H5N1 cases in birds are expected to rise in the coming weeks as migratory species wing their way across the planet. Veterinary epidemiologist Victoria Hall explains why this outbreak is different – and what it could mean for humans.
A record outbreak of avian flu has been devastating poultry farms and birds that flock together on shorelines since 2021, raising new concerns that the virus could become endemic in wild birds. There have already been reports of spillover to other species, including foxes in England, grizzly bears in the US and farmed mink in Spain. And an 11-year-old girl in Cambodia died from an avian flu infection. All of this is stoking fears that we may be on the verge of another pandemic should this virus adapt to more easily infect humans.
With billions of migratory birds now taking flight from their southern wintering grounds to make cross-globe journeys, experts are bracing for a fresh wave of infections.
“This year’s outbreak is causing severe illness and death in much larger numbers than we’ve seen in the past,” says Autumn-Lynn Harrison at the Smithsonian Migratory Bird Center in Washington DC. “Although bird flu has had a series of outbreaks in the past, wild birds are typically asymptomatic – they don’t usually show these high numbers of symptoms or even death.”
Last summer, Harrison was working with shorebirds in Alaska called parasitic jaegers (Stercorarius parasiticus) and Arctic terns (sterna paradisaea) – two of the world’s furthest-migrating species, which travel from the Arctic circle down to South America and Antarctica every year. At her field site, dead birds from both species tested positive for avian flu, or H5N1. “It was the first time I saw some of these predatory seabirds just as random carcasses on the tundra,” says Harrison. She tagged some of the live birds with satellite trackers and followed their fall journey to Peru, where more than 3500 sea lions have died of avian flu this winter. “The effect is global at the moment,” says Harrison.
To learn more about how long this avian flu outbreak will last, how worried we should be about the spillover to mammals and whether it has the potential to become the next pandemic in humans, we spoke to veterinary epidemiologist Victoria Hall. She has expertise in studying ecosystem health, was previously an epidemic surveillance officer for the US Centers for Disease Control and Prevention and is now director of The Raptor Center at the University of Minnesota.
Corryn Wetzel: Avian flu has been around for decades – why are we seeing an outbreak now?
Victoria Hall: The current virus strain that’s been circulating has been acting very differently than past outbreaks. It is infecting way more wild birds than we typically see. And we’re seeing it spill over into bird species that are much more likely to get sick and or die. It’s incredibly devastating and expensive when it gets into poultry operations.
And this outbreak is remarkable because it’s lasting migratory season after migratory season. Often when we see an outbreak, we’ll see [avian flu] get into the poultry operations in an area, and it causes an outbreak for that season, but then it kind of goes away. But with this strain, we’re seeing it being sustained in wild bird populations.
How is avian flu sustained and spread by migratory birds?
Avian influenza circulates the world in migratory birds. There are a lot of species – we think primarily shorebirds, seabirds and waterfowl – that often can carry different strains of avian influenza without showing signs of illness. And they mix strains as they all gather together in migratory groups, and then they take off again and spread it.
Raptors, eagles, hawks, owls and vultures are birds that are very prone to getting very outwardly sick and potentially dying. Poultry – domestic chickens and turkeys – are very prone to getting very sick and dying if they catch it. The virus attacks their brains, and it causes seizing, vocalising and being unable to stand. Birds are lying on their back or just completely non-responsive.
Did you see an increase in sick birds last spring?
We had a huge surge [of infections] in April and May of last year – just astronomical. It really mirrored what was being seen in the poultry industry. We were seeing three to four times as many birds come in last spring as we normally receive, and some days up to 60 to 70 per cent of them had flu.
We saw 213 positive-testing birds in 2022 that came to our centre. Only one survived – a great horned owl. We were just bringing in sick bird after sick bird, and it was just emotionally shredding.
We’re expecting in the next couple of weeks to start seeing cases go back up here as migratory birds come back through.
How does the virus jump to other animals?
For this virus, we think that the majority of transmission is probably by fomites – infected virus particles that get on things. So, anything coming out of the mouth or the cloaca – both ends of an infected bird – is going to be packed full of the virus.
This virus can live for weeks in a cool, damp environment. Then other animals can get it on them [and become infected]. Animals can also get infected after eating a bird with the virus.
We’re now seeing avian flu spill over into mammals in numbers that we’ve never seen before, which would make sense because a lot more wild birds are shedding the virus, and there are opportunities now for it to jump into mammals. We’re seeing raccoons and bears and foxes and even seals and dolphins getting infected with avian influenza right now.
Are humans at risk?
There are cases [of humans contracting the virus] around the world and there have been some deaths associated with the strain as well. But it does not appear that it’s easily transmissible to people, which is great.
Infections can happen when a person spends a lot of time with an infected bird in very close proximity. We think about people that are in close contact with infected poultry, not so much the birds outside your window.
But we know everything about this flu until tomorrow comes because it’s an influenza virus – it can continue to change and mutate.
What can we do to limit the spread?
With migratory birds, the biggest thing the public can do is help us collect information on what’s happening out there in the environment. When there are sick birds, use wildlife rehabilitators or your department of natural resources in your state to get help for that bird. If you see dead birds out there, report it to your state officials.
If you must interact with a sick or dead bird, make sure that you’re using gloves, you’re using a mask to protect yourself, you’re disposing of [the bird] in a manner that’s safe so that you’re not causing any spread of that virus.
It’s also just about spreading that word: we’ve got this virus that’s happening in the poultry world, but it’s in our wild bird species, too.
Can we vaccinate birds?
Vaccines are a hot topic right now – I feel like everyone who has birds of any sort is ready for some vaccines. We would want to make sure it’s just like our seasonal flu vaccine, where it matches exactly what’s circulating or it’s not as effective. And we’ve got so many different species of birds. If we have a vaccine that’s been validated in poultry, what is it going to do in an eagle that lives 30 years versus a chicken that you don’t anticipate to live that long? So, it would be quite a process before you could start doing things like vaccinating birds.
There’s a lot of talk about using vaccines for critically endangered species, where every single bird really matters to that population because their numbers are so low. But [vaccinating birds] would be a long process. [Though avian influenza vaccines exist], they are regulated on a federal level, so it’s not something that you could just go buy from the store.
How long will this last?
Usually, people prepare for an outbreak, respond to the outbreak for a set of months and then recover. But this one’s not stopping. We saw this with covid, too. We do a huge response initially, and then you’re like, “Oh, we have to manage this long term.” That might mean changing our protocols, looking at how we’re using testing and looking at how we’re using personal protective equipment.
Whether you’re in agriculture, or whether you’re in wildlife, people are having to change their mindset from just an acute response to living with this for, potentially, years. I don’t expect it to go anywhere anytime soon.