A Veterinarian’s Take on Bird Flu in Cows

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Had you asked me in November of 2019, before I had ever heard of, quote, COVID-19, what I thought would have caused the next major pandemic, I would have said H5N1 influenza, probably from birds. So you've got to imagine how I'm feeling about this. The CDC has now officially issued an alert.

Hopping around, mainly in migratory waterfowl, and leaving us and our farm birds well enough alone. And ever since it popped, epidemiologists and virologists have been mourning about the possible risks here. And now, a full 30 years later, some of those risks feel a lot more imminent. And that's because it's no longer leaving us and our birds well enough alone. Today, I want to do a deep dive into why.

I want to give you two frameworks for thinking about the risk, and to explain why we're all so worried right now. The first framework is the, quote, epidemiologic triad. It's a fancy way for saying the three things we think about when we analyze the risk of a pandemic. And that triad includes factors relevant to the host, factors relevant to the environment, and factors relevant to the agent. In this case, the H5N1 virus itself.

What about these three things sets us up for mass spread? What's got us all worried right now is the fact that this virus made the jump from birds to cows. So let's think about the features of each that have set us up here. For their part, birds are, well, notoriously mobile. They literally fly from continent to continent every single year.

All the while, they drop infected feces on the ground. That's a pretty great setup for transmission. if you're a virus. What about cows? Well, they're far less mobile, even though people, well, people drive them all over the place.

But there's another part. They've got udders. And, based on new unpublished preprint data that came out this week, those udders are rich in the receptors that the virus loves most. And those udders are milked every single day. And that milk gets all over the place, including into the feed that other cows consume.

They also live in wet, moist environments, which gets us to the environment. part. Corporate farms, where hosts are concentrated together most of the day, that's a banger of an environment if you're a respiratory virus. The workers on those farms are often low-income migrants, who are marginalized out of access to health care and quality workplace protections. And when they're not working the farm, they often sleep in tightly packed quarters where, again, the virus can make quick work out of infecting folks.

And then there's the virus. And here I'm going to give you another framework. When we think about the pandemic potential of a virus, we analyze that virus in three main ways. Pathogenicity, its ability to cause serious illness. Transmissibility, its ability to jump between us efficiently.

And immune evasiveness, its ability to duck and dodge our immune system. The technical term for this virus is highly pathogenic avian influenza. So there's that. That highly pathogenic part points to the fact that since 2003,, there have been 254 reported cases of bird flu in humans. 56% of them died.

Yeah, that's more than half. While it's possible that if a variant gained the capacity to jump between people, it might also be less pathogenic, I'm not holding my breath. Or maybe I should be. As far as transmissibility, this is a big wild card. Because we don't know of a variant that has been able to spread between people, yet, it's not clear how transmissible such a variant could be.

And finally, immune evasion. This is the reason most of us are worried. See, the very biological capacity that the virus has to mutate to infect people is the reason it would likely be able to morph and shapeshift to evade our immunity over time, just like SARS-CoV-2 has. And that's because, just like the SARS-CoV-2 virus, it's an RNA virus. Like all viruses, RNA viruses rely on cellular infrastructure to replicate.

But our infrastructure makes a lot of mistakes when it replicates RNA, meaning that there are a lot of mistakes in the virus's genetic code, too. Normally, when there's a mistake, those viruses die. But sometimes, it gives them mutations that help them escape our immunity, meaning that natural selection amplifies them. It's why we keep having, quote, waves of COVID, and why we have to update the flu vaccine every single year. But for now, the virus is stuck in birds and cattle and a number of other mammalian species that have gotten it.

And I'm no expert in animals. I went to human medical school. So I wanted to invite someone who is. My guest. today is Dr.

Kimberly Dodd, director of Michigan State University's Animal Diagnostics Laboratory and former director of the USDA's Animal and Plant Inspection Service. She joined me to share more about how we should be thinking about the current situation, efforts that need to be taken to contain this, and where we go from here. Here's my conversation with Dr. Kimberly Dodd. Okay, can you introduce yourself for the tape?

But it was there that I had the opportunity to support diagnostic testing needs during large-scale Ebola outbreaks in Africa. So I fell a little bit in love with diagnostics and realized the critical role that our laboratories play in early detection to and response of a public health emergency. So fast forward, a few years. After several years after that, I worked in Africa building laboratory capacity and then had the opportunity to lead MSU's veterinary diagnostic laboratory.

Go back to the beginning of the emergence of H5N1, this avian flu strain that we're all talking about now. When and where did it emerge? And can you give us a little bit about its history?

So it's kind of the same thing in wild birds or, again, migratory waterfowl. What's different in that case is that generally in those birds, they don't show signs of clinical disease. So it circulates in them asymptomatically. We don't worry about it very much, except when those wild birds have contact with our domestic poultry. And so that's how we define highly pathogenic avian influenza.

It's when we have a transmission of an avian influenza strain from wild birds to domestic birds that causes really high morbidity and mortality, so really severe sickness and death.

. So since then, we have been responding, and when I say we, I mean veterinary. diagnostic laboratories across the country have been working together to respond to this ongoing outbreak. Primarily, we've seen disease, again, in our domestic poultry populations, chickens, turkeys, pheasants, et cetera. What's been unique about this particular strain is that, in addition to causing disease in our domestic birds, we've also seen significant mortality in wild birds as well.

That's important because it means that when there are wild birds that succumb to avian influenza, there's more potential interaction of those birds with wild mammals, so specifically carnivores or scavengers. So since the start of this outbreak, we've actually seen the emergence of this virus in fox, skunks, raccoons, other wild mammals that may come across the carcasses of birds that have died from avian influenza and then consume them. So since the start of the outbreak two years ago, we have been able to detect highly pathogenic avian influenza in more than 200 mammal species. Now, up until now, those have been what we call dead-end infections. An animal consumes some of the carcass, becomes sick, and may die, and that's it.

It doesn't spread mammal to mammal. The story is a bit different when we get to the dairy cattle.

But in this particular case, we are seeing that, and that means that basically, you've got weak, sick birds that mammals tend to eat and then tend to get sick from. Is that what's happening?

And two,

it may cause more severe disease in all species. And that's not the case. When we call it highly pathogenic avian influenza, it's referring just to its behavior in our domestic poultry species. So this would be highly pathogenic avian influenza, even if we only saw disease in domestic birds. As I mentioned and you noted, what's different this time is we're seeing disease in the wild birds, which has led to disease in other mammalian species as well.

So that in and of itself obviously has an economic impact, particularly in terms of eggs. There was some discussion about the cost of poultry products as well in the last couple of years, and that's why it's so important that veterinary diagnostic laboratories like ours are working hand-in-hand with state agencies and USDA to really develop strategies and plans to rapidly detect these viruses and then to build the surge capacity and do the necessary testing in the case of a widespread outbreak.

I want to ask you just quickly, I'll take a quick detour. You talked about the culling of 90-plus million chickens. How is that choice made? I know that public policy around the containment of avian influenza often tends to incentivize that. Can you share a little bit more about that policy?

And considering how fast it's spread, the question of how we contain it among cattle has become quite important. I want to start at the top of that story, though. How do we think this avian influenza jumped into cattle?

And that's another really important part of this when we're talking about dairy cattle. The cattle tend to recover on their own in 7 to 10 days and then go back to what we hope will be full milk production.

We, I think, again, as I said, even as virologists, who might be gamblers, didn't anticipate the cause of this being highly pathogenic avian influenza. So what we know to date are a few things. We know that most likely there was a transmission event from wild birds to dairy cattle at some point in the last few months. From that point, there's evidence of cow-to-cow transmission of highly pathogenic avian influenza. There's still lots of questions about the specifics of it.

Is that from direct contact of animal-to-animal? Is there some level of mechanical transmission from milking equipment? There are a lot of things we don't yet fully understand in terms of all the ways in which transmission may occur from cow-to-cow. And, to your point, we also know that there has been one documented human case to date. This is an individual who's working really closely with dairy cattle and developed mild disease, mostly conjunctivitis or inflamed pink eye.

And then, of course, we have the human influenzas. A lot of these are all influenza A viruses. So most of these tend to be species-specific. And I recognize your concern that, I guess, in theory, we look more like cows than we look like birds. On the other hand, viruses are very particular in terms of where they like to live and replicate.

So there are some viruses that are not really particular. They tend to just replicate any part of the body where they can get. Other viruses, like when we think about COVID and things like, something like that in humans, we think about it as a respiratory disease, right? So there's going to be replication and, therefore, transmission from the respiratory tract from one person to another. I cough and I have COVID.

You could potentially be exposed. What's really unique about this strain of highly pathogenic avian influenza in dairy cattle specifically, is that the virus loves the mammary gland. So we don't actually see much virus. If we look at nasal swabs, just like we take of ourselves for COVID, we do the same thing in dairy cattle. And honestly, there's not evidence of much virus there.

But you look in the milk, and that's where you find the virus. So it's a very, while, yes, there are species differences, there are also differences in tropism, or the area where the viruses like to go to replicate. And so, just because we're seeing it in dairy cattle versus birds, I don't think is necessarily indicative of a higher risk to humans. What the concern is, is that the longer this virus is replicating and circulating in the environment, the more likely it is to mutate. That's what viruses do over time.

Again, to use COVID as an example, we have seen it evolve over the course of the last several years. We went through Omicron and Delta and all of the other different versions of it. And so one of the things that our laboratory, as well as labs across the country, are focused on doing, is being really focused on detecting all of the animals that have highly pathogenic avian influenza. So we can then characterize that virus strain, look for any potential mutations that, in turn, could potentially cause a higher risk to the human population.

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So, in studying as many samples as we can and getting a sense of the kind of mutations that are being selected for, we can kind of get a sense of what direction the virus is headed. And, you know, the nice thing about this, and as I think about this from, you know, obviously it's impossible to think about a potentially pandemic illness now without comparing it to COVID. And if there is a nice thing about this, if there is a silver lining in what is a, I guess, milk cloud, it's that we're talking about a virus that we understand pretty well. And so we know what to look for when we think about potential transmissibility of influenza virus in humans. And so, you know, as you're thinking about this, as you're talking about this, we almost know what direction it needs to go.

And so we can get a sense of whether or not it's moving in that direction. And so I think there's some comfort to be taken in what you just shared.

At the same time, we need to maintain that level of surveillance to be constantly looking.

And it opens up a set of questions about the potential risk of transmission through milk. Now, I know that the evidence has shown that pasteurization is extremely effective, but we also know that a lot of people drink raw milk. Now, this virus traditionally, right? When you think about influenza, it's a respiratory virus and ostensibly the pathway of spread is respiratory. But I want to ask two clarifying questions, because you said something earlier that really sparked my interest, which is that the viral burden in nasal swabs in cows is just not that high.

And so is the mechanism of transmission in cows respiratory in the way that we would traditionally think of a flu, or does it have something to do with milk?

So that's all work that's constantly ongoing. Again, this is a pretty recent and unexpected finding to have highly pathogenic avian influenza in dairy cattle. And so there are a lot of folks working on this to be able to better understand the hows and the whys, and then to translate that information to figure out how do we develop the best response plans to eliminate spread within any species, whether it's cows or poultry.

I'd like to come back to the milk for a second, because you talked a bit about it. And I think, you know, we are very sensitive. We were all very familiar with PCR. at this point. Again, another, you know, gratitude to COVID.

there. I often joke that when my mom stopped helping me with my science homework in fifth grade, and then COVID happens and she was suddenly talking about PCR at the dinner table, like an armchair expert. So, I mean, I think we've all become familiar with what that is as a diagnostic test. And in COVID, we use that to identify people who are infected. And that's true.

But what PCR does is it detects genetic material. It tells you whether a virus is or has been in a person or an animal. Now we know that pasteurization kills the virus, but does not eliminate the genomic material. So if I had a milk sample that I knew had virus in it, and so it was PCR positive, and then I pasteurized it, I would still expect it to be PCR positive. And so I think it's a really important thing that, you know, sure.

We all hope that we can prevent any high path avian influenza infected milk from getting into the milk supply. On the other hand, we know that pasteurization kills the virus and keeps our milk supply safe.

Cause we're still learning, but we understand that this virus seems to like mammary glands for some reason or another, that it sort of makes sense that in calves it might not have an opportunity to replicate and cause disease because the calves, by definition, aren't lactating.

they don't have the necessary cellular infrastructure to be able to receive the infection in the same way.

But my, my little doodle can cough in my face and I'm not going to be infected by it because I'm not susceptible to it. And it's not just because I'm a human that I'm not susceptible to it. It's because, as a human, I don't have any of the cellular receptors that those viruses or bacterias go after. Do you know what I mean? So I think it's sort of, you know, that's actually not terribly good example, but my point is is that viruses are highly specific.

So just because they get, they infect a person, it then has to find its way into cells where it's happy and can replicate. And so it requires a couple of things. One, it has to, you might remember, from science class, right? It's blocking key mechanism. They've got to be able to find something in that receptor to let them into the cell.

And then, once they get in there, they have to be able to take advantage of all the cellular machinery to be able to create more of themselves, because that's just what a virus wants to do. It can't replicate by itself, without being in cell of some sort. And so if it can't get into the cell, so if in a calf, there's no cell, that is, you know, that a virus can get into, it can't replicate there. And the animal will get infected.

We're only really seeing this in dairy cattle. Has that changed at all?

And so it opens up a question of, okay, well, are conjunctiva a potential breeding ground for this virus? I don't want to speculate way too far out here, but just as we think about this, how should we be thinking about the real risk among humans, based on what we've learned from this one case?

So there have been a lot of opportunities for humans to have interaction with this virus. And as of now, this is the only, this is the only infection associated with cattle. There was one earlier, in 2022, of a poultry worker who got infected, who had been in very close contact with a large number of infected birds. So it seems like, you know, infection of this virus is really a rare event. And, you know, whether you, I think there's,

you know, you can say it, you know, how did the, how did the infection get to the eye? You know, was there some, was his, did his hand have some milk on it? and he rubbed his eye? You know, there's a lot of opportunities for that. And I think we want to be careful not to utilize these examples, this N of one, to generalize about broader concerns.

I think we can also assume, and I honestly hesitate to say this, but I think it's true that there probably are people consuming raw milk that may contain some virus and we haven't yet seen clinical signs. And I hesitate to say that because I think we can all agree that, from a public health perspective, drinking raw milk is certainly not recommended in this circumstance.

and the question of how aggressively to enforce the, the theoretical public health concern here is one that has come up in real life conversations. I'm sharing with other public officials and folks in the County. And on the one hand, there is a theoretical risk of the transmission of this virus to somebody who's drinking raw milk. And on the other, right, the pathway through which that would happen doesn't even seem to be happening in cows. Right?

I mean, just as you shared, right, we're not seeing massive illness in calves who are literally drinking raw infected milk. And so this question of, okay, so how should we be thinking about this? And to what extent do you then start to say, well, based on the theoretical risk that's posed here of exposure to this novel virus, we should act. And it does pose a number of really interesting scientific questions about exactly the mechanism of action, but it also poses some really important ethical questions about how, how tightly do you regulate on something as a function of a risk that hasn't necessarily borne out yet? And the point you made is, you're right.

There probably are people right out there who are drinking, unbeknownst to themselves, potentially infected raw milk. And, to your point, we've only seen one reported case. Obviously, it's plausible that, you know, that folks aren't reporting and we're not hearing about it, but you know, if, if there had been an outbreak, we would probably would have seen it by now, and there hasn't been. So it does open up some really interesting and important places questions at this juxtaposition between, you know, science and ethics with respect to public health.

Here it's a problem because this is a virus that, you know, we know it's actively replicating across our environment and we know that it could change, right? So at this moment in time, you know, there, there's no evidence that the currently circulating strain is going to be more successful. And I say that's successful from a virus perspective, right? Because viruses are just trying to replicate new hosts, that the virus is going to be successful or, to better frame it, that the virus is likely to cause disease in humans. We don't have that evidence.

Could that change at some point? Yeah. Do we know what that looks like? We don't. So what do we do?

We monitor the virus. We try to understand what, how it's evolving and where the risks are. at the same point. And to your point, it's a much more complicated question is how do we put in risk mitigation before, at this, at this stage in time?

Maybe they're not eating as much. They're, they're just not quite right. We are then testing them for high path avian influenza. And I, I make that point because when we're looking at dairy cattle, we're closely monitoring their production capabilities. And so anytime there's a drop in milk production, we pre this right in peacetime.

We would receive samples from dairies to try to identify what those common or endemic causes of disease might be. What's going on. What's changed now is we're including high path avian influenza in those differentials. And in some case, a sort of a tough top differential. So we've really ramped up our active surveillance to get a sense of where are the cows that are infected?

How many of them are there? The other thing is because we know that there is the potential for cow to cow transmission. We know that the cows that became infected in Michigan, most likely did so because there were cows from Texas that came up and exposed our Michigan cattle. So we know that movement of animals at this point poses a potential for transmission from infected to uninfected cows. And so we're trying to limit movement or at least test animals before they move from one herd to another.

And I'm a veterinarian, but truly more of a small animal veterinarian. So, to be honest, I've learned a lot about dairy management in the last couple of months and especially in terms of how much our cattle move during the course of their lifespan. So those are two major things we're doing, or that state and federal agencies are doing in collaboration with veterinary diagnostic labs like ours. We're also working together to work with some of the herds that have tested positive to again, do additional testing downstream to see how long these animals are shedding, for. You know, when, if ever, are we detecting it in their nasal passage?

Is it only in the milk? And again, trying to monitor how the viruses are changing over time. So it's a, it's a huge, multifaceted effort, coming at it from multiple directions and, you know, kind of because we're both here in Michigan, I feel like it's kind of worth a plug for our state. Cause this is, I'm not from Michigan originally. I've only been here a few years, but this is a highly collaborative state where we have folks from, from the department of agriculture, department of health and human services, department of natural resources, as well as all of our industry stakeholders and MSU as well.

We're going to gather, figure out how can we get our arms around this, understand what's happening and use that information to best inform next steps.

She's a veterinarian and virologist, and she is the director of the veterinary diagnostic laboratory at Michigan state college of veterinary medicine. I'm not going to hold the MSU part against you, but I'll just, I'll just end with this go blue, but no, Dr. Dodd, thank you so much for taking the time. Really appreciate you.

Yeah. I know we've really got to come up with a better. names are distant Omicron descendants, but they've got distinct advantages that have enabled a more efficient transmission by the virus. Some modelers are forecasting that, given current wastewater dynamics, they could end up driving a summer surge. given where we are in the season, though, cases may increase a bit.

I'm not particularly worried about a serious surge. Sure. This may be a bit more transmissible, but remember what we discussed today, host agent environment. Well, COVID may not be inherently seasonal as a virus. There's a reason it tends to spike in winter, and that's our behavior.

It's the time. And most of the country, when we spend the most time indoors and, lucky for us, we're headed into summer. That said, if flirt continues to do its thing into the fall, assuring that next season's vaccine has coverage will be absolutely critical. for some time. The causes of Alzheimer's disease have been a mystery, but a new study in the journal nature medicine offers an explanation for up to a fifth of all cases.

And it's genetic. It turns out that being homozygous or having two copies of a gene called APOE4, as opposed to the more common APOE3 version, is nearly universally predictive of having a particularly aggressive form of Alzheimer's disease. In the study of over 3000 subjects, 95% of the subjects had biological markers of the disease by 55 and nearly all had the characteristic amyloid plaques in the brain by 65.. This changes the way we think about the disease. While only about two to 3% of the population is homozygous for APOE4, they account for nearly a fifth of all Alzheimer's cases.

And because nearly all of them will eventually begin to show disease, it means that nearly one in five cases of Alzheimer's can be diagnosed before symptoms even start just by a genetic test. While we don't know if early and aggressive treatment can delay or even prevent symptom onset, it does open up the possibility here. And all of this fundamentally changes the way we think about the disease itself.

Finally, in a tragedy we've been covering here for some time, northern Gaza is facing full-blown famine, as the opportunity for an immediate ceasefire was dashed last week when Israel rejected a ceasefire deal proposed by Egypt and Qatar and accepted by Hamas. Meanwhile, the Israeli military continues to threaten a full-blown invasion of Rafah, to which civilians had been told to evacuate. early on in Israel's bombardment of Gaza. Last week, they seized control of Gaza's southern border, vastly reducing the flow of already vastly limited humanitarian aid. Why do I keep covering this story?

After all, this is a health podcast. Because war is the inescapable public health issue. So much of what we cover here is about people putting other things ahead of human well-being. Money, power, greed. In most of these situations, though, the impact of those things on health and well-being can help turn the tide.

If you think about it, that's the fundamental thesis of public health. But when humans wage war on each other, they cease making overtures to health at all. They make taking away the other's health the main aim of their conduct. And that, to all of us, should be simply unacceptable. What frustrates me even more about this situation is that there's been so much effort to justify the destruction and dissemination of Palestinian humanity, using so many of the same tropes that we've heard about Arabs and Muslims in this country for so long.

Palestinians are people. Their health matters. They deserve the dignity of our protest and our care. And that's why we need a ceasefire now. That's it for today.

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This show is for general information and entertainment purposes only. It's not intended to provide specific health care or medical advice and should not be construed as providing health care or medical advice. Please consult your physician with any questions related to your own health. The views expressed in this podcast reflect those of the host and his guests and do not necessarily represent the views and opinions of Wayne County, Michigan, or its Department of Health, Human and Veteran Services.