On Saturday, a suspected case of deadly H5 bird flu, also known as high pathogenicity avian influenza (HPAI) H5N1, was confirmed in a brown skua.
This large seabird was found in Cape Le Grand National Park near Esperance, about 700 kilometres south-east of Perth in Western Australia.
The virus is also suspected to have affected another seabird, a southern giant petrel, found at the same area.
Following the initial testing, samples collected from these birds were sent to the CSIRO to confirm the first Australian cases of H5N1, specifically the clade 2.3.4.4b H5N1 lineage. Avian influenza viruses are categorised by subtype (creating the H and N number combination, here H5N1) and specific clades within the H5 subtype.
This virus has devastated wildlife populations in other continents, and this could be the start of a long push to protect Australian birds and wildlife in Australia.
Where did this virus come from?
Avian influenza viruses, of which HPAI H5N1 is just one kind, have been around for millenia. In the vast majority of cases they cause no disease in birds. These strains are referred to as low pathogenicity avian influenza viruses.
However, in 1996 one of these viruses evolved to become disease causing, and since then, this HPAI H5N1 has caused severe disease in poultry, and has become endemic in poultry. With chickens now forming about 70% of all birds worldwide, this is a critical reservoir where the virus continues to evolve.
The devastating effect of HPAI H5N1 is unfortunately not limited to poultry. Since 2021, HPAI H5N1 has caused a global animal pandemic, with enormous consequences for wildlife in all continents. It has killed millions of wild birds and caused significant drops in the global population of some species. It has also spread into wild and domestic mammals, with various species of seals particularly affected.
How it spreads
Part of the challenge in controlling HPAI H5N1 is that it can spread through a wide range of transmission pathways. For example, the virus typically spreads through faeces, especially when in water. Imagine infected ducks in a pond, where the pond water acts as a conduit to infecting other ducks which are feeding or cleaning themselves.
It can also be spread through direct contact and aerosol transmission, particularly in poultry farms. And it is spread through predation and scavenging, where animals like foxes maybe eat the carcasses of infected birds they find.
While it has so far been found in more than 400 different bird species, the spread of HPAI H5N1 in the northern hemisphere is facilitated by freshwater dabbling ducks. Dabbling duck species feed predominantly at the surface of the water, sometimes even grazing on land.
Importantly, ducks have very limited signs of disease when infected with HPAI H5N1, and appear to be able to continue to migrate while infected, allowing them to potentially spread the virus long distances.
Overall, this virus has been devastating for wild birds. For example, 33–47% of all adult northern gannets died in 2022 due to HPAI H5N1. On subantarctic Heard Island, 13,000 baby southern elephant seals died due to HPAI during the 2025–26 summer.
Sandra Standbridge/Getty
Why has it taken so long to reach Australia?
Despite being in Asia since the 1990s, and in Antarctica since 2024, HPAI H5N1 has not been detected in Australia until now. This is likely because there are no duck species which routinely migrate between Australia and Asia, nor are there ducks that migrate through Antarctica.
Despite the lack of ducks in Antarctica, the virus did arrive there in the summer of 2023–24, and subsequently spread thousands of kilometres through the subantarctic in the summer of 2024–25. Available evidence suggests birds like gulls, skuas and giant petrels may have taken on the role of long distance virus carriers in the Antarctic and subantarctic.
The various species of skuas and giant petrels that breed in Antarctic waters go on to roam the Southern Ocean, also venturing into the Atlantic, Indian and Pacific Oceans during the southern hemisphere winter. While rarely seen on our shores, these species are not too far offshore, looking for food and occasionally gathering in large groups.
Now that HPAI H5N1 has been found on mainland Australia, it will not necessarily establish itself and spread across the continent into other birds and mammals, including livestock.
Given that skuas and giant petrels are marine rather than freshwater species, and do not occur on land in large numbers outside the breeding season, there is still a chance that it may not spread further.
The biggest risk is that infected, sick birds are eaten or scavenged by native birds and mammals, which could transmit the virus to ducks.
Try to stop the spread
Once in ducks, the likely spread of the virus increases dramatically, and the outlook would be grim.
But for now, we are a few critical steps away from that happening. Continued surveillance and testing, being led by Western Australia, is critical to reveal the extent of the virus and whether it has spread to local animals.
Vigilance is key – do not touch or take sick animals into your care. Rather, report suspected cases immediately to the Emergency Animal Disease Hotline on 1800 675 888.
For farmers or people who own chooks, its critical to follow guidelines provided by government departments and report any suspicious mortality.
