As members continue to monitor the global spread of H5N1 highly pathogenic avian influenza (HPAI), questions have been raised about what the current international situation may mean for Australia and how the virus behaves in wild bird populations. The following summary is intended to provide practical context for producers and industry stakeholders.

Should Australia expect H5N1 incursions during future migratory seasons?

The short answer is yes.

Given the widespread circulation of H5N1 in wild bird populations globally, it would be reasonable to expect ongoing risks associated with migratory bird movements into Australia. 

The primary concern for Australia is not the ocean-going migratory birds that occasionally arrive on our coastlines and are often found only as isolated cases. The concern is the opportunities for these migratory birds direct and indirect contact with Australian wildlife, increasing the potential for virus introduction and spread within local bird populations. The current migratory bird incursions on the Australian coast are from South of Australia and the subantarctic, with a further risk from the northern migratory pathway that brings more than 20 species of shorebirds (Charadriiformes) to Australia each spring. 

Understanding incubation periods and disease progression

There is sometimes confusion between breeding cycles and disease incubation periods.

For HPAI viruses such as H5N1, the incubation period is generally around 5–7 days. This differs significantly from Australia’s endemic low pathogenic avian influenza (LPAI) viruses, where infection may circulate within poultry populations for several weeks, as the virus mutates from LPAI to HPAI, before clinical disease associated with an H7 mutation event becomes apparent. The concern regarding backyard poultry increases with H5N1. With low numbers in a flock of backyard poultry the population dynamics does not normally result in the mutation of LPAI to HPAI,  unlike with HPAI H5N1 which will result in clinical disease and mortalities.
Importantly, avian influenza viruses behave differently in different bird species:

• Australia’s wild birds commonly carry endemic low pathogenic strains of avian influenza (LPAI) without showing clinical signs.
• H5N1 HPAI can cause illness and death in some wild bird species, with very significant losses.
• However, many Australian waterfowl have previously been exposed to endemic LPAI H5 viruses and may possess some degree of natural immunity or cross-protection against H5N1.

This does not necessarily prevent infection. Birds may still become infected and shed virus, but potentially at lower levels than entirely naïve populations.

One area of uncertainty is how future generations of Australian waterfowl may respond. Young birds lose maternal antibodies over time and may be exposed to H5N1 before developing immunity through exposure to other endemic H5 viruses. This could potentially result in different disease outcomes and mortality patterns compared with adult birds.

Why do some wild birds die while others appear to act as carriers?

The impact of H5N1 varies greatly between bird species.

Some shorebird species and seabirds have experienced significant mortality events overseas, while many waterfowl species may become infected yet display limited clinical signs. 

Current international observations, including vaccine studies using related H5 strains, suggest that prior immunity can reduce disease severity while still allowing some level of virus infection and shedding.

How long can avian influenza survive in manure and the environment?

The risk posed by manure and contaminated environments depends heavily on temperature and environmental conditions.

Avian influenza viruses generally survive poorly in warm to hot conditions, where viability may be measured in hours, dependent on the nature of the contaminated surface and material. However, under cooler temperatures and in environments with significant organic material, survival can extend from days to weeks, and in some circumstances even longer.

Research suggests avian influenza viruses can persist in frozen environments, which is believed to contribute to their maintenance in northern hemisphere ecosystems.

Being an enveloped virus detergents will aid in inactivating the virus while concurrently assisting in reducing the protective bioburden in preparation for terminal disinfection.

For Australian conditions, the key consideration is that infected wild waterfowl continually introduce virus into their environment through faeces and contaminated water sources. If another susceptible bird species subsequently visits the same area, exposure can occur via environmental contamination rather than direct bird-to-bird contact. And recognised as the most common way commercial poultry are infected.

Population dynamics also influence risk. Even if only a small proportion of birds are shedding virus, mixing between different wild bird species can facilitate transmission through direct contact and contaminated environments.

What does international experience tell us?

Internationally, countries across North America and Europe have experienced periods of several months without H5N1 outbreaks in commercial poultry despite the virus remaining present in wild bird populations. In many cases, poultry outbreaks remain closely linked to seasonal wildlife (wild bird migration) movements rather than continuous farm-to-farm transmission.

Australia’s situation is unique because our waterfowl populations are largely resident rather than undertaking international migrations. It remains uncertain how H5N1 may behave once established in such ecological systems.

Another important consideration is the possibility of reassortment, where H5N1 could mix genetically with endemic Australian avian influenza viruses. The outcomes of such events are difficult to predict and reinforce the importance of ongoing surveillance and preparedness.

Endemic H7 viruses remain a major concern

While much attention is understandably focused on H5N1, members should remember that Australia’s endemic H7 avian influenza viruses continue to represent a significant risk to poultry production. Refer to 2020, 2024 and 2025 multiple outbreaks.

Measures that reduce contact between poultry and wild birds are not only important for H5N1 preparedness but also remain highly relevant for preventing outbreaks associated with endemic H7 viruses.

Temporary recommended housing measures, particularly during periods of elevated risk, can play an important role in reducing exposure opportunities and strengthening overall farm biosecurity.

For producers that are concerned with behavioural changes that may result as a consequence of the housing of their free-range layers, or operating mobile systems that cannot practicably allow housing , significant mitigation against cross contamination with wild waterfowl and AI can be achieved by reducing the period that the layers range and restricting the range of the layers to just a few metres from the shed (Verandah type principle). An ongoing approach or transition to complete housing. Producers though need to familiar with ACCC Guidance under these housing recommendations of variations in access to the range.

The unusual timing of Australia’s 2025 avian influenza outbreak highlights that seasonal patterns are not always predictable. However, if future outbreak risks continue to align with traditional higher-risk periods around July–August, strategic seasonal housing and enhanced / reinforced biosecurity during these periods may significantly reduce the likelihood of outbreaks and the associated costs to both industry and government.

Key takeaways for egg producers

• H5N1 remains a credible ongoing risk to Australia while it continues to circulate globally.
• Migratory and Australian resident shorebirds are likely to be a more significant pathway of concern than ocean-going seabirds.
• H5N1 typically has a short incubation period of approximately 5–7 days.
• Some Australian waterfowl may have partial immunity due to previous exposure to endemic H5 viruses, but infection and shedding can still occur.
• Environmental contamination through faeces and water sources remains an important transmission pathway.
• The behaviour of H5N1 in Australian wildlife populations remains uncertain and requires continued monitoring.
• Endemic H7 viruses remain an important threat to industry and should not be overlooked.
• Essential biosecurity practices and measures that reduce wild bird contact continue to be among the most effective tools available to producers.

EFA will continue to work closely with governments, Animal Health Australia and industry stakeholders to monitor developments and ensure members are kept informed of any changes in risk or preparedness recommendations.

Vaccination

There has been a great deal of foundation work undertaken over recent years in relation to vaccines by DAFF, Australian Eggs, CSIRO and Scolexia. 

Department for Agriculture, Fisheries and Forestry (DAFF)

Some members have been surprised to hear that there is a HPAI vaccine in Australia. This relates to a vaccine for emergency vaccination of rare, protected and valuable avian species against high pathogenicity avian influenza (HPAI) in the event of an incursion (or significant threat of an incursion) of a HPAI strain that is known to be a high risk to avian species .https://www.agriculture.gov.au/sites/default/files/documents/ahc-avian-influenza-vaccination-policy-birds.pdf

CSIRO

There are some great webinars about vaccination available on YouTube and audio on Spotify. 
 VetVaccine YouTube channel
Spotify playlist.
 
Further information is available on the CSIRO website: https://research.csiro.au/vetvaccines/