Australia is experiencing 3 different outbreaks of highly pathogenic avian influenzas.
Dr Debbie Eagles, director of the Australian Centre for Disease Preparedness (ACDP) at CSIRO, describes this as “unprecedented.”
“This year ACDP has conducted 3,000 tests on 1,000 samples since the first detection of H7N3 near Meredith in Victoria in May, and subsequently H7N9 Terang in Victoria, H7N8 in New South Wales and [Australian Capital Territory],” says Eagles.
Presently, H7N3 has spread to 7 additional Victorian poultry farms, while H7N8 has spread to 2 commercial poultry farms in NSW, and 1 in the ACT.
“Previously when we’ve had outbreaks in Australia that’s been a single strain, usually then affecting 1 region,” says Eagles.
Prior to this year, there has only been 8 outbreaks of H7 highly pathogenic avian influenza (HPAI) in Australia since 1976.
Avian influenza viruses are described according to the combination of 2 groups of surface proteins: haemagglutinin or “H” proteins (H1 to H16) and neuraminidase or “N” proteins (N1 to N9).
Samples from each of the affected properties sent to ACDP for whole genome sequencing and bioinformatic analysis confirmed that the outbreaks are not linked.
Instead, the 3 strains are more closely related to H7 strains carried by local Australian wild bird populations, which Australia has a good baseline understanding of thanks to the National Avian Influenza Wild Bird (NAIWB) Surveillance Program.
Usually, these circulate in wild waterfowl, such as ducks and geese, as low pathogenic avian influenzas (LPAI), which do not cause signs of disease. However, when H5 and H7 strains get into commercial poultry farms, they have the potential to mutate and become highly pathogenic – causing devastating disease and death in chickens.
“This is basically due to a mutation of a single virus gene … and we’re not saying that these mutations don’t occur in wild birds as well, but the impact is much more significant in commercial chicken farms because of the nature of how birds are housed,” says ACDP senior research scientist and World Organisation for Animal Health (WOAH) expert for avian influenza, Dr Frank Wong.
Wong says that in commercial chicken farms a lot more birds are located in close contact.
“And chickens actually are naive host population for avian influenza viruses, so they’re more susceptible to infection … because often they don’t have inbuilt immunity. So, once a virus turns highly pathogenic, the “attack rate” is very rapid, it burns through the population,” he says.
Why 3 separate strains have made the jump to poultry in just the past few months remains unknown.
“There could be many reasons we don’t really know because … viruses [are] being carried in wild birds [and it] is very difficult to have a continuous picture of what’s going on before they get into commercial chicken farms,” says Wong.
“So it could be many things, the wild bird dynamics at a particular point of time, climate, changes in weather patterns, or just coincidence.”
So, while any new spillover events cannot be predicted before they occur, state authorities in VIC, NSW, and ACT are controlling the movements in already affected areas to minimise and prevent the risk of further spread of existing outbreaks.
Eagles says: “Each of the infected properties has been dealt with by local authorities in terms of the necessary disposal and subsequent ongoing decontamination of those facilities. That is consistent with a response plan that all states and industry agreed to in advance. So, it’s a very well-developed response plan that Australia has.”
And, while Australia currently doesn’t vaccinate poultry against avian influenza, she says there are ongoing discussions around whether it might be used for certain high-risk species and for people in preparation for the HPAI H5N1 clade 2.3.4.4b H5N1.
Viral strains in this clade are circulating internationally causing severe disease in poultry, and species of wild birds and mammals including cattle (in the US) and marine mammals. It has reached every other continent through the movements of migratory waterfowl that do not come to Australia.
“Indonesia and countries like the Philippines within our region already have this virus … it’s been circulating in those countries, our near neighbours, for a couple of years,” says Wong.
“The risk there is more in our regional nomadic duck species … what we call the bridging species, that might be affected and then kind of hop from island to island.”
In response to the threat posed by a potential incursion of H5N1, last week the government announced $1.1 million of ongoing funding to extend the NAIWB Surveillance Program for 4 years.
The risk-based surveillance program focuses on sampling wild birds at locations near both human populations and commercial poultry farms. But, according to Wong, there are plans to expand and increase the efficiency of this surveillance in northern Australia.
“That’s where we think would be the higher risk for an incursion of exotic strains of HPAI viruses,” says Wong.
“But again, the northern part of Australia ironically poses the most challenge in terms of logistics and coverage because they’re remote sites with very low population and a lot of distance to cover.”
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