Understanding bird flu dynamics in Australia
Bird flu in Australia’s wild birds
Last winter the northern hemisphere saw some of the worst outbreaks of avian influenza, or ‘bird flu’, ever experienced.
Canada and the United States reported more than 400 outbreaks of severe bird flu affecting more than 40 million birds, both poultry and wild birds. These outbreaks came after the same virus strain swept through Asia, Africa and Europe in late 2021. It caused widespread outbreaks and millions of deaths in poultry and wild birds.
What might this mean for Australia? Will we see similar outbreaks? Whilst the risk of the same strain arriving in Australia is lower compared to the continents affected so far, we need to remain vigilant to the possibility of incursions because the virus continues to evolve and change.
Until recently, studies of waterbirds in the northern hemisphere provided most of our understanding of the ecology and evolution of avian influenza viruses in Australia’s wild birds. But Australia’s wild waterbirds, like duck and geese, face different environmental conditions and don’t show the same migratory behaviour as their northern hemisphere cousins.
What is bird flu?
Influenza A virus is the cause of bird flu. It is a multi-host virus, which means certain strains can adapt to infect different host species. Different strains of Influenza A can cause seasonal flu in humans, swine flu in pigs and horse flu in horses. The origin of all these strains is wild birds, mainly waterbirds.
Generally, wild birds are infected with low-pathogenicity avian influenza virus. They are part of the natural collection of viruses in wild bird populations. Infected birds are asymptomatic and behave normally, even while transmitting the virus to other birds.
If wild waterbirds shedding low pathogenicity virus come into contact with birds on poultry farms, the virus can be passed on and circulate among farmed birds.
What causes severe outbreaks?
Certain bird flu strains, known as H5 or H7 viruses, can mutate in poultry to become high pathogenicity virus. They cause outbreaks of severe avian influenza resulting in many sick and dead birds in affected farms. Devastating outbreaks often see 100 per cent mortality, with a high risk of the disease spreading to other farms. In rare cases, bird flu infection can jump from poultry to other species, such as pigs and humans.
High pathogenicity virus can pass back into wild bird populations, causing disease and die-offs in susceptible bird species, and further spread through migration of wild birds. Ongoing inter-continental spread of a high pathogenicity H5 bird flu strain is currently occurring in the northern hemisphere across many Asian, African, European and North American countries that share migratory fly-ways. The result is mass mortalities and devastating impacts on both wild and farmed birds.
The bird flu picture in Australia
Scientists at the CSIRO Australian Centre for Disease Preparedness took part in a recent study, the most comprehensive to date, to provide a clearer picture of bird flu dynamics in Australia’s wild birds. This study identified the virus strains present and how they spread by sequencing the largest number of Australian wild bird avian influenza virus genomes since sampling began in 2006.
It showed avian influenza viruses in Australia’s wild waterbird populations aren’t closely linked to strains circulating in the northern hemisphere. Australia is not on a migratory pathway for ducks and geese from the northern hemisphere. Waterbirds in the northern hemisphere follow clear seasonal patterns of migration over long distances. However, Australian water birds are nomadic and mainly stay within the Australo-Papuan region, moving more unpredictably within the Australian continent according to drought and rain cycles.
The study also found avian influenza virus strains can be carried into Australia by small, migratory shorebirds. But these species carry avian influenza less frequently than species of ducks. Australia mostly acts as a dead-end for avian influenza virus diversity. Strains may persist for varying lengths of time in isolation within the Australian continent or eventually go extinct. It’s uncommon for bird flu viruses from Australia to be introduced by wild birds to other continents.
As part of this study we sequenced and assembled the genomes of more than 300 avian influenza viruses, collected by the National Avian Influenza Wild Bird Surveillance (NAIWB) program. These virus sequences, along with those generated by our partners, have been added to global sequence data platforms. They’re now available to the general scientific community to help understand and track bird flu dynamics across the globe.
Early warning and response
This study provides the first evidence-based picture of avian influenza dynamics in Australia. It reveals where the viruses fit in with those in other parts of the world. Scientists in Australia now have greater information available for avian influenza virus risk assessments, evaluation and improvement of diagnostic tests, and early warnings and responses to new virus introductions.
The project was led by a partnership between CSIRO’s Australian Centre for Disease Preparedness, The University of Sydney, Deakin University, the World Health Organization (WHO) Collaborating Centre for Reference and Research on Influenza and the Commonwealth Department of Agriculture, Fisheries and Forestry, in coordination with the National Avian Influenza Wild Bird (NAIWB) Surveillance Program of Wildlife Health Australia.