Disease and Cause

Avian influenza (or bird flu) is a highly contagious viral infection of birds. Some avian influenza viruses, called 'highly pathogenic avian influenza' (HPAI), can cause sudden high mortality (up to 100%) in domestic fowl (chickens) and turkeys.

Avian influenza viruses belong to the influenza A group in the family Orthomyxoviridae.

Species Affected

All commercial or domesticated poultry and many wild bird species are susceptible to infection with avian influenza. However, disease outbreaks occur most frequently in chickens and turkeys.

Avian influenza viruses can be brought into Australia by nomadic or migratory wild birds and then cycle through Australian wild or free-living waterfowl.

But the waterfowl that are the normal hosts of avian influenza, and have spread the H5N1 virus across Asia and Europe, do not migrate to Australia.

Fortunately, the wading birds that do migrate to Australia are not the normal spreaders of the disease.

Australia's strict quarantine measures are aimed at preventing the disease being transported to Australia.

Biosecurity measures in commercial poultry flocks are aimed at preventing infection with diseases such as avian influenza.

Many species of wild birds and waterfowl (especially geese, ducks and swans) carry the virus but generally show no signs of disease. However, if they or their contaminated excretions come into direct contact with and infect domestic poultry (domestic fowl or 'chickens', turkeys, quail etc) outbreaks of severe disease (HPAI or 'fowl plague') occur.

Generally, humans are not affected, but the H5N1 strain of the virus can infect humans who come in close contact with affected birds.

Distribution

Avian influenza viruses are probably ever-present throughout the world in wild waterbirds, with outbreaks of disease amongst poultry occurring as sporadic events.

It now appears that the H5N1 strain of avian influenza is likely to be endemic in several countries in South-East Asia.

Unlike other parts of the world where outbreaks have occurred recently, South Australia has strict biosecurity guidelines and OHS standards that make transmission to commercial farmed birds very difficult.

However, in the unlikely event that commercial poultry is infected, South Australia has high capacity to detect, isolate and stamp-out outbreaks, including AI. A different strain of the virus has been the cause of clinical disease in commercial poultry in Australia; in Victoria (1976, 1985 and 1992), Queensland (1994) and NSW (1997). All previous outbreaks of the disease were quickly detected, isolated and successfully eradicated without spread or human illness.

Clinical Signs in Infected Birds

The clinical signs are variable and depend on a range of factors including the virulence of the virus, the species and age of the birds infected, the presence of concurrent diseases, and the environment.

In very severe forms the disease appears suddenly and birds die quickly. In less severe forms the birds may be off feed and appear depressed.

In some cases, egg production may fall, and soft-shelled eggs may be produced. There may be profuse watery diarrhoea, combs and wattles may become swollen and blue and respiration may be laboured.

In less severe forms, the clinical signs may include decreased egg production, depression, respiratory signs suggestive of a 'cold', swelling of the face, possibly some nervous signs, and diarrhoea.

However, these signs are not necessarily symptomatic of AI infection, but can be signs of other, treatable diseases.

How the Virus is Spread?

In Birds

Direct or indirect contact, (through contamination of drinking water), with wild or free-living waterfowl is the most likely initial source of infection of poultry.

The virus is highly concentrated in the manure and in the nasal and eye discharges.

Spread can also occur through movement of infected birds (eg. at markets), contact of domestic poultry with contaminated eggs or equipment (crates, fillers, feed trucks etc), or via humans (through contaminated footwear or clothing). Unlike many countries where outbreaks have occurred recently, South Australia has high biosecurity on poultry farms. These strict standards provide significant protection against the disease infecting local poultry, though this remains possible.

In Humans

Transmission to humans occurs only rarely, and then predominantly through the handling of live infected birds or close contact with them and their excretions
Although investigations of the South-East Asian outbreaks continue, there is currently no evidence of human-to-human transmission with avian influenza H5N1 viruses.
Biosecurity precautions are high in Australia. People generally have little or no contact with live poultry, unlike in many other parts of the world currently experiencing an outbreak, where it is the cultural norm. Only workers have relatively close contact with live poultry and high biosecurity and strict on-farm OHS regulations are in place to protect them.

Persistence of the Virus

Environmental conditions have a clear effect on the duration of infectivity of the virus outside the bird. Avian influenza virus can persist and retain infectivity for at least 35 days at 4°C in manure.

The virus can be isolated from lake water where infected waterfowl (free-living or domestic) are present.

The virus can remain infective for several days in carcases at ambient temperature and up to 23 days if refrigerated. The virus can persist in poultry meat products but is destroyed by adequate heating (eg. normal cooking temperatures). Thus it is safe to eat adequately cooked poultry and poultry products in Australia.

In those countries experiencing an epidemic of avian influenza in poultry flocks, the World Health Organisation recommends that poultry and poultry products can be safely consumed if they are properly cooked and handled during preparation. To date, no evidence indicates that anyone has become infected following the consumption of properly cooked poultry or poultry products.

Australia's Control Strategy

In the event of an outbreak of avian influenza in Australia, Australia's agreed strategy, is to eradicate the disease by immediate stamping-out and disposal of infected and in-contact birds to remove the major source of infection.

Additionally, there would be:

• 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; and
• zoning to define infected and disease-free areas.

Vaccination may be an option in some circumstances but no vaccine is currently approved for use on poultry in Australia.

If avian influenza were to pose a significant threat (direct or indirect) to Australia's human population, the Australian Government would activate the Australian Action Plan for Pandemic Influenza. This plan provides direction for the development of actions by all Australian Governments, (Commonwealth and State/Territory), their agencies and emergency services in the event of such an occurrence.

South Australia has strict biosecurity guidelines and OHS standards that make transmission to commercial farmed birds very difficult.

In case of an outbreak, South Australia has high ability to detect, isolate and eradicate infection in poultry.

Quick Links

Visit the following websites for additional information and advice on avian influenza:

• Better Health Channel (this link will open in a new window)
  
• World Health Organisation (this link will open in a new window)
• Food and Agriculture Organisation of the United Nations (this link will open in a new window)
• Animal Health Australia (this link will open in a new window)
• AUSVETPLAN is a series of technical response plans that describe the proposed Australian approach to an emergency animal disease (this link will open in a new window)
• ProMED-mail (Program for Monitoring Emerging Diseases) – an electronic outbreak reporting system that monitors infectious diseases globally (this link will open in a new window)
• Department of Agriculture, Fisheries and Forestry (this link will open in a new window)
• Department of Health and Ageing (this link will open in a new window)
• Department of Foreign Affairs and Trade - Information for travellers to international destinations in Southeast Asia - See Travel Bulletin, Health: Avian Influenza (this link will open in a new window)

Related industry websites:

• Australian Chicken Meat Federation (this link will open in a new window)
• Australian Egg Corporation Limited (this link will open in a new window)

Contacts

To report suspected outbreaks or unusual symptoms contact:

• Emergency Animal Disease Watch (24 hour) Hotline on 1800 675 888
• Local PIRSA Animal Health or veterinary officer

The information on this page was sourced from the Victorian Department of Primary Industries www.dpi.vic.gov.au