What Australian farmers need to know | Bird flu explained

The high risk period for such outbreaks is considered to be September to October, as migratory wild birds return from the north.

It may be just a number for most of us, but for scientists the difference in the strains of avian influenza are worlds apart.

They are asking the public to pay close attention.

Today we explain how to better understand this scientific shorthand.

Avian influenza, also known as bird flu and previously called fowl plague, is caused by influenza A viruses, similar to the virus which causes flu in humans.

Experts believe the bird flu is being spread by wild waterfowl which are considered natural hosts for the virus and transmit the virus through their droppings.

Testing has confirmed the outbreak strains are genetically related to viruses previously detected in Australian wild birds.

Wild birds were also blamed for the unwanted arrival of the Japanese encephalitis virus in 2022.

But farmers and consumers have been asked to pay attention to these virus subtypes.

In Victoria, where more than a million birds have already been destroyed in the nation's worst ever animal disease outbreak of its kind, the numbers are just slightly different.

Breaking down the acronyms, HPAI is high pathogenicity avian influenza - meaning the virus is highly contagious.

In April, a low pathogenic HPAI H9N2 avian influenza was detected in a small scale poultry operation in WA.

On May 22, the HPAI H7N3 strain of avian influenza was found on a commercial poultry farm at Meredith, between Ballarat and Geelong.

On May 24, the HPAI H7N9 strain was detected to the west at Terang, said to have direct commercial links to the Meredith farm where the virus was first discovered.

The HPAI H7N3 strain has been confirmed at five more poultry and duck farms in the Meredith/Lethbridge areas since.

The outbreak confirmed at the Sydney commercial egg farm this week is HPAI H7N8.

Experts say this means the NSW outbreak is not directly connected to the Victorian outbreak.

And if the outbreak is not already bad enough, what authorities are most anxious about is the arrival of a type HPAI H5N1 has been circulating through wild bird populations globally.

This strain has jumped species to infect more than 80 dairy farms across 11 states in the US.

To complicate matters further, bird flu in cattle is known as bovine influenza A virus, or BIAV although it does not kill cattle.

A case of H5N1 was confirmed in a Melbourne toddler who fell ill after returning from overseas in March. The child later made a full recovery.

Authorities say Australia "has not been affected by the H5N1 virus but remains at risk via migratory birds plus people and equipment coming from overseas".

Most feared with H5N1, H7N9 was first identified in eastern China in 2013, also can cause serious infections and deaths in humans.

To better understand the science, bird flu viruses are classified into subtypes based on two surface proteins, the haemagglutinin and neuraminidase.

For example, a virus which has HA 3 protein and NA 2 protein is designated as subtype H3N2.

At least 16 haemagglutinins (H1 to H16), and nine neuraminidases (N1 to N9) subtypes have been found in viruses from birds.

Some specific LPAI virus subtypes (subtypes H5 and H7) can evolve to HPAI virus following spillover from wild birds and circulation in poultry.

Australian health officials say there is a very low risk of people becoming infected with avian influenza viruses through normal contact with healthy birds.

They also say properly cooked poultry products (meat and eggs) are safe for human consumption as the cooking process destroys any virus.

Meanwhile, South Australia has this week implemented movement restrictions on live poultry and fertile eggs from Victoria.