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I spend a lot of time talking to people about leptospirosis in dogs and the risks to people. From a zoonotic disease standpoint, I spend half my time trying to raise awareness of the potential for transmission of this bacterium from infected dogs to people. I spend the other half trying to talk people off the ledge because ultimately dog-to-human transmission is actually pretty rare.

Dog-to-human transmission of this potentially nasty infection can certainly occur. Exposure to urine from an infected dog is the main route of transmission. I know of multiple cases of zoonotic lepto infection due to exposure to infected dogs, almost all in veterinary technicians.  But transmission from dogs:

  • doesn’t occur very often 
  • seems to be most likely in veterinary personnel (especially technicians/nurses), probably because of greater contact with urine from infected dogs and urine-soaked items/laundry
  • doesn’t likely happen through casual contact

A recent report in CDC’s Morbidity and Mortality Weekly Reports (MMWR) describes a case of leptospirosis in a person linked to an outbreak in dogs (Waranius et al. 2024). Some of the details are pretty vague, unfortunately, but I suspect the factors above also applied in this situation. It’s a good reminder of the potential risks and that the risks to most people are probably limited, and of greatest concern for veterinary personnel.

The report describes a person in Wisconsin who was diagnosed with leptospirosis in 2023. It was the first reported human case in the state since 1983, but presumably there have been some sporadic cases that were undiagnosed over the intervening 40 years (since leptospirosis in people is most often mild, many cases may have gone undetected). 

The details provided are disappointingly sparse. The report states that the person had “occupational exposure” to dogs.

  • Knowing whether that was veterinary exposure or some other form of occupational contact (e.g. kennel attendant, groomer) would be really informative. Based on later comments in the report, I assume this person was a veterinarian or veterinary technician.

The person had a range of fairly non-specific signs and symptoms, including fever, nausea, collapse, light-headedness, “brain fog,” headache, shortness of breath and muscle pain. After the onset of disease, but prior to being diagnosed, the patient learned from a colleague about several cases of leptospirosis in local dogs (suggesting the person worked in the veterinary field).  The patient passed on the concern about lepto exposure to multiple healthcare providers. Despite this, and despite having signs that fit with lepto, testing for lepto wasn’t done until 8 days after the person got sick.

  • This shows (not surprisingly) that we still have a long way to go when it comes to implementing a “One Health” approach. Too often, zoonotic diseases are diagnosed late or missed entirely, when a bit of basic questioning and communication could have facilitated a much more rapid and appropriate response. Sometimes the delay results in a fatal outcome. Fortunately, in this case it likely just resulted in the person being sick and uncomfortable for a week longer than necessary.

While the patient didn’t have contact with a dog known to have lepto, the person had had contact with body fluids from some dogs that had died from unknown causes.

  • It’s hard to say if those dogs had lepto or not, but on the same day that this person got sick, a local veterinary clinic diagnosed lepto in 3 dogs. That’s a lot of dogs all at once, even in areas where lepto is pretty common.
  • When Wisconsin clinics were asked to voluntarily report lepto cases, 13 cases in dogs were identified between August and October 2023. That means the real number was probably a lot higher, since under-testing and under-reporting are very likely.

There was at least one good outcome from the communications and investigation: more vaccination of dogs.

  • Of clinics that were surveyed after the outbreak, canine lepto vaccination rates went from 5.4% before the outbreak to 33% after.  Vaccination helps protect the dogs and likely helps protect people too, since our canine lepto vaccines are quite good and some are shown to prevent both disease and shedding of the bacterium.
  • Interestingly, rural veterinary clinics recommended the vaccine more frequently than urban clinics. We used to think about lepto as a rural dog disease, from exposure to livestock and wildlife, but over the past couple of decades it’s become very much an urban dog disease, related to exposure to urban wildlife reservoir species like raccoons and rats.

Here are my take-home messages:

  • Leptospirosis is zoonotic. The risk to most people (including dog owners) is likely very low but it’s clearly an occupational risk for veterinary personnel.
  • Good routine infection control practices need to be emphasized to reduce the risks from exposure to infected dogs (known or unknown) in veterinary clinics. 
  • Zoonotic diseases often get overlooked. Even when the concern was raised in this case, there was no action on it for days. This shows the need for better communication and collaboration between human medicine, veterinary medicine and public health.
  • Vaccinate your dog against lepto.

More information about leptospirosis in dogs can be found on the Worms & Germs Resources – Pets page.

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A recent recall of a raw pet food diets in the US due to contamination with Listeria monocytogenes has sparked some concern about the risks to people (and pets) that might have been exposed to these products.

In some ways, the big concerns raised by the recall are misplaced, not because it’s not an issue, but because a large percentage of raw diets are contaminated with pathogenic microorganisms, but most raw food isn’t tested for them. So, this is not likely a rare scenario, it’s just one that we found out about.

It’s not clear what (small) percentage of commercial raw diets actually are tested and how (since when a company doesn’t really want to find anything, they would tend to use methods that don’t look too hard). In this case, “The issue was discovered during a facility inspection conducted by the U.S. Food and Drug Administration (FDA) and The North Carolina Department of Agriculture (NCDA).” It’s not reported whether they identified issues with the facility and processes that triggered the inspection, or if they just collected samples for testing during a more routine visit.

That’s not to say Listeria in raw pet food isn’t a concern. It certainly is, but this recall has only flagged a small number of contaminated raw pet food products.

If we look at past studies of raw pet food, we know that finding bacteria like Salmonella, Listeria and E. coli (including multidrug-resistant strains) is common. A large FDA study in 2014 found Listeria in 16% (32/196) raw pet food samples, but in no dry pet food diets. So it’s totally unsurprising to find this bacterium (and others) in raw diets. It’s actually surprising to me that they bother to recall these diets at all, since it should be assumed that all raw diets that don’t undergo a pathogen reduction step (like high pressure pasteurization) are contaminated with pathogenic organisms. We expect these to be contaminated, whether they’re bought at the grocery store or a pet store. (That’s why we are supposed to cook raw meat and use good food handling practices for human food as well… since we often don’t do those well, it’s also why people end up barfing a lot).

What are the health risks from these diets contaminated with Listeria?

Risks to people

Listeria is certainly a concern in people, especially those who are elderly or pregnant. It can cause serious foodborne infection and outbreaks. In the US, approximately 1600 people get listeriosis every year, and about 260 of those people die from the infection. That’s not a huge number of infections, but that proportion of serious illness and death means we pay attention to it.

I’ve never seen a human infection with Listeria linked to raw pet food, but it’s certainly plausible that it could occur. The risk is probably pretty low, since infection would require ingestion of the bacterium from raw pet food, but given how poorly we often handle food (human or pet) and the potential for cross-contamination with human food, we can’t dismiss the potential, particularly in household with high-risk individuals.

Risk to pets

Listeria can cause disease in dogs and cats, but it’s quite rare since both species are fairly resistant to infection. The health risk to an average, adult, otherwise healthy dog or cat is going to be really low. Risks are probably highest in older dogs or cats, and in pregnant animals.

What should be done if someone has purchased a recalled diet?

Overall, the risks to people in most households are low. The problem is inadvertent ingestion of Listeria from contaminated hands, contact with the dog’s face after it eats or cross-contamination of human food. Listeria exposure is also a concern through consumption of some human foods (classically deli meat) so we have think about this raw food exposure alongside the broader ecosystem of exposures that we have.

The FDA recommends: “If you find that you have products from Lot 21244, please contact Viva Raw at info@vivarawpets.com for a refund on any remaining product—you should then destroy the food in a way that children, pets, and wildlife cannot access. Do not feed the recalled product to pets or any other animals. FDA recommends humans do not touch the contaminated food product with bare hands. While wearing gloves or using paper towels, place the contaminated food in a sealed plastic bag and throw it in the garbage. Areas that may have come in contact with the contaminated product should be sanitized. Do not sell or donate the recalled products.

For pets

If a dog or cat has eaten a recalled diet but still looks healthy, don’t worry. Testing a healthy pet that has eaten one of these diets is not something I’d recommend.

For people

Talk to your physician if you’re concerned” is always the default answer, but realistically it’s very unlikely anything would be done for a person who is healthy. However, if someone is sick and has had contact with the recalled diet (or any raw diet), they should make sure their healthcare provider knows about the potential exposure to Listeria and other nasty bacteria.

Take home messages:

Feeding raw diets to pets carries inherent risks to pets as well as people.

Risks are greatest to individuals (animal or human) who are immunocompromised, elderly, very young or pregnant, so raw diet feeding in household with those individuals poses extra risks.

Raw diets are best avoided since there’s no evidence they are superior to cooked diets. However, if someone really wants to feed a raw diet anyway, those treated with high pressure pasteurization (HPP) are presumably lower risk, because HPP reduces (though does not necessarily eliminate) pathogenic bacteria in the food.

If a raw diet is fed, basic food handling and hygiene practices are the key, focusing on the food, the food bowl, any areas that the food contacts, and the pet’s feces. More information about raw diets and risk reduction can be found on the Worms & Germs Resources – Pets page, including our recently updated infosheet on raw diets done in collaboration with the Ontario Animal Health Network.

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“Update” may be a bit of an oversell in this case, but here’s some more information on the upcoming changes to US dog importation rules that kind of came out of nowhere. We’re still trying to sort out a number of issues, both in terms of the big picture and minor operational details; hopefully we’ll have a much clearer picture soon.

To what dogs will the new rules apply?

The rules will apply to any dog entering the US on or after August 1, 2024, including:

  • A US dog returning home to the US after a visit to Canada or abroad
  • A Canadian dog moving to the US
  • Any dog on a cross-border visit to the US
  • Any dog crossing the border to the US for veterinary care
  • Any US dog returning home after receiving veterinary care in Canada
  • Any dog being sold/rehomed/rescued into the US
  • Service dogs traveling with their owner to the US (yes, even service dogs)

In short, it’s ALL dogs. Full stop.

For Canadians, the Canadian Food Inspection Agency (CFIA) has issued some updated information on what these changes mean for dogs traveling from Canada to the US after August 1 (with a disclaimer that things may still change). Here’s what dog owners should do if they might be crossing the the border (from Canada to the US, either coming or going) with their dog starting in August:

Microchip

Ensure that your dog is microchipped AND that the microchip is ISO compatible AND that the microchip number and date it was implanted are clearly recorded in the dog’s medical record.

  • If the dog has a non-compatible microchip, it will need a new one.

Rabies vaccination

Ensure that your dog has been vaccinated against rabies AND that you don’t allow vaccination to lapse (stick to the schedule on the vaccine label!) AND that the rabies vaccination was done after the dog was given its ISO compatible microchip AND that the dog’s microchip number is recorded on any vaccination documentation.

  • Any vaccines that pre-date the microchip are not considered valid.

We’re still trying to sort out what happens if your dog was vaccinated at a different clinic from the clinic filling out the export paperwork. Common sense would suggest that the new clinic can sign off on the export form if they are confident that the dog was vaccinated based on the records from the previous clinic, but we’re still not sure if that will be considered acceptable. So, if your dog was vaccinated at a clinic that can’t complete the export paperwork, it’s possible your dog might need to be revaccinated again.

Medical records

Six months’ worth of veterinary records will be required to cross the US border. This could include a health certificate, vaccination certificate, invoice or something similar. It’s not a full dump of the dog’s medical record to document the dog’s health status, it’s simply to help prove that the dog has been in Canada (and under someone’s direct care) for at least 6 months (and therefore was not recently brought from a high-risk country and just “laundered” through Canada).

  • The dog’s ISO microchip number must be documented in the medical record and any other documentation.

For those using a USDA rabies vaccination form (including US residents and any Canadians who have their dog vaccinated while in the US), in addition to the above, make sure that the veterinarian who administered the vaccine is USDA-accredited, or at least that a veterinarian in their practice is accredited who can sign off on the form. Not all clinics have accredited veterinarians.

  • Currently it looks like if this form isn’t signed off by an accredited veterinarian, then the rabies vaccination is not considered valid for US import purposes and would have to be done again.

Plan ahead

Forms don’t write themselves, and veterinary clinics and CFIA offices are busy. “I’m on my way to Florida this afternoon doc. What do we have to do?” just isn’t going to work anymore. The vaccination form for a rabies vaccine given in Canada also has to be signed off by a CFIA veterinarian. The process for that is still being worked out, but at least for now some additional lead time has to be built in to get the dog’s veterinarian to complete the forms AND to get a CFIA veterinarian to sign off.

Here are a few other scenarios for dog owner to consider:

Cross border veterinary care

  • There are currently no exemptions to these rules for crossing the border for veterinary care, emergency or otherwise (even if the only reasonably close clinic may be on the other side of the border).

Puppies under 6 months of age

  • Not gonna happen. Dogs less than 6 months of age will not be allowed to cross, regardless of circumstances.

Service animals

  • This is an area for which we don’t have clear answers yet. Currently the US has stated that these rules will apply equally to service dogs, but the US Americans With Disabilities Act provides strong protections for access of service dogs to anywhere their owner goes. I don’t know if that that supersedes USDA and CDC.
  • The concern is that there are a lot of fake “service” dogs and the service dog landscape is a mess. I assume there’s a lot a wariness of opening a loophole that could be abused.

I’ve focused on Canada here since, that’s the main source of dogs traveling regularly to the US. Mexico would be another busy border to which the same rules will apply (but I know nothing about the sign off process for Mexican documentation). The same applies to any other country that’s considered low risk for canine variant rabies. The new process for importing dogs from high risk countries is different, and even more stringent. That’s a bigger topic for another day.

Finding H5N1 avian influenza in mice in the US has caused a lot of angst amongst some – some angst is warranted, but some of it is overblown. That’s not because H5N1 isn’t an issue, or that more species being involved isn’t relevant, but because there are bigger issues to address. Adding yet another species to the susceptible list isn’t a doomsday scenario, even though we’d rather that list didn’t get any longer.

The latest APHIS report involved detection of H5N1 in an additional 36 house mice in Roosevelt County, New Mexico. They’d already found 11 infected mice there earlier in May. Typical of this ongoing outbreak in the US, available details are sparse. I haven’t seen a clear statement about where these additional mice were collected. I assume they were from infected dairy farms, and that’s a pretty basic but critical piece of info. (The first 11 infected mice were reportedly from an infected poultry premise). If the new mice were from farms with infected cattle, it’s not surprising to find the virus in mice at the same location. If they were from other areas, that would be more confusing and more concerning.

How do mice get infected?

I haven’t yet seen any genomic information on the virus found in the mice; it will be helpful to know if they were infected with the dairy cow-associated H5N1 strain, or whether some of the infections might be linked to exposure to wild birds. If we go on the assumption that these mice were from dairy farms, cattle are the most likely source, because we know infected cattle shed lots of virus in their milk, which would make it easy for mice on the farm to be exposed to the virus in the environment. Even though flu virus doesn’t survive long in the environment, if there’s lots of milk loaded with lots of virus (especially in areas where mice are looking for food), mice are likely to encounter some active virus. Fecal shedding of H5N1 in cattle seems to be low, but data are pretty sparse; we need to clarify that risk more since that would be another possible means of exposure for mice (and other animals, and people). It’s obviously highly relevant since cattle produce a lot of feces, and that manure needs to be stored and/or spread somewhere.

If we think about the risks from finding H5N1 in mice, I’d consider four main areas:

1) Risk to people from H5N1 in mice

Yes, there is a risk to humans, to some degree – but we need more information, like the amount of virus the mice were shedding, and how (e.g. fecal shedding vs respiratory shedding). Some infected mammals shed a lot of virus, but others are likely dead end hosts that don’t shed enough virus to spread the infection any further.

Even if mice shed appreciable amounts of H5N1, we don’t tend to have close contact with (wild) mice, so the risk from direct exposure is presumably really low. If someone’s on a dairy farm with infected cattle, mice are very low on the risk scale. Cattle are the biggest risk. Cats are probably #2 on the list.

However, mice do get into peoples’ homes as well, and the risks from that are completely unclear. Flu virus doesn’t survive long outside the host, so it’s not like a virus like hantavirus, where mouse poop in the environment is a significant concern, but we need to know more about virus shedding.

At this point, I suspect the direct risks to people are very low, but not zero.

2) Risk to other species from H5N1 in mice

The biggest risk from this new finding might be mice acting as a bridge from wildlife / livestock to humans, through their potential to infect cats. Cats catch mice, and eating an infected mouse is presumably high risk for H5N1 transmission (just like eating an infected bird). Cats are susceptible to infection, and have close contact with both mice and people (and other domestic species), so anything that increases the risk of cats being infected is a concern.

3) Risk of mice spreading H5N1 farm-to-farm

As we start to (slowly) get more information about H5N1 on dairy farms, we’re seeing more reports of infected farms that did not bring in cattle from other infected farms. That makes us wonder about other sources of introduction, like humans tracking the virus around or spread via wild birds. Fortunately mice, like coconuts, do not migrate (yes, that’s a niche reference – see link below), so they probably pose limited risk for broad geographic spread of the virus because they’re not that mobile (unless they hitch a ride on a human conveyance of some kind…). Mice tend to have very small ranges, so it would probably be tough for them to spread H5N1 even between farms, unless the farms were very close to each other. The bigger risk would be bringing the virus from the barn into the farm house.

4) Risk of virus mutations

The more avian influenza spreads to and within mammals, the more opportunities it has to adapt to mammals. It would take a number of specific genetic steps for an avian flu virus to evolve to effectively infect and spread between mammals (including people), but the more it’s transmitted, the greater the risk that could happen. This is why we don’t want to see avian flu spreading in any mammalian species.

So, while I don’t like seeing more H5N1 infections in more mammalian species, and even though if H5N1 became endemic in mice they could be a long term reservoir, I’m still more worried about birds, cattle and cats at this point.

Back to H5N1 flu in cats

The good news is that infections in cats are still rare. The bad news is that most reported infections in cats have been very severe or fatal. Whether severe disease is the norm in cats, or whether we’ve mainly just tested really sick cats is hard to say. There have been approximately 21 cases of H5N1 influenza identified in domestic cats in the US since the outbreak in cattle was first detected. Other cases have been reported in cats in various parts of the world over the last 2+ years, including in Canada. However, those cases are probably just the tip of the iceberg. We need more surveillance, including testing of healthy and sick cats from locations where H5N1 is present. Cats on dairy farms with infected cattle are at the highest risk, but any cat with outdoor access that might encounter an infected wild bird is at some risk.

What do we need?

More surveillance and more communication. We need broader testing on affected farms, thorough epidemiological investigation of the spread on and between farms and clear (and timely) communications.

I know seals are mammals.

I know rabies virus can infect all mammals.

I’m pretty tuned into rabies and rabies prevention.

Yet, I’m not sure how quickly I’d clue in to any rabies risk from a seal bite. (I’d hopefully get there eventually, but I doubt it would jump to mind like it would with a bite from a dog or raccoon.)

Rabies in marine mammals is rare, but it happens. There are no marine mammal rabies reservoirs, so a rabid seal would have to have been bitten by a terrestrial mammal, survive the encounter, develop rabies then be noticed and tested. That’s a lot of steps to detect a case. But, as we know with infectious diseases, rare doesn’t mean it won’t happen. It means that it will happen… eventually.

A Cape Fur Seal in South Africa was recently found to be rabid. There’s very little detail in the media article, so we don’t have a lot of context. It’s not clear why the seal was tested, or if it was seen to have had neurological disease. I assume they sequence the virus to see what strain it is, which can help infer the source. The two main rabies strains circulating in South Africa are dog variant and mongoose variant. Presumably this seal tangled with another infected wild mammal or an infected dog, initially survived but got infected with this fatal virus, and for some reason was tested after it died or was killed. While this is a really rare situation, it’s probably fair to assume it happens a more than we realize because of the low likelihood that we’d test a marine mammal for it.

Regardless, post-exposure prophylaxis is being recommended “for anyone who has unwanted contact with the creature.” I guess any bite would classify as “unwanted contact.” They also advise the public to stay as far away from seals as possible. That’s never bad advice.

This is yet another reminder that wildlife should be left alone.

  • Watch them? Great.
  • Touch them? No.
  • Any bite from a mammal? Ask about the need for rabies post-exposure prophylaxis.

Image from: https://www.nationalgeographic.com/animals/mammals/facts/fur-seals

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There’s a great new early-release paper in Emerging Infectious Diseases (Oguzie et al. 2024) about the emerging situation with H5N1 influenza in dairy cattle. It provides some important new information, and more details that somewhat challenge the early narrative.

The authors explain some of the limitations of the study to keep in mind…

  • The study was only done on one farm
  • They didn’t direct the response (samples were sent to them)
  • They got involved a bit late in the outbreak

…yet they still have some really interesting and useful findings.

They studied one of the earlier affected dairy farms in Texas. Interestingly, the research team was contacted because of “rumours among cattle veterinarians of possible influenza A virus detection among cattle and conjunctivitis among dairy farm workers.” They also say that cattle had transient respiratory and gastrointestinal signs. That’s different from earlier information that initial concerns were focused on drops in milk production and unusual cat deaths. In particular, the mention of an early concern about human illness is worrying, from the standpoint that we might still be underestimating human infections. No cat deaths were reported on this particular farm.

There’s not much clinical information in the paper, since it’s based on test results, but they report cattle had “decreased appetite, lethargy, increased respiratory secretions, high temperatures (up to 105°F or 40.56°C), abnormal bowel movements, and decreased milk production.” Most of that is unsurprising, but I’m not sure I’ve seen much about respiratory signs before. An increase in respiratory secretions (a runny nose) doesn’t tell us much about the degree of respiratory involvement but suggests there was some. That’s important because it brings in questions about respiratory transmission.

They only got nasal and rectal swabs from cattle for this study, even though milk seems to be the prime source based on what we’ve learned since then. Timing of sampling wasn’t ideal, as is often the case early in outbreaks: illnesses was observed in cattle starting March 6, and several people were sick March 4-6, but samples weren’t collected until March 21, March 28 and April 1. That’s really late to be testing for a virus like influenza that tends to have a fairly short shedding period. They indicated that the outbreak was already waning at the time of sample collection, yet there were 7 PCR positive nasal swabs from 29 sick cattle. No healthy cattle were positive.

It’s been stated from the start that there’s limited respiratory shedding in cattle, and this study doesn’t necessarily contradict that since the PCR Ct values suggested the viral load was quite low in those nasal samples. However, even low shedding in 7/24 (29%) cows is still relevant, especially if samples were collected quite late in the disease process. Peak respiratory virus shedding with flu tends to be very earlier in disease. After a few days, I’d expect shedding to drop, both in terms of the percentage of positive animals and the amount of virus being shed by each one. So, we have to be careful not to take <50% PCR positivity with a high Ct value (i.e. low viral load) as an indication of limited risk of viral shedding.

Rectal samples were all negative for flu. That’s good. The same sample timing disclaimers as above still apply, but with no positives, it suggests that we don’t have much (or as much) to worry about in terms of exposure to feces and manure handling. That simplifies matters.

The human component raises a lot of questions. Details are sparse, but the authors say “Several workers experienced influenza-like symptoms and missed work during March 4–6. A maternity worker visited a local clinic and received treatment for influenza-like symptoms; 2 milkers also experienced influenza-like symptoms and stayed home.”

There’s no mention of anyone being testing and I’d guess that none were. Routine flu testing would be uncommon in mildly ill people at that time of the year if there wasn’t yet any communication about potential influenza exposure from dairy cattle. This furthers the ongoing concern that we are underestimating the amount of cattle-to-human transmission because of limited testing. It’s critical to know how often cattle-to-human transmission occurs and to continue to look at the genome of H5N1 when it infects people (to look for more human/mammalian adaptations).

What this report tells me overall:

  1. We still have a poor understanding of what’s happening with H5N1 flu in dairy cattle.
  2. There is a lack of transparency; we are still not getting all the available information.
  3. Consistent with some other recent reports, there may be more of a cattle health component beyond the drop in milk production than was initially flagged.
  4. Human disease from cattle-to-human transmission may be underestimated.

There’s nothing to panic about here, but it shows that much more work and communication is still needed.

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Adding to the “that was not on my bingo card” theme of the 2020s, there was a recent fatal H5N2 avian influenza infection in a person in Mexico.

First important point: this was H5N2, not the H5N1 strain we’ve been focused on for the past few years in bird (and spilling over into mammals, including most recently dairy cows). This H5N2 strain is very different, and this is the first reported case of H5N2 infection in a person. H5N2 has caused a few outbreaks in poultry in Mexico so far this year, so there’s likely a wild bird reservoir, and potential for more spillover into domestic poultry, but this strain hasn’t caused human disease before. When we see rare spillovers of avian flu into people, they’re usually in individuals with close contact with infected poultry, but that wasn’t the case here.

The infected person was a 59-year-old who was hospitalized in Mexico City after a short illness with signs including shortness of breath, fever, diarrhea and malaise. Surprisingly, the person has no known exposure to domestic poultry, wild birds or other animals. The person had actually been bedridden for 3 weeks, so their recent exposures could be fairly well characterized. It’s a bit unnerving not to have no idea from where an infection like this came. It could be a one-off that we never figure out and never see again, but we have to try to investigate as much as we can in case it’s an early harbinger of yet another new flu problem.

What could have been the source of the H5N2 virus in this patient?

1) Another person: This patient could have been an infected by another person (healthy or sick) who got the virus from a bird. That would indicate bird-to-human spillover (which we know happens occasionally) followed by human-to-human transmission (a bit of a concerning scenario, especially if it wasn’t a very close household contact). Seventeen (17) human contacts at the hospital were identified and tested and were all negative, including one that reported having a runny nose 4-5 days after the patient got sick. Twelve other human contacts near the person’s home were also tested and were all negative. Even so, it’s possible one of those people was the original human source but had eliminated the infection by the time they were tested. It’s good to have the testing information (and good that they looked), but it does not rule out a human source.

2) Birds: Despite the patient history, I’m not sure we can completely rule out bird contact. I’d want to know more about where the person lived and how people and animals moved around on the property. For example, was there any chance a bird got into the home at some point? If there were open windows, there’s still a chance of direct or indirect bird exposure.

3) Other animals: As for birds, I’d want to know how solid the “no animal contact” determination was, and if it covered more than just birds. Cats are great potential bridging hosts, since they can be infected when hunting wild birds and then have close contact with people. I’d want to make sure there was clearly no dog/cat contact, and if there had been any sick or dead cats seen in the area.

4) Food: This is lower on the list, but contamination of food would have to be considered. I don’t mean properly cooked meat (even if it came from an infected bird), but more likely contamination of prepared food with bird poop (possibly from someone’s hands) or improperly cook meat from an infected bird. I’d investigate where the patient’s food was prepared; if birds could have gotten into the area, contamination of food is possible.

That’s all speculation, and I hate to do too much of that, but it’s important to brainstorm possible sources to come up with surveillance plans.

Hopefully this was just a one-off infection. However, it shows us the ongoing risks from endemic avian flu viruses (not just H5N1) and the need to support good surveillance systems in people, domestic animals and wild animals. Despite continued emergence of infectious diseases, we’re seeing underfunding and active dismantling of our public and animal health surveillance and response systems, and inadequate willingness to address these big issues.

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When an unvaccinated person is exposed to rabies, they typically receive post-exposure prophylaxis (PEP) consisting of a dose of anti-rabies antibodies and four (4) rabies vaccines over the course of two weeks. In dogs and cats, it’s a different story. We don’t use formal PEP protocols in pets in most regions.

  • Why not? I’m not sure. Probably because nobody has put that much effort into figuring out whether it would be effective (and it’s not an easy – or cheap – thing to study).

Texas has approached rabies exposure of domestic animals somewhat differently than the rest of the US, particularly when it comes to unvaccinated animals. If an unvaccinated domestic animal is exposed to a rabid animal, they can undergo a PEP regimen consisting of immediate vaccination, followed by a 90 day confinement period with additional rabies vaccine boosters in the 3rd and 8th week of confinement. This is in contrast to most other jurisdictions, where the two options are most commonly euthanasia or a single vaccine dose followed by a 3-6 month quarantine.

Texas also does a really good job of publishing data on their rabies response and control programs in domestic animals, so others can learn from the information. Their most recent publication (Wilson et al, J Am Vet Med Assoc 2024) reports on 1218 unvaccinated animals that underwent the Texas PEP protocol after possible exposure to a confirmed rabid animal between 2010-2019. The animals included 570 dogs, 138 cats, 347 cattle, 93 horses, and a smattering of other species. One cat and two previously unvaccinated dogs (that received PEP) went on to develop rabies.

  • That’s a pretty impressive 99.8% success rate, but we have to temper that a bit. We can’t say the Texas protocol is 99.8% effective overall, since it’s pretty certain that not all potentially exposed animals were actually exposed to the rabies virus. Only 22% of animals that underwent PEP had “direct exposure” to the rabid animal. Another 30% had “probable exposure” and 48% had “low probability” exposures (see table below). Almost half of the low probability exposures were cattle, since sometimes whole herds were managed as “exposed” when a rabid animal was found on the property.

We always err on the side of caution with rabies, and lots of low risk or unknown circumstances get called potential exposure to make sure we don’t miss any relevant exposures.

  • If we just include high risk exposures, the success rate drops to 91% for cats, but stays high at 99.7% for dogs, but it’s possible that even some of those were not true exposures.
  • So, it’s hard to put any type of accurate number on the success rate, but we can reasonably assume that the risk of developing rabies when this protocol is applied is low.

Looking at the PEP “failures” is also important, and in this case it’s a actually a bit of a good news scenario:

  • All 3 PEP failures were in animals less than 12 weeks of age. We don’t normally start rabies vaccination until 12 weeks of age because that’s the age that we know that it will work. In younger animals, there’s the potential that lingering antibodies inherited from the dam can interfere with response to vaccination.
  • Two of the three PEP failures only got their initial vaccine dose (see table below).
    • One dog died before the time of the dose in the 3rd week.
    • One dog just didn’t get its second dose for some reason, and died 31 days after exposure.
    • The cat got a 2nd dose, but signs of rabies developed the next day, so that dose was obviously too late.
  • It’s quite possible that these 3 PEP failures were animals that had no ability to respond effectively to a vaccine based on their age, and the onset of disease was quick enough that they didn’t get a chance to have multiple doses of vaccine during their confinement period.
  • No dogs or cats that were over 12 weeks of age and no dogs or cats that underwent the full PEP regimen got rabies.

Take home messages

Rabies PEP should be considered in domestic animals. There’s no guarantee that it can prevent rabies in an exposed dog or cat, but odds of rabies developing while being managed using this approach appears to be really low.

We can also flag the cases that are of greater risk of PEP “failure” (in this case, young animals that started PEP before 12 weeks of age).

I wonder whether the 3 and 8 week booster timing is too late. If we’re going to give multiple doses and we don’t have the option for anti-rabies antibody, why not approach it more like they do in people: give the vaccine ASAP (which is already part of the protocol), and then on days 3, 7 and 14? I can’t see any reason not to use that type of approach if it could possibly help avoid PEP failures.

Vaccine failures

One “true pre-exposure vaccination failure” was reported, which is an important case to note.

  • It was in a 3-year-old dog that was initially vaccinated at 16 months of age and got a booster 1.4 years later, meaning it was properly vaccinated and not due for a booster at the time it was exposed to rabies. Nonetheless the dog developed rabies and died.
  • On one hand, it’s just one case. That’s great. Rabies vaccine is one of the best vaccines we have. But no vaccine is ever going to be 100% effective, since we can’t guarantee that every animal will respond to a vaccine the way we want them to.
  • This is a reminder that while rabies vaccination is really useful and really important, we can’t dismiss the potential for rabies in a vaccinated dog or cat. It’s just really unlikely.

Two other previously vaccinated dogs also developed rabies. Both dogs were overdue for vaccination, so they are not considered true vaccine failures, but they’re also important to note.

  • One was a 7-year-old dog that was overdue following a 3-year vaccine (last dose given 5 years earlier). I’d really like to know if this dog had multiple vaccines before the age of 2, or just one dose, since I expect pretty solid, long-lasting immunity with a couple doses – but this also illustrates why you can’t rely on that in all dogs, and regular revaccination remains important.
  • The other case was a 2-year-old dog that had received a rabies vaccine as a puppy but did not get the 1-year booster.

The conclusion of the report was “Results indicated that this protocol is a viable option for unvaccinated domestic animals exposed to rabies. Alternative protocols warrant additional consideration.”

I think that’s a fair evaluation. We don’t really know how well PEP works in domestic animals, but it’s likely quite effective. It is certainly much better than doing nothing, and should be an option for exposed animals. However, I’d like to see a more aggressive PEP regimen than those currently used.

On a closing note, we don’t need to worry about PEP regimens for unvaccinated animals if we don’t have unvaccinated animals. All dogs and cats in rabies endemic areas should be vaccinated from 12 weeks of age and up. We’ll still see exposures in animals younger than that, but maximizing vaccination in animals that can be vaccinated is critical.

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For such a potentially big problem, we’re received disappointingly little official information about H5N1 influenza on dairy farms in the US. The more we know, the better we can plan for containment and control, wherever it pops up next. If information isn’t being gathered or isn’t being shared, our ability to address this problem is significantly compromised. It was therefore really nice to see some details from Michigan State University about the H5N1 outbreak on one Michigan dairy farm, but also concerning to see that the situation may not be as straightforward as we were hoping based on the information available to date.

This is how the story went for this Michigan dairy farm:

Widespread fever in the cows was the initial finding. It was detected quickly since most cattle on the farm have a monitoring bolus (in their rumen) that tracks things like body temperature, among other things. Temperature increases of 4-5oF were typical. Shortly after the temperature spike, rumen activity decreased. (The rumen is the largest of the cow’s four “stomachs;” as the cow goes, so does the rumen, so a decrease in rumen activity indicates that something is off with the cow). Fever typically persisted for 2 days. The cows were mostly treated with aspirin and IV fluids.

After the problem was identified, the farm staff tried to contain it. Milk has been implicated as the main route of spread, so the farm started washing all the milking equipment after the affected cows were milked. Unfortunately that didn’t help, and it eventually spread to all the groups of milking cattle on the farm.

  • The subsequent spread to other groups on the farm could indicate that the routine equipment washing procedure was not adequate to stop the spread, or that the virus had already spread before they changed their procedures, or that there are other routes of spread. Some people have said that this indicates milk is not the main route of spread, but I think that’s a bit premature. We need to keep investigating. Some people online are using this as a “gotcha” moment to say that USDA is hiding respiratory spread, but I don’t think there’s enough detail here to make any conclusions like that either.

Over the first 9 days of illness, milk production decreases were fairly mild. Daily milk yield per cow dropped about 5 pounds (with the average cow on the farm normally producing 95-100 pounds of milk). However, by day 12, milk production had dropped by 21 pounds per cow, the somatic cell count (an indicator of inflammation in the udder) increased, and many cows became severely dehydrated. This is more severe than the general descriptions provided to date.

Overall, they suspect that 40% of cattle on the farm were infected.

  • 40% affected is surprisingly low for flu. With all groups having one or more infected cow, I’d expect pretty much all the cows to get infected. I wonder how many of the “unaffected” cows actually had mild disease that simply wasn’t detected.

Unsurprisingly, the impact on farm management was severe. A lot more work was required to manage so many sick cows.

  • That also increases the risk to farm workers, since it means more cow-to-human contact, and that contact is mainly with sick cows. They had to stop breeding cows because they were too busy managing the sick milking cows, which will presumably have at least some long term impact on farm operations.

Some abortions occurred in pregnant cows; it’s suspected that this was because of the high fevers.

  • Flu isn’t something we typically link to spontaneous abortion, but anything causing severe disease can do it. That’s another aspect of disease severity that hasn’t been previously reported in this outbreak.

The good news is all the farm workers remained healthy.

  • It’s not clear whether there was any surveillance for mild or subclinical infections, but no illnesses were reported. Since the farm is providing detailed information, I assume that their assurance of no human illness (so far) is pretty solid.
  • The US CDC recently issued guidelines for working with infected animals, including cattle. They’re pretty standard from a control standpoint, but I also look at them and say “not gonna happen” on a standard, busy and potentially hot farm. In this case, “the farmer encouraged them to wash their hands frequently and avoid touching their face and eyes. All employees were offered safety eye wear or face shields.” That’s probably as good as we’re going to get.

Cost to this 500-cow dairy herd was estimated as $30,000-40,000 USD.

  • That may not seem like a massive number, but if it’s your family farm, that’s a big chunk of income, and you also lost money while having to work a lot harder and in a higher risk situation. It also doesn’t include long term costs from any ongoing loss in milk production, and other impacts on farm operations, such as missed breedings. Some cattle will be culled because of sustained impact on milk production despite apparent recovery from infection. That’s not been reported before either.

We need to remember that people on farms are people. They have to work and live through this. If it’s a family farm where there’s an even closer association with the animals and more direct dependence on income, it’s even harder. The farmer in this case was quoted as saying “It has been a lot of work, stressful on the cows and frankly overwhelming.” I suspect that’s an understatement of the potential impact on the mental health of farm personnel.

The article states “[The farmer] believes it is important for the industry to understand the disease. He knows that his is not the only farm to get HPAI and hopes that the more we can learn from his experience, the better we can prevent more herd infections, reduce the impact and potentially be better prepared against other diseases.

  • We need more people like this. They managed a new and potentially scary problem to the best of their ability and were willing to tell their story. That’s too rare. We also need more groups like the MSU Extension Service who will write about events like this, so we understand more about this outbreak. A lot of questions remain and a few new questions and uncertainties have come up based on this information, but information is power. We need good information to plan and to contain. There’s been too much hiding of information, unwillingness to share, and unwillingness to cooperate (at many levels), and that’s compromised our ability to respond.

We need to thank people like this and support people/farms/veterinarians/government officials who are willing to stick their necks out to provide critical information, despite the risks (social, political, economic or other).

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I was at the airport the other day and, as per usual, there were lots of traveling dogs there too. As I was watching one dog getting lots of random attention while in line to board, I could only smile given how happy the dog and the people looked – a key reason why we have pets and work hard to keep them healthy!

However, the infectious disease side of my brain never completely shuts off, so “this would be a nightmare for contact tracing” also trickled into my thoughts.

The vast majority of random dog-human encounters are totally benign, but a miniscule fraction are not, and those can be a real pain. Tracing human contacts even within a specific neighbourhood is tough. We can flood local social and conventional media with “if you might have touched this dog, give us a call” notices, and if most people are still around town that can be reasonably effective. When we’re dealing with exposure of people who hopped on planes to various cities and countries around the world… that’s a whole other ball game.

A recent paper in Zoonoses and Public Health (Williams et al. 2024) describes a slightly easier-to-contain situation involving international travel: exposure of passengers on an airplane to the uncommonly discussed but concerning bacterium, Brucella canis.

Brucella canis is a bacterium that flies under the radar a bit. It’s more common that most people recognize, as we found out a few years ago when we did a surveillance study of B. canis in dogs in breeding kennels in Ontario, and we found quite a bit of it. In dogs, it can cause a range of disease, with reproductive problems being the biggest issue. Human infections are uncommon, but can be serious and hard to treat. The greatest risk of infection is when people are in contact with infected dogs that are giving birth or aborting stillborn puppies.

Here are the highlights from the paper (Williams et al. 2024):

  • A pregnant 10-month-old French bulldog (Dog A) flying in the cabin of a commercial airliner started to abort three fetuses during a flight from Poland to Chicago.
  • A second 12-month-old dog (Dog B) from the same facility was on the same plane, flying in cargo.

It’s stated that the two dogs were to be imported by a breeder, but importing a pregnant dog is sometimes a way to bypass rules against importing puppies (which are very valuable in terms of sales), so I have to wonder if this was really a breeder purchasing new, high quality breeding stock versus a puppy mill situation. The fact that they were French bulldogs, a common and lucrative puppy mill breed, heightens my concerns.

  • Dog A’s distress was reported by the pilot 1 hour before the plane landed (I’m impressed with that) and on arrival the dog was evaluated at US CDC’s Chicago Port Health Station.
  • An infectious cause of abortion was on the list of possible causes, so testing was performed and Port Health Officers interviewed the crew and passengers that sat by the dog, paying particular attention to whether there were any who were pregnant, or children.
  • Potentially contaminated areas of the plane were disinfected (but that’s tough to do effectively with the types of surfaces found on a plane…) and presumably the plane took off with a few hundred more passengers not long after.
  • Both dogs were sent to a veterinary clinic, where Dog A aborted a fourth fetus. Both dogs were otherwise stable, though underweight. Dog B was also pregnant (more “puppy mill” alarm bells going off).
  • Samples were collected from both dogs for testing. Dog A was positive for B. canis and was euthanized at the request of the importer. (I suspect that’s because one of the key components of treating this infection is spaying the dog, and spayed dogs don’t generate profitable puppies.) Testing for B. canis can unfortunately be complicated by a few factors (veterinarians can access fact sheet on B. canis from the Ontario Animal Health Network).
  • Dog B was negative for B. canis, but if she was only recently exposed (e.g. from the other dog), we’d have to wait at least a month and retest to have confidence that she wasn’t infected too. So, rather than isolate the dog and retest it, the importer decided to ship the dog back to Poland (making it two long trips for a young pregnant dog… not great from the dog’s standpoint). The dog was then presumably lost to follow-up. (Unfortunately it’s quite plausible the dog ended up back on another plane to the US, Canada or elsewhere the next day. Who knows.)
  • Five people (3 crew and 2 passengers) were determined to have had high risk exposures because of direct contact with Dog A (including one crew member who apparently tried mouth-to-mouth resuscitation on one of the aborted puppies). Staff members at the veterinary clinic were also evaluated, including two who were pregnant. Exposed people were provided with information about the risks, told to monitor for symptoms of disease and to discuss post-exposure prophylaxis with their healthcare providers. It’s not clear if any got post-exposure treatment.
  • The CDC estimated the cost of their investigation at over $22,800 USD. The importer was on the hook for $16,500 in veterinary expenses for both dogs. They also estimated costs to the veterinary clinic (where the dogs took up space while being isolated that could have been used to house clinical patients) at $10,000. Overall, the authors estimated the total cost of the entire incident to be close to $50,000. It would have been higher if the importer hadn’t shipped Dog B back.

Fortunately, it doesn’t sound like anyone got sick as a result of exposure to these dogs.

There’s an inherent risk associated with dog (or any animal) movement, but there are also things that increase the risk. Here, there were several red flags that this was a higher risk situation. The combination of a high risk dog in a densely packed airplane is a recipe for problems.

This scenario raises another question too: what if the dog hadn’t aborted on the plane? If it had happened the day after, it’s quite possible that no one associated with the flight would have known, no one would have investigated, and there’d be more ongoing exposure risk to these dogs in the community. While it was a bad luck situation for the people on the plane, perhaps it was a good luck situation more broadly.

Regardless, this type of incident won’t be entirely prevented by the new US CDC canine importation rules (which mainly target rabies risk), but increasing the number of hoops and health measures for imported dogs will probably have some impact, as it’s a disincentive to ship dogs to the US. Unfortunately for us north of the border, shipping those same dogs to Canada is much easier and, as we saw when the US increased dog import restrictions a few years ago, that meant more dogs of questionable health status coming to Canada instead.

The paper’s conclusion raises some good points: “In conclusion, a multifaceted approach is needed to appropriately reduce public health risks posed by B. canis in imported dogs that are sexually intact. Efforts that could reduce the public health risks include: strengthening import surveillance; development of better screening and diagnostic tests for B. canis; increased brucellosis screening and quarantine by importers, breeders and organizations involved in the sale or adoption of dogs; and increased awareness by owners of the importance of procuring dogs from responsible sources. Airlines may also consider adopting policies that promote readiness to respond to ill animals and to prevent the transport of pregnant dogs to reduce the risks posed by B. canis.“