As H5N1 continues to cause mortality in wild birds, are we closer to a flu pandemic?

“The Illinois Department of Natural Resources would like to remind the public to report any large mortality events of waterfowl and other waterbirds during seasonal migrations.”

So began a news release issued on December 11, 2024, which reported that “dozens of waterbirds, mostly snow geese, were recently found dead at Baldwin Lake State Fish and Wildlife Area.” The suspected cause of these wild bird deaths is H5N1, the strain of bird flu that has been circulating globally for several years now. 

The statement also provided the following cautionary remarks to hunters and anyone else who happens upon deceased wild birds in Illinois:

Rubber gloves and a mask should be worn when disposing of any deceased wild birds, and carcasses should be double-bagged in sealed plastic bags. The bags can be buried away from scavengers or placed in the garbage if approved by the local waste service provider. Anyone handling deceased birds should thoroughly wash their hands and any other clothes or tools with soap and water after disposal.

The department reminds waterfowl hunters to take precautions and thoroughly cook game meat to an internal temperature of 165 degrees Fahrenheit. Avoid handling sick or dead waterfowl found in the field. Do not allow dogs and other pets to consume waterfowl and poultry that died from unknown causes.

This is but one example of the impact that fall migration has on the spread of diseases, like H5N1.  As noted in this report, migratory birds like snow geese are traveling through various pathways that traverse the United States.  When these types of birds travel, and if they are infected with the virus, they take H5N1 with them on their travels and spread it, sometimes leading to spillover into other species. One of the most recent and high profile examples is the spillover from wild birds into dairy cattle in Texas, leading to an unstoppable outbreak amongst hundreds of cattle herds. 

But there has also been an uptick in another aspect of H5N1 ecology and virology: increasing mass mortality events in wild waterbirds. This is unusual, as the natural reservoir for avian flu is wild waterfowl like ducks, geese, and swans.  So these birds have typically not been known to get very ill with these viruses, but have acted as asymptomatic carriers of H5N1. Although there have been instances of mortality in the past, the emergence and global circulation of H5N1 clade 2.3.4.4b has led to what the scientists have consistently called unprecedented mortality events amongst a growing number of wild bird species.

Recent H5N1 mass mortality events in wild waterbirds:

On December 10, 2024, the day before the Illinois report, the Missouri Department of Conservation reported in a news release that it was “monitoring reports of dead geese and ducks across the state.” H5N1 is the suspected cause.  This notice also cautioned the public not to handle any dead waterfowl or other birds and to prevent pets from having contact with dead birds “to help prevent the spread of disease.”

A few days before that, on December 6, 2024, a wildlife rehabilitation group in Kansas called Operation Wildlife posted on its social media page that it had received many reports of dead waterbirds, mostly snow geese:

“With the uptick in migration we have been receiving calls on ‘geese falling out of the sky.’ 

The majority of these have been snow geese (40) in the last 3 days.  Just this morning we received calls from Atchison, Overland Park, Olathe, Lawrence, Tonganoxie, Kansas City KS, Shawnee, Clinton Lake.

They may show signs of injury when brought in but rapidly decline & exhibit symptoms of avian influenza.”

While “geese falling out of the sky” seems like something you would see in a pandemic movie, it reminded me of something else. A while back I listened to a bird flu episode of a podcast geared towards duck hunters, and one of the hosts described a strange encounter one morning in Arkansas: 

“I was on the river in my boat. I look up and there’s a snow goose on the river, way out of its element, circling above my head, acting really strange.”  (Ducks Unlimited Podcast, Episode 488). 

This was anecdotal but I thought of it after reading the social media post above from the Kansas wildlife group.  A key symptom of H5N1 infection in wild birds and wild mammals is strange behavior, typically indicative of neurological issues. Indeed, with the increasing number of mortality events in wild birds there have been reports of sick birds exhibiting neurological symptoms prior to death. In the past few years there have been many instances of mass mortality in wild water birds, such as:

• • In September 2021, thousands of dead pheasants kept on hunting estates in Finland died of H5N1.

• • In May 2022, over 33,000 wild waterbirds, including gulls, terns, and pelicans, died from H5N1 on an island in the Caspian Sea off the coast of Russia.  

• • In March 2023, over 500 pheasants died of H5N1 at a pheasant game farm in New York state.

• • In April 2023, over 1700 wild waterbirds, including pelicans, gulls, and terns, died in Senegal and Gambia from H5N1.

• • In November 2023, an H5N1 outbreak in Argentina killed 220 flamingos in the north-west province of Catamarca.

• • In January 2024, an outbreak of H5N1 killed 675 swans in a nature reserve near Lake Karakol, Kazakhstan.

This is only a snippet of what has become a growing list of mass mortality events throughout wild bird populations around the world.  Not to mention the alarming mass mortality events in sea mammal populations.

Why are so many different wild birds dying from H5N1?

While H5N1 infections in wild birds are not unexpected, the massive amount of deaths is unusual.  Again, the natural reservoir for H5N1 is wild waterfowl.  These birds have spread the virus as they migrate but were not typically seen as vulnerable to the virus themselves. 

But that has changed.  The question is why.  Why are so many wild waterfowl birds dying from H5N1? 

It could be that H5N1 clade 2.3.4.4b viruses are just more fit for it, in that this strain of H5N1 has characteristics that make it better at infecting different species and causing enough severe disease to induce deaths in some populations, even in those wild bird species that typically were not as vulnerable to the virus.  The precise mechanism behind that increased fitness is the subject of ongoing scientific research, and it might never be fully understood.

It could also relate to the ecology of the virus. Beginning in late 2020, this clade of H5N1 began infecting more species of wild birds than H5N1 had ever infected before.  As it moved through populations of shorebirds and seabirds in Europe, it became clear that this was something different about this bird flu virus.  In early 2021, H5N1 emerged in Canada, and from there made its way south through the United States and onward, causing massive mortality in numerous bird populations in coastal areas in South America.  With so much bird flu virus in the environment, there is some level of infection pressure on organisms in that environment, making it more likely these animals, like birds, will get exposed and infected at some point.  

Moreover, as H5N1 was able to spread far and wide through migratory birds, the virus was maintained in those populations throughout the year, so that when the birds returned, they continued to circulate the virus.  As H5N1 circulated, it continued to spillover into poultry flocks, other wild birds, wild terrestrial mammals, sea mammals, and most recently, livestock like dairy cattle.  Sometimes the virus would spill back again into wild migratory birds, thus continuing the cycle. 

The question is, if the cycle continues, what are the risks to human health?

A potential pandemic flu threat?

The risks with this continuous H5N1 circulation is tethered to the nature of the virus itself: the ability of H5N1 to constantly change.  

As an RNA virus, H5N1 is constantly mutating at a very fast rate.  Indeed, all flu viruses mutate at a very fast rate.  This particular strain of H5N1 has shown a greater ability to reassort with other avian flu viruses, so H5N1 can essentially “meet up” with another flu virus and swap around their genes, thus creating new iterations of the virus, or even an entirely new flu virus.  

It is that type of virus mix & match scenario that keeps scientists awake at night.  On any given day, someone or some animal may be infected with H5N1 and another flu virus, like H3N2 or H1N1 human flu (what we call “seasonal flu”).  On that day, H5N1 could meet up with that seasonal flu virus, and by this reassortment comes a novel flu virus, one that takes the best (or worst) or both worlds: a virus that has the transmissibility of a human flu and the pathogenicity of an avian flu.  

That would not be a good day.  

Whether a pandemic will emerge from the ongoing havoc being caused by H5N1 cannot be known.  It’s certainly possible, but how likely a possibility is this?  Given the high rate of change with these viruses, there are always new versions being churned out, but there are not always pandemics.  So it’s really not that likely an event, right? Indeed, it’s one of those events that are low probability but high impact if it happens.  Like a large comet hitting the Earth, although I think a pandemic is much more likely than that.  

It’s really like a slot machine at a casino, with an almost unlimited amount of choices.  You watch as the machine tick tick ticks away, sometimes getting some things right, but missing others.  You have to wait for that exact right moment, that point in time where there is a convergence of all necessary factors, where the slot machine cranks out the exact combination of numbers and letters, in just the right way, at just the right time.  But you do not win when the machine finally hits the jackpot.

So it doesn’t happen often, but it has happened, and it will happen again.  Flu pandemics are an inevitability of nature, the same way that hurricanes and earthquakes are.  To think we can prevent them from happening is hubris.  

We cannot prevent pandemics, but we can prepare for them.  We can take measures during pandemics and in the early stages to save lives and mitigate the effects.  More importantly, we can, and do, employ the tools of scientific technology to try and predict when another pandemic will emerge.  A key example that comes to mind is flu surveillance, which is how the CDC, the WHO, and other health authorities track influenza and pinpoint novel strains when they emerge.  This is why we know so much about how this current clade of H5N1 is infecting so many different species of wild birds, because scientists are out there taking samples and analyzing them.  

But the surveillance system isn’t perfect.  At the time of the 2009 H1N1 pandemic, the world was concerned (again) about H5N1, although that was a very different H5N1.  All of a sudden a novel H1N1 strain emerges, causing a pandemic that no one saw coming. Even now, H5N1 in dairy cattle took everyone by surprise.  We knew H5N1 was being spread by wild migratory birds, that it had infected mammals all over the world.  We knew that the global environment (except Australia) was becoming saturated with H5N1, which led to growing concern about increased exposure to the virus.  

It’s just that no one was looking for it in livestock.  

And that’s just the thing about bird flu, it keeps breaking the rules.

Until next time.