H5N1 bird flu and Australasian birds

The H5N1 virus transfers between birds by close proximity such as in foraging, roosting or nesting individuals. Migratory seabirds and shorebirds annually move from the Northern Hemisphere to the Southern Hemisphere, often in high numbers, and have the potential capacity to introduce the virus to Australia.

Extensive testing and monitoring of waterfowl, shorebirds and seabirds are occurring throughout Australia. Since the Northern Hemisphere outbreaks more than two years ago, two seasonal influxes of migrating shorebirds and seabirds into Australia have resulted in no detections or evidence of infected birds in the Australasian region. As infection rates in the Northern Hemisphere subside, the risk of transmission to Australia could be expected to reduce.

The spread of H5N1 through the Americas over the last 18 months has been enabled by the connected landmasses with small jumps to Subantarctic islands and to the Antarctic Peninsula. Australia’s and New Zealand’s isolation are contributing to the apparent absence of H5N1 in the region. Various additional hypotheses have recently been proposed for the current absence of H5N1 in Australia, including high levels of endemism in the avifauna, the prohibition on importing live poultry into Australia, and the absence of migratory waterfowl that are known to have spread the virus in the Northern Hemisphere (https://www.nature.com/articles/d41586-024-03208-5), suggesting a potentially stronger freshwater (rather than marine) transmission route.

Various hypotheses have proposed entry via the East Asian – Australasian Flyway for migratory shorebirds, and the return migration from the North Pacific Ocean for shearwaters, skuas and some petrels. A highly speculative study recently suggested kleptoparasitism was a potential avenue for H5N1 into Australia’s avifauna, and another study suggested Black Swans might be at greatest risk due to their genome.

In reality, it is impossible to know how (if) or when H5N1 will arrive in Australasia, and if it does, which taxa will be affected or to what extent. The various H5N1 outbreaks in the Northern Hemisphere have impacted different bird families in different areas at different times, so it is impossible to predict likely consequences here. In many ways, it is counter-productive to make assumptions about potential consequences of H5N1 in Australasia.

Wildlife Health Australia has an extensive resource of H5N1-related information freely available online, including fact sheets and risk mitigation and reporting protocols (https://wildlifehealthaustralia.com.au/Incidents/Incident-Information/category/high-pathogenicity-avian-influenza).

It is important to remain alert and vigilant to the potential arrival of H5N1 to our regions, and to adopt and implement the WHA recommendations at all times.