A mountain lion, bear and skunk are some of the latest victims of bird flu virus spreading around the world.

The highly pathogenic avian influenza (HPAI) known as H5N1 has scientists worried.

Since 2021, the virus has gone gangbusters and made its way to every continent except Australia and Antarctica.

"We know the virus is extremely widespread in the Northern Hemisphere and is now starting to move into South America, which it's never done before," said Ian Barr, deputy director of the World Health Organization (WHO) Collaborating Centre for Reference and Research on Influenza.

The situation has become so dire that countries in the European Union and the US Biden Administration are now considering testing avian vaccines.

Until now, many countries including Australia have been reluctant to vaccinate poultry because of the risk of bird flu spreading from vaccinated but asymptomatic poultry into other animals, as well as export trade implications.

Chicken being injected with a vaccine
Experts believe the pandemic is so bad that vaccination is warranted — as long as it is done correctly.(Getty Images: China Photos)

A spokesperson from the Australian Department of Agriculture, Fisheries and Forestry (DAFF) said the government was monitoring the international situation and supported vaccination when effective — and regularly updated — vaccines become available. 

"We encourage countries currently experiencing significant losses of poultry due to HPAI outbreaks to take up vaccination," they said.

While routine vaccination for bird flu is currently banned in Australia, that could shift in the future.

"If Australia were also suffering or facing such losses, we would be encouraging our own industry to adopt vaccination," the spokesperson said.

So why have things become so grim, so fast? And what is Australia doing to keep it at bay?

Let's start with the virus itself.

Evolution of H5N1 

Bird flu is caused by a handful of viruses. Most of these are low-pathogenic viruses that circulate all the time in wild birds and cause little to no disease.

Only certain strains of two subtypes — H5 and H7 — cause severe disease and death. These highly pathogenic subtypes first evolved in poultry then spread out to wild birds, then back again.

Golden ring-shaped virus particles in larger green cells
Digitally colorised microscope image of avian influenza A H5N1 virus particles (seen in gold).(Supplied: CDC/Cynthia Goldsmith)

H5N1 first appeared on the scene in 1996 but it only started to go global in 2003, according to Marcel Klaassen of Deakin University who has been monitoring avian influenza in wild birds over the past two decades.

Then in 2014 a new lineage appeared in Korea and before long, it jumped from Europe into North America.

"Then I thought, 'Oh, man, now the shit has really hit the fan,'" Professor Klaassen said.

Over the following four years there were more waves of bird flu, but nothing like the current wave that started in October 2021, driven by a new variant known as

Professor Barr said there is now evidence this variant is hooking up with other bird flu viruses in North America, making it even more virulent.

"It's concerning that there's so much virus out there that has spread into so many species," Professor Barr said.

How bad is bad?

The death toll is staggering.

Around half a billion poultry birds around the world — more than 58 million in the US alone in the past year — have died of H5N1 bird flu.

And it's not just poultry. 

As headlines about turkey shortages in the lead up to Thanksgiving rang out in the US last year, veterinarians in Spain detected the virus in a mink farm that killed nearly 52,000 animals.

Meanwhile, the official numbers only tell part of the story for wild birds, Professor Klaassen said.

Dead pelican on beach
A pelican succumbs to deadly H5N1 bird flu in Peru.(Getty Images: Ernesto Benavides)

"The number of wild birds recorded thus far is 100,000, but I think it's grossly underestimated.

"It's in the millions, rather than in the hundreds of thousands reported in the databases."

Colonies of gannets have disappeared in Scotland, and at last count the disease has ripped through about 236 different wild bird species as diverse as bald eagles, vultures, pelicans and penguins.

"We have no idea how our wild birds are really impacted by this current lineage in the Northern Hemisphere," Professor Klaassen said, adding that COVID and the war in Ukraine had prevented monitoring of populations in Siberia.

Why are we worried about the mink farm?

The mink farm outbreak raised fears the virus had evolved to spread between mammals for the first time.

"If it is true, it's concerning because we haven't seen mammal-to-mammal transmission before," Professor Barr said.

But, he said, it was still too early to tell if there had been mammal-to-mammal transmission, or if the minks, which were kept in open sheds, had come in contact with infected birds.

"I don't think you can jump to the conclusion, because there was an outbreak at the mink farm, that it was transmissible, even though it did affect a lot of animals."

Mammals were known to be infected by H5N1 well before the mink farm outbreak.

Two white mink in a cage
The spread of H5N1 bird flu in a mink farm has raised questions about intensive farming practices.(Getty Images: Mads Claus Rasmussen)

"When this virus first broke nearly 20 years ago, it killed zoo animals like tigers when they were fed carcasses of birds that were infected," Professor Barr said.

Since January 2021, there have been 186 outbreaks of H5N1 in mammals affecting 17 species including foxes, otters and seals, in addition to bears, mountain lions and skunks.

Despite the name "flu", highly pathogenic strains of avian influenza cause more than a respiratory illness, often affecting the central nervous system and brain of mammals.

The concern is if H5N1 becomes prevalent in mammals, it could mutate and spread more widely to humans.

But so far the risk to humans from H5N1 is low, according to the WHO, which has registered a total of 868 cases and 457 deaths since 2003.

"Considering the number of wild birds and poultry that have been infected and disposed of, sometimes with not all the care you might like, the number of infections has been remarkably low in humans," Professor Barr said.

"It's concerning, but it's not panic stations at this time."

Currently, another lineage of HPAI known as H7N9 is more of a problem for humans.

What are we doing in Australia?

If H5N1 entered Australia, it would decimate poultry and wild birds just as it has overseas, and there are fears some species, such the Australian black swan, could be wiped out. 

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