The Decibel - The pandemic potential of avian flu

Episode Date: May 29, 2023

Avian influenza is getting more serious each year, as an unprecedented number of birds either succumb to the virus or are culled to prevent spread. After a dog in Ontario and thousands of sea lions died from the flu, there’s growing concern about this strain’s ability to infect mammals.Dr. Samira Mubareka is an infectious diseases physician, medical microbiologist and scientist at Sunnybrook Research Institute. She explains what’s going on with avian flu right now, where it could be headed and what we’re doing to stay ahead of it.Questions? Comments? Ideas? Email us at [e-mail]

COVID-19 is no longer a public health emergency, but scientists are always on the lookout for viruses that could become a similar threat. And something that's on their radar is bird flu. The latest strain of avian flu has led to an unprecedented outbreak. 7.6 million birds across Canada have died from the flu or from cullings in the last year. And experts are watching it closely in case it adapts and starts to spread in humans. Dr. Samira Mubaraka studies infectious diseases at Sunnybrook Health Sciences Centre in Toronto. Her research looks at how viruses can transmit between species

and what we should do now to avoid another pandemic. I'm Mainika Raman-Wilms, and this is The Decibel from The Globe and Mail. Samira, thank you so much for joining me today. Thank you for having me, Mainika. I just want to start by asking you, how worried are you about avian flu right now? So I'm certainly more worried than I was this time last year for a number of different reasons. You know, we've had highly pathogenic avian influenza virus outbreaks in the past, but they've been fairly limited, very well controlled. And the virus did not become

established in Canada. Now, since 2021, the virus has become established, unfortunately, in wild birds, so shorebirds, migratory waterfowl, but it's also caused a substantial number of outbreaks. So we've never seen this many outbreaks. And just to be specific, these are outbreaks in domestic poultry. We've not had any outbreaks in humans. But the numbers are substantial. They just to be specific, these are outbreaks in domestic poultry. We've not had any outbreaks in humans. But the numbers are substantial. There are over 300 outbreaks across nine provinces. This has led to the depopulation of over seven and a half million birds. So that in and of itself is concerning. But the other concern that really has come up recently, which is making me even more worried today than I was three months ago, has been the spillover into mammals. So

mammals being, you know, foxes, skunks, those kind of animals. But more recently, as listeners have probably heard, there's been spillover into a domestic dog in Ontario. That's right. There was a dog that died in Ontario. That's correct. There was a dog that died in Ontario. That's correct. And also feral cat as well. Now, again, to be clear and hopefully reassure some of your listeners, you know, in Canada, we've had no infection in humans or among humans, and there hasn't been any sustained human-to-human transmission. But certainly we're observing things about this virus that we hadn't seen before. Okay. And we will talk about the current outbreak,

but I think maybe we should just back up for a moment here. Let's just describe this a little bit. When we're talking about avian flu, what exactly are we talking about? Yeah, so there are a broad range of influenza viruses. And because of their biology, they're more likely to infect avian species or birds versus mammalian species, which include humans, but also a number of other different animals. Now, when you think about avian influenza viruses, some of them have low pathogenicity in birds. And that just means like deadliness or dangerousness, I guess. That's right. So they're less likely to make the bird sick. They can still cause illness, but it'll be less severe

relative to what we call a highly pathogenic avian influenza virus. And again, those are biological features of the virus that lead to more severe disease. And the virus we're talking about now is not only an avian influenza virus, but a highly pathogenic avian influenza virus. And again, the high pathogenicity means that it causes more severe disease in birds. But, you know, when you're thinking about avian influenza viruses, the types that circulate in birds are very different from the ones that circulate in humans on a seasonal basis. And, you know, this is not an uncommon trait for viruses because they are so diverse and they can mutate and adapt to really preferentially infect one species versus another. But again, there's always the possibility of spillover between species.

Okay. Okay. And so let's then come back to the virus that we are seeing today, because as you said, this is something that is a little bit more concerning potentially than we've seen in the past. What is different in the virus today than what we've seen before? So not surprisingly, you know, avian and other influenza viruses, they mutate, they change. Some of those changes are small. Some of them are more substantial. So we call that reassortment, where there are large components of the genome that are exchanged. With this particular virus, it's a genotype that seems to reassort quite readily. So we're seeing even once the virus landed in Canada in late 2021, we've already seen a number of reassortments happen, mainly of the internal genes, but still it shows that the virus is on the move.

Can we think of this as kind of like a mutation? Like we talked about this a lot with COVID-19, the changes in the virus, right? Is this kind of what we're talking about? So it is a gain in viral genomic diversity, but the mechanism is quite different. There are two potential mechanisms with influenza virus that have been most well described. And one of them are point mutations, like you just mentioned. So those are single changes in the genome. But then there are larger pieces of the genome that might be completely exchanged.

And so we're seeing some of that with the internal genes of this H5N1 virus, but we're also seeing those small changes. In addition to that, and what's concerning about the small changes is that some of them reflect mammalian adaptation. So, you know, the sequence of the genome for avian influenza viruses differs somewhat from the ones that typically infect mammals, including humans. And sometimes when you start to see those mammalian adaptations in the avian influenza viruses, that's a signal that the virus is adapting to potentially a new host. Okay, so this virus can spread from birds to mammals. Can it also spread from mammal to mammal? The spread from birds to mammals most likely is through predation. So a lot of the mammals who became infected probably got infected because they ate infected birds. And in the wild, at the moment, there's no clear cut evidence for transmission among mammals,

although we are seeing large die-offs of sea mammals, for example. And we don't know if it's because of a common exposure to the many, many infected seabirds and probably the contaminated environment around them, or if they're transmitting to each other. And when you say sea animals, what animals are we talking about? Sea lions, for example, unfortunately have been significantly affected. And then there was also an outbreak among farmed ferrets in Spain. And again, did they transmit to each other or was there a common exposure? It's fairly difficult to say, but we do know now from some work that was led by federal scientists, both at the Public Health Agency of Canada, but also the Canadian Food Inspection Agency, that experimentally ferret-to-ferret or mammal-to-mammal transmission has been demonstrated in that setting. transmission at this stage, no sustained mammalian transmission, at least for what we'll call

terrestrial animals or mammals, I should say. But still, the possibility exists. What about this virus spreading to humans then? How likely, how easy is that? So clearly, there's been substantial viral activity among avian species, both wild and domestic, but we haven't been seeing spillover to humans with very few exceptions, just the occasional case. So that suggests that there's still a biological barrier to transmission. But again, this is why it's so important to continue to do surveillance and track the virus and look for mutations that might change that bottleneck and that might enable transmission. Ideally, we'd like to pick them up before we start seeing any kind of human-to-human transmission.

Yeah. And then the humans that have been infected, do we know, like, is there a pattern to how they got infected? Well, most of them have been exposed to infected birds. That's been the main mechanism. But they've all had a clear epidemiological link or exposure. So we knew they were dealing with birds or handling birds? Exactly. Yes. What do we know about how this virus plays out for people and how serious it is? You know, that's a really important question. I mean, most of our information is more historical because, you know, this is a fairly new virus. And fortunately, we haven't seen a lot of human disease. There is a bit of a bias in

recognizing cases. So, you know, you find some, it's probably the tip of the iceberg, but the mortality rates, at least in the past with past H5s and other highly pathogenic avian influenza viruses like H7 tend to be quite high. So you'll see numbers of 40%, 50%, 60%. It's like 50% mortality rate we're talking. That's right. But again, bearing in mind that, you know, you're finding the most severe cases. Yeah. Okay. So that's an important distinction then. So, you know, the mortality rate could be around 50%, but we're only measuring people with the most severe cases. We don't know about the less severe cases or maybe even the asymptomatic cases then. That's correct. I mean, that's something we learned with the pandemic, right? The initial

cases that were detected, of course, were the most severe because they're the ones that came to attention. But then as the pandemic unfolded, we started doing broader testing and understanding what natural course of disease was, what proportion of the population was asymptomatic versus mildly symptomatic, as opposed to severely ill. Okay. So at the moment, at least, this virus is mainly affecting birds. So I guess why is it important for us as humans to pay attention to it? Well, a couple of reasons. Number one, we know that from an economic perspective, it's having a substantial impact on the agricultural industry. So of course, you know, there are many knock-on effects to that, obviously immediately relevant to the industry, you know, people's livelihoods, employment, etc.

But then also other knock-on effects like, you know, contributing to the cost of groceries and food, relating to food insecurity, also implications for hunters and indigenous harvesters who might be harvesting wild birds, you know, and the risk of exposure there. So there are substantial implications for human health, both directly and indirectly. I also wonder, though, about, you know, the COVID-19 pandemic probably started in animals, like, should we be paying attention to this because of the potential that this could get bigger and actually affect us in that way? So you're absolutely right in the sense that the next pandemic will likely circulate in animals before humans, right? So if we're more likely to see them in animals before we see them

in humans, we really should be shifting a substantial amount of attention to animal health and also to surveillance, both for biodiversity and also because we know that our health is interconnected with their health as well. We'll be back in a moment. Let's talk about some of the things we can be doing here. So we're faced with this issue. Recently, the U.S. government started testing vaccines for birds. So I want to ask you, could a bird vaccine actually help this outbreak? So there's certainly potential for an avian or bird vaccine to play a role here. It would have to be done in a really thoughtful manner for a number of different

reasons and their implications for trade, for example. And we also need to understand, we need to, first of all, appreciate that, you know, vaccinated poultry could potentially still get infected. Right. We know vaccines are not, you know, it's not the one solution, right? It's a part of it. That's right. That's right. So really need to understand the benefits versus the risks of having or implementing a vaccine program. There's no question that it can't exist in isolation. It would have to come along with surveillance and also many other potential interventions as well, including ongoing biosecurity and biosafety. So it wouldn't really replace the control measures. A lot of the ways we deal with avian flu right now are just to essentially kill the birds that are infected. Why is that the option we're going

to right now? Is this really the best thing at this point in time? Yeah, unfortunately, those measures are necessary, right, just to mitigate the risk, not just to people, but also other premises, you know, around you really want to limit the zones of containment. And not only that, but also you want to limit the possibility that other species like swine, for example, that might either be on the same premise or on nearby farms get infected. So you want to limit that interspecies spillover and also limit the size of the outbreaks. I mean, this is really emphasizing that, you know, what happens in nature is going to affect humans, right? How we can't really separate ourselves from the natural world and what goes on. I mean, it sounds like that's a really important part of understanding what's happening here.

And I think it's important to underscore that the threat here isn't nature. You know, a lot of the drivers and the reasons we're seeing spillover is because of the impact we as humans are having on nature. And just examples of that are things like how we use land, land use, habitat fragmentation, climate change. All of these things will really affect the ecology of the viruses who normally will just circulate in reservoir species. But once you change that dynamic, it gives those viruses opportunities to adapt to humans and ultimately spill over. So I think we need to look at it both ways. Yes, animal health will impact human health,

but we also need to appreciate the role that we're playing as humans on driving that spillover. And so, Samira, when we're talking about this last, the COVID-19 pandemic, are there any lessons that we can take away from our management of that and kind of learn for maybe what comes next? The COVID-19 pandemic, again, the viruses are very different, but there are definitely some principles that are common among a number of different pandemics, regardless of the pathogen. And one thing that we should have learned before, but I think now is another opportunity for improvement, is that the relationships and the systems that become established

between pandemic periods are critical. That's where things kind of stalled and stuttered, is where things were sort of being established and know, established and invented during a crisis. That's really the worst time to be doing that. And that's why I'm a little, I'm heartened by the fact that there were a lot of relationships established during the pandemic. So leveraged from before the pandemic, you know, fortified during the pandemic. But there's still other things around capacity that we haven't learned. So for example, you could probably count on one hand the number of labs in Canada that can work on highly pathogenic avian influenza viruses.

So that means that there are very few people who are skilled and trained to do that work. So now is the time to train the workforce to ensure that the tools are in place so that if we do need to start rapidly developing vaccines and diagnostics, in fact, we should just be doing that now, you know, rather than wait for a spillover to happen. So we've made some progress, but I don't think we fully implemented the lessons that we learned from the pandemic. How hopeful are you that we can actually get there, though, and implement those things before the next one rolls around? I'm an optimist, a cautious optimist. You know, the cycle of panic and neglect is a chronic cycle in infectious diseases. So I think if we make sure that now that we've trained, now that we've acquired all this capacity, we need to really keep it maintained. We've emphasized capacity a lot on the human health side. I would say we should be

putting as much, maybe even more effort and focus on doing it on the animal side, because in Canada, it is a little bit siloed, you know, particularly wildlife health has been under-resourced for a very long time, and I think that needs to change. Samira, thank you so much for taking the time to speak with me today. Thank you so much, Mainika.

That's it for today. I'm Mainika Raman-Wilms. Our producers are Madeline White, Cheryl Sutherland, and Rachel Levy-McLaughlin. David Crosby edits the show. Adrian Cheung is our senior producer, and Angela Pachenza is our executive editor. Thanks so much for listening, and I'll talk to you tomorrow.