Impacts of a potential HPAI H5N1 incursion on Australian wildlife

The recent avian influenza outbreak (caused by HPAI H5N1 clade 2.3.4.4b) has caused the largest animal pandemic in recent history, affecting >400 species of wild bird (Klaassen and Wille 2023) and 40 species of mammalian wildlife (EFSA et al. 2024; Campagna et al. 2024). Oceania is currently the only region free of HPAI H5N1 (Wille et al. 2024; https://wildlifehealthaustralia.com.au/Incidents/Incident-Information/alert-h5n1-h5-bird-flu-global-outbreak), but each spring brings the highest risk period of incursion from migratory shorebirds and seabirds arriving from the northern hemisphere (Wille et al. 2024; Banyard et al. 2023) or Antarctica. Incursions in other continents resulted in rapid spread and mass mortalities, such as the nearly 600,000 birds that died in South America in 2023 (Banyard et al. 2023). Australian wildlife is similarly likely to face severe consequences, particularly in waterbirds, shorebirds, seabirds, and potentially other species of conservation concern (CMS 2023; NatureScotland 2023). Key transmission modes include contact with contaminated water, infected faeces, and direct interactions between individuals (EFSA et al. 2024), putting water-associated and/or colony-breeding birds at higher risk. Raptors and scavengers are also susceptible, primarily through predation of infected prey and carcasses, which is similarly the main infection route for most affected mammalian species (Wille and Waldenstrom 2023). While most mammalian cases are sporadic, ongoing disease spread amongst marine mammals in South America highlights potential risks to Australian pinnipeds (CMS 2023).

Overall, the impacts on affected populations have been dramatic (Klaassen and Wille 2023), although there are differences in disease outcomes across different species and populations (Teitelbaum et al., 2023) which may relate to immune system architecture, previous exposure, or other ecological factors (Barber et al. 2008; Dewar et al. 2023; McPhail et al. 2024; Tarasiuk et al. 2022). While some populations are showing signs of recovery (Harris et al. 2023), HPAI H5N1 is tied to significant conservation concern due to the immediate and cascading impacts of mass mortality events (Banyard et al. 2023; Campagna et al. 2024; Wille and Waldenstrom 2023; CMS 2023). Efforts to mitigate the impacts of HPAI H5N1 once it arrives in Australia require action by governments and organisations responsible for animal health, such as those under obligations from CMS and the Ramsar Convention on Wetlands via both broad and site- and species-specific risk assessments (CMS 2023). Responses include enhanced surveillance of wild populations, protecting habitat to increase species’ resilience, establishment of rapid response plans (for example, with defined biosecurity measures in natural settings) to manage outbreaks, and vaccination of endangered and threatened species (CMS 2023; Wille and Waldenstrom 2023; Banyard et al. 2023; WOAH 2023).

Figure 1: Global spread and host range of the current HPAI H5N1 clade 2.3.4.4b panzootic. A) Notifications of HPAI H5N1 since September 2021. Arrows show significant spread events. Distribution of notifications across different wild (B) avian and (C) mammalian taxa by order (white text and similarly coloured boxes) and family (black text), with box sizes indicating relative abundance of disease notifications for a specific order/family. Data from WOAH WAHIS database (accessed November 2024). Animal silhouettes from phylopic.com.

Figure 2: Freckled duck (Stictonetta naevosa), a threatened species in Victoria, with teals (Anas sp.), which are known reservoirs for low pathogenicity avian influenza in Australia. Their interaction suggests transmission pathways of avian influenza between known carriers and threatened species, who could be hit hard by HPAI. Photographed by Tobias Ross.