Background
The current panzootic of high pathogenicity avian influenza (HPAI) H5N1 has been catastrophic for wildlife, and following substantial geographic spread, clade 2.3.4.4b is found in every region aside from Oceania. Herein, we report the results of our third year of targeted surveillance of incoming migratory seabirds and shorebirds into Australia.

Methods
From October to December 2024, we captured and sampled 946 migratory shorebirds (Charadriiformes) and seabirds (Procelariiformes) in Australia to rule out the arrival of HPAI H5N1.

Results
We did not find evidence of HPAI H5N1 in any of the birds tested, and there were no reports of HPAI H5N1 in wildlife tested through other surveillance schemes in 2024. Unlike previous years, we detected a diversity of low pathogenicity avian influenza (LPAI) viruses in shorebirds. Through phylogenetic analysis, we revealed that the H3N7 and H4N7 viruses recovered from Red-necked Stints were complex mosaic viruses, comprising segments of Eurasian, Australian shorebird and Australian waterfowl segments. One H1N7 virus detected comprised a wholly Eurasian introduction, confirming this incursion route for avian influenza viruses into Australian ecosystems.

Conclusions
These results provide further evidence for the key role of long-distance migratory shorebirds in introducing novel LPAI viruses into Oceania. While our focus on northern migration routes remained appropriate for HPAI H5N1 surveillance in 2024, the continued spread of HPAI H5N1 to sub-Antarctic Islands demands consideration of a potential southern incursion route for Oceania in future.