First identified in 1996 in domestic geese in Guangdong Province, China, highly virulent H5N1 avian influenza, commonly known as bird flu, gradually spread across the globe and by 2023 it seemed inevitable that it would become established in Australia, given that Australia and Antarctica were the only two continents that remained untouched.
Many epidemiologists considered that the virus would probably arrive in Australia with migratory shore birds coming south from breeding grounds in the northern hemisphere. So, it was quite a surprise when the virus spread into birds and mammals in Antarctica and finally reached Australia in Skuas (Stercorarius antarcticus) and Giant Petrels (Macronectes halli), both large scavenging seabirds likely to have fed on other dying or dead marine species.
The H5N1 virus has since spread to Greater Crested Terns (Thalasseus bergii), and Silver Gulls (Chroicocephalus novaehollandiae), native Australian shorebirds which feed mostly on surface schooling small fish and crustaceans. This adds further confusion because it is difficult to identify a ready infection pathway between predatory birds like skuas and terns.
However, we should not be surprised that virus spread doesn’t follow our expectations given our limited knowledge of the ecological web of our surrounding oceans and sub-Antarctic waters.
Because viruses are ‘tricky’, as one scientist put it, and do unexpected things, we should be looking at the many ways in which the virus might spread onwards from seabirds. Here it is asked whether rabbits may play a role because they are a widespread introduced species and probably the most common wild mammal living near beaches where infected marine birds have come ashore. The prospects are as follows.
European rabbits (Oryctolagus cuniculi) and American cottontails (Sylvilagus sp.) have both been experimentally injected with H5N1. They did not die, but showed elevated temperatures for a few days, shed virus from lesions in the lungs over six or seven days, and formed antibodies within a fortnight.
Plateau pikas and Daurian pikas (Ochotona curzoniae and Ochotona dauurica respectively, also lagomorphs like rabbits and hares) have been naturally infected with H5N1 bird flu in China. Research suggests they could function as intermediate hosts where similar viruses could recombine, potentially helping H5N1 adapt to mammals.
Antibodies to H5N1 have recently been detected in a wild desert cottontail (Sylvilagus audubonii) in Arizona (USA). This is despite little routine testing being done on animals such as rabbits because they are considered unlikely hosts of the virus.
In Europe, surveillance of mammal species to detect the presence of antibodies against H5N1 avian influenza has almost exclusively concerned species likely to consume dead water birds. Antibodies against the virus have been widely detected in red foxes and wild boar as well as domestic cats and dogs. There has been little attention given to surveillance of rabbits simply because they don’t share common food resources with waterbirds which are the main reservoir for avian influenza.
The H5N1 virus can apparently remain viable after passage through an insect’s gut, as is the case with Rabbit Haemorrhagic Disease Virus, making it possible that blowflies feeding on dead seabirds could spread H5N1 to animals feeding on vegetation that the flies also inhabit.
Researchers have argued that there could be transmission of avian influenza viruses in both directions where birds live alongside rabbits. Consequently, consideration should be given to the fact that seabirds such as mutton birds or Short-tailed Shearwaters (Ardenna tenuirostris) and Little Penguins (Eudyptula minor) share burrows with wild rabbits, especially on coastal islands.
It is also worth noting that wild rabbits are the major prey of introduced red foxes (Vulpes vulpes) and feral cats (Felis catus) in Australia. Although foxes are more likely to become infected with H5N1 avian influenza by directly scavenging dead seabirds, feral cats may be more likely to become infected by eating diseased rabbits because they generally seek live prey.
Because rabbits and foxes usually survive H5N1 infection, yet form antibodies against the virus, they could be ideal animals to use for detecting and monitoring disease spread. Sera collected from shot animals could be quickly assessed using virus antigen and antibody tests. The genetic sequences of any H5N1 viruses found could also give insights into the origin of the virus by comparing them with those from nearby seabird remains.
If the connections between infected seabirds and rabbits outlined above prove to be important, H5N1 bird flu could begin to spread extensively in Australia in September or November when rabbit populations reach their annual peak of abundance and large numbers of carrion feeding flies arrive in southern Australia with the first hot winds from the north. Rabbits with immune systems compromised by myxoma virus infection will also be more common at that time, especially in higher rainfall areas where European rabbit fleas rather than mosquitoes are the major disease vectors during early spring. That will make the rabbits more prone to infection with other diseases.
It is currently unknown whether H5N1 will become widely established in Australia, and even if it does, rabbits may prove to be unsuitable or unimportant hosts for the virus. However, in terms of assessing risk it pays to consider all options. Canvassing possibilities now provides a head start should further action be needed.
Selected References
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Bird Flu (Avian Influenza). Australian Centre for Disease Control. https://www.cdc.gov.au/diseases/bird-flu-avian-influenza
Catling PC. (1988) Similarities and contrasts in the diets of foxes, Vulpes vulpes, and cats, Felis catus, relative to fluctuating prey populations and drought. Wildlife Research 15, 307–317. https://doi.org/10.1071/WR9880307
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Zhou J, Sun W, Wang J, Guo J, Yin W, Wu N, Li L, Yan Y, Liao M, Huang Y, Luo K, Jiang X, Chen H. Characterization of the H5N1 highly pathogenic avian influenza virus derived from wild pikas in China. J Virol. 2009 Sep;83(17):8957-64. doi: 10.1128/JVI.00793-09. Epub 2009 Jun 24.
About the Author:
Dr Brian Cooke is Patron of Foundation for Rabbit-Free Australia
Date: August 2026