Avian Flu Diary: Preprint: Surveillance of migratory shorebirds and seabirds in 2024 in Australia reveals incursions of a diversity of low pathogenicity avian influenza viruses, but not HPAI H5N1

#18,938

Although Australia and New Zealand have both experienced outbreaks of homegrown HPAI viruses (see here and here), the HPAI H5Nx viruses currently beleaguering the rest of the globe have yet to reach Oceania.

At least, not in avian or mammalian wildlife.

Since in May of 2024, Australia reported their first imported human infection of H5N1 - in a toddler who was hospitalized with severe respiratory distress in Melbourne - after visiting Kolkata, India, during February 2024 (see EID Journal: Influenza A(H5N1) Virus Clade 2.3.2.1a in Traveler Returning to Australia from India, 2024).

Oceania's resilience has often been attributed to the Wallace and Weber lines; imaginary dividing lines used to mark the difference between animal species found in Australia and Papua New Guinea and the rest of Southeast Asia (see 2008 study Will Wallace’s Line Save Australia from Avian Influenza?).

On the western side you'll find large mammals, like Elephants, monkeys, leopards, tigers, and water buffalo. While on the eastern side, you'll mostly find marsupials (kangaroos, Koalas, wombats, etc.).

These stark faunal differences also extend to birds, reptiles, and even insects.

But these `lines' are not believed to be impenetrable, and the introduction of H5N1 to Antarctica two years ago may now provide the HPAI H5 virus with an alternate southern route that could circumvent the Wallace and Weber lines altogether.

In late 2023 OFFLU warned:

Given movement data demonstrating connectivity between the polar front to both the Antarctic and Subantarctic islands of Oceania, and Oceania itself, it is plausible that if HPAI H5 were present in the Antarctic region directly south of Oceania, it could be introduced to Oceania.

Readers with good memories will recall that last year we looked at a study from Michelle Wille (@duckswabber) et al. (see Virus Evol. : Contrasting Dynamics of Two Incursions of Low Pathogenicity Avian Influenza Virus into Australia) which examined samples collected from wild birds in Australia between 2020-2020, looking for signs of incursion of avian flu viruses from other regions.

While no sign of imported HPAI viruses were detected, they did find evidence that two LPAI virus subtypes had recently entered Australia; notably an H4 virus of Asian lineage; distinct from those previously seen in Australian waterfowl.

The also found a novel (and more competitive) H10 lineage had emerged in wild waterfowl, poultry and captive birds across Australia, largely supplanting the preexisting strain.

This week, Dr. Wille et al. are back, this time with an updated preprint, which looks at avian samples collected in 2024. While once again, no HPAI H5 viruses were detected, they found even more evidence of Asian and European origin LPAI flu viruses entering Australia via migratory birds.

Due to its length, I've posted the Abstract and a short excerpt. Follow the link to read it in its entirety. I'll have a postscript after the break.

Surveillance of migratory shorebirds and seabirds in 2024 in Australia reveals incursions of a diversity of low pathogenicity avian influenza viruses, but not high pathogenicity avian influenza H5N1
Michelle Wille, Robyn Atkinson, Ian G. Barr, Alexander L. Bond, David Boyle, Maureen Christie, Yi-Mo Deng, Meagan Dewar, Tegan Douglas, Min He, Rosalind Jessop, Lindall Kidd, Hiske Klaassen, Jennifer L. Lavers, Hilda Lau, Ila Marks, Eric Miller, Matthew J. Neave, Tobias A Ross, Vittoria Stevens, Duncan R. Sutherland, Marcel Klaassen
doi: https://doi.org/10.1101/2025.11.06.687052
This article is a preprint and has not been certified by peer review

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Abstract

The current panzootic of high pathogenicity avian influenza (HPAI) H5N1 has been catastrophic for wildlife, and following a significant sweep, 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.

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. A H1N7 virus detected comprised a wholly Eurasian introduction, confirming this route for avian influenza viruses into Australian ecosystems.

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.

(SNIP)

Discussion

Herein, we report the outcomes of the third year [16,20] of targeted surveillance undertaken in Australia to rule out a putative incursion of HPAI H5N1. Despite massive, global expansion of HPAI H5N1 since 2021 [3,36,37], Oceania remains free of HPAI H5N1 [20].
In 2024, as in 2022 and 2023, there was no evidence of incursion of HPAI H5N1, which might be attributed to the limited movement of waterfowl between Australia and the rest of the world, despite the arrival to Australia of millions of individual migratory birds from other species.
Waterfowl have been implicated as an important disperser of HPAI H5N1 given there is evidence that some species (e.g. Mallards Anas platyrhynchos) have no or limited clinical disease [38,39] and have been demonstrated to migrate whilst infected with HPAI H5N1 virus [40,41].

Importantly, however, with the exception of Australian waterfowl venturing into the northern parts of the Australo-Papuan region and vice versa, there are no waterfowl species migrating between Australia and Asia, the latter being a hotspot for HPAI H5N1 [18].

(Continue . . . )

While the news remains positive for now, there is a general feeling it could be short-lived. HPAI H5 continues to expand its (avian and mammalian) host range (see DEFRA: The Unprecedented `Order Shift' In Wild Bird H5N1 Positives In Europe & The UK), and there are multiple `flyways' by which it could arrive.

Major bird migration flyways - Credit CDC EID Journal

A little over a year ago we looked at an informative webinar, held by Australia's Biodiversity Council, on how they are preparing for HPAI H5's almost inevitable arrival. The 1-hour video is available on YouTube, and you'll find a link to a detailed summary below.

Note: Some of the video clips of affected birds may be hard for some people to watch.

Although it is still far-removed from the Australian mainland, just over two weeks ago the Australian government released a joint statement on the discovery of unusual mortality - consistent with HPAI H5 - among elephant seals on the remote island of Heard.