoirs for Borrelia, but heavy use of tetracycline on farms, especially in feed, could lead to exposure of mice to the antibiotic (when they get into stored or spilled feed, for example), and then theoretically there would be some resistance selection pressure if those mice are carrying Borrelia.

Does this happen?

I don’t know. I’m not sure it’s been investigated. Resistance doesn’t currently seem to be a big deal in Borrelia . However, it makes sense biologically.  While it’s not likely to cause a rapid increase in resistant Lyme disease, we worry about the longterm, cumulative impact of any antibiotic use, in any species (humans and animals). So, I wouldn’t discount it, and it’s yet another reason for us to try to minimize and optimize antimicrobial use in livestock and reduce environmental contamination with antimicrobials (from livestock and other sources).

Image from https://www.idexx.com/files/flex4-head-to-head-white-paper.pdf

As World Antimicrobial Awareness Week 2022 winds down, I’ll touch on a statement that I’ve seen a lot over the past week. “We need to reduce misuse and overuse of antibiotics” or “Misuse and overuse of antibiotics are driving antimicrobial resistance (AMR).” Those are great sound bites but largely miss the mark.

Yes, misuse and overuse are problems, but that’s only part of the story.  Focusing on misuse and overuse alone can lead to overly simplistic and ineffective approaches to combating AMR.

Anytime an antimicrobial is used in people, animals or plants, there’s some degree of selection pressure and risk of further dissemination of AMR.  It doesn’t matter if we consider it to be overuse, misuse or appropriate use. It’s what happens to the bacteria that are exposed to the drug that matters.

  • Misuse is important because there’s risk of selection for AMR with less clinical benefit.
  • The same applies for overuse: we create extra AMR risk without extra benefits.
  • But ANY use still potentially cause problems.

So, we have a problem with antimicrobial USE. Period. Misuse and overuse are part of that, but not the whole story.

Misuse and overuse are also sometimes subjective. We can say that antimicrobials shouldn’t be “misused,” but if we can’t clearly explain to prescribers and users what that means, we don’t achieve anything.

We absolutely need to reduce misuse and overuse. They contribute to resistance risk while providing little to no significant benefits.  For an issue like AMR, where there’s always risk, cost-benefit considerations are key.

But just as important is the need to IMPROVE use of ALL sorts. That often includes reducing use, but not always. It can involve changing things such as drug selection and duration or timing of treatment, to maximize the benefits and minimize the risks.

So, how to do we address antimicrobial “use” overall?

  • Pay attention to misuse and overuse, and try to eliminate those.
  • Better understand and communicate what constitutes “appropriate” use.
  • Develop robust surveillance systems so we can understand how antimicrobials are used, so we can know what’s actually happening and where we can intervene.

What’s as important, though, is reducing the need for any use at all by preventing infections before they start.

Antimicrobial resistance is an outcome of antimicrobial use, and antimicrobial use is an outcome of animal (and human) health issues. If we improve animal management systems, we improve animal health and we reduce the need for antimicrobials. That can include things like better raising of farm animals, vaccination, use of antimicrobial alternatives and improved access to veterinary care.  Improving public health and human healthcare likewise improves human health, and reduces the need for antimicrobials in people.

Healthy animals need fewer antibiotics.  The same is true for healthy people.

Improving health makes sense but gets less attention. There’s nothing sexy about it. It’s usually low-tech, and often involves improving use of routine measures such as maintaining water quality, sanitation, hygiene, ventilation and preventive medicine like vaccination. We’re not likely going to “tech” our way out of AMR. We’re going to improve things by using myriad basic health strategies to reduce our need for antimicrobials and preserve the efficacy of the ones we have.