Australia's surveillance of bird flu has been described as a possible "model" to follow globally, with the spread of the H5N1 strain of the virus causing concerns for international health authorities.

The World Health Organization said there needed to be global action to strengthen surveillance of animals that were known to be susceptible to infection.

"For us at the WHO, we are always in a constant state of readiness as it relates to influenza, because it isn't a matter of if, it's a matter of when," WHO epidemiologist Maria Van Kerkhove said.

"We're not in that situation yet, but we do need more vigilance."

How is Australia dealing with bird flu?

Australia is yet to deal with H5N1, which is the deadliest strain of bird flu.

There has only been one reported case of avian influenza in a human in Australia.

The infection was contracted overseas, the person received treatment in Australia and later made a full recovery.

But between May and July this year, there was an outbreak of three different strains of bird flu discovered in 16 farms across Victoria, New South Wales and the Australian Capital Territory.

The outbreak led to almost 2 million chickens being killed.

Avian Influenza has dozens of different strains: Australia's 2024 outbreaks were all subtypes of the H7 strain.

There are two ways avian influenza strains are described: low pathogenicity (LPAI) or high pathogenicity (HPAI).

LPAI strains cause little to no signs of disease in birds, while HPAI strains — such as those that made their way to Australia mid-year — cause severe disease and high mortality rates.

HPAI strains often kill almost all infected chickens within about 48 hours.

Chair of epidemiology at Deakin University Catherine Bennett said the WHO's message highlighted the importance of early reporting and detection to deal with potential outbreaks.

Professor Bennett said the H5N1 strain was very infectious and more thorough surveillance was needed to manage outbreaks before the virus spread across different populations of wildlife.

"The good news from Australia's point of view is that we've had a focus on this for some time with the establishment of the interim CDC, there was a real early focus on one health," she said.

Professor Bennett explained the "one health" approach was a definition, developed by WHO, meaning to have a unifying approach to balancing the health of people, animals and ecosystems.

It's been adopted by Australia's new Centre for Disease Control.

"We have to be looking at the whole picture, rather than just trying to fix things once they hit the humans."

Australia a model for other countries dealing with the spread of bird flu

Australia is the only continent in the world free from H5N1 bird flu strain.

The government announced in October it was investing a further $95 million to prepare wildlife, agricultural industries and the economy against the strain.

Professor Bennet believes this places Australia as a "world leader" in its surveillance of the virus.

"Clearly, we have put that investment in, but it sounds like there are these blind spots that the WHO are worried about globally, so it would be good if Australia is a bit of a model to other countries," she said.

"It makes it harder in Australia if other countries don't have that same investment, and so there are these blind spots globally, which can mean that something can flare up and be quite well-established as a local area of concern before we even hear about it."

North America has seen the bulk of cases.

The US Centers for Disease Control and Prevention reported last week that there had been 55 human cases of H5N1 bird flu in that country this year.

Why is surveillance important?

Professor Bennett said the biggest risk factor for a pandemic was a crossover of pathogens from the animal population to humans.

She explained a combination of both human and avian influenza, which was possible, could create a "pandemic threat".

"Because you have a new human virus that has those elements that allow the virus to attach on to human receptors and to cause illness in humans, and for humans to spread human to human," she said.

"But it also has enough genetic difference that comes from the animal strain that helps it evade our immune system, so it makes us more vulnerable to these viruses, and that's why they can take off as a new pandemic."

The WHO has already made efforts to increase surveillance by contacting its partner agencies the World Organisation for Animal Health (WOAH) and the Food and Agriculture Organization (FAO).

"We have not seen evidence of human-to-human infection. But again, for each of these human-detected cases, we want to see a very thorough investigation taking place," WHO epidemiologist Maria Van Kerkhove said.

"We need much stronger efforts in terms of reducing the risk of infection between animals to new species and to humans."