The Science of Birds - Avian Flu

Episode Date: June 12, 2022

This episode—which is Number 53—is all about Avian Influenza. Or colloquially what we call the Avian Flu or Bird Flu.Depending on where you live, you might have noticed news headlines in recent months about the frightening spread of Avian Flu among both domestic and wild birds. I thought you might have some questions about this emerging disease, and so here we are with an entire podcast episode on the subject.~~ Leave me a review using Podchaser ~~Links of InterestCurrent U.S. Bird Flu Situation in HumansLink to this episode on the Science of Birds websiteSupport the show

Hello and welcome. This is the Science of Birds. I am your host, Ivan Philipson. The Science of Birds podcast is a lighthearted, guided exploration of bird biology for lifelong learners. This episode, which is number 53, is all about avian influenza, or colloquially what we call the avian flu, or what kids on the school playground call bird flu. Depending on where you live, you might have noticed news headlines in recent months about the frightening spread of avian flu among both domestic and wild birds.

I thought you might have some questions about this emerging disease, and so here we are with an entire podcast episode on the subject. I should tell you up front that I'm not an expert on avian diseases or anything. He said he's an expert. No, no, I said I'm not an expert. Not an expert. No, I'm just a dude. A dude with a podcast, a PhD in zoology, and a passion for birds. To research this episode, I pulled together notes from a bunch of online sources. I'm doing my best here to summarize a lot of information so that it's easily digestible. That's one thing I love about creating these podcast episodes.

And one thing I love about studying birds. By diving into the biology of birds, we get carried down many diverging and interesting paths. We end up learning things about the wider natural world along the way. Today, our interest in birds is taking us down a path leading into the world of viruses, outbreaks, and pandemics. Naturally, you might expect this episode to be riddled with lots of jokes and silliness. I mean, death and disease are always good for a laugh, wouldn't you say? Hilarious stuff.

Yeah, I know. Not so much, actually. This topic isn't necessarily a gold mine for comedic material. I'll do what I can to keep the light-hearted tone that you've come to expect on the Science of Birds podcast. However, our discussion today may not be as upbeat and LOL-inducing as usual. But stick with me, my friend, because this is important stuff to understand. Let's start with with a little bit. a quick overview of viruses in general. After the last couple years, we should all feel like

experts on viruses, right? But just as a refresher, let's think about what a virus actually is. A virus is a tiny bundle of organic molecules that infects the cells of organisms and then reproduces inside those host cells. I hesitate to call viruses themselves, because biologists are still debating whether viruses are actually alive. By most definitions of life, however, viruses are not alive. In any case, viruses are definitely not made of cells. Bacteria, on the other hand, are made of cells. Each individual bacterium is a single cell. But viruses are much simpler than that. A virus is only about one one hundredth the size. size of a bacterial cell. Pretty much every virus is made of two key components, a crunchy outer

shell made of protein molecules and a creamy filling of genetic material, either DNA or RNA. Those shell molecules have several functions, like protecting the genetic material inside, interacting with the host cell, and injecting the genetic material into the host cell. The genetic material provides the all-important instruction manual for how to build more viruses. Once the DNA or RNA has been injected into an unfortunate host cell, the viral genes get to work. They hijack the machinery inside the host cell to crank out new copies of the virus. The newly assembled viruses eventually burst out of their host cell, often killing it in the process. then the adorable baby viruses head off into the world.

Each is full of wide-eyed innocence and optimism as they seek their own host cells to infect. Precocious little buggers. Viruses have probably been doing this sort of thing since the earliest cellular life evolved on Earth, about three and a half billion years ago. Today, viruses are found in every habitat you can think of, and there are thousands,

or maybe even millions of types of virus out there. But right now, we are interested in the influenza viruses. There are four quote-unquote species of influenza virus. A, B, C, and you guessed it, D. The A-type species is the bad boy of the bunch, the one most responsible for causing sickness in birds and mammals. But it's most strongly associated with birds. birds. Influenza A viruses hang out in the cells of birds, and then occasionally some

will bounce over to infect unsuspecting mammals like pigs, horses, or humans. Influenza A viruses of one strain or another are the ones that circulate every year among humans, causing the flu. Now, you might be trying to imagine what these viruses look like. An influenza virus is usually shaped like a ball. It's more or less spherical. The ball has many spikes sticking out in all directions from its surface. Each of the maybe 500 spikes on a single virus is made of one of two different types of protein, hemaglutinin or neuraminidase. Their functions are to bind the virus to the host cell, and later to help release the progeny viruses from the host cell. Influenza viruses can sometimes do all of their infecting and replicating without causing sickness in the host.

Symptoms and severity of the infection vary from one influenza strain to another, and also from one individual host organism to another. Some birds or other animals show zero symptoms, while their next door neighbors might get so sick that they die within a few days. When a bird or person has the flu, their symptoms are caused not only by the destruction of their cells by the virus, but also by the response of their own immune system. In fact, the latter is what usually causes the worst symptoms. Let's dig deeper into the biology of how able to be able to do. Influenza works. The avian influenza virus is of the A type or species, but we can divide our type A viruses further into subtypes of avian influenza. First, there are two major subtypes

based on their potential for causing disease. In other words, their pathogenicity. One subtype has low pathogenicity and the other has high pathogenicity. Low pathogenicity avian influenza has been circulating in populations of many bird species probably for millions of years. Birds infected with this subtype rarely get very sick, if they get sick at all. But highly pathogenic avian influenza, HPAI, is another story. Some strains of this type cause major flu outbreak. of sickness and death in bird populations. I should point out, though, that the terms of high and low pathogenicity are mostly in reference to

how the virus affects domestic poultry flocks, rather than wild birds. If a virus strain causes lots of deaths among domestic chickens, for example, it gets labeled highly pathogenic. So we have two major subtypes, one that doesn't cause much trouble, and the other one that causes heaps of trouble. Biologists have also subdivided the viruses further, based on the proteins bristling on their outer shells. Remember those spikes?

Some of them are made of hemaglutininin protein. We'll just call that H. And the other spikes are made of neuraminidase protein, which we call N. There are several flavors or forms of both the H and the N protein. Avian influenza strains can have different combinations of these H and N flavors. For example, you might have a strain with an H2 combined with N7, or an H1 and an N1.

What's that spell? H1N1. Does that sound familiar? H1N1. A strain of H1N1 avian influenza caused, the terrible Spanish flu pandemic of 1918. In the century since then, H1N1 strains have reared their ugly heads every so often, causing other major outbreaks around the world.

Anyway, that's where the H&N and their associated numbers come from in the names of avian flu strains. Only a handful of these strains have actually infected humans. Among birds, avian influenza is spread. from infected to healthy individuals through contact with secretions from the eyes, nostrils, and mouth. But bird poop is one of the most effective ways that the disease spreads. Avian influenza is naturally at home in the water. So when an aquatic bird leaves some droppings in a lake or wetland, the virus is easily transmitted to other birds floating around

in that same water body. The viruses can survive up to several months in cool water, lying in wait for some birds to infect. What types of birds carry avian influenza viruses, and which are the most susceptible to getting sick from the viruses? Waterfowl and shorebirds are well known as carriers of avian influenza. These are birds of the biological orders and seriformis and caradreiformis, respectively. We're talking about ducks, geese, sandpipers, plovers, gulls, and those sorts of critters.

Birds like these are the natural hosts, the natural reservoirs for avian influenza viruses. They can carry both low and high pathogenicity viruses. Ducks and geese, in particular, can carry some. some wicked virus strains without showing any symptoms without getting sick. They flap around from one pond to the next, unwittingly spreading the disease across the land. Dabbling ducks like mallards have acted like super spreaders in some outbreaks. It goes without saying that waterfowl and shorebirds spend a lot of time in water, which, of course,

means they're pooping in the water and leaving countless viruses behind in their wake. And many of these same birds are highly migratory. They can literally transport avian influenza from one side of the world to another in just a few weeks or months. Once upon a time, in the pre-industrial days, it seems that avian flu rarely caused major outbreaks of sickness and death among wild birds, or even in domesticated poultry, for that matter. Back in the day, the low pathogenicity type of avian influenza was pretty much the only game in town. But things have changed for the worse, and we'll get to that in a few minutes. As far as we know, songbirds are not especially susceptible to sickness from avian flu. So that's well over half of the world's bird species, the more than

6,000 species of songbirds. They do not typically carry the disease either. What about your pet bird? It's very rare for companion birds like parrots to get avian flu, as long as they don't spend much time outside where they could come into contact with an infected wild bird. So if you're a pirate and you've got one of those wise cracking parrots perched on your shoulder, well, have you noticed all the gulls wheeling in the sky around your pirate ship? Pooping on your pirate ship? Those gulls are swarming with viruses, my friend, so I'd say your parrot's days are probably numbered. You might want to start shopping around for a teeny tiny parrot-sized casket. But here's good news for the rest of us. Rock pigeons, aka your friendly neighborhood feral pigeons, seem to be pretty much immune to

avian flu. Multiple scientific studies have shown that these birds don't get infected by the virus, and they don't seem to carry it around. Good for pigeons and good for us, I suppose. Because if pigeons were carriers of avian flu, that might be worrisome, given how ubiquitous they are. And given how much of their poop rains down upon the world. So most wild birds like ducks and gulls have, it seems, acted mostly as carriers of avian influenza, as vectors. At least historically, they may not have suffered mass outbreaks of disease and death from this type of virus. But in recent decades, the story has changed. The vectors have started to become the victims. When avian flu makes the headlines, most of what you'll hear is how the disease affects

people, directly or indirectly. Like, the virus is killing countless domestic chickens, and that's why your eggs are going to cost a bit more this month. Is bird flu going to cause the next pandemic in humans? Is this the beginning of the avian apocalypse? Stuff like that. Why has avian flu become so scary to us? Why is it so unpredictable and potentially world-shattering?

It all has to do with the ability of influenza viruses to mutate and to form new gene combinations. New gene combinations or mutations can result in novel versions of the proteins on the outer shell of the virus. In rare cases, these new proteins are much better at their jobs than the previous iterations. better at infecting, replicating, et cetera. This is called antigenic shift. Practically overnight, a relatively benign strain of avian influenza, one with low pathogenicity, might spawn an entirely new strain that is highly contagious and deadly.

Yeah, scary, I know. Many of these new strains affect only birds. But some make the leap to infecting the cells of mammals, including humans. Diseases that suddenly jump from wild or domestic animals to humans are called zoonotic diseases, or zoonoses. Also, fun fact, if you see the word zoonoses spelled out, it looks like zoonoses. See, that's funny. Zoo noses. Who said disease and death aren't funny?

Other zoo noses, I mean, zoanoses, you might have heard of include rabies, Zika virus, and Ebola. Less familiar diseases include hamster pox, manatee fever, and goldfish plague. These are less familiar because they don't actually exist. But what if? You might want to keep an eye on your pet hamster, just in case. One of the main pathways for avian influenza viruses to become zoonotic is when domestic birds, pigs, and humans are all rubbing elbows on a farm. The animals are often kept in large numbers, packed together in tight spaces.

It's the opposite of social distancing, social huddling, if you will, social cramming, I don't know, whatever you call it, hygiene in this situation is often sorely lacking. And here comes the farmer, whistling a happy tune. Little does our farmer know, influenza A viruses from wild ducks have infected the chickens. And then viruses from the chickens infected the pigs. And guess what? Now some human viruses have also worked their way into the pigs. Every so often, a single pig cell gets infected by both bird and human virus.

Pigs are special because they can be easily infected with both types of virus, so pigs can act as intermediate hosts for avian flu. The infected pig cell then acts as a sort of petri dish, where nature conducts mad science experiments with genetic material. And that's where genes from all those viruses have the opportunity to get mixed and matched. It's sort of like random, randomly swapping pieces from several different Lego play sets. Most of the new combinations are lame, nothing special. But there is a remote chance you'll get lucky and randomly put together something awesome, like a super rad Lego spaceship with a dinosaur head and a fire engine ladder.

Now we're talking. In our pig patry dish, the equivalent but decidedly less awesome situation is when a new and terrible influenza A virus comes into existence through antigenic shift. The virus bursts out of a pig cell by the thousands and escapes into the world. It can infect humans and human immune systems are defenseless against it. Things aren't looking good for the farmer. This is pretty much how the H1N1 swine flu originated back in 2009. Remember swine flu? There's a good chance that some of you listening right now got infected with it and had a very unpleasant experience. The more captive birds and pigs there are all

swapping viruses like this, the more opportunities there are for the genetic mix and match game to produce new zoonotic diseases. Avian influenza viruses have crossed the gap from birds to mammals before. And now they're doing so more and more often. Human shenanigans are the reason these diseases have been showing up. There are five man-made environments that are hotbeds for avian flu. One, indoor commercial poultry facilities. Two, poultry ranges. Three, live poultry markets, four, backyard poultry enclosures, and five, captive bird collections involved in things like cockfighting. In some countries, there are also increasing opportunities for wild waterfowl and domestic birds to mingle. In Bangladesh, for example, many farmers now heard

hundreds of domestic ducks to and from wetlands and rice patties on a daily basis. Those same habitats are home to thousands of wild migratory waterfowl. Is this a recipe for an influenza disaster? Perhaps. In any case, my understanding is that the indoor commercial poultry facilities are the worst offenders. They play the biggest role in spreading highly pathogenic avian influenza. Commercial facilities are where the birds are kept in crowded conditions. They also get transported around from place to place. Commercial poultry production has exploded around the world since the 1990s. During the 90s, the global population of chickens and other poultry increased 23% in developed countries,

and 76% in developing countries. Much of this growth was because of increased commercial production. This has all resulted in more and more outbreaks of highly pathogenic avian flu. More outbreaks among domestic birds means more opportunities for the viruses to infect humans. New strains could appear that have the ability to spread easily among humans. Since some strains of avian influenza have already made the zoonotic leap, it's possible for people to contract viruses directly from birds. But at least so far, it's been extremely unlikely for the average person to contract.

the virus from birds. The people most at risk are those in direct contact with lots of birds on a regular basis. People who handle birds. This means poultry workers, people who have backyard chickens, and wildlife professionals. And even when people have been infected, the chances of the virus then spreading from one person to another has been very low. There's still reason for concern. Some strains of avian flu have high mortality rates in humans, like up to 60% mortality. For those strains, you may be unlikely to get infected, but if you do, there's a good chance you might die. And one of these strains could evolve at any time through antigenic shift, becoming highly contagious in human populations. If that happens, we'd have another potential pandemic on our hands.

So antigenic shift and zoonotic disease can create a danger wherever there's a high level of close interaction among humans and populations of wild birds, domestic birds, and domestic mammals. And maybe hamsters. Let's keep an eye on hamsters, okay? Avian flu is what scientific. call an emerging disease. The World Health Organization defines an emerging disease as one whose incidence has increased in the past two decades. The most notorious strain of avian flu is

H5N1. It was first discovered in domestic geese in China back in 1996. Ah, 1996. Those were simpler times, weren't they? That was when the number one song of the year was the Macarena. You know, I don't think I've ever listened to the Macarena song from beginning to end. Not once. And yet, that devilishly catchy tune will

randomly pop into my head way too often. I'll be pulling weeds in the garden or rearranging books on my shelves when Oh no, here it comes again. No! So, 1996, there we were all just dancing to the macarena, when H5N1 quietly became a thing over in China. The Chinese government cracked down on the disease, and H5N1 seemed to disappear for a few years.

But then it popped back up in 2003. Since then, strains of this avian flu have resurfaced repeatedly, causing outbreaks around the world. H5N1 has wreaked havoc on poultry farms, of course, but starting in the early 2000s, it was also killing large numbers of wild birds. In 2005, for example, 6,000 waterbirds of multiple species died of the flu in a Chinese lake. There have been many other outbreaks like this among wild birds in very very many. parts of the world. How has the virus spread around the planet so effectively? Well, as I mentioned, some ducks are super spreaders. They spend lots of time in the water where they mingle with other birds,

and they migrate long distances. Wild geese are also known to be carriers. Some species of wild geese spend a lot of time foraging close to human settlements. So these birds may sometimes transmit viruses long distances from one poultry population to another. However, the biggest culprit in spreading avian influenza is the commercial trade in poultry, of both live birds and their body parts. Chickens, turkeys, and ducks are transported all over the place, at local scales, and all of the way up to the international scale. Biosecurity efforts, while critically important, haven't been able to prevent ever. disaster. But it's easier for people to simply blame wild birds like ducks and geese for spreading

disease. Rather than own up to their own failures, commercial poultry producers can just point at wild birds and use them as scapegoats. Unfortunately, many ducks can't afford to hire a lawyer, so they can't sue for defamation. This disproportionate blaming of wild birds can create an unjustified overblown fear around them. The world's birds are having a hard enough time already, right? We don't need to persecute them any more than we already have. In late 2021, about 8,000 common cranes died in the Hula Valley of Israel. Every year, cranes stop over in the Hula Valley during the winter on their migration from breeding areas in Finland down to Ethiopia. The cause of death for the cranes was, of course, avian influenza,

H5N1. The loss of 8,000 cranes represented about 20 to 25% of the entire wintering population. The Israeli government called this event, quote, the deadliest wildlife disaster in the nation's history. People in Israel love and celebrate their cranes, so this event was just devastating. in many ways. Photos and videos of this outbreak are heartbreaking to look at. You can see cranes stumbling through the wetlands and thrashing around on the ground as they suffer. Dead birds are everywhere. Workers wearing hazmat suits are clearing away the bodies. The total mass of crane carcasses added up to about 25 to 30 tons. Local farmers in Israel were forced to slaughter thousands and thousands of chickens in the wake of this flu outbreak.

Since the fall of 2021, this highly infectious strain of H5N1 has spread through Europe, the U.S., and Canada. It may be only a matter of time before it reaches South America and Australia. There have been over 3,000 outbreaks. Well over 70 million chickens and turkeys have been killed in efforts to prevent the spread of the virus. This strain of H5N1 is so infectious that if even one chicken gets it, the virus can spread rapidly through the flock, killing most of the birds in days. My wife and I have a handful of backyard chickens. We absolutely adore them.

To keep our precious little hens as safe as we can during this wave of avian flu, we have them on flock down lockdown. They've been confined to their run for a couple of months now. It's a spacious run, thankfully, but our hands are pretty eager to get back out into the yard. The primary danger, even though it's probably a very remote one, is that some wild bird might transmit the flu virus to our chickens. So, for now, we've taken down all of our bird feeders. So, as I'm recording this, we are experiencing a global wave of avian influenza. A key feature of this wave is that it's killing.

wild birds at much higher rates than ever before. For example, 1,000 lesser scop died of the virus in Florida recently. Lesser scop are ducks, FYI. Canada geese have been dying too. Normally, we would think of birds like these as only carriers of the disease. But this virus strain isn't killing only waterfowl. There were the common cranes in Israel. Then there have been mass deaths among Gannets, scuas, and puffins. Corvids like crows and jays are succumbing. And raptors, too. Dozens of bald eagles have died of the flu, which they may have contracted by eating ducks and geese. In North America alone, over 60 wild bird species have been affected. This is the deadliest outbreak of avian influenza we've ever seen in North America. And yet, that we know of, only two people have been infected.

one in the U.K. and one in the U.S. The person in the U.S. was involved in slaughtering chickens. He ended up with only mild symptoms from the virus and recovered fully. So this latest wave of avian flu is a disaster mostly in terms of how many wild and domestic birds are dying from it. At least for now. Some scientists think that this strain of H5N1 might keep circulating among wild, bird populations for many years to come. Who knows what that means for birds in the future?

Or what it means for us. Yes, that was a lot of gloom and doom. I know. But hey, this is science, yo. Sometimes we have to get serious for a little while. I hope you learned a few things here today and that you feel at least a little more informed on the subject of avian flu.

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Tom Walenda, and Cameron Behe. welcome and thank you guys all for the amazing help if you my friend are wondering how you can support this podcast to keep the episodes flowing just cruise on over to my Patreon page at patreon.com forward slash science of birds you can also shoot me an email if you have a comment about the podcast or if you'd like to tell me which song from the 90s

randomly pops into your head way too often In any case, my email address is Ivan at Scienceofbirds.com. I can't always reply right away, but I really try to answer everyone who writes to me. You can check out the show notes for this episode, which is number 53, on the Science of Birds website, scienceofbirds.com. This is Ivan Philipson, and I hope you're having an awesome day. Cheers.