Why is this bird flu outbreak so bad?

What about this strain of avian flu has meant it can be so infectious and fatal to birds?
14 February 2023

Interview with 

Louise Moncla, University of Pennsylvania


A poultry farm


What’s surprising is that H5N1 influenza is not a new kid on the biological block. We’ve known about it for nearly 30 years. So why is it surging so significantly now. As Ed was just saying, poultry farming is critical to the equation here, because it looks like the virus has passed back and forth between wild birds and poultry farm stock, now with devastating effects, as Will Tingle heard from the University of Pennsylvania’s Louise Moncla…

Louise - The first reported case of avian influenza was reported in 1996. So in 1996, geese in Guangdong China came down with this highly pathogenic avian influenza that we now know was an H5N1 influenza virus. This led to a series of outbreaks among domestic poultry in China that then sparked infections in humans. Since that initial introduction event, highly pathogenic avian influenza of the H5 subtype has spread worldwide. And so that brings us to our outbreak that we're having now. The outbreak that we're currently experiencing in North America began in December of 2021. The birds were infected in Newfoundland and Labrador that then has spread throughout North America. The European outbreak began a little bit before that, but this has been ongoing since 2021.

Will - And as you said earlier, the first instance of this ever recorded was in 1995. Why has it then taken so long for avian flu to spread so far with such a devastating impact compared to something like COVID 19, which didn't take nearly as long?

Louise - COVID 19 was able to propagate really, really quickly because it was transmitting really well among people. And humans move around a lot. We're highly, highly interconnected. And so if a virus that infects a person in China can rapidly spread through airline travel across many continents in a very short period of time. Avian influenza is different because predominantly it's sustained by birds, and they on average travel a lot less far. What we think happened is that this initial introduction event in 1996 led to these viruses being introduced into domestic bird poultry populations in China. These then spread outward into Southeast Asia, and then they've spread outward from there into Asia, Africa. And this has happened when these viruses that were circulating in domestic birds got transmitted back into wild birds and then these wild birds because their migratory can spread these viruses very long distances. So what we think is that introduction to these wild birds then allows these viruses to spread into Europe and now into North America.

Will - And there have been outbreaks in the past, but this one is particularly harmful to avian species. What do you think is different about this strain that makes it so much more impactful than the previous ones?

Louise - The thing that has differentiated this outbreak from past ones is that it appears that this virus is much better at replicating and transmitting among wild birds. And that makes it much more challenging to control. The US, in North America as a whole, had a large outbreak a few years ago, and in that outbreak when we saw these outbreaks in domestic bird populations, the country just employed this mass culling approach. So they killed a ton of birds and this stopped transmission. What's different about this outbreak is that despite employing that same protocol, detections keep occurring in domestic birds. And it appears that the reason for that is that this virus is just being transmitted much more efficiently among wild birds. Another thing about this outbreak that is unique is that we're seeing a much larger number of mammal infections. So in past outbreaks we've seen that most of the animals that are infected are these poultry or wild bird species. But in this outbreak we've had this weird number of mammal infections. So we've seen infections in foxes, bears, and a couple of people have been infected. And then of course we had the recent mink outbreak, which was totally unprecedented.

Will - And I'm sure a lot of people have noticed that egg and chicken shortages are starting to appear at supermarkets. But what has been the effect on poultry farms of this spread?

Louise - Highly pathogenic avian influenza is very severe in chickens in particular. And so these chickens who get high path avian flu have very, very severe symptoms. So these chickens will often die really quickly. But as part of outbreak control, when you detect high path avian influenza on these poultry farms, the protocol is generally to cull the entire flock. So the US alone has, I think, culled at least over 50 million poultry just from this outbreak alone. So as you can imagine, all of this culling really impacts the agricultural industry.

Will - Do poultry farms themselves act as a vector or a hotbed of spreading this virus?

Louise - They absolutely do. So chickens in particular have this unique feature where when these highly pathogenic H5N1 viruses are transmitted through chickens, they often acquire this highly pathogenic phenotype. So we think that actually this high pathogenicity phenotype was acquired after these viruses were introduced from wild birds into domestic birds. And so what can happen is that a low pathogenic virus can get into chickens, it can acquire this high pathogenicity phenotype, and it's spilled back into wild birds. So there is transmission going on between wild and domestic birds, and then chickens and domestic birds in general are also clearly important because they're the species that we interact with the most. So most past human infections of H5N1 viruses have been linked to people who directly interact with sick birds, often through the poultry industry.

Will - And not just poultry, or livestock and domesticated animals as well. There's been a massive impact on wild bird species as well, and particularly endangered ones as well have seen themselves quite threatened.

Louise - Yes, this is one of the saddest things about the outbreak in my opinion, is that we've had these widespread outbreaks among these quite charismatic wild birds. So we've had these huge die-offs of cranes and raptor species and pelicans. And so yeah, the integration of high path avian influenza into our American flyways and the impacts on these wild bird species has been really devastating. I mean as a hopeful note, we do have these really wonderful mRNA vaccines that were developed for the SARS COV two pandemic. And I believe that there's some hope that we could deploy these strategies to vaccinate populations, for example, poultry workers or to vaccinate domestic birds or to have ready in case there ever were a human transmissible, H5N1 strain. So that's one bright note.


Add a comment