Avian influenza information for veterinarians

About avian influenza (AI)

Avian Influenza (AI) (also known as bird flu or fowl plague) is a highly infectious viral disease of birds which occurs worldwide.

There are many combinations of subtypes (strains) of avian influenza virus that cause infections of different severity. These range from low pathogenic or mild strains (causing ‘low pathogenicity avian influenza’ or LPAI), to highly pathogenic strains that are associated with severe disease and high mortality in poultry (highly pathogenic avian influenza or HPAI).

Chickens, ducks, geese, turkeys, guinea fowl, quail, pheasants and ostriches are included in the more than 140 species that are susceptible to AI. Many species of wild birds, including waterfowl and seabirds, can also carry the virus without showing any signs of infection.

The virus is mostly spread by wild birds, particularly ducks, contaminating food or water supplies.

Migratory birds, predominantly shore birds and waders from nearby countries in South East Asia, can pose a risk if they harbour AI infection and then mingle with, and transmit this infection to waterfowl that are nomadic within Australia. These nomadic birds can then mingle with and spread the infection to domestic birds such as poultry.

It is not unusual for AI virus to be detected in wild birds in Australia. Wild birds can carry the virus without showing any signs of infection.

AI can also spread by the movement of eggs, birds, people, vehicles and equipment between farms, and by clothing, footwear, aerosols, water, feed, litter, biting insects and vermin.

There is currently no effective treatment available for birds once clinical signs of AI appear.

Vaccines are available for certain subtypes of the AI virus, which may protect poultry from clinical signs of disease if they subsequently become infected. However, routine vaccination for AI is not permitted in Australia.

Veterinarians who suspect AI MUST report it IMMEDIATELY to Agriculture Victoria by calling the all-hours Emergency Animal Disease Watch Hotline on 1800 675 888.

Avian influenza is rarely spread from birds to people. AI viruses can infect people following close contact with poultry or materials contaminated with infected poultry feathers, faeces or other waste from poultry facilities.

The transmission of the AI virus from bird to humans has been reported with some strains of the virus such as H5N1, H7N9 and H7N7. Some AI viruses can cause severe and fatal infections in humans, however the number of human cases around the world has been small relative to the number of outbreaks in birds.

The majority of human cases have had direct or indirect exposure to infected poultry or contaminated environments. Humans infected with an AI virus do not easily transmit the infection to others. People are not infected by eating thoroughly cooked chicken meat or eggs.

Investigating suspected cases

Veterinarians investigating suspected cases of AI MUST IMMEDIATELY notify Agriculture Victoria by calling the all-hours Emergency Animal Disease Watch Hotline on 1800 675 888.

Agriculture Victoria will advise on samples required, sample transport requirements and any additional activities required.

Clinical signs

The clinical signs of AI infection are variable and influenced greatly by:

  • the virulence of the viruses involved
  • the species affected
  • age
  • concurrent bacterial disease
  • the environment.

Signs of low pathogenicity avian influenza (LPAI)

Clinical signs range from inapparent to mild or severe and can include:

  • respiratory distress (can be confused with infectious laryngotracheitis)
  • coughing, sneezing or rasping respiration
  • rapid drop in feed intake, water intake and egg production
  • typical 'sick bird' signs — for example, ruffled feathers, dopiness and closed eyes
  • death of small proportions of the chicken flocks of 3% to 15%.

Signs of highly pathogenic avian influenza (HPAI)

HPAI should be considered as a possible cause if a high proportion of a flock or group of birds become ill very quickly, progressing from normal to gravely ill or dead within 24 to 48 hours.

Clinical signs may include:

  • sudden death
  • respiratory distress
  • swelling and purple discolouration of the head, comb, wattles and neck
  • coughing, sneezing or rasping respiration
  • rapid drop in feed intake, water intake and egg production
  • typical 'sick bird' signs — for example, ruffled feathers, dopiness and closed eyes
  • diarrhoea
  • occasionally, nervous symptoms.

Differential diagnoses of AI include Newcastle disease, acute fowl cholera and other septicaemic diseases, infectious laryngotracheitis, duck plague, acute poisonings and bacterial cellulitis of the comb and wattles.

Gross pathology

Birds that die of peracute AI may show minimal gross lesions, consisting of dehydration and congestion of viscera and muscles.

In birds that die after a prolonged clinical course, petechial and ecchymotic haemorrhages occur throughout the body, particularly in the larynx, trachea and proventriculus and epicardial fat, and on serosal surfaces adjacent to the sternum. There is extensive subcutaneous oedema, particularly around the head and hocks. The carcase may be dehydrated. The pancreas, liver, spleen, kidney and lungs can display yellowish necrotic foci. The air sacs may contain an exudate. The spleen may be enlarged and haemorrhagic.

Good biosecurity is important

Regardless of whether your clients are commercial producers or just keep a few chickens in their backyard, there are several biosecurity practices they should be putting in place to protect their birds from disease:

  • Restrict contact between kept birds and wild birds. Contact with wild birds can be minimised by making the free-range environment less attractive to them, for example, place feeders and water sources inside sheds, rather than in the open where wild birds will have easier access. Using fencing or netting for free-ranging birds, are other options.
  • Keep poultry sheds, yards and aviaries clean, including equipment. Clean thoroughly with a detergent before applying a disinfectant.
  • Quarantine new birds before introducing them to the resident flock.
  • Limit visitors to your birds. Check if essential visitors have recently visited other premises where poultry is kept.
  • If attending bird shows, always practice good hygiene.
  • Always wash hands before and after handling birds and eggs.
  • Poultry farmers should change into clean footwear before entering poultry houses or hen facilities, to stop the potential transfer of disease from outside.

Best practice farm hygiene and biosecurity practices are adopted in the Australian poultry industry and are standard practice. National biosecurity manuals outline these measures.

Further information

  • Visit the dedicated avian influenza page on the Agriculture Victoria website
  • See the AUSVETPLAN disease strategy for AI
  • Contact your local Agriculture Victoria District Veterinary Officer or Animal Health Officer
  • Contact the Agriculture Victoria Customer Contact Centre on (03) 4334 2715 (Monday – Friday 9 am – 5 pm) if you require information about movement controls during the AI response.
  • If you have had contact with birds on an affected property and you are experiencing cold or flu symptoms, call your doctor or the Department of Health and Human Services on 1300 651 160 for medical advice.
  • Visit the national pest and disease outbreak website.
Page last updated: 09 Mar 2021