According to Dr Frank Wong, a virologist and avian influenza expert at the CSIRO’s Australian Centre for Disease Preparedness, avian influenza H5N1 has arrived in wild birds in Australia, representing a major milestone for a pathogen responsible for the deaths of millions of birds and mammals across the globe since it mutated in southern Chinese poultry farms in 1996. The arrival follows a decades-long global spread that transformed a relatively harmless virus in migrating wild birds into a highly pathogenic strain.
How the H5N1 Avian Influenza Virus Evolved From Poultry Farms
The current lineage of concern traces back to 1996, when geese in poultry farms in the Guangdong province of southern China fell ill with a virus causing bleeding, neurological dysfunction, and death, according to the source articles. The strain killed about 40% of infected geese. Unlike low pathogenicity avian influenza viruses that cause mild or no symptoms, high pathogenicity strains cause serious illness and death. According to Dr Frank Wong, until 1996 an H5 virus had never been seen spilling into domestic geese to become highly pathogenic in domestic birds, providing an immediate red flag for researchers.
Variants appeared in markets and farms in Hong Kong the following year. By 2002, nearly a million poultry birds were culled in Hong Kong after H5N1 detections. According to Prof Marcel Klaassen, a bird flu expert and ecologist at Deakin University who has studied the strain for 20 years, ducks and geese were free-ranging in the 1990s when outbreaks of highly pathogenic avian influenza occurred. Klaassen notes that the Guangdong goose virus circulated in Hong Kong and East Asia before being detected in wildlife in 2005. By that point, the virus had evolved to survive in certain wild birds, which acted as Trojan horses carrying the pathogen to Europe and Africa.
Global Spread Across Continents and Mammal Species
After re-emerging in Europe in 2021, the lineage swept across the continent, through North and South America, into Antarctica, and finally to Australia. According to Dr Frank Wong, influenza virus impact is a numbers game where allowing the pathogen to infect multiple host animals without control increases its chances of picking up new traits. The virus has infected more than 400 bird species and over 100 mammal species, particularly seals, sea lions, and dairy cattle in the US.
Did you know? Wild ducks function as natural carriers or “Trojan horses” for avian influenza because they have evolved alongside the viruses, allowing them to transport the pathogen across continents without experiencing severe symptoms themselves.
Avian influenza viruses evolve rapidly due to errors during continuous genetic replication, according to Dr Frank Wong, who notes that dense poultry farming acts as an incubator that selects for high pathogenicity. Prof Marcel Klaassen goes further, describing the pathogen as a man-made virus driven by high-density poultry environments rather than wild ecosystems.
Impact on Marine Mammals and Risks in Australia
Since 1997, about 500 human deaths from H5N1 have been recorded, almost entirely among individuals working in close contact with infected poultry. Health authorities maintain that the risk to humans remains low, with no recorded human-to-human transmission. However, the virus has exacted a heavy toll on marine mammals. According to Dr Rachael Gray, a veterinary scientist at the University of Sydney who monitored the disease in Antarctica in late 2023, tens of thousands of pinnipeds have died in South America and Antarctica.
Gray describes witnessing dead elephant seals lining beaches and notes that infected animals display neurological signs such as uncoordinated movement, seizures, and corneal clouding, typically dying within days of symptom onset. The three resident pinnipeds of Australia—the New Zealand fur seal, the Australian fur seal, and the endangered Australian sea lion—are a source of profound concern for Gray. Although researchers hoped Australia’s geographic isolation would protect it, migratory seabirds ultimately brought the virus from the sub-Antarctic during the local winter.
Frequently Asked Questions
How did H5N1 first emerge?
The virus first emerged in 1996 on poultry farms in the Guangdong province of southern China, where a strain in migrating wild birds mutated into a highly pathogenic form in domestic geese.
Can humans catch H5N1 bird flu?
While human cases have occurred primarily among poultry workers, health authorities state that the risk to the general public is low and there is no recorded human-to-human transmission.
Which animals are most affected by the current H5N1 strain?
The virus has infected more than 400 bird species and over 100 mammal species, causing significant mortality among wild birds, seals, sea lions, and US dairy cattle.
How did the virus reach Australia?
Genetic testing confirmed that the virus arrived in Australia via migratory seabirds from the sub-Antarctic, bypassing geographic isolation during the southern winter.
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