What is avian influenza H5N1, also known as bird flu, and why has it been found in US dairy cows?

By Fiona Broom, ABC Rural

Viruses are tricky things. They are incredible at mutating to find new hosts in animal and human bodies.

They can adapt to unlock, enter and infect a cell, and can change over and over again.

The bird flu that is sweeping the world has now infected hundreds of species of animals.

Scientists say we are living through a panzootic - that's an animal pandemic.

What is bird flu?

Avian influenza, commonly known as bird flu, is a highly contagious virus that affects bird species and can spread to other species, including humans.

Just like human influenza, there are many types of bird flu and they can all have different effects on wild birds, poultry and other animals.

Avian influenza viruses can be classed as high or low pathogenicity, a reference to their potential to kill chickens, not how infectious they are.

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• Bird flu detected in Antarctica

What is high pathogenicity avian influenza H5N1?

This is the type of bird flu that has caused so many problems around the world in recent years.

It's not new: highly pathogenic bird flu H5N1 was discovered more than 20 years ago and there have been outbreaks in different parts of the world.

However the global spread has deepened since 2020, and the virus is now in Asia, Europe, the Middle East, Africa, North America and South America.

It has even been found in Antarctica.

Millions of poultry have died worldwide; in 2022 more than 131 million domestic poultry with H5N1 died or were culled across 67 countries on five continents.

Wild bird communities have also been devastated, with an unprecedented number of deaths among some species, including endangered species.

H5N1 has also spread to other wild animals - everything from foxes to seals, porpoises, bottlenose dolphins and grizzly bears have been affected - and farmed animals such as minks and dairy cows.

How has bird flu spread to cows?

In March, scientists discovered that a dairy herd in Texas had been infected with H5N1 after its milk production had dropped.

A dead farm cat and an unusually high number of dead pigeons were clues that suggested the cows had bird flu - domestic cats in the United States were known to have contracted H5N1.

Within a week, three other dairy herds in separate states were also diagnosed with avian influenza.

Wild birds are thought to be the primary source of the outbreak, but US scientists are investigating if cow-to-cow transmission is already occurring.

Can humans get bird flu?

One dairy worker in the United States has tested positive; they had conjunctivitis-like symptoms and were treated with anti-viral medication.

Symptoms can range from mild (conjunctivitis and upper respiratory symptoms) to severe or critical disease leading to pneumonia, multiple organ failure, sepsis and death.

The US Centres for Disease Control and Prevention (CDC) asked state health officials to prepare for further human cases while saying the risk to the public remains low.

Since H5N1 was discovered in the late 1990s, there have been about 900 confirmed human cases across 23 countries, mostly among livestock workers.

More than half of people who contract H5N1 die with the disease.

However human cases have dropped substantially since around 2015, with only a handful reported worldwide since 2022 and human-to-human transmission is not believed to have occurred.

Despite this, health authorities worldwide are not taking bird flu lightly.

Zoonotic diseases - those that can jump from animals to humans - are increasing around the world and scientists are alert to potential pandemic-causing viruses.

Evidence suggests Covid-19 was introduced to humans through animals, though it has not been confirmed.

Are there any vaccines for bird flu?

There are avian influenza vaccines for poultry but they are not used in every country, largely because they are considered ineffective.

No vaccines have been developed to immunise other livestock, such as cows, against bird flu.

And while humans don't yet have a bird flu vaccine, the research community's rapid Covid vaccine development has shown how quickly they can be produced.

It has led to the global partnership CEPI (formerly the Coalition for Epidemic Preparedness Innovations) setting a 100-day target to produce a safe, effective vaccine for the next global disease outbreak.

Will Australia be affected by the H5N1 bird flu outbreak?

For now, Australia remains one of the last places on Earth where this type of bird flu has not been found, the ABC said.

This is thanks mainly to its isolated geographic location, which is outside many bird migration routes.

But it's inevitable that H5N1 will reach Australia, scientists say. Spring is the highest risk time, when migratory birds are returning from their summer in the Northern Hemisphere.

An Australian government assessment says there is an increasing risk of a bird flu outbreak, and the country's chief vet, Beth Cookson, says authorities are closely watching global developments.

A review of the global H5N1 control and prevention strategy from the UN's Food and Agriculture Organisation and the World Organisation for Animal Health is expected in May.

Australia is not immune to zoonotic disease outbreaks; a domestic bird flu detection in Victoria in 2020 resulted in almost 500,000 birds being destroyed and international trade of poultry halted.

- This story was first published by ABC.