Bird Flu: Must-Knows For Backyard Chicken Keepers (And Breeders)

REPUBLISHED:
Original publication July 25, 2024 – Lay Me A Rainbow
by Jane Cowan

Exhortations to prevent contact with wild birds to avoid avian influenza can be a source of anxiety for chicken keepers. It’s near-impossible to exclude all birds from even an enclosed run and locking up chickens comes with its own risks — overcrowding, stress and exposure to higher manure loads, to name a few. 

Simplistic advice focused on wild birds also conveys the wrong message about the most likely way a backyard flock could become infected with highly pathogenic avian influenza, known as HPAI. An understanding of the mechanism by which this deadly form bird flu arises, and spreads, reveals it’s not wild birds that pose the greatest threat. The most likely way a small backyard flock would contract HPAI is via contamination, spread from an infected commercial poultry farm. 

Here’s what you need to know: 

1. Wild birds only transmit the low pathogenic form of bird flu (LPAI) that causes no or mild symptoms.
2. The “low path” version has to mutate in order to become “high path” which is deadly to chickens.
3. High density commercial chicken farms provide the conditions conducive to large amounts of viral mutation, thus increasing the probability that the highly pathogenic form (HPAI) will emerge.
4. Whilst it’s possible for high path bird flu viruses to arise in backyard flocks, it is highly unlikely (one study identified 2 instances globally in the 56 years from 1959 to 2015)
5. The most likely source of infection for a backyard flock is a commercial poultry farm, via the movement of contaminated vehicles, machinery, equipment, birds, eggs or people.
6. High path bird flu does not transfer back into wild birds from infected poultry (again, possible but the scientific literature records only a single documented case of HPAI in a wild bird in Australia, dating to 1985).
7. Biosecurity should be a priority, focused on preventing entry of contaminants from big poultry farms either via movement of machinery, people, bird, equipment etc or cross-contamination at feed stores and other hubs.
8. H5N1 will be a different story as it can be spread directly from wild birds. If this form of bird flu arrives in Australia, the measures required to protect your flock will need to be much more stringent and focused on eliminating contact with wild birds especially waterfowl or water contaminated by their droppings.

Note: This article relates to the current bird flu outbreak in Australia, caused by H7 variants of bird flu. These variants are different to the super bad H5N1 variant responsible for devastation in poultry, wild birds and mammals overseas. 

As a small breeder of heritage and rare breed chickens, and a former investigative journalist of two decades, I have been scouring the scientific literature and seeking expert opinion in order to understand what’s going on with bird flu in Australia. This article is not intended to be exhaustive. I don’t rehash the stock standard information you can find elsewhere. Rather, my hope is to fill in some of the potential gaps in your (and my own) understanding. 

My thanks to poultry veterinarian Dr Jose Quinteros, lecturer in poultry health from the University of Sydney Veterinary School and member of the Poultry Research Foundation, who gave generously of his time in granting Lay Me A Rainbow an exclusive extended interview.

Weighing The Threat: Wild Birds vs Big Poultry Farms

Wild ducks, geese and swans are the natural hosts for bird flu. Many different bird flu variants circulate constantly in the wild bird population but they’re what’s known as “low pathogenic” avian influenza, or LPAI. All the available evidence suggests that HPAIs do not arise in the wild and (with the exception of H5N1) do not cross back from infected poultry into wild birds.

Attempts to find highly pathogenic forms of bird flu (HPAI) in Australian wild birds have been unsuccessful, except for a single case in 1985. A starling caught in an infected shed on a commercial poultry farm tested positive for HPAI. Other wild birds on the farm were tested including sparrows, swallows, pigeons, magpies, wagtails, ducks, galahs, honeybirds, spoonbills, ibis, plovers, ravens, grebes, doves, blue cranes, mudlarks and finches. All were negative. 

Furthermore, a 2016 study published in the Proceedings of the National Academy of the Sciences USA found, “In countries where long term surveillance is conducted in the wild bird system (more than 43 years), no novel emerging HPAI virus subtypes have ever been isolated. ”

Size Matters 

Every outbreak of bird flu in Australian from 1976 to 2024 has arisen on a large, commercial poultry farm. Poultry vet Dr Jose Quinteros teaches poultry health at the University of Sydney and is a member of Australia’s Poultry Research Foundation. He told Lay Me A Rainbow, “Mutations to highly pathogenic flu do not happen in wild birds, because their flocks are constituted by a relatively low number of individuals.”

“However, when a poultry farm gets infected with a low pathogenic variant, due to the high number of individuals in that flock, the virus mutates to produce a highly pathogenic form. That is why you don’t see wild birds sick or dying, and that happens in poultry farms.”

“It is the high density that allows the virus to mutate multiple times, until a highly pathogenic variant emerges. It is the same reason why highly pathogenic variants do not emerge in wild birds: flocks are too small to provide that mutation rate.” Dr Jose Quinteros, Poultry health academic

According to a National Avian Influenza Surveillance Dossier published by the Australian Government in 2010, most Australian meat chicken farms at that time housed about 50 000 birds per shed and 300 000 birds per farm. Even meat breeder farms contained 7000 to 10000 birds per shed and 20 to 40 000 per farm. 

Compare that to the small flock free-ranging in the average backyard. According to the Bureau of Statistics’ most recently published census of Australian backyard poultry ownership in 1992, most backyard chicken keepers keep between two and ten birds. Even poultry enthusiasts who show and sell their pure breeds, typically average 50 birds per flock.

The census estimated another 3000 to 5000 niche poultry growers kept small flocks up to 500 birds for meat and egg production. In terms of risk, even 500 birds is many orders of magnitude smaller than the smallest commercial poultry operation.

Small Flocks: It Can Happen

While safer, it’s not impossible for HPAI to arise in a small backyard flock. A 2018 study published in Frontiers in Veterinary Science examined the 56 years from 1959 to 2015 and found a total of 41 instances worldwide where a bird flu virus mutated from LPAI to HPAI. All but two of those instances occurred in commercial poultry farms. 

The study notes two cases where HPAI arose in what it describes as “backyard flocks”, however it’s not clear how many birds each flock contained.:

• A backyard rural flock in Italy in 1997 
• A backyard broiler farm in France in 2015 

The researchers observed the overwhelming pattern was for highly virulent avian influenza to evolve within intensive poultry production systems. They acknowledged the possibility that HPAI viruses could be emerging in less intensive settings, but going extinct before being detected. 

Alternatively, they hypothesised that HPAI cannot develop in small flocks because in these settings the most virulent variants are simply unable to find enough susceptible hosts. As a result, the chain of transmission is broken and the virus dies out. In contrast, within a high-density setting, the evolutionary cost to the virus of gaining virulence decreases. It can kill its host quickly and still find enough other hosts to perpetuate itself i.e. being highly pathogenic doesn’t limit transmission here. 

Interestingly, the researchers also made comment that “all in, all out” practices where whole cohorts of birds live and die as one prevent the emergence of HPAI-resistant chickens. HPAI is said to cause near-100 per cent mortality in chickens. But the researchers seem to leave room for the possibility that some individuals may be able to survive it. We don’t see it though, because (they say) any birds potentially capable of surviving an HPAI outbreak are culled along with the sick, precluding selection for natural resistance within the poultry population. 

The researchers contrast this with what may go on in a backyard setting. “Birds that may have survived a local outbreak would possibly be used to restock with the possibility to select natural resistance genes, and mathematical models indicated that this may influence the evolution of virulence and host resistance.”

Note, the infection of a backyard flock in Canberra is not being treated as a separate outbreak or “spillover” of an LPAI virus from wild birds, mutating into HPAI within the backyard birds. The flock was within the quarantine area, which would seem to make infection via contamination from the nearby infected poultry farm the most probable scenario. 

Veterinary virologist Dr Andrew Read is one of the chief scientists currently involved in bird flu surveillance in NSW and the ACT, based at the Elizabeth MacArthur Agricultural Institute. Dr Read told the ABC’s 730 program on July 16th that the virus can travel as far as one kilometre “on the wind”. 

Biosecurity In The Backyard Flock 

Yes, it’s sensible to minimise contact with wild birds and prevent chickens drinking water that may be contaminated by duck droppings. But focusing on these measures overlooks the most likely way deadly bird flu would enter a backyard flock – via contamination, spread from an already-infected poultry farm. 

Do you know where your nearest commercial chicken farm is?
If you’re a breeder, does the same truck that delivers your bulk chicken feed deliver to poultry farms? Does the poultry farm buy from the same local ag supplies store as you? What about less obvious threats – the gas bottle delivery guy, the repairman or the tree lopper? Have they recently done work on a poultry farm or at the home of someone who works at a poultry farm? 

Incidental visitors and shared service providers can unwittingly bring virus from the big chicken farm to your backyard flock. Without disinfection, the bird flu virus can persist for quite a while on surfaces and in the environment – although exactly how long is unclear. This is how the NSW outbreak spread to the ACT – via a shared egg collection facility. Lay Me A Rainbow understands eggs from a NSW farm were sent to the collection facility before that farm was diagnosed with HPAI, due to the lag between infection and the development of outward symptoms. 

Small changes like changing shoes upon entering poultry areas are easy enough to implement. Proper biosecurity means restricting entry to your property and disinfecting all vehicles that enter. You might, for instance, keep a backpack at the gate and spray the tyres. 

What About Vaccines?

A vaccine for bird flu exists but is not currently commercially available in Australia. This is primarily because Australia is aiming to regain its status of “free of bird flu without vaccination”, important for Australian poultry producers to retain maximum access to international markets.

When diagnosed in a country, HPAI blocks the export of poultry products.Post-outbreak, countries that are free of HPAI, but only by means of vaccination, cannot export to countries that are free without having resorted to vaccination. Being “free without vaccination” allows a country to export anywhere in the world, a huge competitive advantage. Once a country declares HPAI as endemic, vaccines are commonly used, but export markets become limited.

The University of Sydney’s Dr Quinteros suspects it may reach a point where the global poultry industry recognises the entire world as HPAI-endemic and moves toward vaccination without any accompanying loss of market access. The use of vaccines may exert its own selection pressure on viruses, with the possible emergence of super mutants. Biosecurity will remain paramount. 

Keeping Eggs To Save Genetics

The main mode of transmission for bird flu is horizontal, i.e. between individuals within a flock. But what about the next generation? Eggs from infected hens can carry the virus on the eggshell. It’s also possible for the virus to penetrate the shell and be carried inside the egg, which has been demonstrated experimentally and naturally.

There is no proof, poultry vet Dr Quinteros says, of transovarian transmission which would constitute true vertical transmission. In any case, he says, highly pathogenic forms of bird flu are lethal to chicken embryos, so an infected egg will not hatch. The only prospect of saving your genetics would seem to be by keeping a store of eggs so that, in the event of a diagnosis, you might have some that were collected before the hens contracted the virus and still remain viable. 

The incubation period for HPAI depends on the particular variant, its virulence, the size of the dose the bird received and the exact route of exposure. Onset can be sudden – chickens may exhibit clinical signs within three days of exposure. The first thing you know about it may be a shed full of dead birds that seemed fine when you locked them up the night before. 

On a flock basis, the time from exposure to symptoms is thought to be 14 days. But University of Sydney poultry vet Dr Quinteros says it can take as long as three weeks for clear clinical signs to show themselves on a farm. In the event of a HPAI diagnosis, eggs collected longer than 14 days to 3 weeks earlier should be disease-free, although they’d be borderline too old to garner high hatch rates. 

End In Sight? 

Australia must go two months without a single new case before the current bird flu outbreak can be declared over. 

• Victoria hasn’t had a new case since June 24th. 
• New South Wales’ last detection was June 22nd. 
• The ACT’s most recent farm case was June 27th followed by the July 5th in a nearby backyard flock. 

All previous outbreaks of bird flu in Australia have been successfully eradicated by culling and quarantine. But even once this outbreak is eradicated, the big one could unfortunately be around the corner. Right now, Australia, New Zealand, Papua New Guinea and the various Pacific islands making up Oceania are the only places in the world free of the catastrophic H5N1 variant of bird flu. This variant kills wild birds as well as poultry, crosses from birds to mammals and can kill people. The pharmaceutical company Moderna is already developing an H5N1 mRNA vaccine in case of a human outbreak or, worse, pandemic.

Until recently there had been quite a bit of hope that Australia was protected from incursions by H5N1 because Australian ducks don’t cross Wallace’s Line, a hypothetical boundary that passes between the islands of Bali and Lombok, separating the highly distinctive faunas of the Asian and Australian biogeographic regions. 

The CSIRO’s bird flu expert Dr Frank Wong still considers the risk of H5N1 reaching Australia “relatively low, however, the risk has slightly increased because of H5N1’s ability to infect additional species of wild birds. This increases the chance of introduction through regional or bridging species.” Dr Frank Wong, CSIRO

The national broadcaster is reporting that many Australian authorities are now treating the arrival of H5N1 as inevitable, potentially as soon as this spring when migratory birds return to our shores. The fear is that the shorebirds could bring the virus back, infect local ducks and then ducks could then carry the virus to poultry farms. 

Best case scenario, the relatively short period of viral shedding in faeces, combined with relatively long migration journeys to Australia could mean shorebirds are no longer infectious by the time they get here. Ducks will also be nesting in spring when the shorebirds arrive, making them less mobile and possibly less likely to mingle with the shorebirds. 

It’s probably a long shot, though, to think that Australia could remain forever free of a virus that’s invaded every other corner of such an interconnected planet. If and when H5N1 does arrive, the current difficulties will pale in comparison. At that point, contact with wild birds will become much more risky for backyard chickens. Now is the time to plan for what you’ll do. 

References

Cross, Garry M. “The Status of Avian Influenza in Poultry in Australia.” Avian Diseases, vol. 47, p96–103, 2003

Dhingra MS et al, Geographical and historical patterns in the emergences of novel highly pathogenic avian influenza (HPAI) H5 and H7 viruses in poultry, Frontiers in Veterinary Science, vol. 5, p84, 2018

Frew, Bianca, Expert Commentary: What’s going on with bird flu in Australia? CSIRO, July 19 2024

Hanson, Britta Ann, Temporal, Spatial and Species Patterns of Avian Influenza Viruses Among Wild Birds, The University of Wisconsin – Platteville, 1995

Krauss S, Stallknecht DE, Slemons RD, Bowman AS, Poulson RL, Nolting JM, et al. The enigma of the apparent disappearance of Eurasian highly pathogenic H5 clade 2.3.4.4 influenza A viruses in North American waterfowl, Proceedings of the National Academy of the Sciences USA, 113(32):9033–8, 2016

Swayne, D. E., Suarez, D. L. and Sims, L. D. Influenza. In: Diseases of Poultry. Swayne et al (Ed). John Wiley and Sons Inc. 210.256, 2013

Tracey John P et al, The role of wild birds in the transmission of avian influenza for Australia: an ecological perspective, Emu 104, 109-124, 2004

Webster RG, Bean WJ, Gorman OT, Chambers TM, Kawaoka Y. Evolution and ecology of influenza A viruses. Microbiological Reviews, 56(1):152–79, 1992

Wildlife Health Australia Fact Sheet: Avian Influenza in wild birds in Australia Fact Sheet, June 2024