Australia has confirmed its first case of H5 avian influenza, marking a significant milestone in the global spread of the virus and prompting renewed warnings from scientists about the potential impact on the country’s wildlife, livestock and ecosystems.
The Australian government announced on June 20, 2025, that the virus had been detected in a brown skua, a migratory seabird found in a remote national park near Esperance on the southern coast of Western Australia. Testing conducted by the CSIRO’s Australian Centre for Disease Preparedness confirmed the presence of the virus, while a second bird, a giant petrel, was undergoing further analysis after returning an initial positive H5 result.
The discovery means the highly pathogenic avian influenza virus has now been detected on every continent, including Antarctica, where outbreaks among wildlife had already been recorded.
The infected birds are migratory species that travel vast distances across oceans, making them likely carriers of the virus into Australia. The detection site is located near the Recherche Archipelago, an ecologically important region that supports a wide range of wildlife, including Australian sea lions, fur seals and numerous seabird colonies.
Scientists have warned that the arrival of the virus presents a new challenge for Australia because the strain differs from previous bird flu outbreaks experienced in the country.
“This strain is different from the avian influenza viruses Australia has dealt with before,” said Dr. Robin Alders, an honorary professor at the Development Policy Centre at the Australian National University.
“It can infect and cause serious illness or death in many more species, not just poultry. That makes it much harder to detect, monitor and control,” she said.
Researchers are particularly concerned about the potential impact on Australia’s unique wildlife. Alders identified the endangered Tasmanian devil as one species that could face elevated risks if it scavenges infected bird carcasses. Similar concerns extend to other scavenging animals across mainland Australia that may come into contact with infected wildlife.
The fears are not merely theoretical. Overseas outbreaks have demonstrated the virus’s ability to cross species barriers. In the United States, H5N1 infections have been detected in cats and dairy cattle, while cases have also been reported in alpacas and sheep. Human infections, although relatively rare, have likewise been documented in several countries.
The Australian confirmation comes as new scientific findings continue to reshape understanding of how the virus behaves in mammals.
A recent study conducted by researchers at the University of Pittsburgh School of Public Health examined the unprecedented outbreak that struck dairy cattle in Texas during 2024. Veterinarians were initially puzzled because the disease did not behave like a typical influenza infection.
Rather than attacking the respiratory system, the virus primarily caused severe mastitis, an inflammation of the udder that affects milk-producing animals.
“Mastitis is a classic disease of dairy animals, and veterinarians carefully investigated all the usual suspects, such as bacterial pathogens,” said Dr. Suresh Kuchipudi, the study’s senior author.
“When it turned out to be bird flu, everyone in the field was genuinely surprised. We never even considered that cattle could serve as hosts for H5N1,” he said.
To understand why the virus targeted cattle in such an unusual way, researchers analyzed glycans, sugar-based molecules that act as receptors for influenza viruses in different tissues.
The study found that while glycans are present in cattle respiratory systems, the specific receptors preferred by H5N1 are far more abundant in mammary tissue. This helps explain why the virus established infections in udders rather than lungs.
During infection, large quantities of viral particles were shed into milk, creating transmission risks for farm workers and animals that came into contact with raw milk before processing.
Scientists emphasize that pasteurized milk remains safe because the heating process destroys the virus. However, raw milk can present a potential pathway for transmission.
Researchers believe the findings may help identify which species could be vulnerable to future outbreaks.
“We can screen different species and tissues in advance to assess their susceptibility,” Kuchipudi said, suggesting scientists may eventually be able to predict which animals are most at risk and how infections are likely to manifest.
Although health authorities stress there is currently no evidence that H5N1 can spread efficiently between humans — a critical requirement for a pandemic on the scale of COVID-19 — experts caution against complacency.
Dr. Michelle Wille, outreach coordinator at the WHO Collaborating Centre for Reference and Research on Influenza at the Doherty Institute, said the ecological consequences of the virus have already been severe in many parts of the world.
“Unfortunately, wherever this virus appears, the impacts can be truly catastrophic, with mass mortality events in wildlife and, in some locations, population declines at the species level,” Wille said.
She urged the public to remain vigilant and report unusual wildlife deaths rather than attempting to handle animals themselves.
“Please do not touch carcasses, but observe carefully and document what you see. Reporting is absolutely crucial,” she said.
Australian authorities have echoed that advice, urging residents not to handle sick or dead birds or other wildlife and to immediately report suspicious findings through the national Emergency Animal Disease Hotline.
The arrival of H5 avian influenza in Australia ends years of anticipation among disease experts who had watched the virus spread across the globe. While the immediate risk to the general public remains low, scientists say the country’s unique wildlife now faces a new and potentially significant threat that will require close monitoring in the months and years ahead.
