CASE NOTES

Avain Influenza: Global situation and risk to NSW

Brendan Sharpe, Senior Veterinary Policy Officer, NSW DPI

Posted Flock and Herd November 2024

Introduction: GLOBAL DYNAMICS

Avian influenza (AI) is a highly contagious viral infection, caused by type-A influenza virus. Influenza viruses are enveloped RNA viruses that are prone to mutation, reassortment and recombination. AI viruses are classified as being of high pathogenicity (HPAI) or low pathogenicity (LPAI), associated with specific characteristics at the Haemagglutinin (HA) cleavage site. AI is a notifiable disease in NSW, and HPAI is prohibited matter in NSW.

Australia is currently free of HPAI. HPAI of the type H5Nx has been reported on all other continents within the last three years and has been the cause of significant economic, ecologic and welfare impact, including mass mortality events in domestic poultry, wild birds (e.g. several thousand kittiwakes in Norway Aug 2023) (ProMED, 2023) and mammals (e.g. sea lions, Argentina Aug 2023) (ProMED, 2023), and several spillover events into humans.

The purpose of this article is to provide an update on the global HPAI situation and describe the structure of the NSW commercial poultry industries so that veterinarians are aware of the AI risk profile and likely impacts on food production in NSW.

EPIDEMIOLOGICAL FEATURES

Influenza A viruses have been isolated from most major bird families and almost all HA and Neuraminidase (NA) types have been detected in birds. Furthermore, AI viruses can infect and cause disease in a range of mammalian species and humans. Infection in birds, mammals and humans can range from being asymptomatic through to fatal. AI viruses of subtypes H5 to H10, (particularly those of H5 subtype) have zoonotic potential.

LPAI is an endemic infection in wild bird populations with an estimated prevalence of 1.9% in Australian wild bird populations (Grillo et al. 2015). Wild birds, particularly waterfowl and shorebirds, are considered the natural reservoir host for AI viruses. These birds, particularly in the case of LPAI, often do not display any clinical signs of infection, despite actively shedding the virus.

Australia has experienced eight HPAI outbreaks to date, all H7Nx Australian lineage viruses (1976 VIC, 1985 VIC, 1992 VIC, 1994 QLD, 1997 NSW [Tamworth], 2012 NSW [Maitland], 2013 NSW [Young], 2020 VIC) (Scott et al. 2020). Australia has never recorded HPAI of H5Nx type.

The possible pathways for HPAI establishment in Australia are:

Australian-origin LPAI viruses (endemic in wild bird populations) evolving to become HPAI. The most likely scenario is an LPAI carried by asymptomatic wild birds contacting domestic poultry and evolving to a HPAI virus. This transmission risk pathway is always present and has been the 'traditional' scenario preceding all HPAI outbreaks in Australia to date. The ongoing shift of Australian commercial poultry to free-range production systems increases the potential for exposure of domestic poultry to LPAI, increasing the potential for HPAI in these flocks (Scott et al. 2018).
Exotic HPAI variants entering via natural wildlife movements.

Migratory birds come to Australia via the east-Asian Australasian flyway. Birds entering via this flyway are shorebirds (e.g. Short-Tailed Shearwater) or sea birds coming via the Pacific Ocean from as far north as Alaska and Russia, down through Eastern (and parts of Central) Asia. Many of these jurisdictions have or have recently reported HPAI due to H5Nx.
Local Australo-Papuan wild bird movements.
Potential introduction of wildlife between Antarctica and Australia. The level of risk here is unknown but has received recent attention with H5N1 being recently identified in dead wild birds on the Antarctic mainland.

Entry of HPAI via personnel, equipment or bird/bird products legally or illegally coming into Australia from overseas.

Traditionally seasonal/temporal trends of AI follow the natural migratory movements in wild bird populations, given that they represent natural reservoirs for AI (WOAH, 2023). In the ongoing Eurasian-Americas HPAI epidemic, H5Nx HPAI viruses are being maintained in wild bird populations year-round and are being transmitted directly between wild bird populations and onward to domestic poultry and mammals. This infection spread pattern represents a notable transition in the epidemiology of AI. There is concern surrounding HPAI H5Nx becoming endemic in wild bird populations and the implications endemic infection in wild bird populations could have on at-risk wild bird and mammal populations, the economics of poultry farming and human health.

Considering the risk of exotic HPAI H5Nx virus subtypes establishing in Australia, several factors potentially lower the risk:

Migratory birds to Australia are shorebirds, as opposed to waterfowl. Shorebirds do not move far inland when in Australia and tend to shed the virus at a lower rate than waterfowl (the latter do not migrate to Australia).
The distance of migration potentially means that shorebirds infected with HPAI do not complete the journey. Questions remain about pathogenicity of HPAI H5Nx in shorebirds, i.e. could infected shorebirds be capable of completing the migration?
In 2022 and 2023, researchers Wille and Klaasen surveyed migratory birds upon their arrival from the Northern Pacific to known colonies in VIC and WA and did not find any evidence of exotic H5Nx virus (2022 results - Wille & Klaasen, 2023; 2023 results - still to be published).

NSW POULTRY PRODUCTION: WHERE IS THE RISK?

NSW hosts significant commercial poultry industries, including chicken meat, eggs, duck meat, turkey meat, and other small-scale industries including game/quail.

Chicken meat production

The gross value of chicken meat production in NSW in 2023 was $917M (PDI, 2023), with NSW being the largest producer, accounting for 35% of national production. Chicken meat production in NSW is predominated by a small number of vertically integrated processors. These processors typically own the genetics, hatcheries, feed mills and processing facilities and contract out the growing of broiler chickens for processing. Contract growers have traditionally been family farms but increasingly this end of the industry is being dominated by corporates.

Two imported hybrid lines dominate the Australian market (Cobb and Ross). These genetics are imported into Australia at the Great-Grandparent (GGP) level and in NSW there is an import quarantine facility in the Riverina. Table 1 summarises the distribution of chicken meat production in NSW by region. It can take up to two years for the flow through from GGPs to Broilers, which highlights the importance of preserving the biosecurity of higher-level breeding stock.

Table 1: Distribution of chicken meat genetics by NSW LLS region

Great Grandparents	Grandparents	Parents	Broilers
Riverina	Central West Greater Sydney North-West South-East	North-Coast North-West Riverina	North-Coast North-West Greater Sydney Hunter Riverina

Table egg production

The gross value of table egg production in NSW in 2023 was $354M (PDI, 2023), with NSW being the largest producer, accounting for 34% of the national production. Compared to the chicken meat industry, the egg industry is much more geographically dispersed throughout the state with a genuine mix of large-, medium- and small-scale producers. Free-range production systems continue to expand, accounting for ~57% of grocery sales in 2023 (PDI, 2023). Vertical integration is also not a feature of the NSW egg industry, in that the genetics (breeding stock) are owned separately to table egg producers. The industry is predominated by the imported hybrid lines Hyline and ISA.

Duck meat

Duck meat is a growing industry in NSW. The Greater Sydney and Hunter LLS regions host the majority of commercial duck farms with smaller scale independent producers scattered throughout the state.

Turkey meat

Turkey production in NSW involves the growing (under contract) of turkey poults destined for slaughter, focused in the Hunter and Greater Sydney LLS regions and controlled by the two largest vertically integrated chicken meat processors. There are a small number of smaller scale independent turkey producers throughout the remainder of NSW.

Other avian enterprises

Smaller niche industries involving other avian species, including for example quail, are located throughout the state, notably the Greater Sydney and Riverina LLS regions.

MANAGEMENT OF RISK THROUGH SURVEILLANCE AND ENGAGEMENT

Surveillance

Active (targeted) surveillance for AI in wild birds occurs in Australia under the National AI Wild Bird (NAIWB) surveillance program. The program is managed by Wildlife Health Australia, with funding provided by the Commonwealth and significant in-kind support provided by the state/territory jurisdictions.

Targeted surveillance focusses on sampling from Anseriformes (waterfowl) at sites where there is mixing between Anseriformes and Charadriiformes (shorebirds) and in proximity to poultry and humans. In NSW this surveillance has been conducted in the Hunter Valley. In 2023, NSW successfully applied to increase the number of samples and sampling sites as part of the NAIWB surveillance program. Included in this increase were two significant wetland sites, one in the Riverina and a second in the Northern Tablelands LLS region. These sites are near to the North-West and Riverina LLS regions where there is significant poultry production. This change is in line with geographical changes to the poultry industry in NSW (away from the Greater Sydney and Hunter LLS regions) that have occurred since the inception of the NAIWB program.

Passive surveillance in NSW occurs in both domestic and wild birds by way of submissions to the NSW Animal and Plant Health Laboratory (EMAI) by private and government veterinarians. NSW DPI communications around testing requirements for avian influenza include:

Wild bird mortality events of five or more deceased wild birds, as guided by Wildlife Health Australia
In conjunction with the National Newcastle Disease (ND) Management Plan, AI and ND testing be conducted on commercial flocks, meeting the following criteria:

Any shed/flock experiencing unexplained mortalities of 1% or more in 24 hours (after the first week of placement),
Any shed/flock experiencing increased mortalities of more than 0.5% per days for 3-5 consecutive days,
Any shed/flock with nervous signs regardless of duration,
Any shed/flock experiencing a 10% drop in egg production or appearance of 5% shell abnormalities over 2-3 consecutive days.

Engagement

NSW DPI has enhanced engagement activities in recent times in light of the ongoing global AI situation, including:

Establishment of the Wildlife Health Interagency Group, which includes NSW DPI, NSW Health, NSW EPA, NSW Planning & Environment (National Parks and Wildlife Service), Wildlife Health Australia, and Australian Registry of Wildlife Health. The group meets quarterly and is working toward establishing roles and responsibilities in the event of an AI incursion in wildlife and assessing the risk status from an ongoing perspective.
Ongoing engagement with industry via the NSW Poultry Health Liaison Group. This group meets every six months and includes representatives from DPI, LLS, other state jurisdictions and industry. The global AI situation and relevant risk mitigation strategies are discussed at these meetings.
In 2023, NSW DPI facilitated Exercise Phoenix with the NSW poultry industry, based on a hypothetical AI outbreak in NSW. DPI are currently working on the outcomes of this exercise, including working with industry on deficiencies around destruction and disposal and the development of instructional material to guide sampling for tracing and surveillance during an AI response.

References

Grillo VL, Arzey KE, Handsbro PM et al. (2015) Avian influenza in Australia: a summary of 5 years of wild bird surveillance Australian Veterinary Journal 93(11):387-393
PDI, (2023) NSW Department of Primary Industries Performance, Data & Insights. Available from: www.dpi.nsw.gov.au
Scott A, Hernandez-Jover M, Groves P & Toribio J-A (2020) An overview of avian influenza in the context of the Australian commercial poultry industry One Health 100139
Scott AB, Toribio J-ALM, Singh M, Groves P, Barnes B, Glass K, Moloney B, Black A and Hernandez-Jover M (2018) Low- and high-pathogenic avian influenza H5 and H7 spread risk assessment within and between Australian commercial chicken farms Frontiers in Veterinary Science doi.org
Wille M & Klaasen M (2023) No evidence of HPAI H5N1 2.3.4.4b incursion into Australia in 2022 Influenza Other Respiratory Viruses 17:e13118
WOAH (2023) Avian influenza: understanding new dynamics to better combat disease World Organisation for Animal Health Available from: www.woah.org