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Dairy cows produce a lot of milk. That’s great when you’re producing it for sale. It’s not great when you have to get rid of it.

It’s clear that this H5N1 flu virus has an affinity for the udder, and a lot of virus is shed in the milk of infected dairy cattle. It appears that it’s often obvious when a cow’s udder is affected: milk production drops and the milk looks abnormal. Abnormal-looking milk is disposed, so it doesn’t go into the human food chain. With the odd sick cow on a farm, diverting this amount of milk isn’t hard. With a lot of sick cows on a farm, it becomes more problematic – it can be a lot of milk.

There’s also the issue of the clinically healthy cattle on farms with H5N1 infected cows. At this point, we don’t understand enough about the virus in cattle to know if exposed cows could be shedding the virus in their milk before they look sick. With influenza infections in other species, we know that virus shedding in respiratory secretions is common prior to the onset of illness. This “pre-clinical” period is a big problem when it comes to infection control, because individuals can be infectious before anyone has any clue they’re infected.

  • We don’t know yet if this pre-clinical / sub-clinical virus shedding happens in cattle.
  • We might be lucky if when virus is shed in milk, it’s always identifiable by visible changes in the milk.
  • We might not be lucky if virus can also be shed in milk that looks normal (and our luck when it comes to infectious diseases hasn’t really been great in the 2020s).

If cattle have a period where they are shedding virus in milk without any outward signs of illness, we have to consider what that means. We’re pretty confident that pasteurization is highly effective against this virus (the other day @SafeFoodCanuck and I wrote a commentary on why the risk of H5N1 flu from pasteurized milk is likely still low in The Conversation). However, raw milk still poses a risk, and we also need to think about exposure of people who handle milk before it’s pasteurized. That raises the question about whether all milk from infected herds should simply be dumped. That’s a lot more milk. I can argue both ways at this point.

Regardless, with influenza circulating in dairy cattle, we’re going to have to dump milk. Maybe a lot of it. An unfortunate waste to be sure, but dumping that much milk is also not as simple as it sounds.

Dairy farms aren’t plumbed into municipal wastewater systems, and don’t have their own septic systems to handle waste. You can’t just flush hundreds of litres (or more) of milk down a drain. It usually goes into manure pits or lagoons, then is eventually spread on fields. That’s fine for the relatively small volumes of milk that typically are dumped from sick cows, but when we have large amounts of milk potentially contaminated with a concerning virus like H5N1 flu, what do we do with it all? There are a few options, but none are great:

  1. Dump it in the manure pit / manure lagoon as usual.
    • That’s the easiest and most practical means of disposal. However, at this point we don’t know how long the virus would survive in a manure pit / lagoon, or on a field after the manure is spread. So this could result in exposure of lots of wildlife, including more mammals (bad for continued mammalian transmission and adaptation) and wild birds (bad for spillback into birds and subsequent transmission over wide areas).
  2. Pasteurize the waste milk before it’s dumped into the pit / lagoon.
    • Some farms have small pasteurizers on site for milk that’s used to feed to calves. Probably no farms have pasteurizers that could handle their full production capacity, so this isn’t a realistic option if all the milk has to be dumped.
  3. Send the waste milk away for disposal.
    • Sure, farms could conceivably contract someone to come pick up the waste milk and dispose of it another way (perhaps into a wastewater treatment plant?). But, that’s not cheap or easy, and might open up a whole new can of worms.
  4. Cull the affected cows (so they’re not producing milk that needs to be dumped).
    • Not a viable option for many reasons.
    • Animal welfare is one reason. Killing an animal that has a short-term, usually mild, infection is extremely hard to justify.
    • Economics is another reason. Individual dairy cows are valuable animals; dairy cows don’t start milking until they’ve had their first calf, which is usually around 2 years of age, so each one represents a significant investment of time and resources. Some can also have very high genetic value. You can’t just clear out a herd of dairy cattle and repopulate the farm next week and be up and running, like you can with poultry.
    • In addition to the animal welfare issues and economic costs, if the cows were culled then farmers would also need to figure out what to do with hundreds or thousands of dead animals.
    • Last but not least, if a dairy farm was depopulated but the virus is still circulating nearby or present in the environment, any new cattle brought to the farm could be re-infected at any time, and it would all be for nothing.

There might be other options, but none jump to mind as practical to me. For example, there might be some other potential on farm virus inactivation approaches, but the cost, logistics and timeframe would likely not make sense in this scenario.

So, we’re most likely left with the option of dumping the contaminated milk into manure pits, going on the assumption (hope) that the virus will die quickly (since it’s not very tough) and it won’t be a source of further spread. It’s not an unreasonable approach, and is probably the least-bad way, but isn’t ideal.

When we talk about “worms” in dogs or cats, we’re usually talking about parasites that can infect pets or (less commonly) that harbour other pathogens. However, there are also certain worms that can cause other problems for our furry friends. For example, the hammerhead flatworm (Bipalium adventitium) produces a very potent paralytic neurotoxin, tetrodotoxin, which is the toxin famously associated with human deaths from improperly prepared pufferfish.

(Disclaimer: I’m neither an entomologist nor a toxicologist, so I’m drifting out of my lane here.)

Headlines about this worm can be pretty sensational…

…but the buzz may be greater than the actual risk.

There’s been another round of new reports recently following identification of the hammerhead worm in southwestern Ontario this spring, but it’s not actually a new problem. The first report of these worms in Canada actually dates back to 2018 when they were found in Montreal. Some interesting crowd-sourced tracking of hammerhead worms shows that they’ve likely been present in Ontario for at least a couple of years (including just down the road from me).

What’s the actual risk from hammerhead worms in the environment?

It’s hard to say. These worms are small and the amount of tetrodotoxin toxin in them is limited. I haven’t found good data on how much worm exposure would actually pose a health risk to an animal. Hammerhead worms are present in other parts of the world, yet I can’t find any reports of disease in humans or animals linked to them, despite lots of media reports saying “they’re toxic to kids and pets.”

As they say, “absence of evidence” isn’t “evidence of absence” but a lack of reports of something as dramatic as acute paralysis suggests that the risk from exposure to these worms is limited. I’d still avoid eating hammerhead worms of course, and I wouldn’t dismiss the potential that ingestion of one or more worms by a small animal (and we’ll include kids in the small animal definition here) could cause a problem.

What should pet owners do?

  • Relax (as is often the first step with topics like this).
  • Ultimately there’s not a lot that can be done specific to these worms. The main prevention measures are awareness and avoidance. We’re concerned about the potential impact of ingesting or touching hammerhead worms, so try to avoid any direct contact with them; unfortunately that may be easier said than done in some cases, especially with dogs like mine (Labradors) that consider anything (organic or non-organic) to be a viable food source.
  • The good news is that these worms are pretty obvious if you find one (since they have a very unique head). The bad news is, as with most wildlife, if you see one, you can be pretty sure there are lots more in the area that you don’t see. If you come across a single hammerhead worm, they are probably already well established in your area.
  • If you know that this worm is in a particular area, avoid the area if you can, or at least prevent uncontrolled (e.g. off-least) access to it by your animals. Walking a dog through an area where hammerhead worms are present is low risk. Letting a dog root around in areas like that increases the risk of worm contact. Knowing the dog’s behaviour (and any tendencies to eat random things on the ground) also helps with the risk assessment and determining how strict to be about controlling animal access.

An advantage we have in Canada is our (historically) tough winters (yes, there is a bright side to really cold weather), because cold weather kills a lot of parasites. However, we’re losing some of the protective effects of winter with climate change. We’re seeing the potential for expanding ranges of various critters (large and small) and a greater ability of those critters to survive Canadian winters. Given the number of reports of hammerhead worms over the past few years, and the massive underestimation of how common any particular worm is based on the number of reports, we have to assume that hammerhead worms are well established in various parts of Ontario and Quebec (and maybe beyond), and that they’re probably here to stay, at least in some areas.  Common sense would dictate that we should raise awareness and take some basic measures to avoid contact with these worms. We should probably also add Bipalium-associated tetrodotoxin exposure to the differential diagnosis list in the very rare situation when we see unexplained acute paralysis (or weakness) in an animal (or child) with potential exposure to worms. My guess is that this is a minor- or non-issue around here, but more information would be nice.

Image from: https://en.wikipedia.org/wiki/Bipalium_adventitium – by Sanjay Acharya – Own work, CC BY-SA 4.0

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As H5N1 avian flu continues to infect dairy cattle in the US, and because we still don’t really understand some important aspects of how it’s being spread on and between dairy farms, questions keep coming up about the risk of transmission of this strain of the virus from milk.

TL;DR?

  • Relax. There’s really nothing to be concerned about.

For a more detailed answer, let’s start with a quick refresher on pasteurization:

Pasteurization was a revolutionary public health intervention that had huge impacts on human health. It was first developed in the 1800s, and ultimately became used as a way to practically and effectively reduce the risks of infectious diseases transmitted through milk, and extend the shelf life of milk (and other food products). Typically pasteurization of milk involves heating it to 72 Celsius (162F) for at least 16 seconds before cooling, or heating it to 63C (145F) for at least 30 minutes before cooling.

Does pasteurization kill H5N1 influenza virus?

We don’t have specific data on the effectiveness of pasteurization to inactivate the current circulating strain of H5N1 in milk. The US Centers for Disease Control has stated (repeatedly) that “… pasteurization has continually proven to inactivate bacteria and viruses, like influenza, in milk” – which is an accurate statement. It doesn’t specifically say we know it kills H5N1 influenza, but we are confident in it because we know what pasteurization does to other organisms, including those that should be harder to kill than a flu virus

Why can’t we get a defiinitive answer to this question?

There wasn’t a lot of interest in testing the efficacy of pasteurization to inactivate flu in milk until now. We haven’t recognized cattle as a relevant source of flu virus in the past, so it’s not something anyone would study (or, probably more importantly, get funding to study).

Is testing now being done to confirm the efficacy of pasteurization against H5N1 flu?

Hopefully. We’ve had some discussions about it here, but it’s complicated because of the need to handle this virus using containment level/biosafety level 3 conditions. Most laboratories that work with milk pathogens (or most infectious diseases in general) use a lower level containment (Level 2); level 3 labs are much less common (because they’re also much more expensive to run). We’ve been arguing for years to get one at the university here… despite a series of new threats over the years when we’ve said “this is why we needed Level 3 lab!” no one’s ponied up the money; so we still can’t do this kind of testing here.

There are Level 3 labs elsewhere, and while they tend to be heavily used due to their limited number, presumably (hopefully) someone is working on this now. With the right level of containment, it’s not too complicated to do.

Does pasteurization work against other viruses?

That’s not been studied very intensively, since the main public health risks from milk are bacterial. Antibacterial effects of pasteurization are well described, and pasteurization methods are designed to kill those important bacteria. The good news is that influenza viruses tend to be much less stable than many of the bacteria that pasteurization is designed to kill.

What do we know about pasteurization and flu at this point?

We know that flu viruses aren’t very heat tolerant. That’s a good start. Based on that, and knowing how pasteurization is performed, we can come up with some reasonable interpretations of the available information.

There is a study that examined thermal tolerance of an older H5N1 strain in chicken meat (Thomas & Swayne, 2007) – thanks to @SafeFoodCanuck for sending this. It’s not the same as milk or pasteurization, but still gives us useful heat tolerance information. It showed that at 61C (lower than milk pasteurization temperature), the D value (the time required to eliminate 90% of viable virus) was 33 seconds. At 70C, the D value was 0.28 seconds. When we consider that milk pasteurized at 72C is held for at least 16 seconds and milk pasteurized at 63C is held for at least 30 minutes, that provides pretty good confidence that the process will inactivate flu virus.

What about that study that showed pasteurization wasn’t good for killing viruses?

There’s been a lot of social media buzz about a study that showed incomplete inactivation of foot and mouth disease virus (FMDV) in milk by pasteurization (Tomasula et al. 2007). However, FMDV is a very different and much tougher virus: it’s a non-enveloped virus that’s tolerant to lots of stressors, including heat.

Even so, there was still pretty good reduction of the viral load in milk; it’s not like it didn’t do anything. They found “residual infectivity was still detectable for selected pasteurized milk samples,” so pateurization didn’t consistently and completely eliminate this really tough virus, but still had a pretty big effect. They concluded “Although HTST pasteurization did not completely inactivate viral infectivity in whole and 2% milk, possibly because a fraction of the virus was protected by the milk fat and the casein proteins, it greatly reduced the risk of natural transmission of FMDV by milk.”

As a result, we can’t use that study as an indication that flu virus won’t be inactivated by pateurization. Actually, I find it a bit re-assuring that there was such an impact on a much tougher virus like FMDV.

Beyond pasteurization, there are other layers of protection when it comes to the risk of transmission of H5N1 through milk:

1) Diversion of milk from sick cows

Dairy cattle and their milk are very closely monitored. Milk from sick cattle should not make it into the food chain. It’s usually discarded. That’s not a complete guarantee that all potentially contaminated milk will be discarded, since we don’t know whether cattle infected with H5N1 can shed the virus before they show signs of disease or if there can have subclinical infections (infections that don’t result in apparent disease). However, such cases would presumably be uncommon and contribute a proportionately very small amount of milk on any farm.

2) Dilution

A typical glass of milk doesn’t come from a single cow. All the milk from dairy cows on a farm that’s acceptable for human consumption first goes into a big bulk tank on the farm. That milk is then picked up and loaded into an even bigger tank on a truck. Then, it gets mixed with more milk from other farms, so there’s a massive dilutional effect. If a small amount of flu virus got into the bulk tank on farm, it would end up at a really, really low (and probably irrelevant) concentration in milk, even before it got to the pasteurization step.

Can we guarantee that there’s no ability of H5N1 to evade pasteurization?

No, but there’s not really any basis for concern. Personally, if/when H5N1 hits dairy cattle here in Canada, I’ll still confidently give my kids (pasteurized) milk.

While details about the ongoing H5N1 influenza outbreak in dairy cattle in the US have been really sparse, a new pre-print about the early H5N1 cases in Texas dairy herds posted on bioRxiv earlier this week (Hu et al. 2024) has provided some important information.

  • A pre-print is a non-peer reviewed version of a paper that’s typically posted online on an open access server. This situation highlights the value of being able to release pre-prints: it allows good labs to get good data out faster to let people know, and to get quick feedback before (or while) going through the process to have the study peer reviewed and published in a properly refereed journal. Unfortunately, there’s also a lot of complete crap on pre-print websites, posted by dodgy groups to get publicity or advance their specific cause, when there’s no hope of their material ever being published in a reputable journal.

We have to be careful about relying on information from pre-prints, but with this research group (from Iowa State University) and the quality of the data in this report, I’m not worried about this one. Here are some highlights:

H5N1 disease in dairy cattle

The report describes what has largely been reported to date for clinical signs in cattle: Infected animals had decreased appetite, decreased milk production and abnormal-looking (thickened) milk. Clinical signs peaked about 4-6 days after they started, and cows got better on their own within 10-14 days. That’s pretty “flu-like” when you consider how other strains of flu present in other species (including humans). Affected cows were most often older cows in the middle of their lactation periods. The problems seem to have started in late February 2024.

H5N1 detections in other species on farm

Dead birds and cats were reported on and close to affected farms. Not long after the virus was detected in the cows, it was also isolated from a local skunk, and then from a dairy worker with conjunctivitis. The pre-print mentions virus from “humans in Texas during March 2024”, but to date only one human infection associated with the cattle outbreak has been reported. It’s not clear whether there are more unreported cases, or whether “humanS” was a typo. (Let’s hope it’s a typo and there was just one human infection.)

Identification and characterization of H5N1 flu virus from dairy farms

The virus was identified in milk samples from affected cattle and in lung and brain samples from dead farm cats. The virus was classified as clade 2.3.4.4b, which is the main clade that’s been circulating in wild birds in the area (and across North America). The genomes of the viruses from the cattle, cats, local wild birds and the person with conjunctivitis were nearly 100% identical and shared a common ancestor, confirming they are linked (see figure below and at the bottom of the post).

More detailed study of the virus genome indicated that it was a reassortment of the H5N1 genotype B3.7 and a low pathogenicity avian influenza (LPAI) virus. The B3.7 ancestor emerged in 2023 from an H5N1 virus and a different LPAI strain. This highlights the tendency of influenza viruses to evolve and mix with other flu viruses (reassort), and is a major reason we do surveillance testing of flu viruses. This current strain is a bit of a nothingburger for humans, but we’re worried about what it could become if it keeps spreading, spilling over to other species and reassorting.

Surveillance for important genetic mutations in H5N1 flu from cattle

This is still an avian influenza virus. It can spillover into mammals but isn’t (yet) well adapted for sustained transmission between mammals. There are some genetic markers in flu viruses that indicate a greater ability to infect mammalian cells and therefore spread between mammals, including people. The H5N1 isolates from the cattle and cats on these farms had some changes that might increase their ability to infect people, but none contained the mix of other mutations that are also important for this. So this strain, while potentially able to spread cow-to-cow via milk, doesn’t have the range of genetic signatures (yet) that would suggest it’s going to be a problem for humans.

It’s good to see some more details about what’s been going on, and it’s good to see that the virus hasn’t yet evolved to something that would be expected to cause widespread problems in mammals. The lack of epidemiological data and information about how this virus has spread between dairy farms is still a big issue. It’s been a textbook example of how NOT to do outbreak communications, which is incredibly frustrating, and has hampered risk assessment and contingency planning. We’ll hopefully get more relevant information in the near future, as some scientific reports like this one start to come out.

This is less of a content update and more of a “here’s what I really want to know,” but it’s still an update, I guess. It’s a bit hard to say where we currently stand with this problem, at least in terms of the most important aspects. That’s not uncommon with emerging diseases, but we’re in more of an information vacuum than I’d like.

What do we know about the current outbreak of H5N1 influenza in dairy cattle?

The case count keeps going up, but there aren’t a lot of details available about the new cases; some media reports about new cases have actually been quicker and more comprehensive than USDA reports. Currently, I think we’re at 21 confirmed infected dairy herds in 7 states. I’m guessing there will be more affected herds, possibly in more states, that we’ll hear about in the near future, as there’s no doubt some reporting lag, there could be continued spread, and in some cases it may be a matter of slower identification of ongoing problems. The latest USDA map is below, but it’s missing the most recent state to identify a dairy herd with H5N1 influenza, North Carolina. The total number of animals affected isn’t reported, but that’s not as important as the farm and state numbers that tell the bigger picture.

What do we not know about the current outbreak of H5N1 influenza in dairy cattle?

Hopefully it’s more of a “what’s not being released” versus “what’s not known” – presumably there’s more information somewhere than what’s been released. That’s not uncommon in a situation like this. Sometimes there are good reasons for certain information to be kept within certain circles, such as information that may be very sensitive or data that are still just preliminary. Sometimes, the information would just be for interest’s sake, but not particularly critical for the average person or stakeholder, so there’s no urgency to release it. But all too often, there’s too much restriction, resulting in information that could inform action being withheld or only slowly released. With emerging diseases, we need balanced and effective action, and if we lack important details, we can’t tailor the appropriate response.

What do we need to know about the current outbreak of H5N1 influenza in dairy cattle?

Inter-farm transmission: We really need to know how this virus is spread.

  • If spread between farms is based on movement of cattle, we can intervene through changes in how cattle are moved and how they are handled after being moved (e.g. isolation requirements at a new farm). We can think about testing associated with cattle movement (e.g. if you’re buying a cow from another farm, test if before it leaves +/- after it arrives) and biosecurity practices to prevent a person from tracking the virus from another farm. This scenario would also suggest that aggressive action now could result in at least temporary eradication of this strain in cattle. Since we don’t have (as far as we know) long term carriers of flu, if we contain the virus on an infected farm, it should die out. If we contain transmission on farms and transmission between farms, we can (theoretically) get this flu strain off farms altogether.
  • If the cases that are occurring on different farms across different states involve repeated wild bird-to-cow transmission, our risk and management approaches are different. It would mean that keeping a closed herd (not allowing new cattle in, and using good biosecurity practices with workers and visitors) would not be enough to prevent exposure. Even if we locked down the affected farms, cattle could still be exposed by contact with wild birds. Preventing exposure to wild birds is really tough on a dairy farm.

From a Canadian standpoint, this is also really important for our risk assessment. If it’s just farm-to-farm spread, we have limited risk of it being tracked across the border if the industry adheres to good basic biosecurity practices. If there’s ongoing spread by birds, we will almost certainly have it up here before long as the spring bird migration continues.

This also ties into the risk to beef cattle. If this strain is being spread by wild birds, beef cattle will be exposed. If it’s being spread via dairy cattle, beef farms will have very limited risk (apart from buying in surplus dairy calves).  

Genomics: Understanding the makeup of the virus is important for a few reasons.

  • Does the strain infecting dairy cattle have more mammalian adaptation markers? There are some genetic changes that make flu more able to infect and transmit between mammals, including people. We want to know if these are cropping up as the virus gets transmitted to more and more cows. The virus is currently a long way from being able to readily infect people, but we need to keep looking to know it’s not continuing to change.
  • Are the strains found in cattle in different states the same? And are they different from birds in some of those areas? This would help sort out the route of transmission. If the virus in cattle from different states is basically identical, and particularly if the strain found in birds from each of those areas is different, that suggests it’s spreading via movement of cattle. If there’s more genetic variation between isolates from cattle in different states, and the strain in one herd is more like those from birds in that state than cattle in another state, it suggests that bird-to-cow transmission is playing a bigger role.

Intra-farm transmission: We could also use more details about how the virus moves around within a farm. It’s been reported that cows seem to mostly shed virus in their milk (with very little in their respiratory secretion), and that transmission between cows on a farm is therefore likely via milking equipment. Having some on-farm epidemiology to support this would be nice. If milk is the main source of transmission, there might be some corresponding disease patterns in the milking cows. I’d also expect to see no (or very few) infections in non-milking cows (i.e. younger animals (heifers) that have not yet calved, older cows that are between lactation cycles). Young calves could also be an interesting part of the story, looking at whether there have been infections in this group, and if so, whether those calves have been fed discarded milk from potentially infected cows (milk from sick cows is not allowed to go into the bulk tank for shipping). If infections are found in non-milking animals, we need to figure out how they might have been infected, because it helps us figure out if the infection control emphasis on farms should be with milking practices or if we have other issues with which to contend.

Cattle illness: More information about what clinical signs H5N1 virus causes in cows would be helpful. Some information has been released, but it’s sometimes vague, and I’ve seen conflicting information about illness being very mild versus fairly severe but short-term, and very obvious mastitis. Knowing the typical signs and range of disease is important for farmers and veterinarians on the lookout for disease. More details about test results are also important, particularly whether the early reports of the virus being present at high levels in milk but not in respiratory secretions are holding. That has major implications for transmission, and therefore infection control measures.

Infection in other species: I assume there’s been testing of other animals on these affected farms. It would be useful to know the numbers and results; negative results are as useful as positive results. It was reported that there were affected cats on at least one of the Texas farms. Is that unique or common? Have there been other positive farm cats? Were they sick, and if so what signs of illness did they show? If not, how many cats have been tested and were negative? This has both animal and human health implications. From a veterinary standpoint, I want more information about disease in other species, both to help care better for those animals and to protect people working with them.

Infection in humans: Obviously, we’re worried about human infections. How many people have been tested, and how many have been monitored in terms of their health?

  • If they are monitoring +/- testing hundreds of people with regular contact with cows and their milk, and no one has been sick, that’s great, and it’s important information to gauge risk for others.
  • If there’s limited surveillance and testing in people, we can’t be as confident about the risk.

Concerns have been expressed about the willingness of tenuously employed (and sometimes undocumented) workers reporting signs of illness, so “we haven’t heard of any more sick people” really isn’t a good enough answer in this scenario. Hopefully there’s a robust surveillance program in place, but that’s not something I’ve seen described.

Hopefully a lot of this information is available at least within certain circles, and simply has not yet been released publicly. If that’s the case, hopefully it will be released soon. As I said, there are some reasons to hold some data, but in general, more transparency and more communication makes for a much better response, and also helps to assuage public concerns, fears and mistrust.

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In case you need a break from all the discussion about H5N1 influenza and the multitude of species it now seems to be able to infect, there’s nothing like a good zoonotic parasite story to make your skin (or pants in this case) crawl. (I promise that this will be a normal-length blog post… ahem.)

There was a recent research letter in Emerging Infectious Diseases (Hobbs et al. 2024) that caught my eye – particularly because it includes a picture/video which you should definitely check out.  The letter was about the finding of a sizable – and motile – adult roundworm in the diaper of a 2-year-old girl in Mississippi (now that’s got to be uncomfortable…).  The worm was identified from the video taken by the child’s mother (before she disposed of both worm and diaper – can’t say I blame her) as Ascaris lumbricoides.  That may not sound terribly noteworthy, as A. lumbricoides is the primary species involved in human roundworm infections globally, but it is usually spread by ingestion of eggs from human feces in areas where the is very poor sanitary infrastructure (e.g.  where human feces are more likely to be found in the general environment due to “promiscuous defection”) – but not in a region like northern rural Mississippi, on a farm with two flush toilets.  However, pigs have a very closely related roundworm that was previously known as Ascaris suum, that was more recently determined to actually be the same species as the human roundworm, A. lumbricoides.  Ascariasis is not uncommon in some farmed pigs even in the US, particularly those raised outdoors. In this case, no one in the family had traveled outside the US, and there was no reason to suspect there was human fecal contamination in the environment, but there were pigs on the property.  The two young kids were also reported to occasionally eat dirt from house plants, which has to make one wonder if they may have eaten other “dirt” on the farm as well (along with some pig feces and the parasite eggs therein).  Unfortunately by the time the Department of Health conducted their field visit, the family’s pigs had all been sent to slaughter, so it was not possible to confirm that the pigs were carrying the same parasite, but the story all fits together (admittedly it would have been nice to have some more definitive proof).

Fortunately the child was treated promptly by her pediatrician, and did not expel any additional worms, and suffered no further ill effects.  A fecal sample collected within 24 hours was negative for any parasite eggs, so they suspect there was only one adult worm present (I’m sure finding that once in the girl’s diaper was quite enough!). 

One more reason not to eat poop (from any species!) and wash your hands and veggies (or at least do the best you can, if you’re two years old :p).

There’s not a lot new to report since last week about the finding of H5N1 influenza in dairy herds in multiple US states (see map below). That’s often a good sign.

  • I haven’t heard of any new affected farms.
  • There have been a few more reports that the virus is not being found (or is present at only low levels) in respiratory secretions from infected cattle.
  • No additional human cases of H5N1 flu have been reported.

The investigation is focusing more and more on milk as the key means of virus transmission on affected dairy farms. Viral loads seem to be quite high in milk, which is really surprising, as is the limited to no apparent shedding by the typical respiratory route. These two factors support the hypothesis that transmission has been driven by milk, or more specifically by milking practices that result in cow-to-cow exposure via virus in milk, such as milking equipment that is used on multiple cows. If that is indeed the case, I’d expect the cases to be limited to milking cows, and not younger cows (heifers) or cows not currently lactating (dry cows). I haven’t seen any data on that yet, but it will be informative to learn more about case distribution on affected farms.

With the same strain of H5N1 flu being reported on multiple farms across multiple states, contact tracing will be critical. If there’s a solid link between these farms, then cow-to-cow transmission (probably via milk) would explain things. If there’s no known movement of infected cows between all the affected farms, that would suggest there’s a variant circulating in birds that may be more amenable to infecting cattle, and that wild birds on each of the farms are the most likely (but possibly not the only) route of entry. I can argue for either situation being both good and bad:

Scenario 1: The virus is moving with the cows

If this was a single introduction of a cattle-friendly strain with multistate spread, then it might be containable through good testing and management of exposed and infected cattle. That would be good. If the outbreak is being driven by transmission on farms, and not repeated reintroduction from birds, then containment in cattle might work. Flu virus isn’t usually shed for long in most animals, so I assume that will be true in cattle as well, which makes containment more feasible than for some other viruses that can be shed for a long time. The bad part of this scenario is the unexpected transmissibility of this strain of the virus in a manner and species that really wasn’t on the radar, and the potential that this has spread more widely between dairy farms than we know yet.

Scenario 2: The virus is moving with wild birds

If there’s actually only been limited cow-to-cow spread and the virus wasn’t tracked between farms on cattle, that’s good from the standpoint that it would mean the virus actually does not spread well between cattle. However, it would also mean that there’s a broader reservoir of infected birds across the US (and presumably beyond) with a strain of H5N1 that’s amenable to infecting cattle, such that multiple farms were infected by birds. So, we couldn’t just use a really aggressive containment strategy in cattle and expect that we could eradicate the strain. If we eliminated it from cattle, there’d still be a risk of exposure from bird reservoir.

Both scenarios need good on-farm infection control to limit cow-cow spread via milking and perhaps other contacts. Scenario 1 focuses more on the need for strict measures to prevent farm-to-farm spread. Scenario 2 means the long-term focus needs to be on preventing re-introduction from birds into more cattle herds. That’s really tough since it’s hard to strictly isolate cattle from birds, especially cattle on pasture. So, scenario 1, while it has some concerning aspects, is probably what we’d prefer at this point. Given the bits of epidemiology that I’ve seen and the strain similarity across farms, it’s probably the leading candidate too, which I guess is good.

Regardless of which scenario turns out to be true, what’s needed right now is:

  • Continue and increase H5N1 surveillance in cattle (and other animals).
  • Be on the lookout for new infections in cattle, where disease is likely going to be subtle.
  • Work with farms to increase routine practices that help prevent cow-to-cow spread (e.g. routine hygiene and infection control, review of milking practices and equipment management).
  • Work with farms to reduce the risk of inter-farm spread through movement of cattle (e.g. short term quarantine after arrival, health checks before introducing new animal to the main herd). That includes precautions when bringing animals onto dairy farms, as well as when sending animals off dairy farms (such as when excess calves are sold).
  • Ensure farmers and veterinarians are using routine, and when necessary enhance, infection control practices to reduce the risk of occupational infection.

As with any emerging disease, we have more questions than answers, but we can make some interim assessments based on general principles of infection control, and what we’ve learned over the past couple years about this particular H5N1 influenza A virus that’s been circulating in wild birds all over the world, and spilling over into many different species of mammals (including cats), along the way. The details are likely to change over time as we learn more, but this is where I see things at the moment.

Cats can get infected with this H5N1 influenza strain

We’re known this for a while. There have been infected cats (big and small) in various countries over the past couple of years. It’s a bit cumbersome, but there’s good tracking of avian influenza cases in mammals worldwide on the WOAH (World Organization for Animal Health) website.  As with most infections, we no doubt only diagnose a small subset of infections that actually occur (just the tip of the iceberg).

Infections with H5N1 influenza in cats are rare

Notwithstanding my comment above about underdiagnosis of cases, we need to keep this in context. There have been millions upon millions of infected birds all over the world in the last few years. There are lots of cats in areas where infected birds have been present, and cat-bird contact is far from rare. So, there’s likely been lots of exposure, but disease (at least serious disease) in cats has been rare; that’s a bit of good news.

Although H5N1 infections in cats can be severe, social media claims of “100% mortality” are overblown

As we’ve seen in many other mammals with spillover infections (but fortunately not humans so far), infected cats can have very severe disease, including fatal infections, typically with severe neurological signs. It can be very bad, but it’s presumably nowhere near 100% fatal.

  • We’re missing a lot of context because of testing bias, because we’re mostly only testing cats with severe signs of illness, or cats that are found dead in areas where birds have avian flu.
  • We don’t do enough testing of other cats that have been exposed but are still healthy, or only have very mild disease. We just don’t know enough yet to say what the true morbidity or mortality rates are in cats.
  • For all the hype, getting samples from exposed cats to test is a challenge. I’ve been set up for a while to get samples from cats with wild bird contact, but despite there being lots of outdoor cats and lots of infected birds, I haven’t been able to get any samples. (But when the dairy cow news broke this week, I made sure my PAPR was charged and my sampling kit was ready, in case there’s now more motivation to test.)

We don’t know whether H5N1 infected cats can be infectious to others

With only a small number cats tested, it’s hard to gauge the risk of transmission from cats to other animals (or people). Hopefully we’ll get more information about the cats on infected dairy farms. A challenge with multiple cats being infected in a situation like this is sorting out if they were all exposed to infected birds, all exposed to infected cattle (especially contaminated milk) or whether there may have been some cat-to-cat transmission of the flu virus. There’s very little we can do to sort that out when investigating a single farm at a single point in time. We can infer some things from testing results (particularly from quantitative viral loads in respiratory and fecal samples), but it’s still a bit of a guess without more testing and epidemiological investigation.

What can the average cat owner do?

If possible, keep your cat inside, as it minimizes any risk of exposure to infected wild birds (which are still the main source of H5N1 influenza). That’s not always possible though, since some indoor-outdoor cats simply won’t tolerate being inside 24/7, and some outdoor cats can’t be moved indoors.

Take our three cats as examples:

  • Milo is an indoor only cat. He’s low risk.
  • Rumple was adopted through the Guelph Humane Society’s working cat program as a barn cat since he was deemed unsuitable for indoor living. He’s actually a huge suck and now spends a lot of time inside, but he wouldn’t tolerate it full time (I’m not sure he’s ever used a litter box).
  • Alice is an outdoor cat that Rumple adopted. She was a scrawny, completely feral cat who started living with Rumple in the garage, and on our deck. She’s a sweetie around us now, but only on her terms. She will take a few steps in the house (very warily) and then dart back outside, but when outside she’ll roll around on us and purr her head off. She cannot be moved inside. We can make sure she and Rumple are well fed (they’re both on the chunky side), but can’t guarantee they won’t hunt anyway. So they (especially Rumple) are a risk as a bridge from outside to inside. We know that and accept the risk.

People who have indoor/outdoor cats should assess the risk, the ability to change their cat’s living arrangements, and their risk tolerance.

We can also try to discourage mixing of cats and birds. Removing bird feeders from yards is a simple step that I’d recommend at this point.

What if an indoor/outdoor cat gets sick?

Most of the time, the cat won’t be sick from flu, but it’s a possibility, and the risk would be higher if the cat is a known hunter and if there’s recent flu activity in local wild birds. In that event, I think it’s reasonable for owners to limit close contact with the cat, consider wearing a mask if close contact is required, and talk to their veterinarian about testing (for flu and/or other causes). We can’t freak out every time a cat gets sick, but acute onset of severe respiratory and/or neurological disease in an adult indoor/outdoor cat would raise a lot of concern, since that’s uncommon in otherwise healthy mature cats. (Young kittens are a completely different story – they’re upper respiratory snot factories at the best of times.)

What should veterinarians when presented with a sick cat?

I don’t think we’re at the point of saying respiratory PPE should be worn for handling every sick cat. A risk assessment is always appropriate, and ideally there’s a triage process over the phone prior to any sick cat entering the clinic. If the cat has outdoor exposure, especially known exposure to wild birds, and the cat has an acute onset of respiratory or neurological disease, it makes sense to start off with enhanced PPE (e.g. mask, eye protection, gown, gloves) until the situation is sorted out

Are there any concerns about H5N1 influenza and raw meat diets?

Maybe. There are a variety of reasons why raw diets create disease risks (Salmonella being a big one), but there are some specific concerns about the H5N1 virus in these diets too. Last year, there were reports of outbreaks of H5N1 infection in cats linked to raw diets in Poland and South Korea. However, confirmatory data has been lacking, so it’s unclear how strong the link is. It’s probably also mainly or solely a risk from very fresh diets.

I’d use this as yet another reason to avoid raw diets. If someone wants to feed a raw diet, high pressure pasteurized diets should be considered as that likely eliminates influenza virus.

What am I doing about H5N1 influenza in cats right now?

I’ll keep an eye on Rumple and Alice for any signs of illness. If they get sick, I’ll keep them away from everyone, sample them, and go from there. If they have severe illness, I have a plan to manage that, but that’s more medical than I want to get into here. Beyond that, I’m staying aware of the situation and will act (and adjust) as necessary.

What about the risk of H5N1 influenza in dogs?

Separate species. Separate story. But, we know dogs can be susceptible to H5N1 influenza too (but likely even less commonly than cats). Keeping dogs away from potentially infected birds is important at this point, especially dead birds that are higher risk for having died from infection. (That’s something that’s important for me since we live in the country and own Labradors that consider basically anything (live or dead, organic or not) to be a potential snack.)

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There’s been a lot of concern about the recent identification of H5N1 avian flu in cattle in the US, along with a single human infection in a person working with infected cattle. Some of the concern is warranted, but some is overblown.  We need to balance awareness versus paranoia, and try to better understand the problem and reduce the risk, while avoiding excessive, ineffective or harmful responses. That sweet spot is hard to define early on with emerging diseases. We should liberally apply the precautionary principle, but also ensure we keep re-assessing the risks based on emerging evidence.

Here are some initial thoughts on what we can all do regarding the current situation at this stage:

Cattle farmers

  • Be on the lookout for sick animals. Based on what we’ve seen do far, flu will likely cause mild signs in cattle such as decreased appetite and decreased milk production.
  • Call your veterinarian as soon as possible if you suspect a problem in your herd (good advice at any time!), and allow testing of suspect cases (good to know what’s going on, whether it’s influenza or not).
  • Although it’s tough, try as much as possible to keep wild birds out of barns. Also try to discourage migrating waterfowl in particular from entering cattle housing areas or taking up residence in fields.
  • If you’re sick, stay away from cattle. We don’t want human and animal influenza viruses mixing, and putting an infected person in a barn with potentially infected cattle increases this risk. Farmers are notorious for “sucking it up” and working as long as they’re not fully dead, but we need to encourage a culture shift that limits contact of sick people with animals. If that’s not possible (which is often the case), farm personnel that might have the flu should minimize contact with animals as much as possible, and wear a mask to reduce the risk of spread.
  • If there’s flu activity in wild birds in the area, it’s not unreasonable to wear a mask around cattle, but I realize that’s unlikely to happen.
  • Consider adjusting grazing practices to reduce exposure of cattle to infected birds or their feces, especially if there is flu activity in wild birds in the area, and particularly if dead birds are found in the pasture.
  • If your cattle might have flu, definitely wear a mask and eye protection around and sick animals, and limit close contact. Also, think about high risk items and surfaces that may get contaminated by sick cattle, and take additional measures as appropriate (e.g. increasing routine disinfection, reducing direct contact, wearing appropriate PPE when contact is required). Contamination with respiratory secretions from sick animals were the main initial concern, but recent information suggests that milk could be more important for potential cow-to-cow transmission during milking (e.g. shared milking equipment). Contact with milk and milking equipment might pose a risk for people too, meaning we should take extra precautions with contact with the udder, milk and any in-contact surfaces. I’d also take care around cattle feces until we better understand if cattle can also shed the virus that way (but there are lots of other reasons to avoid contact with cattle feces besides flu too).
  • Keep cattle away from any other species that might carry or acquire an influenza virus, which basically means keep cattle away from all other mammals and birds, but with a particular focus on avoiding higher-risk flu species (i.e. domestic poultry and pigs).
  • If you develop flu-like illness, make sure your physician knows you have contact with cattle. If your cattle are sick at the same time, absolutely make sure your veterinarian, physician and public health know so the situation can be properly investigated.

Veterinarians

  • As for farmers, consider flu in cattle and on beef and dairy farms, and be on the lookout for it.
  • Communicate with farmers, infectious disease specialists, labs and government agencies if you have concerns about flu in a particular herd.
  • Use standard infection control practices to minimize the risk of farm-to-farm spread of flu (and other pathogens). That route of transmission is pretty unlikely for flu, but there is potential for veterinarians to track flu between farms, which can’t be ignored.
  • As for farmers, if you might have the flu, stay away from animals (at least birds and mammals) as much as possible. Yes, that’s tough since that means not working, but we don’t want co-infections of people or animals with different flu viruses.
  • Consider wearing a mask around cattle. I realize that’s not likely to happen routinely, but definitely wear a mask and eye protection if you suspect flu might be present in cattle you’re seeing. Take particular care around handling the udder and with milk sampling.
  • If you develop flu-like illness, do the same as mentioned above for farmers.

Governments

  • Support testing for influenza A in cattle. We don’t know what we don’t know. We need a fairly wide net of testing to understand this issue. That costs money, and it’s hard to expect farmers to cover all the costs of this kind of testing, especially when there’s limited direct benefit to them (because so far flu only causes mild disease in cattle, and there’s no specific treatment).
  • Don’t make it hard to get testing done. Sometimes, we run into barriers when we want to test for emerging diseases. Don’t make veterinarians jump through permission processes to limit testing. We need more information, not push back against getting more information.
  • Support farmers who have suspected or confirmed cases of influenza in cattle. We need to see a balance of measures that are adequately restrictive to contain flu, but not so extreme that they drive the situation underground. If the response is over-the-top, there will be a strong disincentive for anyone to test for flu, and that just makes the situation worse.

Consumers

  • Relax.
  • Don’t drink raw milk (for lots of reasons).
  • Avoid fearmongering Twitter threads.
  • Relax.

Public farm events/petting zoos

  • I really have no idea what to say here. Petting zoos or other similar animal exhibit events can result in large numbers of random people have contact with cattle, with limited hygiene, no health screening  and no contact tracing. There’s a risk, but it’s too early to say how much of a risk. We need to see how the situation evolves.
  • Fortunately, these kinds of events are most common in the summer and early fall, so we have a bit of time. At the moment, if there’s flu activity in wild birds in the area, it’s reasonable to say that we shouldn’t allow random access to cattle, pigs and other flu-susceptible species.
  • If visitor contact is allowed, make sure cattle are assessed daily to confirm none look sick, try to keep sick people away, try to maximize ventilation in animal areas, and facilitate (and encourage) hand hygiene.

As with any emerging disease, guidance will change. People don’t like that, but it’s actually a good sign – it means we’re learning and responding. We shouldn’t be so arrogant to think that what we recommend now will ultimately be the optimal approach. Hopefully we’re pretty close, and we can make good recommendations based on what we know now, but I’d be disappointed if we don’t change them at least a bit (because that would more likely mean we didn’t adapt than we knew it all from the start).

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H5N1 avian influenza has been found in cats on a dairy farm in New Mexico where cattle were infected with the same virus. As part of the farm investigation, some (number not reported) sick (type of illness not reported) cats were tested, and three were positive. There’s no way to know for sure, but I’d guess that the cats were infected by the same source as the cows (i.e. from infected wild birds), not from the sick cows themselves.

It’s totally unsurprising, since there are various reports of cats from several countries around the world being infected with this virus, which continues to circulate widely in the wild bird population. Cats hunt birds, and birds that are sick with avian flu are a lot easier to catch. Eating a sick bird is a clear way to get infected, so it’s not surprising at all to find infected cats in areas where there’s lots of flu activity. I’d guess there have been hundreds of infections of cats worldwide, but most of them have gone unrecognized.

This isn’t a game changer, but it’s yet another reminder to pay attention. Fortunately, cats (like cows) don’t have their own influenza A virus, and they tend not to be very susceptible to human flu strains. So, there’s less risk of them being infected with the H5N1 virus and another flu virus at the same time, and acting as a mixing vessel for creation of a new, more problematic recombinant flu strain. However, every spillover into any mammal poses some extra risk, and cats are potential bridges between wildlife and people, since people often have close contact with cats. That’s why we’re on the lookout for these spillover infections, and ideally want to limit exposure of cats to infected wild birds.

If you have cats that go outside and you can’t prevent that (not all cats can be indoor only), be on the lookout for flu. If an outdoor cat gets sick, especially with respiratory or neurological disease, and it’s had potential contact with flu-infected birds, it’s important to talk to your veterinarian (and ideally get the cat tested so we can gather more information on the virus’ behaviour, and also try to contain the infection).