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The Dose Transcript for December 12, 2024

Host: Dr. Brian Goldman

BRIAN GOLDMAN: Hi, I'm Dr. Brian Goldman. Welcome to The Dose. There have been several developments lately regarding H5N1, also known as avian flu. As you may know, the virus was first detected on U.S. dairy farms in March 2024. As of the afternoon of December 11th, the virus has shown up at hundreds of dairy herds across 16 states. Late last week, the U.S. Department of Agriculture said it will begin testing raw milk from dairy silos across the nation. The virus has also been showing up more frequently in wastewater in the U.S. Close to 60 human cases of H5N1 have been reported across seven U.S. states. Here in Canada, in November, B.C. health officials confirmed that a teenager was in critical condition after getting infected with H5N1, though it's still not clear how the teen caught the virus. A study published earlier this month in the journal Science suggests that H5N1 might be a single mutation away from being able to spread rapidly from person to person. So this week we're asking: How concerned should I be about H5N1 here in Canada and elsewhere? Hi, Lynora. Welcome back to The Dose.

LYNORA SAXINGER: Thanks for having me again.

BRIAN GOLDMAN: So how closely are you following the H5N1 story right now?

LYNORA SAXINGER: I would say that, like a lot of ID people, we're watching this with a fair amount of attention. Like it's not panic level, but it is definitely sustained attention deserving. Because it's been quite a kind of news item, hasn't it, with all the different food animal production issues coming through. And the fact that, you know, even in the avian outbreaks increasing over the last couple of years, it definitely is something that's very active. And we would, of course, be very concerned if it should reach pandemic potential.

BRIAN GOLDMAN: Which is why we're glad that you're keeping a close eye on it. But before we begin our conversation, can you give us a hi, my name is? Tell us what you do and where you do it.

LYNORA SAXINGER: Sure. Hi, I'm Dr. Lynora Saxinger. I'm an infectious diseases specialist at the University of Alberta.

BRIAN GOLDMAN: Okay, let's begin with the situation in Canada, where a teen infected with H5N1 is admitted to a critical care unit in British Columbia. What do we know about how that particular patient's doing?

LYNORA SAXINGER: I haven't had any clinical updates. Last I'd understood that they were still extremely ill. Having said that, I mean, usually in that kind of an illness, in the acute phase is when you would start to see people, you know, passing away from the infection, and then the prolonged phase is dealing with hospital complications. So hopefully they are recovering. And it's an interesting case because also, as far as I understood, they hadn't really determined what the source of that infection was yet. Although the strain seemed not to be the same strain as the strain being found in dairy cattle.

BRIAN GOLDMAN: That's what the Canadian Food Inspection Agency has said. So we don't know how the teenager actually caught the virus.

LYNORA SAXINGER: Yeah, so it looks like it might be more compatible with one of the wild bird strains. And so it could have been, you know, an animal exposure of some kind. And that's one of the things that makes this a bit challenging, is that H5N1 seems to be quite talented at infecting a pretty wide range of animals. Even like a pet dog was infected, probably from picking up dead birds. And so anything that is exposed to birds and could maybe eat birds is a potential host for this infection. And so as physicians, when we're taking a history about, you know, exposures, we actually have to cast a pretty broad net in terms of the exposure history for this kind of virus. And I don't think that's necessarily, like, the natural thing that we're doing right now.

BRIAN GOLDMAN: Let's turn to the United States where I think we know a lot more. What is the latest on the bird flu variant circulating in the United States?

LYNORA SAXINGER: It seems to be pretty much the same thing across all the cattle herds. And also the human cases are very dominantly two different types of people. Mostly people who have been exposed to infected cattle, and also people who have been exposed to infected chickens. And so it really is mostly pretty defined exposures where it's someone who's a food animal production worker of some kind or someone who's had direct contact. There's only a couple of cases in the U.S. that don't seem to have that kind of an exposure history, as currently reported.

BRIAN GOLDMAN: So, you know, when we hear that several dozen, you know, 60, more or less... you know, we have to be cognizant of the fact that the numbers can change with a story that's changing as rapidly as this one. It doesn't seem like a lot of human cases, but it's possible that there's lots of people who've been infected who aren't diagnosed with H5N1. Am I right?

LYNORA SAXINGER: Yeah. And I mean, there was a bit of a hint of that when they did some of the outbreak, I think, tracing. They did serologic testing to see if they've been previously exposed. And so these people hadn't come to medical attention with an acute illness, but then were found to have had evidence of a prior infection. And so there might be more widespread infection in people than we think. And so a big part of this is going to be making sure everyone who's, you know, in that industry, dealing with the animals face to face so to speak, or milk to face, which is I think the bigger issue, are really very aware of the need to be monitoring themselves very closely and get tested. Because the concern, of course, is if the virus adapts to a new host and mutates such that it's able to spread person to person, it would be a big deal. So far, you're right. I mean, there's like a lot of virus in these settings, and not that many people have been diagnosed with infection. So, so far, it doesn't seem to be favouring spread in humans at all. And, you know, even officially worldwide they haven't highlighted that as a current concern. It's just like how many steps would it take, and would we be ready.

BRIAN GOLDMAN: How unusual is it for H5N1 to infect dairy cattle?

LYNORA SAXINGER: I was surprised, but I guess there was a hint of this before. Because there had been a little bit of animal work done showing that the virus could infect mammary tissue and be passed in milk before. And that had not really been, I think, part of the common thinking. And so, you know, we expect that wild birds -- who don't always get super sick with it but may die from it -- can carry it, so they can be carriers or also become ill. And then they infect domestic poultry flocks. And then it comes to attention because there's these mass die-offs and culling and stuff like that. And so that move was a bit of a surprise to me personally anyways. But it does illustrate again that this particular strain is quite adept at infecting quite a wide range of species. And the cattle spread I think is thought to possibly be related to, um, basically spread kind of cattle to cattle through the milking machines potentially. Because there's a lot of virus in milk. And for the people who are exposed, there's also concern that some of it could be exposure to like mucous membranes or inhalation of droplets related to the milk itself as well. So it is a bit of a surprise to me. That's not something that I think we've really heard talked about before.

BRIAN GOLDMAN: The U.S. Centers for Disease Control and Prevention has detected bird flu in wastewater in California. What does that tell us?

LYNORA SAXINGER: You know, and wastewater's so interesting because it's hard to quantify how much is there. Because when you're doing molecular testing, you can find very trace amounts. And the wastewater systems in general can also collect agricultural run-off depending on where they're sampling from. And so it's a little unclear to me whether we're saying that the wastewater is due to human infection or due to animal infection. But California has been quite hard hit with the H5N1 in cattle. Like a lot of the activity is there and quite a lot of the cases have been there. And so I think that it just tells us that there's a lot of H5N1 around. And of course, California is also a place where I think the raw milk industry has been quite popular. I know you'd done a piece on that not that long ago. And so raw milk is kind of a, I guess, a trend. And that's concerning because the milk, when unpasteurized especially, can carry quite a lot of virus. So I think that that is a pretty active area to keep an eye on.

BRIAN GOLDMAN: And we know that of the 700 or so or more dairy farms that have tested positive for H5N1 across the United States, something like 500 of them are from California. So California is a major locus for the dairy farm industry and is being very hard hit by H5N1 at the present time.

LYNORA SAXINGER: Yeah, and we're probably going to find now that the testing is, I think, going to become more standardized, we might find that there's more extensive spread than we'd anticipated in places that might not have been testing as much as well. So I think, you know, we might be looking at a tip of the iceberg situation with the cattle industry. Cattle who become sick with this don't usually die and they're not usually culled, but it can suppress their milk production for quite a while. And so that can affect consumer dairy prices as well if it becomes very widespread. You know, so there's all sorts of different levels of issues with these viruses.

BRIAN GOLDMAN: How robust is the bird flu surveillance system in Canada?

LYNORA SAXINGER: You know, I think like all Canadian surveillance, there's a fair amount of variability across the country. And there has been a specific effort set up to standardize that. And for a long time I think most of the testing was done for cause. Like there'd be a wild animal die-off, they'd be tested. Now I think they're doing more routine surveillance, and had done some surveillance suggesting that it's not on Canadian dairy farms as yet. And so there's always a possibility of new introductions into different animal species and adjacency, and then, you know, establishing infection within a particular, for example, herd or flock. And so I think that there has to be very careful attention. It's actually easier to detect avian flu in avians, especially poultry, because they become so sick. Whereas for other species it might not be as obvious and they might be more scattered. So I think that intensifying the human-animal interface surveillance is something that's incredibly important for all viruses. Like even looking back to SARS-CoV-2.

BRIAN GOLDMAN: I mentioned in my introduction a study, which I want to talk about right now. Scientists at Scripps Research Institute in California published an article in Science detailing how a single mutation could allow the bird flu, the H5N1, infecting U.S. cattle to infect humans. How concerned were you by that study?

LYNORA SAXINGER: When you say it like that, it sounds pretty terrible. But at the same time, we've had widespread avian influenza circulating the globe for a couple of years, and it's not necessarily that easy to gain a specific mutation. Influenza most commonly sort of shifts and drifts, right? So there's smaller mutations that makes it adapt more slowly. It is the reason that we keep on getting an epidemic of influenza every single year. And then, you know, in previous times in history, it's always been a reassortment event with different virus strains from different animals co-mixing probably in a single species or animal, and then being a more new thing. And so of course it's concerning, but it wouldn't necessarily fit the most common pattern for it to do that. So, you know, hope springs eternal. We're sick of pandemics.

BRIAN GOLDMAN: Absolutely. The impression I've got is that there hasn't been much person-to-person transmission of avian flu at the present time. Am I right about that?

LYNORA SAXINGER: You are right about that. So, you know, there's not been any well-documented human-to-human transmission of this H5N1 that we're talking about. Most of the avian influenza, before we started seeing all this food animal involvement, has been extremely rare, usually like little kids who got entangled with backyard chickens, you know, and would get really, really sick, sometimes with, you know, a really high mortality rate. And that's not at all what we're seeing now. We're seeing fairly mild infections in the people who are affected so far. So it is behaving differently. Even in those settings, I think that any time they've wondered about person-to-person transmission, there's also been a possibility that it was a source-to-person transmission. So it's not been well documented as an occurrence in the avian flu cases in humans.

BRIAN GOLDMAN: What would you be watching for right now to change your mind about that, to make you think that there is person-to-person transmission?

LYNORA SAXINGER: One interesting thing is it might be just the mode of transmission that's occurring with the people who are in the food animal industry. But they sometimes appear to have fairly minimal symptoms. Like actually conjunctivitis is a big one, which isn't what we usually think about for influenza. And then sometimes respiratory symptoms or upper respiratory symptoms. If you don't have respiratory symptoms, you're not as likely to carry a lot of virus and you're not likely to spread it. Like people don't usually touch eyeball to eyeball. And so the thing that would change my mind is if they were doing expanded serosurveillance of people who were exposed to people who'd been demonstrated to have infection and found household contacts had been infected. I think that would be a notable finding that would make me pay a lot of attention. Public health is really pretty cautious about looking at these cases and assessing for signs of secondary spread, and really trying to investigate broadly to see if there is signs of secondary spread. So far so good, but, you know, that kind of attention is going to have to be sustained, because if we were starting to see that, I think it would actually have to change, you know, national-level planning about what might happen.

BRIAN GOLDMAN: So the big thing that you'd be looking for as an indication of person-to-person spread would be spread amongst close household contacts.

LYNORA SAXINGER: Yep. That would be the place that you would look.

BRIAN GOLDMAN: So we've seen some patients who have been infected with H5N1 currently have respiratory symptoms -- you know, cough, shortness of breath, fever, chills, the usual kinds of flu-like symptoms. You mentioned that some have had, or a surprising number have had conjunctivitis or pink eye. What's going on there? Why is that happening?

LYNORA SAXINGER: Well, I think a theory, at least, is that if people are exposed through kind of facial exposure to milk splash or droplets, that it might be just direct inoculation to the eyes. In which case, you know, workers in that setting wearing goggles would make a lot of sense. That can be a bit unpopular, but I still think it would be -- at least a face shield -- would be a really good intervention to consider. Because otherwise it's a little hard to tell why you'd have conjunctivitis as a dominant symptom. I understand in the B.C. case as well, that the young person had presented with conjunctivitis initially, but it kind of fairly quickly moved to a severe respiratory infection, which certainly has not been the case with the strains in the U.S.

BRIAN GOLDMAN: We had another guest on talking about H5N1 previously, who mentioned that the mortality rate from H5N1 could be as high as 50%. Now, I mean, my first thought is that the sample size is so small. You know, there's just such a small number of human beings who've been infected that it would be misleading to try to come up with a mortality rate, let alone that it's 50%. But that sure sounds worrisome.

LYNORA SAXINGER: Yeah. And I think that that number is... I mean, that's the number. That's what's quoted. And that applies to usually H5N1 and other strains of avian influenza. When they do infect people, it can be more severe. And that's been what's classically been seen in the small number of cases that have been reported. That 50% does not seem to be applying to the strain that's becoming more widespread in North America so far. So it does seem to be behaving somewhat differently in that regard. And whether it's just the actual strain of the virus itself or whether it's the mode of transmission not involving like an inhalation event from infected poultry, maybe that's the difference. It's not clear. But, you know, we're not seeing a 50% mortality rate in the U.S. cases. I don't think any of the reported U.S. cases actually have died. And many of them had subclinical infection, so very mild infection.

BRIAN GOLDMAN: Well, that's certainly at least somewhat reassuring. But again, the sample size is very, very small. We heard recently that the U.K. is going to be contracting with local vaccine manufacturers in the U.K. to purchase up to five million doses of avian flu vaccine. How effective will avian flu vaccine be against H5N1?

LYNORA SAXINGER: You know, it's always a bit of a gamble when you're pre-buying an influenza vaccine because of the strain changes. And that's why, of course, we only have, you know, our seasonal. Flu vaccines are manufactured based on the recent circulation and giving enough time to make them and ship them. And so it's usually a very in-the-moment process for these vaccines. But, you know, there is some reassuring work that would suggest that, you know, using current strains should provide some cross-protection, even if there was some shift in the virus. And so I think that's why they're going ahead with it. And I'm-- I actually think that a lot of the avian influenza vaccine interest is specifically looking at targeting people who are working in settings that are at risk, like in food animal production and dairies. Not necessarily for the general public, but then having doses available for, you know, risk-based vaccination strategies if needed. And there's also been some development work on getting mRNA vaccine against these strains. And of course, mRNA vaccines, now we have quite a polished pipeline for making those and updating them, and it can be quite responsive as well. So I think a lot of countries are looking at doing mRNA vaccination strategies for avian influenza.

BRIAN GOLDMAN: Has Canada acquired or is Canada planning on acquiring vaccine?

LYNORA SAXINGER: I'm not on the inner circle of that, but my understanding is that there are some kind of basically provisional approvals already in place for avian flu vaccines. I don't know if contracts have actually been signed yet, but it's definitely something that is under active review, I would have to say.

BRIAN GOLDMAN: And finally, winter and the holidays are almost upon us. H5N1, thankfully, likely won't be circulating among us, but other respiratory viruses will. What are the common sense recommendations as we gather more indoors?

LYNORA SAXINGER: Well, I mean, all of the viruses now. Of course we have COVID, which still remains more severe than influenza. Influenza, which is severe for a proportion of people every single year. And the things that we've learned still work. So, you know, if you're sick, don't expose yourself to others. People who are at high risk should be tested because if you're at high risk and you're tested and you're found to have COVID or influenza, you might be eligible for treatment. And, you know, masking and paying attention to ventilation, especially if anyone might be ill or has been recently exposed to someone who's ill, would make a lot of sense. And so those things are always a really useful consideration when we're looking at gathering in the current times. If you are exposed to any ill animals and you became sick, you would want to mention that exposure. The current lab testing will pick up these strains, but not necessarily right away. So they'll usually try to type it as one of the current H3N2 or H1N1 strains first. And then if that typing doesn't work, they would go on to do further testing. But mentioning that you've had an animal exposure, especially an exposure to a sick animal, would make that testing a step faster, which could become important at some point. Hopefully it won't be, but it could become important at some point to try to rapidly find any cases of novel influenza.

BRIAN GOLDMAN: That is an incredibly practical piece of advice. Dr. Lynora Saxinger, as usual, you're knowledgeable and practical, and I want to thank you for coming on The Dose to talk about avian flu.

LYNORA SAXINGER: Thanks very much for having me.

BRIAN GOLDMAN: Dr. Lynora Saxinger is an infectious diseases specialist with the University of Alberta. Here's your dose of smart advice. H5N1 is a subtype of avian influenza that mainly infects birds but has been identified in other animals and has caused sporadic infections in humans. Current or recent outbreaks have been detected in domestic and wild birds and some mammals across Canada, the U.S., Europe, as well as Central and South America. As of the afternoon of December 11th, 774 dairy herds have tested positive for H5N1 across 16 U.S. states. The virus has also been showing up more frequently in wastewater in the U.S. Close to 60 human cases of H5N1 have been reported across seven U.S. states in the past few months. A B.C. teen was infected with H5N1, but there's no evidence it's the same strain that has infected U.S. dairy farms. The virus mainly affects the respiratory tract, but can also cause gastrointestinal symptoms like nausea, vomiting or diarrhea as well as headaches. Doctors say conjunctivitis or inflammation of the inner lining of the eyelids also appears to be a common symptom at present. H5N1 infection can progress to severe illness and death. At present, there is no evidence that the current strains of H5N1 can spread from person to person. However, that could change fairly readily should the virus mutate. Antiviral medications that are readily available can be prescribed to treat H5N1. However, there have been no clinical trials measuring their effectiveness against current strains of avian flu affecting humans. There is no H5N1 influenza vaccine available in Canada for public use. Recently, the U.K. ordered more than five million doses of a vaccine based on H5 avian flu from a local vaccine manufacturer as part of its pandemic mitigation strategy. As we gather indoors during winter and the holidays, remember the basics of infection control. Wash hands, wear a mask, and if sick, avoid indoor gatherings. Tell your health care provider if you fall ill after exposure to farm animals. If you have topics you'd like discussed or questions answered, our email address is thedose@cbc.ca. If you liked this episode, please give us a rating and review wherever you get your podcasts. This edition of The Dose was produced by Sameer Chhaabra and Prapti Bamaniya. Our senior producer is Colleen Ross. The Dose wants you to be better informed about your health. If you're looking for medical advice, see your health-care provider. I'm Dr. Brian Goldman. Until your next dose.

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How concerned should I be about avian flu? - Transcript

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