Avian influenza - About the disease
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About the disease
Avian influenza is a highly contagious viral infection. The disease is caused by a virus belonging to the family Orthomyxoviridae.
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. The virus can persist in poultry meat products but is eliminated by adequate heating/cooking.
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 Organization website.
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 of H5N1 avian influenza in Asia is unusual in its pathogenicity, its wide geographic spread and in the ability of the virus to infect humans who are in close contact with infected birds.
Symptoms
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
How the disease is spread
The virus is highly concentrated in manure, 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.
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:
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 DPI&F or an experienced private veterinarian.
To help protect Queensland, early detection and reporting of unusual symptoms are the key elements in successful disease control. This will allow the possibility of avian influenza being involved to be readily assessed and appropriate measures to be taken.
Want more information?
- Email us your questions
- Phone the DPI&F Call Centre on 13 25 23
- Contact your local DPI&F Biosecurity office
back to Avian influenza home
Last updated 21 October 2005
