Avian influenza

AI is caused by a virus Orthomyxovirus, type A.

Outbreaks of AI in Australia have occurred in domestic poultry since 1976 in Victoria, New South Wales, Queensland and the Australian Capital Territory.

Overseas, an outbreak of HPAI virus of H5N1 strain occurred in Asia, Africa and Europe in 2003, affecting millions of poultry, some species of wild birds and, infrequently, humans.

The 2021–2022 HPAI epidemic season was the largest ever observed in Europe, with nearly 48 million birds culled in over 2,000 outbreaks recorded to September 2022. Significant outbreaks have also been seen in wild birds and poultry in Africa, Asia and North America.

Mammals, especially carnivores and marine mammals have also been affected by HPAI H5N1 outbreaks.

Wild water birds are the natural hosts of low pathogenicity avian influenza (LPAI) viruses and frequently the source of AI infection in domestic poultry. Wild birds (especially wild waterfowl) may contaminate domestic poultry feed or water supplies which, when ingested, may lead to infection or disease.

AI can be confused with other diseases that have similar clinical signs. Early detection and reporting any unusual signs is essential for rapid control of the disease.

Clinical signs are variable and can be affected by the co-infection of other pathogens, the age of the birds, the environment and the severity of the virus itself.

In very severe forms the disease appears suddenly and birds can die very quickly (within 24 hours), sometimes without showing the classical signs of the disease which include:

• depression
• excessive lacrimation (secretion of tears)
• coughing, sneezing and rales (rattling sound in the lungs)
• swelling of the head, eyelids, comb, wattles and hocks
• purple discoloration of the wattles, combs and legs
• decrease in egg production
• production of soft-shelled eggs
• profuse watery diarrhoea
• difficulty breathing
• high mortality (could be up to 100%).

In less severe forms, signs may also include:

• respiratory signs (nasal discharge, coughing and sneezing)
• swelling of the face
• nervous signs
• diarrhoea
• reduced egg production.

Veterinarians can submit samples to the Biosecurity Sciences Laboratory from birds showing clinical signs of avian influenza virus infection.

An outbreak of highly pathogenic (HPAI any subtype) or low pathogenicity (LPAI H5/H7) avian influenza in Australian poultry could have serious social and economic impacts. Trade and markets will likely be disrupted and infected properties will have requirements (including movement control) imposed to control the disease under legislation.

It is critically important that any suspicion of this disease is immediately reported. If HPAI or LPAI (H5/H7) is detected, it is important to eradicate it as quickly as possible to control further spread and reinstate Australia's disease-free status for trade purposes.

Low pathogenicity strains of the AI virus are found in some wild bird populations in Australia, in particular waterfowl such as ducks and geese.

Spread from wild birds or waterfowl to domestic flocks occurs by either direct contact with infected wild birds or through in-direct contact such as contaminated pasture, water or feed.

Infected backyard poultry could also be a source of AI virus for commercial poultry through proximity to the commercial poultry farms, contaminated equipment, clothing or footwear.

Once a flock has been infected, the virus has the potential to change from a low pathogenicity strain to a high pathogenicity strain and potentially cause a significant disease outbreak.

In recent overseas incidents, spread of AI virus between flocks has been mainly due to poor biosecurity involving:

• movement of infected birds
• movement of contaminated feedstuffs, equipment, vehicles, personnel clothing and footwear on commercial or non-commercial properties
• live bird markets (movement of infected birds, contaminated crates and contaminated vehicles)
• egg collection
• depopulation activities that infect nearby properties with birds through wind-borne spread (dust, droplets)
• use of the same transport vehicle for dead bird pickup or waste collection from different premises.

Incubation period of 3–5 days. The virus is able to survive in the environment for variable amounts of time. It will usually survive the longest in water and the faeces of infected birds.

It is important that all poultry farmers and owners, bird fanciers and wild bird carers and watchers are aware of this disease and remain vigilant for any unusual disease occurrence.

Birds which appear to be ill or dead should not be handled without suitable protective clothing and equipment (face mask, gloves).

The period of greatest concern is September to November, when migratory birds return from the northern hemisphere to Australia.

Comprehensive plans to respond to and control an outbreak of highly pathogenic avian influenza in poultry exist at a national level and have been developed in consultation with peak poultry industry body groups.

The nationally agreed response strategy is outlined under AUSVETPLAN for the poultry industry. It includes:

• immediate stamping out and disposal of infected and in-contact birds to remove the major source of virus
• strict quarantine and movement controls to prevent the spread of infection
• decontamination to remove and reduce the virus
• tracing and surveillance to locate the source of infection, locate other infected premises and determine the extent of the infection
• zoning or compartmentalisation to define infected and disease-free areas.

Prevention

Prevention of AI is through routine use of on-farm biosecurity measures that can help to prevent the introduction of the disease into the flock. It is the responsibility of all bird owners (commercial and non-commercial) to implement biosecurity measures to protect their animals from pests and disease.

In free-range situations, the risk is increased as birds are outside and have a higher chance of coming into contact with wild birds or their droppings, compared to flocks that are kept indoors. A high level of vigilance is needed in monitoring the health of your flock.

Vaccination

Control of AI without the use of vaccination is preferred. Vaccination has not been necessary in Australian outbreaks to date, but its usefulness has been demonstrated in overseas outbreaks. If the disease is spreading at a significant rate, vaccination, enhanced biosecurity and other infection control measures may be implemented to protect flocks from infection.

National protection

The Australian and Queensland governments understand the importance of protecting our poultry industry. Measures taken to heighten biosecurity in Australia and Queensland for avian influenza include:

• banning the importation of live poultry, aviary birds and eggs into Australia from countries that have avian influenza
• inspection, quarantine and testing of poultry products (meat and/or egg products and products including feathers) and live birds at airports, seaports and international mail handling facilities
• investigation of reported suspect infection in birds or poultry by Biosecurity Queensland veterinary officers and inspectors
• screening of relevant bird samples submitted for diagnostic purposes by Biosecurity Queensland veterinary laboratories.