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Avian Influenza

Avian influenza is a highly contagious viral disease primarily affecting avian species.

Avian influenza viruses are divided into high pathogenicity and low pathogenicity pathotypes.

Overseas, the emergence of high pathogenicity avian influenza subtype H5Nx clade 2.3.4.4b has produced a significant increase in the intensity, frequency and geographic range of HPAI outbreaks in both wild birds and poultry. Mortalities in wild birds have been observed in a wide range of species, seen as individual bird deaths and mass mortalities. Clade 2.3.4.4b has also resulted in unprecedented morbidity and mortality events in terrestrial and aquatic mammals.

At the time of writing, HPAI subtype H5Nx clade 2.3.4.4b has not been detected in Australia.

LAST UPDATED: 5 April 2024

If you suspect avian influenza in birds, immediately notify your private veterinarian, jurisdictional department of primary industries or equivalent or call the Emergency Animal Disease Hotline: 1800 675 888.

Key points

  • Avian influenza (AI) is a contagious viral disease primarily affecting avian species. Avian influenza is divided into two pathotypes – high pathogenicity avian influenza (HPAI) and low pathogenicity avian influenza (LPAI).
  • HPAI can be spread by domestic and wild birds. Domestic birds can become infected through exposure to virus from wild birds, and vice versa.
  • HPAI can cause severe illness and death in infected birds.
  • The HPAI subtype H5Nx clade 2.3.4.4b has resulted in illness and deaths in birds globally, as well as terrestrial and aquatic mammals.
  • All previous HPAI outbreaks in Australia are suspected to have arisen from viral lineages already present in Australia.
  • As of 4 April 2024, HPAI H5N1 has been detected in Indonesia and a sub-Antarctic island (South Georgia). While AI has been detected in mainland Antarctica, it is not yet fully typed. More details on the locations of historic and current outbreaks are available at WAHIS.
  • HPAI subtype H5Nx is not present in Australia, however it is advancing globally.
  • Though the likelihood of HPAI H5Nx being introduced to Australia through migratory birds’ annual flight paths has increased with the globalisation of HPAI H5Nx, the likelihood is still considered to be low.
  • Humans are susceptible to infection with AI viruses. Natural exposure to some AI pathotypes, including HPAI subtypes, has caused human disease in various forms, ranging from mild or inapparent infection to death. Most of the HPAI viruses circulating in birds do not readily infect humans. Where human infection does occur, it is usually via direct contact with the infected bird or its excretions.
  • There is no evidence that HPAI virus can be transmitted to humans through properly handled and prepared food.

An HPAI virus, subtype H5Nx clade 2.3.4.4b, is spreading globally, causing unprecedented outbreaks in domestic poultry and wild birds. Some terrestrial and aquatic mammals have also been infected, primarily by ingestion of infected birds.

AI viruses are being detected in a growing number of bird orders. With this increase, HPAI may be becoming endemic in geographical regions such as Europe where HPAI has historically been seasonal. This is resulting in resurgent outbreaks and difficulty in eradication.

The global situation with AI is dynamic, and continued vigilance is necessary.

AI viruses are divided into two pathotypes — high pathogenicity AI (HPAI) and low pathogenicity AI (LPAI) — based either on the lethality of the virus in experimentally inoculated chickens or on the molecular characteristics of the virus. Wild birds are the natural host for LPAI and it does not result in significant disease.

Influenza A viruses have been isolated from most major bird orders — to date, at least 485 bird species, of which 258 are newly-affected since 2021 have been reported. Experimentally, AI virus can infect almost all commercial, domestic and wild avian species. Humans are susceptible to infection with influenza A viruses.

AI viruses are widely distributed throughout the world, and outbreaks have occurred in Australia. Wild birds in Australia actively carry and shed LPAI virus without suffering noticeable clinical signs. All Australian outbreaks to date have arisen from endemic LPAI H7 viruses which evolved to acquire high pathogenicity.

The new HPAI subtype H5Nx (‘x’ due to the variety of neuraminidase subtypes detected, including H5N1 and H5N8) viruses have the ability to infect and cause disease in a wide range of avian species including poultry and wild birds. These new strains (particularly H5Nx clade 2.3.4.4b) differ significantly from previous HPAI H5 viruses in their increased outbreak frequency, geographic range and ability to spread via a wide range of avian species.

Source: Department of Agriculture, Fisheries and Forestry

The clinical signs of AI virus infection are variable and influenced by the virulence of the virus, the species infected, the age of the infected individual, concurrent infection with other disease-causing agents, acquired immunity and environmental factors such as temperature. Pathogenicity in poultry can vary during an outbreak. Some birds may remain sub-clinically infected.

In severe forms, the disease appears suddenly and birds can die within 24 hours, sometimes without showing signs of the disease. In many cases, an increase in flock mortality is the first indicator of infection with HPAI. In chickens and turkeys, clinical signs include:

  • lack of energy and reduced feed and water consumption
  • severe respiratory signs with excessively watery eyes and sinusitis
  • neurological signs such as tremors and paralysis
  • cyanosis of the comb and wattles
  • oedema of the head, resulting in swelling
  • misshapen or soft-shelled eggs
  • significant drop in egg production.

Ducks tend to predominantly display neurological signs, with decreased activity and lethargy as a common finding.

Clinical signs alone are suggestive but not confirmatory. The possibility of HPAI must be investigated by laboratory testing. HPAI is nationally notifiable.

Strains of HPAI virus could be introduced to, or arise in Australia through:

  • migratory birds and other natural non-migratory movements of infected wildlife
  • illegal importation of contaminated goods
  • importation of contaminated poultry products, fomites, inanimate objects or people
  • evolution of domestically-circulating Australian lineage LPAI viruses to acquire high pathogenicity.

If an outbreak of HPAI involves the poultry industry, the largest impact will be on the domestic economy. Chicken meat and eggs are produced very efficiently in Australia and provide the cheapest source of animal-based protein available to the population; this is reflected in the consumption rate. Loss of availability of these products would cause economic stress to the majority of the population and the domestic economy.