As the H5N1 ostrich debacle in British Columbia has come to a close, part of me wants to ignore all the crap that’s coming in, but there’s value in recapping and trying to move forward.

Quick catchup….the flock was infected with H5N1 influenza in Dec 2024. Contrary to legal requirements, the farm hid the issue and didn’t do anything that would be required in response to this high consequence virus. It’s been reported that 69 birds died and 300-400 remained (they never could come up with an exact number). When it was discovered, the Canadian Food Inspection Agency (CFIA) got involved, as is their mandate. As per standard approaches to H5N1 in poultry (which ostriches are considered by international designation), a cull order was issued. However, the farm fought back and did so by suing and appealing, while taking no infection control practices (including posing with the birds without PPE and inviting a convoy onto the grounds). Ultimately, it made it to the Supreme Court of Canada, which issued a temporary stay order, but then declined to take up the case. As a result, CFIA culled the herd.

First off, the ostriches are the victims here. They had bad luck in being exposed to H5N1 and being in a situation that had little chance of avoiding a standard cull because of the mess of a farm they lived on. This moved quickly from being about disease to being about politics and fundraising, and the birds got caught in the middle.

Why was a cull done?

A cull is a standard approach to this virus because of the risk to animals and people. It’s done to contain it and reduce the risk of further transmission to birds, spillover into mammals (which increases the risk of adaptation to mammals), infection of people (this virus has a high mortality rate historically) and, most concerningly, recombination with other animal and human flu viruses. That’s how all pandemic flu viruses originate.

Were these birds infectious?

In December, yes. This group was probably highly biohazardous and at great risk of infecting wild birds, wild mammals and any people or domestic animals on the farm. It was subsequently determined that the strain that was involved was a variant that has caused human infection and had some potentially concerning mutations.

Were they infectious when they were culled?

Probably not. In a group like this, flu probably burned through in January or February. Longterm shedding of flu virus in an infected bird is unlikely, so for there to be a risk there would have to be continued circulation of the virus. With a group this size and over 10 months, that realistically means birds would have to get reinfected to sustain transmission.

Can that happen?

Maybe. Probably not, but ‘probably’ isn’t an acceptable threshold for this disease. If we don’t know the virus is gone, prudence would dictate we assume it’s still there. That’s the approach that CFIA (understandably) takes.

Was there an alternative?

Maybe. It’s a big ‘maybe’ with lots of caveats. While culling is the international expectation, countries can take alternative approaches if they can show adequate containment. That’s not defined so it’s a tough grey area for a regulatory agency that doesn’t like to dance in the grey zone. It would require solid isolation, strict infection control practices, testing, monitoring and documentation. That’s tough in general. It’s really tough with outdoor birds and uncooperative owners.

What could be done with an alternate approach?

At the time the outbreak was happening, it would have been fair to say it’s not reasonable. The risks are too high with that setup.

10 months later (after the ball had been dropped, but that’s where we were) testing could make more sense. That’s not easy, though. These are big birds that can do a lot of damage to people handling them, especially when there are poor (to non-existent) handling facilities. Sticking a swab down the throat of a large bird that can split you open with a kick is hard to sell.

If we could test them, we’d have to be able to catch them all, identify them all, sample them and get negative results for all. That’s theoretically possible, and if there were zero positives, I’d be pretty confident the group is negative.

However, there’d likely be a need for ongoing monitoring and confidence in that. Since the farm hid the disease initially and has shown no interest in disease control, it would be hard to convince anyone that’s an effective approach.

Further, even if WOAH (the World Organization for Animal Health) thought the approach was OK, that doesn’t mean all countries would. Any country could restrict importation of BC or Canadian poultry (or other food products) on the premise that Canada has shown it cannot protect its food supply. Even if it’s a dodgy claim, a country with an agenda or that wants leverage for negotiations could play that card…..successfully.

When there’s potential risk to animals, humans and multi-billion dollar industry, the bar is obviously going to be high.

So, is it possible? Yes. Easy? No.

Easy shouldn’t be a requirement but it’s not just that it’s a hassle, it’s that it might not be possible.

What about the research value of these birds?

The farm has talked a lot about how these are no longer meat birds. They’re a ‘research floc’k. However, they’ve not been able to present any viable information about valid research that’s been done. They haven’t indicated that there’s ethics approval for research on the farm (a basic requirement for research involving animals). They don’t even know how many birds they had or have any form of identification (tags, microchips). If you don’t know who’s who and don’t even know how many birds you have, this is not a legitimate research operation.

These birds survived H5N1 flu. Was there research value?

Not much. Yes, these survived. We don’t know how many fought off the infection (something we know many birds of some species do) or weren’t actually exposed. The birds that survived an infection may have antibodies against H5N1, but so would any other animal that survived or was experimentally infected. So, there’s not a lot of unique value here.

What about herd immunity?

For the supporters who were comprised of a large proportion of anti-vax (and anti-PCR, and anti-public health and some people that don’t believe viruses exist), they put a lot of attention on herd immunity (which is something we try to achieve through vaccination). It’s very unlikely this group was immune to H5N1. Those that were exposed and fought off the infection would have some immunity, but we know that immunity to influenza after natural infection isn’t great or longlasting. That’s why we can get it repeatedly. Some of the birds might have been immune, or at reduced chance of severe disease. Some were probably previously infected but are not immune. Some might not have been exposed and are not immune. As a group, it’s very likely that there would be susceptibility to re-infection if there’s another exposure.

Where do we go from here?

Hopefully we can look back and get something positive from this mess and unfortunate ending for the birds. There are a few key components.

The Supreme Court has re-inforced the appropriateness of CFIA’s disease response. This is important since it might reduce the chance of future lower court successes with appeals and stays. It’s fair to have oversight and to criticize CFIA. It’s also fair for CFIA to say ‘we have to contain this disease for the protection of animals and people, and we need to do it quickly’. No one at CFIA celebrates when they have to cull. They do it as an unfortunate but necessary part of their mandate to protect animal health, human health, agriculture and the food supply.  Allowing people with agendas to weaponize the court system creates risk.

There may be valid arguments for approaches other than a cull, in certain situations, as this is now an endemic disease. However, this needs to be done carefully, with a lot of transparency, effort, structure and excellent care. In other words, exactly the opposite of what was done here. A mechanism to promptly evaluate a potential alternative, with a clear approach, set criteria to review (what, who…), a very rapid response and no appeal process would be interesting to investigate.

As part of that, there needs to be excellent interim containment. If a farm wants to convince CFIA to take a different approach, they need to do absolutely everything possible to contain the problem while this occurs. If it can be done with minimal risk, it’s potentially viable. If it creates risk in the interim, it’s not. Even if this farm had done the exact opposite of what they did, and diagnosed the issue quickly, reported it, properly disposed of dead birds and enacted strict infection control practices, it’s debatable whether an exemption during the acute disease period would have been viable. You can’t contain a few hundred large birds (producing lots of virus-laden snot and feces) outside in an area with abundant wild birds, and with no indoor isolation options and handling facilities.

If you don’t have an appropriate facility and management, it’s not an option. That’s not CFIA’s fault. That’s a choice by the farm about how they operate. Raising birds outdoors isn’t bad, it just create risk that any farm needs to accept. And when that results in disease, there are consequences.

We had a high consequence virus on this farm, they handled it horribly, the virus in question had some mutations that created even more risk, and nothing bad seemed to have come from it (that we know of, at least). Does that mean none of this makes sense?

No. We got lucky. You only get lucky so many times with a high consequence infectious disease that has pandemic potential.

It’s really sad how infectious disease control (and beyond) has gotten so politicized. This went from an issue with one group of infected birds to having a convoy on the (quarantined) farm, massive misinformation, dodgy ‘media’ stirring up hate, threats to experts and people doing their jobs, massive fundraising and grift, largely by people who likely don’t give a crap whatsoever about those ostriches. It also cost the taxpayers a huge amount of money. The ostriches were political pawns and an excuse to complain, raise money and have a party at the farm. We need to move beyond that component of this issue and come back to the valid disease control questions that can and should be discussed going forward.

New World Screwworm (NSW) is a nasty parasitic infestation (with a very high ick factor) that’s back on the radar in North America, re-emerging after several decades of highly successful control and eradication efforts that had pushed its northern reach back as far as Panama. It has now made to back as far as northern Mexico, within a few hundred kilometers of the US border, and there’s significant concern that it will continue to move north, despite concerted efforts to halt its progression. The primary risk is to livestock, which can be infected when the flies (Cochliomyia hominivorax) lay their eggs in any tiny wound or break in the skin. Importing animals from affected regions, including much of South America and some Caribbean countries, is a huge risk for moving NWS to new area, which is why the US closed its border to livestock from Mexico months ago. But NWS can also infected companion animals, and lots of dogs also get imported to the US and Canada from endemic countries. While the parasite can’t establish itself in the northern US or Canada thanks to our cold winters, it’s still very important for veterinarians here to be on alert for NWS in imported animals.

Treatment of NWS infections involves first and foremost physical removal of the maggots (ick), followed by administration of anti-parasitic drugs to try to kill any deeper maggots we can’t see or remove. Some anti-parasitics can also help to prevent disease by killing developing larvae after the fly eggs hatch, before they start destroying the living tissues of their host.

There isn’t a licensed drug for NWS in Canada or the US, not necessarily because nothing works, but because manufacturers haven’t sought this approval for any existing products, because it’s a very time consuming and expensive process to do so, and the disease has been eradicated from the region for decades.

Fortunately, we do have some off-label options. A few different antiparasitic drugs that we routinely use in dogs and cats can be effective. This would classically focus on ivermectin (shown to have some effect in cattle) and the related drug, moxidectin. There are also a variety of drugs that are authorized for flea and tick prevention / treatment which could be effective.

  • It’s important to note that the label doses of ivermectin and moxidectin that we use for heartworm prevention in dogs are substantially lower than the doses that might be effective for treatment of parasitic infections like NWS, so having a dog on heartworm preventative won’t prevent screwworm infection.

Earlier this year, the US FDA posted information for veterinarians on a few drugs that may be potential options for off-label treatment of NWS, including ivermectin, moxidectin, nitenpyram, afoxolarner, lotilaner, sarolaner, milbemycin and spinosad, mostly based on an assumption that they could work, rather than any hard data showing they do (or don’t) work.

New EUA for Credelio (lotilaner) for NWS in dogs

New this week, the US FDA issued an Emergency Use Authorization (EUA) for Credelio (lotilaner) for the treatment of NWS in dogs and puppies. They concluded that:

  • “Based on the scientific evidence available to the FDA, including data from published scientific literature, it is reasonable to believe that Credelio may be effective for the treatment of infestations caused by NWS larvae (myiasis) in dogs and puppies, as described in this authorization, and when used under the conditions described in this authorization, the known and potential benefits of Credelio outweigh the known and potential risks for dogs of all ages and weights because NWS is potentially fatal in dogs if left untreated, therefore justifying including dogs less than 8 weeks of age or less than 4.4 lbs in this authorization.”

The authorization is based largely on a 2023 study of dogs in Brazil with naturally occurring NWS infection (Vale et al. 2023). It was a very small, single arm, open label study that involved treatment of 11 naturally infected dogs with a single dose of lotilaner, which showed 100% efficacy at expelling and killing larvae after 24 hours. It’s a small study, but still very useful, as such a high success rate provides pretty good confidence in the efficacy of the drug.

Does having this EUA for Credelio (lotilaner) in the US change anything?

Yes and no. Veterinarians have always been able to use the drugs on the FDA list in an extra-label manner in companion animals, so in that sense having the EUA doesn’t change this kind of access. However, it’s an impetus to consider lotilaner first since it’s now authorized and has some supporting data. That provides more confidence and backing when it’s used to treat an infected dog.

It doesn’t necessarily mean that lotilaner works better than the other drugs on the list for treating NWS? It just means the drug has been given an EUA. Presumably that could have happened for other drugs with some efficacy data, such as ivermectin, but since ivermectin is off-patent and available in a variety of products, it’s unlikely a manufacturer would go through the time and effort to get an EUA. Nonetheless, it’s ideal to use authorized drugs whenever we can, so this should lead to preferential use of lotilaner for treatment of NWS in dogs.

Should lotilaner be the tick preventive of choice now, since it also helps treat screwworm?

That’s a tougher question, and presumably will be a big talking point for all companies marketing ectoparasite preventatives. The EUA is for treatment, not prevention of NWS, but the two go hand-in-hand to some extent as treatment of early infection is basically the same as prevention. Since NWS is (hopefully) going to be a very rare occurrence in dogs in the US (and even rarer in Canada since our climate prevents the fly from living here much of the year), it’s to use this as a reason to say lotilaner should be the ectoparasite preventive of choice. However, it would be a fair consideration in areas where the risk of NWS is high (e.g. if it establishes a foothold in southern Texas).

It’s great to have an EUA for a treatment product for dogs, to help guide treatment choices and provide veterinarians with some backing when managing a case, but the EUA isn’t really a game changer. It’s nice that the manufacturer pursued it, even though it might have been driven by marketing advantages more than anything else. Emerging and rare diseases are often neglected and efforts by companies and the FDA to support their management are useful.

Image from https://www.cdc.gov/new-world-screwworm/about/index.html

The other day, I did a half-hearted tick drag while walking Ozzie in our back field (yes, I know that’s strange, but let’s move on…). It was far from a professional job – just me dragging a blanket through the field as we walked, but it did the job. It quickly picked up a tick, that I quickly dropped – by accident (I’ve fortunately moved beyond the point of being freaked out about ticks). However, I had a an more effective tick-dragger with me: Ozzie. When we got back to the house, my towel was clean, but my dog was not – we found not one but three ticks on him (and none on me… I checked). It really didn’t stress him out too much.

Although we’d been walking through a hay field through which I’ve cut a walking path, Ozzie of course trolls through the longer plants and leaf litter along the side of the field, which is classic tick territory, so it’s not overly surprising that he’d pick up some ticks. Not surprising these days at least, but it would have been about 5 years ago. Up until then , I’d never seen a tick on one of my animals (or myself, or my kids). Things have changed a lot in those years.

It’s noteworthy that Ozzie picked up black legged ticks, Ixodes scapularis (first picture below).

That’s the first time I’ve seen that type of tick here, but I’ve been expecting it as it’s been steadily moving into the area. Ixodes scapularis is one of the vectors of Lyme disease and anaplasmosis, diseases that affect both dogs and people. When we first started seeing ticks in this area, they were all American dog ticks, Dermacentor variabilis. The next picture below is one of these ticks which we found on Ozzie earlier in the year. We’ve traditionally considered that tick to be pretty benign in Ontario, but the recent detection of Rocky Mountain Spotted Fever in Long Point, Ontario might change that.

Tick exposure risk definitely varies over the seasons of the year.

Tick exposure risk drops substantially in the winter, because when the temperature is below 4C (or maybe 0C), ticks aren’t looking for hosts (questing). Ticks also tend to stay hidden in protected areas during hot, dry weather, so there is also usually a lull in tick exposures in late summer.

There’s also seasonality to what tick species dogs or people are likely to encounter. Fall is black legged tick season here, with almost none of the American dog ticks we see at other times, but the American dog tick season here may be getting longer as we seem to be finding them later and later in the season lately.

Ozzie’s on tick prevention medication, so any ticks that attach should die within hours. That’s great for preventing Lyme disease and anaplasmosis, as those take at least a day to be transmitted from the tick. It’s a bit less effective for Rocky Mountain Spotted Fever, since ticks can transmit the bacterium that causes that disease (Rickettsia ricksettsii) much quicker, and there’s overlap between the potential transmission time and the time that it takes tick preventatives to work. The preventatives are still very useful, but they aren’t 100% effective at stopping all pathogen transmission. So, other risk reduction measures such as avoiding high risk areas and tick territory (e.g. long grass and leaf litter) and doing regular tick checks are also important. We’re fortunate that Ozzie is a yellow Lab, as it’s not hard to find ticks on a dog with a short light-coloured haircoat. Darker dogs and dogs with long hair are a much bigger challenge. Tick checks are likewise far from 100% effective, but they’re an important part of the toolbox.

There’s also an important dog factor to consider with regard to the risk of human exposure to ticks. The ticks we found on Ozzie after the walk weren’t yet attached to him, they were just wandering around in his hair coat. If left alone, they’d most likely they’d attach to him quickly and subsequently die because of the tick preventative he’s on. However, loose ticks can also fall off a pet or be transferred to people or other animals that weren’t necessarily exposed to the environment where the tick originated. I’ve found the odd tick free in the house that presumably hitched a ride in on Ozzie. Ticks checks on dogs can therefore also help protect people by preventing loose ticks from ending up in the indoor house environment.

Knowing about local ticks and tickborne diseases is important for everyone, dog owner or not. It helps us understand when and where the risks are highest, and informs the types and intensity of prevention measures we need to use.

Public Health Ontario has a relatively new online interactive vector borne disease tool that shows high risk areas for black legged ticks, and provides information about the incidence and distribution of various vector borne diseases (in people). The black legged tick risk map shows our property just within one of the risk zones, which fits with the changes we’re seeing.

Last month, the Public Health Agency of Canada (PHAC) issued a somewhat vague notice about an ongoing outbreak investigation of Salmonella infections linked to dog food and treats. At the time they were still unable to identify a specific brand or manufacturer to which the outbreak had been linked.

This week PHAC posted an update on the outbreak investigation, which has linked some (but not all) outbreak cases to Puppy World and Puppy Love brand dog treats. So far, the outbreak strain of Salmonella Oranienburg has been identified in Puppy World Lamb Lung Treats, Puppy Love Chicken Wing Tip Treats, Chicken Breast Treats, Beef Chew Treats and “Twisty Jr” Beef Treats.

People often forget that many dog treats are in fact raw animal-based products. Even if they are freeze dried or dehydrated, they are still raw and therefore associated with increased risk of contamination with Salmonella and other pathogens (including H5N1 influenza virus, as has been seen in the US). Salmonella-contaminated dog treats may pose more risk to people than contaminated dog food as people tend to have more contact with treats. I’d guess (or at least hope) that most people feeding raw diets would handle the food carefully and use basic hygiene practices to prevent cross-contamination of surfaces, hands and human food. But when treats don’t look or feel overtly “raw,” it’s easy to see people skipping those basic measures (like hand hygiene).

The number of human infections in the current outbreak is now up to 31 (including a second case in Ontario). That means the true number is probably in the hundreds, as it’s been estimated that 26 people are infected for every reported case of salmonellosis (which would be up to 806 cases for this outbreak). The other cases are still mostly from BC and Alberta, and one case from the Northwest Territories, showing the widespread exposure and highlighting the challenges of such an investigation, even when tied to a fairly small manufacturer. This outbreak has been slowly burning along from February to September, and is potentially still ongoing. Other sources of the outbreak strain may still be identified as well.

Seven people have been hospitalized, with still no deaths to date. Hospitalized cases are unlikely to be missed, as patients in hospital are much more likely to be tested so the outbreak Salmonella strain would be less likely to go undetected compared to a less severe case in the community. The age range of cases remains unchanged (0-87 years), but is another important reminder about the risk of indirect spread and the need for basic hygiene – an infant is unlikely to be feeding a dog treats (although people do strange things), so cross-contamination of surfaces (including the floor) or peoples’ hands would be the likely source of exposure (or possibly picking up a dog treat left behind by the dog).

There’s been no recall of the implicated treats. The company does not put expiry dates on their products, so that complicates tracking and messaging. There’s no mention in the Public Health Notice about specific lots, just the product names. To be safe, for now I would assume that any bags of those products, and realistically anything from that company, is contaminated.

As is unfortunately typical with websites of raw food companies are implicated in disease outbreaks, there’s currently no mention of this risk or the investigation anywhere I can find on the manufacturer’s website. I will give them credit for at least mentioning Salmonella and the need for hygiene when handling their products; the information isn’t very comprehensive and some is a bit questionable, but it’s a start, and it’s better than other companies that ignore or blatantly misrepresent the risks from their raw products.

Treat image from Puppy Love Pet Products.

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There are a couple of new voluntary recalls because of Salmonella contamination of pet diets or treats. Both are US products, and the recalls were posted on the FDA website just before (Canadian) Thanksgiving.

One recall is for possible Salmonella-health risk associated with a raw frozen beef dog food from Raw Bistro Pet Fare (MN). That’s not very noteworthy, since Salmonella contamination of raw diets is common. Focusing on the odd batch of food with known contamination when we know that a large percentage of these diets at retail are actually contaminated doesn’t really help much (but the recall is still worthwhile). It’s fair to assume that any raw diet that’s not been high pressure pasteurized is harbouring Salmonella, E. coli, Listeria and/or other pathogens. High pressure pasteurized diets are much lower risk, but not zero risk.

The other recall is for possible Salmonella contamination of specific lots of Raw Dog Barkery, BellePepper Cats, and Kanu Pets brand freeze dried treats from Foodynamics (WI). Recalls of pet treats in particular are worth discussing, since raw animal-based treats are commonly contaminated, but people often don’t often think about them as “raw” unless the word is right in the name (which it often isn’t). You can find dried or freeze dried treats made of pretty much any animal part (e.g. liver treats, rawhides, hearts, pig ears, bully sticks) in most pet stores. If there was no cooking step in preparing the treat, it should be considered high risk for contamination with Salmonella and other bacteria (and raw poultry-based treats can also be a risk for contamination with H5N1 influenza virus in some regions theses days).

As opposed to diets, treats are not often marketed as raw or prominently labelled as raw. People may assume that dried treats have been cooked. They may also erroneously assume that freeze drying eliminates bacterial contamination (when in fact freeze drying is an excellent way of preserving bacteria for long term storage). Some of these treats, like liver treats, are even common in veterinary clinics, because even there people may not make the connection with any risk.

I’ll give a shout out to Fooddynamics for the voluntary recall for their freeze-dried treats in this case. Although kudos shouldn’t we warranted, we’ve seen pet food companies other pet food companies ignore and deflect in response to contamination of their products, instead of doing the responsible thing by issuing a recall, so it’s good to this company doing the right thing.

Impressively, the FDA reported that “Foodynamics successfully traced 100% of the product distribution within hours of the recall notice and has contacted all direct customers. No adverse health effects have been reported in pets or humans to date.” Presumably these are pretty small production lots and sales are online so the company can easily trace who bought what. Still, it’s impressive to see that a company willing and able to track down all purchasers.

It’s also nice to see that “Foodynamics has ceased the production and distribution of the product while it works with the FDA to continue its investigation into what caused the problem.” Again, that shouldn’t be surprising or encouraging, but we’ve seen so much “deny and deflect” by other companies that it’s refreshing to see this type of response.

It was also noteworthy that contamination in both cases was detected through routine FDA surveillance, not in response to animals or people getting sick. That means we got lucky to some degree, since only a miniscule percentage of retail products are tested, but it also shows that surveillance can help prevent problems in two ways:

  • They got contaminated food off the market.
  • It led to an investigation that will hopefully reduce the risk of future problems for the company, if the investigation identifies anything that can be improved.

However, with raw diets, there may not be a lot the company can do. The critical control point is cooking, and if they don’t do that by nature of the product being sold raw, then there’s always going to be a risk of contamination of the final product. Good manufacturing practices can help reduce cross contamination and ongoing contamination from equipment, but can’t prevent Salmonella contamination in the ingredients themselves. If Salmonella comes in and products aren’t cooked, it’s going to come out with the final product.

So, there’s a mix of good and bad in this scenario. Ultimately, there’s still the question of risk from treats and how to reduce said risk.

  • Should we avoid treats? No.
  • Should we avoid raw treats? Yes.

Determining whether a treat is raw can be a challenge for the average consumer:

  • If the label says “raw” then it’s obvious.
  • If the product is freeze-dried, there’s unlikely a cooking step involved, so assume it is raw.
  • If the treat looks like a piece of an animal (e.g. pig ear) and it doesn’t say it was cooked, odds are it was just dried; treat these as raw too.
  • If the product looks like a kibble or other non-anatomical shape, they were probably extruded / cooked and are therefore lower risk (though still not zero based on the odd chance contamination occurs after the cooking step).

I remember the first case of fly myiasis (aka fly strike, maggot infestation) in general practice. I was a very new grad called to look at a lamb owned by someone who had a few sheep. The complaint was that the lamb wasn’t doing well. It was laying down when I arrived and I grabbed it’s back… and immediately off came a big patch of skin, revealing hundreds of maggots underneath, and a smell that you never forget.

The owner threw up. I fortunately managed to avoid doing the same, but we euthanized the lamb. That wasn’t even a case of New World screwworm (NWS), but provides some idea of what these infections can be like – gross, potentially devastating, and not something we want to see in any animal (or person).

New World screwworm 101

New World screwworm myiasis is caused by the larvae (maggots) of a particular species of fly (Cochliomyia hominivorax). It’s estimated to cause billions of dollars in loses in livestock production, unquantified impacts on companion animals and wildlife, and hundreds of human infections each year.

This image illustrates the general life cycle of NWS:

The adult fly is attracted to wounds or even minor skin lesions on warm blooded animals (i.e. mammals and birds). It doesn’t need to start out as a big wound wound or an infected wound, although those kinds of breaks in the skin provide a much larger target for the female flies, and that is where they lay their eggs. When the eggs hatch, the larvae (maggots) burrow into the tissue, causing lots of damage as they grow. Unlike “regular” maggots from other kinds of flies that only feed on tissue that is already dead / necrotic, these maggots will destroy previously healthy / living tissue, so they can cause a lot of damage, and the infection can even be fatal. After a week or so, the larvae drop out of the wound and finish maturing in the soil, emerging as new adult flies. The wounds they leave behind can be very painful, and can be prone to secondary bacterial infections too (not to mention being attractive to more adult screwworm flies).

A couple of pictures from the USDA-APHIS NWS photo gallery illustrate just how devastating these infections can be:

For decades beginning in the 1950s, massive efforts were undertaken to eradicate NWS from the Southern US, Mexico, and Central America. The eradication programs relied heavily on the release of millions upon millions of sterile male screwworm flies. As a fortunate happenstance of this fly’s biology, females only mate once in their lifecycle – if they mate with sterile males, they lay sterile eggs, and there are no maggots or new adults produced. While it still took a lot of hard work, this technique was highly effective, and NWS was gradually pushed all the way back to Panama. The fly remains endemic in South America, and unfortunately eradication there isn’t likely achievable because the fly’s range is so large and much of the area is very remote. So there is always the potential for NWS to re-invade Central America (or to be imported via people, animals or products) and begin to move north again, which appears to be exactly what’s happened. Starting in 2022 it was detected again in Panama, and has now come within a few hundred kilometers of the Mexico-US border.

Having NWS once again so close to the US border has caused a lot of concern, as it’s estimated that re-establishment of NWS in the US could result in economic losses of close to $2 billion in Texas alone. The US has initiated more surveillance, increased border controls (including bans on livestock importation from at-risk areas) and is significantly ramping up sterile fly production. Cattle producers have also asked for permission to feed ivermectin (an anti-parasitic) to their animals as a preventative control measure.

  • While ivermectin and some other drugs can be given prophylactically to help prevent myiasis, injectable or topical treatment of individual animals in extremely large herds is logically difficult, so that’s why daily in-feed treatment has been discussed. While it could be effective for NWS, it also brings up potential for development of resistance issues in other parasites… but that’s a topic for a different day.

A sliver lining to Canadian winters

However, it’s one of these things that should be aware of in Canada but fortunately don’t have to be too concerned about because of our climate.

While we sometimes complain about the cold weather in Canada, a cold climate helps us avoid a lot of infectious disease risks, particularly where insects are involved. We are well outside of the plausible geographic range for this insect, even with a changing climate. It can’t survive our winters, or even most of our springs and falls. Development of the larvae in the soil is slower the colder it gets, and when the temperature drops below ~8C, larvae in the soil die. Of course we have periods of the year when these flies could successfully reproduce here, but it would be limited, local transmission that would end with the first cold snap. It won’t be able to establish itself here long term.

But we still need to be aware of the problem given the amount of people and animal movement between Canada and some of these affected areas, especially if it reaches the southern US again. The potential impacts on individuals animals and even short-term local transmission during warmer months (which could be long enough to see several generations of flies) should not be ignored. If a cow in Ontario got infected in early summer, there could be transmission to other cattle on the farm, other species on the farm (including people and pets) and spread to wildlife. They could do a lot of damage before the cool fall weather finally stops the fly’s lifecycle again.

While the focus of attention regarding NWS is on Central America and South America, it’s also endemic in some Caribbean countries (e.g. Jamaica, Cuba, Dominican Republic), and we import lots of dogs from those areas, so the potential for an infected dog to reach Canada is very real. If an infected dog or other pet was imported into Canada, the odds of further transmission are likely limited, since a veterinarian would hopefully see and treat the animal before it could seed the environment with maggots, but it’s not impossible. The more important concern in these cases is the health of the individual infected pet, because of the tissue damage these maggots can cause if the infection is not identified and addressed immediately.

What Canadian veterinarians and animal owners should do

Just being aware of the risk of NWS is a good start. It’s unlikely any given veterinarian or animal owner will see an infected animal here, but all it takes is one to be an issue, so we want to maximize our ability to detect and respond quickly and efficiently.

Addressing health problems in recently imported animals is important for many reasons, and this yet another one. If we identify infested animals early, we can manage them better, both to reduce the risk of severe disease and to prevent transmission (i.e. not letting any larvae make it to the soil).

Flagging importation history is the key. Too often, we have animals with health problems and we don’t find out relevant importation history until later in the course of disease. Owners of recently imported animals should have a low bar for seeking veterinary care if there are any issues. Ideally, we’d see every imported animal shortly after they arrive, to give them a good health check and review vaccination and other preventative care needs.

If maggots are found on an animal imported from an area endemic or at risk for NWS, larvae should be removed immediately, placed in ethanol to kill them (NOT thrown in the garbage or on the ground outside!) and they should be submitted for identification via the Canadian Food Inspection Agency (because NWS is a federally immediately notifibale disease in Canada, and is also notifiable to provincial health authorities in some provinces). Physical removal of as many maggots as possible is the mainstay of treatment, though anti-parasitics are often used in parallel to try to kill any deeper embedded larvae. Significant wound care may be required, depending on the location and severity of infection.

These larvae can also infect humans, as I mentioned briefly above. In Canada, it’s a travel-associated disease, a case of NWS was reported earlier this year in Ontario in a patient who had recently travelled to Costa Rica. As with many infectious diseases, the key is basic awareness.

Oh Darwin’s… here we go again.

Yet again, the FDA has issued a “Do not feed certain lots of Darwin’s Natural Pet Products” warning. It’s a pretty regular occurrence. And, once again, Darwin’s is dragging their feet on responding.

In July, Darwin’s ignored an FDA request to recall diets contaminated with E. coli O157 and Salmonella, two serious foodborne pathogens that can cause disease in pets and people.

The latest advisory is due to contamination with Salmonella and Listeria monocytogenes. These two bacteria were found in different samples of Darwin’s products, after an investigation was launched because of a consumer complaint. Presumably, that complaint was based on someone (a pet or a person) getting sick, but those details aren’t provided.

The implicated diet is frozen 2 lbs packages of certain lots of Darwin’s BioLogicals All-Natural & Grain Free Beef Recipe for Dogs. I wonder if there’s broader risk though, based on the frequency of contamination of their products, and the fact that Listeria in particular could be cross-contaminating other product lines via processing equipment.

The FDA recommended that the products be recalled. In response, the company did not recall the diets but (apparently? maybe?) sent a letter to consumers notifying them about the Listeria issue, but not the Salmonella. I have to wonder who they actually contacted and how. Maybe they contacted everyone that ordered the product online – that would be possible if all their sales are direct to consumer. It’s unclear, though, as is what they may have actually said in the letter. I can’t find anything on their website about this issue. The FDA notice says “The firm reportedly sent a letter…” suggesting FDA hasn’t actually seen what the company sent either, or if they actually did anything at all.

The FDA notice also says “Although Arrow Reliance may have notified its customers that it is withdrawing the two lots for L. mono, the firm has not yet provided sufficient documentation to the FDA to show that this action has removed affected product from the marketplace and customers’ freezers. Consumers may want to check Darwin’s BioLogics All-Natural & Grain-Free Beef for Dogs products for the affected lot numbers prior to feeding to pets.”

If you have any of the implicated diets, don’t feed them to any animal, and dispose of them safely. Personally, I’d say the same even for any non-implicated diets from this company, because of their repeated contamination issues and lack of appropriate response.

Any regular reader will know I have concerns about raw animal-based diets for pets. There’s no evidence they provide a benefit over an appropriate commercial or cooked diet, and they create risk to pets and the people around them. I’m pragmatic enough to know that some people will continue to use these diets anyway, so I focus on risk reduction in situations where raw diets are fed. That’s why we have an infosheet on raw meat diets on the Worms & Germs Resources – Pets page. In addition to the standard recommendations of using good basic hygiene practices and choosing a high pressure pasteurized diet, I’d add “don’t use products from companies that have recurrent FDA safety advisories.”

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The H5N1 influenza situation in North America has been quieter lately (apart from saga with the BC ostriches, but that’s a different story). There’s been less spillover into domestic animals recently and less attention in the news, but the virus is still out there and causing problems. (H5N1 flu activity has already started to increase in some areas as the fall wild bird migration gets underway.)

I’ve written about the risks of H5N1 flu (and other pathogens) from raw pet food many times, so the latest report about 2 cats from a household in California that got sick and died after eating commercial raw pet food isn’t a surprise. It doesn’t change anything, but it’s yet another reminder that this virus is still a risk, and there are completely avoidable death occurring in pets (primarily cats).

Both of the cats from the report were nominally indoor only. That narrows down the potential sources nicely to start. Both cats were fed a commercially available raw pet food. The first cat got sick and rapidly deteriorated and developed severe neurological disease. That’s quite common in cases of H5N1 influenza in cats that have been reported to date, but the first cat wasn’t tested. Five days after the first cat got sick, the second cat became ill with similar signs, starting with fever and loss of appetite and ending with severe neurological disease. It tested positive by PCR for H5N1 influenza after it died.

  • With that time frame, we have to consider whether the second cat could have been infected from the diet or from the first cat. The latter would be the worst scenario, as cat-to-cat transmission would be a significant concern, and also indicate potential risk of cat-to-human transmission. Unfortunately there isn’t any way to determine the transmission route in this type of situation.

Further testing showed that it the genotype of the virus from the second cat was the B3.13. That’s the main strain found in dairy cattle in the US, though it is also still possible to find it in wild birds and poultry. Presumably a poultry-based raw diet was the source, but since it was B3.13, I assume they investigated raw milk exposure too, as well as direct or indirect exposure to dairy farms.

The implicated raw diet is currently being investigated. It’s the logical source of infection in these cats, but confirmation would require detection of the virus in the food. Unfortunately, the time lag from ingestion to illness to diagnosis to investigation in cases like this often means the food that was the potential source is long gone before testing can be done, especially with raw diets that are often made in small batches (vs kibble diets). If the lot of the diet is known, then there’s the potential to find other samples from the same lot, but we also don’t know how evenly distributed the virus (or any other contaminant) would be within a batch of food. It can therefore be hard to show a definitive link, but it’s been done before so we clearly know raw food-associated H5N1 flu is an issue.

The report does not name the commercially available food that’s being investigated.

  • On one hand, you can understand why: the link is not confirmed at this point.
  • On the other hand, if there is contaminated food out there that’s yet to be eaten, or if there are sick cats that haven’t been diagnosed because people don’t know about the risk, holding back the information can be a problem.

I understand why this particular information is being withheld at this point, but hopefully more information will be released as the investigation continues.

What should cat owners do?

  • Avoid feeding raw poultry-based diets to cats (and other pets that may be susceptible).
  • If a raw poultry-based pet food is to be fed, use a high pressure pasteurized diet; this will be lower (but not zero) risk for pathogens like H5N1 flu.
  • If signs of illness occur in a cat that’s eaten a raw poultry-based diet, a veterinarian should be contacted ASAP and the raw diet exposure history should be explained. Fever, lethargy and decreased appetite are probably the most common initial signs. Respiratory disease may not be apparent. Neurological disease is a big concern but typically occurs later. If these signs occur in a cat that has been fed a raw diet, H5N1 should be considered, testing is warranted, and there might be value in providing antiviral therapy (if it can be given early enough).
  • We should assume that cats that might have H5N1 are infectious to other pets and possibly people. The risk is probably highest to other cats (since cats are quite susceptible to the virus and cat-to-cat transmission has been shown experimentally) but we can’t rule out the potential for cat-to-human transmission. Keeping the sick cat isolated and using good infection control practices are critical.

The LA County Deptartment of Public Health is monitoring household members and veterinary personnel who were in contact with the cats from this report, and are offering flu testing to anyone who gets sick, but there is no evidence of human disease at this point. That’s great. The risk is probably low, but it’s not zero. When we see a low risk situation over and over again, it eventually ceases being low risk, and then it becomes a bigger problem.

One last thought: Why are we seeing another report of H5N1 in cats from LA County?

  • Do they have lots of people? Yes, it’s a huge county.
  • Do they have lots of cats? Yes, more people generally means more cats.
  • Do they feed raw diets to pets more often? Maybe, but probably not that disproportionately.

The main reason is likely the fact that LA County has an exceptional public health system that does at great job integrating animal health. That raises the concern that more situations like this are likely occurring elsewhere but are going unrecognized. The less robust the local surveillance and communications, the fewer cases are found. I assume there are many more cats that have died from H5N1 flu after eating contaminated food than we know about.

I’ve had a lot of questions about this week’s somewhat (understandably) vague notice from the Public Health Agency of Canada (PHAC) about an ongoing outbreak investigation of Salmonella infections linked to dog food and treats. The information available is pretty sparse, but there are still some important messages related to what we do know.

From February to August 2025, there have been 27 people infected with Salmonella Oranienburg across Canada, mostly from out west (13 from Alberta, 12 from British Columbia). Six cases were hospitalized, and the outbreak may still be ongoing.

  • Reported Salmonella cases are always the distinct minority. For every case that gets reported, someone has to get sick, THEN go to the doctor, who THEN has to order the test, and THEN the person has to actually submit the fecal sample, and the lab THEN has to isolate Salmonella and THEN report it. That’s a lot of steps where things can get derailed for one reason or another. It’s been estimated that there are likely as many as 26 cases Salmonella in people for every case that gets reported to public health.
  • Hospitalization are probably less underestimated since testing is more common in sicker people. Regardless, six hospitalization highlights how serious these infections can be.

The link to pet foods is presumably based on interviews of infected people. When a cluster of infections caused by a specific (and uncommon) strain of Salmonella like this occurs, investigators try to find common exposures among the cases to help narrow down potential sources for further investigation. Sometimes finding the source is straightforward, such as when everyone reports eating the same kind of food from the same source around the same time. With outbreaks that are more spread out over months and across the countryidentifying the source is tougher.

“Many” (unclear how many) cases in this outbreak reported handling dog kibble, dehydrated pet diets and freeze-dried treats prior to getting sick, but no common supplier was evident. The fact that not everyone reported that type of contact doesn’t rule out pet food/treats as the source, since no one’s recall is perfect (especially if they were interviewed weeks or months after the were ill). Some people could have had indirect exposure through environmental contamination or from a dog that was infected by eating contaminated food/treats, or through visiting someone with a dog, without realizing they could have been exposed. It’s also possible there’s some other risk factor that just couldn’t be identified, or that the pet food/treats is a proxy for some other exposure (but I don’t have a good idea what that could be).

The fact that kibble, dehydrated pet diets and freeze dried treats are all mentioned shows there’s no clear direction towards what might be the source. If I had to rank the probable risk from these products, I’d put dehydrated diets first, treats next and kibble last.

  • Dehydrated diets are raw diets. Raw animal-based products are high risk for Salmonella and other pathogens. Dehydration is not a pathogen elimination tool. It will have an effect on some bacteria, but not all.
  • Freeze-dried treats are also primarily raw animal-based products, and are therefore also high risk for Salmonella and other pathogens. Freeze drying is likewise not a pathogen control tool, in fact it’s a pathogen storage tool – if we want to preserve a bacterium for a long time in the lab, we can freeze dry it so it’s shelf-stable. Myriad raw animal based treats are available too. Go into any pet store and you’ll likely find bins and bags of dried animal bits of various sources (e.g. liver, pig ears, rawhides, bully sticks and much, much, more). Bulk bins of these pose even greater risk because one contaminated item can cross-contaminate the whole bin.
  • Kibble is initially cooked and extruded, which should kill any pathogenic bacteria in the raw ingredients. However, it’s still a plausible source of Salmonella as there have been infections linked to kibble. This may occur from post-extrusion contamination (e.g. contaminated flavour enhancers that are sprayed on the kibble after), or through contaminated machinery. The risk is really low, particularly compared to raw diets, but it’s not zero. Kibble is also probably a less likely source in this outbreak because a specific product would likely be more easily identified during the interviews. However, if contamination occurred because of an ingredient that was sourced by different companies, or if different companies’ food was produced in the same plant (which does happen), then the link would be harder to identify.

Hopefully we’ll get more details as the investigation continues. If the outbreak is ongoing, there will be more data that could help identify the source, and now that public health personnel are aware of the potential dog food/treat link, there might be more detailed questions and quicker testing of products.

  • Testing of dog food and treats to confirm the source requires rapid identification of the issue so that the source food/treat is still possibly available to test. The longer it takes, the less likely that is.
  • It’s unclear if any testing of products has been done so far in this outbreak. At this point, with no clear source, testing of food and treats in affected peoples’ houses would be a fairly low yield fishing expedition, especially given time delays. It would be easier to pick up in kibble, since there could be more bags of the lot around to test, if an entire lot was implicated. Dehydrated diets and treats are usually made in smaller batches, so by the time an issue is identified, there may be none left to test.

It’s hard to say if we will get a final answer as to what caused this outbreak, but in the meantime, it’s a good reminder of some basic infection control practices. PHAC’s advice is pretty basic but like a lot of things in infection control, basic practices are the core prevention methods:

  • “To prevent illness, individuals are advised to practice good hand hygiene and frequent handwashing after contact with dogs, their food and treats.”

Good basic hand hygiene, preventing cross contamination of pet food and human food, keeping higher risk people (especially young children) away from pet food and food bowls, avoiding raw diets and raw animal-based treats (which are abundant, and people don’t often realize are raw) and good hygiene when handling pet feces are all easy, reasonable and critical core prevention practices, especially until (and even if) the true source of this outbreak is identified.

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Yesterday, I was in Birmingham, UK, giving a keynote address at the British Equine Veterinary Association Congress (and HRH Princess Anne was in the audience and I didn’t put her to sleep… I’ll take that as a win).

After finishing my talks I was walking back to the conference centre when I heard someone yelling. It’s a big city with lots of noise and interesting characters, so I didn’t think much of it initially. It continued, though, and as I got closer, I could year someone yelling “get him off me!”

I then saw a person on the ground with a pit bull-type dog latched onto his forearm and a someone who was presumably the dog owner trying unsuccessfully to get the dog to disengage.

Perhaps stupidly, I got involved – I grabbed the leash and the dog, to try to help control the dog while the owner continued to try to pry the dog off. After what probably seemed like a lot longer than it actually was, the dog let go.

The dog jumped away and I lost my hold on the leash, so I then had a big dog with a decidedly unfriendly look on his face staring at me from 2 feet away.

  • My next thought was “oh, crap.”

Fortunately for me, the owner then grabbed the dog and sprinted away.

A bystander had called the police, but I doubt the dog or owner will be found – they were long gone. The person who was attacked had some pretty deep bite wounds on his forearm and unfortunately had no interest in seeking medical care, talking to the police or even giving his name. Hopefully he ended up getting some care for his wounds somewhere.

That’s a long lead-in to the question “what should you do if you’re bitten by a random dog on the street?”

The approach is somewhat different in Canada versus the UK, because of the difference in rabies prevalence in the two countries. In this incident, I suspect there may have been a token effort to find the dog, since odds are low the police would be able to spot him, and that might have been the end of it. But let’s review the approach that would generally apply in other jurisdictions like Canada.

#1 Get safe.

  • If the dog is still around and uncontrolled, get away from it. If there’s a risk to yourself or others, call the local animal control agency (if there is one). If the danger is very high and immediate and there are no other readily available options, call the police – but only if it’s really an emergency.

#2 Do a quick assessment of your injuries.

  • It’s important to deal with bite wounds promptly, but they don’t all necessarily require emergency care. Washing wounds thoroughly with soap and running water for 5-10 minutes is an important first step and should be done immediately. For young children, elderly individuals, pregnant women and anyone who is immunocompromised or doesn’t have a functional spleen, it is particularly important to seek medical care as soon as possible (urgent, but no an emergency). This also applies to bites to the face, over joints or other sensitive structures (e.g. pretty much any bite to the hands or feet). If you or someone else is very badly injured, is feeling faint after the attack or if there is a lot of bleeding, you may need to call an ambulance. If in doubt, seek medical care for bite wounds.

#3 Identify the dog and owner, if possible.

  • If the owner says at the scene, get their contact information and information about the dog. A picture is a good idea of you can get one. We want to know who’s involved for a couple reasons. From a rabies standpoint, we need to be able to identify the dog to do a proper risk assessment and to do a 10 day observation period in most cases (more on that below).
  • (I’d advise against telling the owner what you really think of them or their dog at the time, chasing someone down or doing anything confrontational.)

#4 Report the incident to public health.

  • If you seek medical care for a bite wound, the healthcare provider should contact public health automatically (in Ontario, that’s mandated through the Health Protection and Promotion Act), but one way or the other it’s important for public health to assess the risk of rabies exposure from the bite. Rabies in dogs is really rare in Canada, but since rabies is almost invariably fatal, we don’t take chances. Public health can investigate, do a risk assessment, and work with the dog owner (if identified) to ensure the dog is observed for 10 days for any signs of rabies. This helps determine if you will need rabies post-exposure prophylaxis / shots.
    • If the dog was rabid and shedding rabies virus in saliva at the time of the bite, it will show signs of illness within 10 days, and die shortly after. That puts the bite victim at very high risk for rabies and post-exposure prophylaxis should be started asap.
    • If a dog is alive and neurologically normal 10 days after the bite, it could not have transmitted rabies at the time of the bite, so there’s no need for post-exposure prophylaxis.
  • If the dog can’t be identified, there’s no way to know for sure whether or not the dog was rabid. As mentioned before, rabies in dogs in Canada is rare, but the risk isn’t zero and there are scenarios where the risk can be higher, so the need for post-exposure prophylaxis still needs to be considered very carefully. That’s why identifying the dog is so critical, as it can help rule out rabies in most cases if the 10 day observation period can be completed..

#5 Consider reporting the incident to municipal animal control or other authorities, depending on the circumstances.

  • Some dog bites are more concerning than others. An unprovoked, vicious attack (like the one I witnessed) raises a lot of concern about the dog and the owner, and police and/or animal control (depending on the area) should be involved. If the dog had grabbed the person’s neck or attacked a child, that could have been fatal.
  • Other bites might be less concerning based on the circumstances, but it’s good to have some degree of investigation of any bite to assess future bite risks.

Ozzie was bitten by a dog at a Guelph off-leash park a few weeks ago. (I started a post about that but got distracted… maybe I’ll get a chance to finish it off). It wasn’t a severe bite, but there are obvious owner and dog issues when an unprovoked bite occurs at an off-leash park. The owner took off with the dog in that case too. Heather was with Ozzie, but only had a vague description of the dog and owner, so it’s unlikely they would be found, but she reported it nonetheless to make sure it’s documented. If there are other reports of similar incidents with similar descriptions of the dog and owner, that would be a reason to investigate more and maybe warn park visitors.

So, I got to meet British royalty, talk with Birmingham police, and meet some people on the street, along with giving a couple of talks. Overall it was a pretty eventful 48h in the UK.