It’s back: The looming peril of avian flu

Researched by: Nirmal Bhansali & Priyanka Gulati

Remind me about bird flu..

Say hello to the H5N1 virus: There are many strains of avian influenza, but the most deadly is the H5N1. H5N1 first surfaced in 1996 at a goose farm in China—and has since showed up in at least 63 species of wild birds. In 2002, the virus resulted in the death of more than 140 million birds—due to disease and culling to prevent the spread. The virus is highly contagious, and infection can wipe out 90% of farm birds within 48 hours. Worse, it has also shown the ability to jump to mammals such as bobcats, harbour seals and bears.

Point to note: What’s also worrying is that the virus has spread from domesticated poultry to wild birds—who have carried the virus far and wide because they travel long distances: 

I think we used to cling to this idea that we can control the virus in poultry, we’re set, no problem. And now we’re facing a new era because if it has become established in wild birds, that’s a far more complex situation in terms of figuring out how to control it and predict where it will go next.

In 2020, migratory birds carried the H5N1 virus to Africa, Asia, and Europe—and in late 2021 it popped up in North America. 

The threat to humans: The disease can spread to humans—but requires prolonged contact in a contaminated environment:

Most people who have come down with bird flu spent a more-than-casual amount of time around birds, usually while working with or around sick flocks. “If you look at all the H5 infections over the past two decades or more, the vast majority of those reported exposure to sick or dying poultry prior to the infection,” said [virologist] Richard Webby.

A major outbreak in 1997 left 6 people dead and 18 infected. To date, over 800 cases of human H5N1 infections have been reported—with a horrific fatality rate of 53%. In other words, while the chances of contracting the disease are small—for now—it is far more lethal than other forms of influenza. 

The symptoms & treatment: The list of symptoms is long—vomiting, fever, cough, diarrhoea, sore throat, eye infection, muscle aches, respiratory distress. It is also unhelpful since it can mimic many other diseases. Much like Covid, it requires a nasal or throat swab to confirm an infection. There are human vaccines for bird flu that offer protection against severe disease. But they may prove ineffective if the virus mutates. Other antiflu medicines are mostly ineffective against the virus. 

So what’s happened now?  

As we noted before, migratory birds carried the H5N1 virus to North America in late 2021. It has since been detected in 47 states—and resulted in the culling of 58 million birds—and is considered the largest avian influenza outbreak in US history. Nearly 6,200 infections among wild birds were reported just last week. The virus was also detected in 3,500 wild birds across Europe in the 2021-2022 season—and has been reported in 37 countries. There are worrying reports from South America. More than 13,000 seabirds died, including 5,500 pelicans in Peru.

Point to note: Experts warn that the current outbreak has likely resulted in the deaths of thousands of wild birds—resulting in the mass destruction of wildlife. But accurate numbers are almost impossible to estimate:

For example, of the approximate 8,000 sandwich terns that died in the Netherlands, only a handful are included in the official numbers – in this case a more than 200x difference between reported numbers and observed. The lack of appreciation for the scale of wild bird mortality is concerning as there may be species/population level ramifications.

One distressing example: The virus has killed 10% of the near-threatened Dalmatian pelican in 2022.

The big warning bell: The virus has now spread to mammals. Late last year, 50,000 infected minks on a farm in Spain were culled. A study of the outbreak showed that the virus was spreading from one mammal to another—for the very first time! Until now, mammals (including humans) were only infected after exposure to infected birds. The worrying reason for this shift: The H5N1 virus has gained at least one mutation—T271A—that allows it to spread between mammals. 

Point to note: In 2020, millions of minks were killed because they were infected with a mutated strain of the coronavirus—due to worries it may spread to humans.

Wait, is there a risk of another pandemic? 

The happy news is that no one working on that mink farm was infected—other than one person with the sniffles. But scientists are now worried about future mutations that may trigger human-to-human transmission. Before the coronavirus came along, they were closely tracking bird flu as a potential threat: 

There is concern about it having pandemic potential… anything that has the ability to replicate and evolve rapidly, and anything that has that ability to infect a lot of different hosts is kind of on borrowed time.

But, but, but: As Vox notes, to trigger a pandemic, the virus has to have three qualities: 

It must spread easily among humans, particularly through the air. It must cause human disease. And it must be something that most of our immune systems haven’t encountered before — that is, it must be novel.

Right now, while the H5N1 virus is more contagious, it lacks one critical element—which protects humans from infection.

The wrong receptor cells: Viruses infect a cell by binding to receptors on its surface. And they tend to specialise in infecting certain species—and evolve to bind to their receptors. This makes them less effective when they infect other species:

Avian flu viruses are adapted to bind to birds’ receptor cells. Humans and other mammals have some avian-like receptors, but they’re typically buried deep in the lungs. Because of this anatomical quirk, it would take an enormous load of H5N1 for one infected mammal to dredge up enough of the virus to infect another mammal. Unless, of course, the virus evolved to bind to mammalian cells in the upper respiratory tract.

So the virus can’t easily bind to cells in our airways—and are therefore much harder to transmit—and therefore can’t cause a pandemic.

The big reason to worry: A virus that is mutating to allow mammal-to-mammal transmission could soon acquire a mutation that enables it to spread among humans. Influenza viruses are highly changeable—and are prone to undergoing big shifts called reassortments:

Reassortment is like something out of science fiction: When two influenza viruses infect the same cell in the same host, they can trade entire chunks of their genomes with each other, yielding a variety of Franken-flus.

This is what would happen if pigs—which can contract both the human and avian flu—get infected with both: “Should these two viruses meet inside these animals, they might swap parts, producing an avian flu that can more easily infect mammals.” 

Looping back to those minks: Since minks are also susceptible to avian and mammalian flus, scientists are worried about the outbreak at the Spanish farm:

In theory, that could lead to the creation of a virus with all of H5N1’s other bad personality traits — its ability to cause severe disease, for example — with the added advantage of, say, being able to easily infiltrate cells in our airways.

Voila, the bird flu virus would suddenly meet all three criteria to trigger a pandemic.

Point to note: The 1918 flu pandemic—which killed an estimated 50 million people worldwide—was triggered by a genetic mingling of swine flu and avian flu viruses. It was followed by two avian influenza pandemics in 1957 and 1968—which involved both reassortment and additional mutations. Each of these pandemics killed about 1 million people worldwide. But these involved different strains of the avian flu.

The silver lining: Scientists agree that the mutations that allow the virus to spread among new species will also make it less lethal. For example, the fatality rate among those minks was only 4%.

How does climate change come into this?

Scientists say it explains why bird flu outbreaks are becoming more frequent and widespread. Warming temperatures affect the behaviour of birds—such as migratory patterns and breeding seasons:

Studies have found that changing weather patterns fundamentally affect the way birds behave in ways that could influence the spread of bird flu. Rising temperatures and the seasonal changes they induce force birds to adjust their migratory patterns and converge in new combinations. Rising sea levels also affect where birds make their nests and lay their eggs, prompting species that don’t typically interact to make contact and share disease.

As a result, avian flu virus has been detected during the summer in Italy—when high temperatures ought to have destroyed it—and in winter in Canada, when migrating birds are few and far between. To be clear: experts are still figuring out exactly how global warming is linked to these changes.

The bottomline: Scientists do not claim that a bird flu epidemic is inevitable or even imminent. They are instead making a strong case for closely tracking the virus—so we can detect the threat and eliminate it. Prevention is always better than a cure.

Reading list

Vox, NBC News and The Guardian offer the best overview of the latest H5N1 outbreak—and how it might mutate. The Guardian also looks at the devastation it has wreaked among wild birds. Grist is excellent on the connection to climate change. Science has the original study on the mink farm in Spain. New York Times op-ed explains why we should all be concerned about vaccine supplies—and the state of surveillance systems. Also in the Times: A connection between seal strandings and bird flu.