Avian influenza is a highly contagious viral infection of birds. All commercial, domestic and wild bird species are susceptible to infection but disease outbreaks occur more frequently in chickens and turkeys. Avian influenza can cause up to 100% mortality in domestic fowls. Many species of waterfowl, especially geese, ducks and swans carry the virus but generally show no signs of disease.

Environmental conditions have a marked effect on virus survival outside the bird. The avian influenza virus can survive for at least 35 days at 4°C in manure. The virus can be isolated from lake water where waterfowl are present. The virus can survive several days in carcasses at ambient temperature and up to 23 days if refrigerated. While the virus can persist in poultry meat products it is eliminated by adequate heating/cooking. Thus it is safe to eat properly 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.

There are many strains of the avian influenza virus, some of which cause no clinical signs while others can be devastating to susceptible birds. These virulent strains are referred to as highly pathogenic avian influenza.

The highly pathogenic H5N1 strain is currently circulating in domestic poultry in a number of Asian and eastern European countries. Other strains have recently been found in Japan and the Philippines. For the latest information on the countries affected visit the World Health Organisation website [External site - opens in new window]

Avian influenza viruses are distributed widely throughout the world with migratory waterbirds acting as the natural reservoir.

Many countries have experienced outbreaks of highly pathogenic avian influenza viruses. The virus has been the cause of clinical disease in commercial poultry in Australia in Victoria (1976, 1985 and 1992), Queensland (1994) and New South Wales (1997). None of the Australian outbreaks has involved the H5N1 virus.

The current outbreak and spread of H5N1 avian influenza in Asia is unusual in its pathogenicity, its wide spread and in the virus' ability to infect humans who are in close contact with infected birds.

Symptoms in infected birds

The clinical signs of avian influenza in birds are variable and can be affected by the existence of other diseases, the age of the birds, the environment and the severity of the virus itself.

In very severe forms the disease appears suddenly and birds die quickly, sometimes without classical signs of the disease

Signs may include:

• depression
• decrease in egg production
• production of soft-shelled eggs
• profuse watery diarrhoea
• combs and wattles may be swollen and become blue
• reddening of the legs
• laboured respiration.

In less severe forms, signs may also include:

• respiratory signs suggestive of a cold
• swelling of the face
• possibly some nervous signs
• diarrhoea.

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

To report suspected outbreaks or unusual symptoms in birds contact:

• your veterinarian
• Emergency Animal Disease Watch (24 hour) Hotline on 1800 675 888
• Your local PIRSA Animal Health or veterinary officer.
  

How the disease is spread?

The virus is highly concentrated in the droppings and in nasal and eye discharges of infected birds. Direct or indirect contact with wild birds (most likely through drinking water) is the most likely source of infection in commercial poultry species.

The disease can also be spread from one farm to the next through contaminated equipment or via faeces on shoes or clothes. (Transmission through the egg is not known to occur, although contamination of the outer egg shell does occur.)

South Australia has strict biosecurity guidelines and OHS (Occupational Health and Safety) standards that provide significant protection against the disease infecting local poultry unlike many other parts of the world where outbreaks have occurred recently, though this remains possible.

Similar diseases

Avian influenza can be confused with a number of other diseases that have similar clinical symptoms.

Other diseases that can also cause a large numbers of sudden deaths of birds include:

• Newcastle Disease
• Infectious laryngotracheitis
• Duck plague (not present in Australia)
• Acute poisonings

Other diseases that can cause swelling of the combs and wattles include:

• Acute fowl cholera (Pasteurella multocida) and other septicaemic diseases
• Bacterial cellulitis of the comb and wattles

Other diseases that cause respiratory problems include:

• Chronic respiratory disease

Note: Respiratory or gastro-intestinal symptoms can look similar with the less severe strains of avian influenza.

The large number of diseases with similar symptoms to avian influenza reinforces the need to promptly report any health problems in any birds to PIRSA or an experienced private veterinarian.

To help protect South Australia, early detection and reporting of unusual symptoms are the key elements in successful disease control.

To report suspected outbreaks or unusual symptoms in birds contact:

• Your veterinarian
• Emergency Animal Disease Watch (24 hour) Hotline on 1800 675 888
• Your 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