ONE Health Live
Examining the issues of importance to animals, humans and the environment to help those across the food production system better understand the issues from a science-based perspective.
ONE Health Live
Avian influenza, dairy cows, and human risk: A One Health perspective
Avian influenza has transformed from a periodic poultry concern into a persistent global health threat that crosses species barriers with alarming versatility. In this illuminating conversation, veterinary pathologist Dr. David Swayne draws upon his 38 years of experience to reveal how the current H5N1 virus has fundamentally changed since emerging in 1996.
The virus we face today is unlike its predecessors. Where once avian influenza would disappear seasonally, this lineage maintains year-round transmission cycles in wild bird populations before spilling over into poultry and even some mammals. Dr. Swayne walks ONE Health Live hosts Sarah Muirhead and Dennis Erpelding through the science behind these adaptations and explains why the recent jump into U.S. dairy herds represents a concerning new development rather than just another isolated event.
Perhaps most compelling is Dr. Swayne's exploration of how human health outcomes directly improve when we address disease at the animal source. He points to dramatic reductions in human infections following poultry vaccination programs in Asia, demonstrating the tangible benefits of a One Health approach. Yet challenges remain, particularly in establishing effective communication channels between public health authorities, agricultural sectors, and environmental agencies – gaps that became painfully apparent when the virus suddenly emerged in Latin American countries unprepared for cross-sectoral collaboration.
The conversation also tackles complex questions about virus nomenclature, zoonotic risk assessment, and the essential role of international organizations in coordinating global responses. Throughout, Dr. Swayne emphasizes that solving these multifaceted challenges requires breaking down traditional silos between environmental, animal, and human health sectors to develop integrated solutions that protect all species.
Curious about how avian influenza affects your food systems, wildlife conservation efforts, or public health? Subscribe to One Health Live for more expert insights that bridge the gaps between science, policy, and practical solutions to our most pressing health challenges.
Welcome to One Health Live, where we examine the topics of importance to animals, humans and the environment. Our goal is to help those across the food production system better understand the issues at hand from a science-based perspective. In One Health Live, we're striving to bring you thought-provoking and fact-based information as we take a look at the latest news and provide insight. I'm Sarah Muirhead, and with me today is One Health Live co-host, dennis Erpelding, founder of Global Farm View, and our guest, David Swayne, a veterinarian with specialization in veterinary pathology. For the past 38 years, Dr Swayne has been focused on the control of avian influenza, and that is our topic here today. But, dennis, as we kick things off, I want you to give us an update or an overview of what One Health is. I know some folks here have probably heard about it or may have never heard about it, so let's kind of frame that up what is One Health and what is One Health Live?
Dennis Erpelding:Sarah, thanks, Delighted to be here with you today, with Dr Swayne, who's one of the global experts in avian influenza. So pleased to have David with us this morning. As I look at One Health, we look at it more of an integrated, unifying approach as we think about the optimization of health for people, animals and the ecosystem. It recognizes the health of humans, domestic and wild animals, plants, the wider environment, are closely linked, they're interdependent. So it's taken a collaborative approach that we look at from a local, regional, national and global approach. We want to achieve optimal health outcomes so we acknowledge that interconnection between people, animals, plants and their shared environment. So a very important topic today as we think about the combination of One Health and linking back to avian influenza aspects of it.
Sarah Muirhead:Yeah, avian influenza, I think, is a great example of a One Health issue where the health of animals, the health of people, the health of the ecosystem they're really all intertwined when we take a look at that big picture. So, David, you've been engaged globally and you're a recognized expert on avian influenza. How do you look at avian influenza in the context of One Health?
Dr. David Swayne:Great question. It's actually one that's commonly asked of me and the answer may be more complex than simple, but a lot of it is part of the process of high path AI, or highly pathogenic avian influenza, having changed greatly over the last 30 years, let's say, of my career, and the issue has become one particular lineage. And we track these viruses by their hemagglutinin subtype, and this one's an H5. But there are different virus groupings of these viruses and what has happened is that we've had a change in one particular hemagglutinin that emerged in 1996. Has happened is that we've had a change in one particular hemagglutinin that emerged in 1996. And what makes it so important to One Health is that it has changed so much that it causes infections, disease and death in a diverse number of wild and aquatic birds, as well as in wild and aquatic mammals and even terrestrial mammals, including humans. And because of this multiple species infectivity of the virus, it crosses really all three sectors in this triad of human health animal health and environmental health.
Dennis Erpelding:So, David, as you think about the One Health and you reference on there a little bit, the zoonotic disease concerns obviously come top of mind. As we think about that potential transfer from human to animals Related to AI, can you place that zoonotic concern in perspectives? We think through the last 10 to 20 years, what we've learned and understand about this high path AI that you referenced?
Dr. David Swayne:Yeah, so it's really very, very broad, the zoonotic concerns.
Dr. David Swayne:And you know, maybe we can go back further than that 10 or 20 years, dennis.
Dr. David Swayne:We go back to the 60s, 1960s and 70s, which seems like a long time ago, but really that's where the science emerged to kind of help us understand and explain human zoonotic concerns and the, the pandemics and you know, in a pandemic just means a a huge, uh, human outbreak of sudden occurrence.
Dr. David Swayne:It caused lots of illness and death and we know, mostly from the last century, the word spanish flu, as you know, one of these great zoonotic diseases which really, um, looking at the science from the 50s and the 60s and up into the 70s, shows that really all human influenza A viruses over long periods of time were derived from avian influenza viruses that had moved into a new host and they had changed, either by mutation and the term we use is drift, that means a change genetically in an individual gene and or by what we call reassortment, and that means that the genes that are contained in the influenza A virus have combined between different influenza A viruses to produce a hybrid that's better at surviving in this new host.
Dr. David Swayne:And so really this has happened multiple times in history with H1 and H2s and H3s, h2s and H3s. So far we haven't had a pandemic of H5 or H9, but there is concerns because of the viruses causing these sporadic human infections and it's something for us to keep an eye on and to watch and try to minimize that human exposure to these viruses, to decrease the chances for mutations and reassortment events and kind of keep this virus mainly as an avian virus and not develop ability to do human to human transmission.
Sarah Muirhead:So, David, I mean, we've all followed AI for quite a while and historically, it seems like every I don't know, maybe five years or so it comes to the surface, but now it seems like it's a little more endemic and ongoing. Are there thoughts? I mean, is that an accurate assessment and, if so, why?
Dr. David Swayne:Yeah, I think in general that's a pretty good assessment because today, with this one particular virus lineage, this hemoglobin lineage, which arose in 1996, as scientists we generally call it based upon the first isolate in that lineage and then we track it. From then on it's called Goose-Gwandong-related viruses. It arose in 1996. And, yes, when it first arose it was just like any other high path AI virus. It was mainly infections of domesticated poultry ducks and chickens and turkeys, and there was no wild bird infections. There was no human infections initially, but very quickly that changed and the virus adapted to a wide variety of wild birds and was causing spillover events in humans. And what has happened is it has changed to be able to infect a variety of different species, especially wild bird species. And so you're right, the last five years it seems like it's in the news all the time there's always infections of poultry and wild birds. That's because this virus has changed.
Dr. David Swayne:There is some seasonality to it. So like, if you do, if you look at the actual data on a calendar, you'll see. Oh yeah, there's more.
Dr. David Swayne:In the Northern hemispheres, north America, for example, we have more cases in wild birds generally in the fall. North America, for example, we have more cases in wild birds, generally in the fall. That's because you have all these susceptible juvenile ducks that have hatched out in the northern breeding grounds during the summer and now they're going to migrate southward for their winter living times and they congregate in these big lakes and they exchange their microbial flora, which includes even influenza viruses, and so with this we have a peak in the fall and it drops off kind of late in the winter. It's very low level in the summer and it comes back up. But the last five years, instead of going all the way down to zero, we find that it's actually there kind of bubbling under the surface, sometimes being exposed to resident wild birds Could be our Canada geese that are not migratory, or could be other birds such as predatory birds, buzzards and such the like, and so it's passed even in the summer times among these resident birds.
Dennis Erpelding:So, dave, as we think about the context again of that human zoonotic risk transfer, if I remember back in the early 2000s, specifically in Asia, it seemed like we had a lot of human deaths that were associated with avian influenza back then. Today, as we think about what's going on, we don't see the human death. I think we've had one reference here in the US related to it. Can you give context for why what was happening, let's say, in the early 2000s, when we saw more human deaths and kind of a secondary question is relative to that human-to-human transfer, how high of a risk is that based on our knowledge today? So kind of a two-part question.
Dr. David Swayne:Yeah, okay, we'll see if we can tackle that, maybe in a couple of ways. But yeah, ever since this virus emerged and the first human infections, which were actually 1997 in Hong Kong, the Centers for Disease Control in the US but also the World Health Organization, has been tracking these viruses and they have expert panels that assess these viruses, to kind of put a context on. You know what is the risk of an individual virus strain out of this grouping of viruses of becoming a human pandemic virus, and they kind of help focus attention to particular virus strains so that more research can be done on those or intermission mitigations can be done to kind of reduce the risk for humans. And so, yes, back in the early 2000s there were quite a few human infections, and we're saying probably up between 700 and 800 in Asia, related to human exposure to these viruses from infected poultry. The vast majority of those were actually in the live poultry markets which are very, very common in low and middle income countries in Asia. So you would go to the market and you would buy a chicken or a duck or a goose and it'd be slaughtered in front of you while you're waiting to pick it up. And that process of the slaughtering process aerosolizes virus and you breathe it in, and from that there were human infections and those that were hospitalized. There was a fatality rate between 40 and 60% depending on the country.
Dr. David Swayne:And so, yeah, but what changed in Asia so we see much fewer numbers of these human cases is the implementation of vaccination poultry, which then decreased the number of clinical infected poultry, which decreased the number of chickens or turkeys or other birds that are secreting the virus in the environment, causing this human exposure, and with that the number of human infections and then the fatalities decreased dramatically in Asia. And so I think what you can do is fast forward to today and say, okay, well, asia, because of the heavy vaccination going on in China, vietnam, in Egypt, where most of the cases were occurring back in the 2000s, that vaccination has a direct positive impact on reducing human infections. That's a great thing. So today, most of the cases we have are in countries that either have no vaccination, that are in Asia, such as Cambodia, so they still have infections of people in live market or in the household where they raise poultry, or, like us in the United States now we have some cases that are occupational risk exposures, for example.
Dr. David Swayne:The vast majority.
Dr. David Swayne:I think we're up to about 41 cases in workers on dairy farms that are exposed to infected cattle that they're milking and cleaning up and that process probably generates aerosols and that cleaning process and they breathe that in and cleaning up and that process probably generates aerosols and that cleaning process and they breathe that in and that's how they get infected. Or contact with contaminated milk and touching their eyes or their mouth and mucus membranes and other possible. And then the other big grouping in the United States I think we've had about 23 human cases and these have been in individuals that are working in depopulation crews when we depopulate infected poultry farms and they have a large exposure at that time. Now these are generally healthy individuals so there's no fatalities in them. But there was unfortunately in Louisiana one individual who had backyard poultry that became infected and he or she I'm actually not sure the gender became infected and passed away from that and that's an unfortunate occurrence. They also had other health issues that makes them more susceptible to the lethal effects of this virus, so there's complications in that.
Dr. David Swayne:So I think we can see is that if we can decrease the exposure to humans to this virus from the poultry source and vaccination is one way to do that that also has a positive impact on the human health side, the zoonotic side, by doing an intervention in the agricultural side.
Sarah Muirhead:You mentioned AI in dairy cattle. We've seen it affect some cats and other species. Do you think this is a virus, evolution or just a spread? How do you frame that up?
Dr. David Swayne:That's a great question and I'd have to say that we probably don't have the full knowledge today to completely have the final answer on that question. But if you go back and look in history you can see that the mammary gland cells, the milk-producing cells of the udder, have shown susceptibility to influenza A viruses and this has been shown back in the 1950s and the 60s, up into the 1990s, of infections in cattle by a variety of influenza A viruses, including avian viruses but also swine and human viruses causing infections, the high path H5, that's probably unique that it was the first case this was discovered here in the US and it transmitted from farm to farm, dairy cow to dairy cow. But the susceptibility of those epithelial cells in the mammary gland was already known and established previously to other influenza A viruses. So it's sort of maybe new information because it was a high path virus but it's still an influenza A virus that has shown that susceptibility. But there's also other species of mammals that have been infected. They have been I'll use the word dead-end infections.
Dr. David Swayne:So we have, you know, the United States have had at least one instance of infection in a backyard, a small farm that had a few pigs.
Dr. David Swayne:That was a spillover event from infected poultry on that farm and it was a dead-end infection. Those pigs were put down. There's also been one in alpacas and goats and in the UK and sheep and those were sort of isolated events with infections of just a few animals or one animal. In the case of the pigs, in a very limited scenario, when it didn't pass on to animals within that same species pig to pig it would not have happened. So at least at this point the virus is not highly adapted to other mammals and it appears that only the dairy cattle issue is one we face and you could theorize just based on the information that it was a very rare event that allowed the right kind of exposure in the first dairy cow that allowed the infection. Then it spread from that dairy cow to others and then it spread from that dairy cow to others and then since then there's actually been probably documented three separate instances of the US of transfer from the wild bird reservoir of the H5N1 high path virus into dairy cow.
Dennis Erpelding:So, David, that makes me think, as we think about the species and we think about nomenclature and we think about how we clearly communicate to, let's say, consumers, but also key stakeholders, are there some things we need to think about from a nomenclature standpoint, Because we often say even influenza we've been talking about mammalian, bovine Are we dealing with like an influenza that's highly pathogenic or lowly pathogenic? But observation on nomenclature are there things there that we need from a better clarity standpoint, to communicate about this one?
Dr. David Swayne:Yeah, nomenclature is one of those kind of sticky issues and you have. Maybe there are different perspectives on nomenclature if you talk to different people. I think for myself as a scientist and other scientists we like to have consistent nomenclature and use that.
Dr. David Swayne:And so right now, scientifically we name the viruses and we'll say they're avian influenza, based upon the species of origin for the whole virus and that virus's ability to cause disease. Yeah, and if it moves to a new species, you know, naming it say, for example, bovine influenza virus is kind of a little bit deceptive because the virus was a spillover event to bovine, but it's retained all of its properties as the original avian virus, including its high pathogenicity. So you know, if you're describing it, it's probably more scientifically correct to call it an influenza A virus, which is what it is by classification. Which is what it is by classification. Now you may have within that viruses that are specific for humans, adapted to humans and spread human to human the seasonal flu viruses, the H1 and the H3s that we have, as well as influenza B. We have in swine at least two subtypes, an H1 and an H3, most of the H1N1, but some H1N2s and H3N2s, and those viruses may have an origin decades ago from genes that were in avian influenza viruses. But those viruses now really pass pig to pig and are truly swine unique viruses.
Dr. David Swayne:But they also have exceptions, so that turkeys are susceptible to swine influenza viruses. But when we have a virus that we identify in a turkey of an H1 or H3 that has the genes based on sequencing of swine, we usually call it a swine influenza virus. But they're all influenza A viruses and I think probably in communication, as long as we communicate what kind of virus it is, it's OK, unless we're trying to hide something. And I think that's where nomenclature becomes the sticky wicket, in that if we're going to call a virus based on one species but it's highly susceptible and deadly for another one, say, if you want to call it bovine virus so you can downgrade maybe its risk, it's really not downgrading risk. It's still highly susceptible to birds for poultry and can cause high mortality.
Sarah Muirhead:Now, when we look at these issues. Global international intergovernmental organizations play an important role. Which are the ones that you consider relevant when it comes to AI, and what roles do they have?
Dr. David Swayne:Yeah, so there are several global, international and governmental organizations that do have a role in avian influenza and it crosses basically into the One Health concepts and many of them have maybe a primary focus. But they've had to grow their collaboration between themselves so that these problems can be solved and they can be managed Now for example, probably on the animal health side.
Dr. David Swayne:This is the poultry health side. The world organization for animal health, which is an intergovernmental organization based in paris, and the us is a member. Us department of agriculture animal plant health inspection service is the representative for the us in that organization and they set the standards that are used for trade and disease control for animal health. That's the Terrestrial Animal Health Code of the World Organization for Animal Health and the World Trade Organization uses those guidelines in resolving disputes on trade between countries. We also have the Food and Agriculture Organization of the United Nations, which has a huge role in even influenza.
Dr. David Swayne:That's inter-country, intergovernmental. They work primarily in middle and low-income countries, but they do have engagement of high-income countries because their goal is to help feed the world. And, of course, low and middle income countries have more poverty and they need to work on how to improve agriculture, including animal agriculture, to feed their own people. The final piece is the World Health Organization, based in Geneva, which helps work on global issues that concerns humans, including avian influenza, virus infections of humans and how to control that and how to look at understanding it and helping in solving this complex one health problem.
Dennis Erpelding:So, David, as we think about the international and governmental organizations government, which you've been involved in directly yourself for several decades we often use the word public-private collaboration. How do we see the roles of each of those and how do they be leveraged, based on your perspective and experiences?
Dr. David Swayne:Yeah, that's a great question, Dennis, and for a successful avian influenza control program you have to have a very strong interaction between the public organizations, and that would be generally the government organizations, either at the local, state and national level.
Dr. David Swayne:But we also have to have engagement at the private level, because all of our production is in the private sector, and so that's engaging at the company level, the farm level all the way up to commodity organizations such as in the US we havea National Turkey Federation, egg Producers, the National Chicken Council and other allied organizations that all help promote that commodity and help working out issues in the commodity that are important for us in pricing, production, health, etc. Those are all critical. And so you know you can't really solve a health problem that impacts farms across large geographic areas without having a private industry public interaction, because you can't dictate from the top, from the governmental side, what the farm is going to do and then still be able to produce affordable, high-quality food products for their citizens to use. They have to work together to understand each other's needs and then solve that problem in concert, not in isolation from each other.
Sarah Muirhead:What about final thoughts, David, on avian influenza, One Health, just final things to leave our audience with here today.
Dr. David Swayne:Yeah, I think that One Health has a major role in helping us to solve the avian influenza problem, because it impacts a lot of different individuals in both the wildlife, environmental sector, the animals that we have either as food animals or pet animals and we really haven't talked about cats and dogs, which have also been negatively impacted by avian influenza and then, of course, on the human health side.
Dr. David Swayne:So I think we really have to look at it as not a isolated problem involving just one species. Typically it was agriculture, but, yes, it has ramifications across all parts of our lives and really for us to solve these issues, we have to work together across these sectors, across the aisle, and I'm reminded that when this virus first moved into Central and South America this was in late 2022 and 2023, many of those countries were really caught off guard in being able to solve the problem because they hadn't set up within their countries the ability for cross interactions and communications between, for example, public health and animal health at the governmental level, and they didn't have the same and they had the same issue is they didn't have interactions between the private sector with the governmental agencies too. So those were relationships that had to be developed very quickly in 2022 and 2023 among our Latin American colleagues to be able to solve the high path of the app problem in their own country.
Sarah Muirhead:Dennis, any closing comments from you?
Dennis Erpelding:I first of all want to say thank you to Dr David Swayne, definitely a global health expert that's been very involved and integrated this on a global basis and well-respected. I think he really summarizes that we really need to take that one health holistic approach. We need to collaborate between the public and private sector and through that collaboration we can best address this in a holistic approach where we look at the human, the animal and the environment. And how do we truly optimize this? So I really appreciate Dr Swayne perspective and insights based on his decades of experience in this area.
Sarah Muirhead:Our sincere thanks to Dr David Swayne for this discussion today, for sharing your insight. We truly appreciated that. One Health is an important topic and we look to bring you a lot more discussions in this area as One Health Live rolls out. We hope you enjoyed this inaugural episode. Subscribe today on your favorite podcast channel so you don't miss upcoming episodes. Until next time, have a great day and thank you for listening.