Avian influenza (AI), commonly called bird flu, is a highly contagious viral disease of birds worldwide. The virus is spread by wild waterfowl (such as ducks, geese and swans) and shorebirds because they are natural reservoirs meaning they can carry the virus but show no signs of disease.
There are many strains of the AI virus that cause different infections, ranging from strains that produce little or no symptoms (low pathogenic) to highly pathogenic strains producing severe disease and high death rates in birds. The H5N1 strain in particular is a highly pathogenic virus that has caused severe disease and devastating bird deaths in many parts of the world. While the virus does not usually cause disease in humans the H5N1 and H7N9 strains have been linked to deaths in humans [1, 2]. Australia is currently declared free from H5N1 avian influenza.
What are the clinical signs of bird flu?
The clinical signs of AI depend on many factors including how pathogenic the virus is, the species and age of infected birds and whether they have other diseases. In very severe forms, such as H5N1, clinical signs and death can occur suddenly affecting a large number of birds, whereas in lower pathogenic strains the clinical signs are often less obvious.
Common clinical signs of AI include [1, 2]:
- sudden death in several birds
- ruffled feathers, unusual head or neck posture, droopy appearance
- watery eyes
- birds unable to walk or stand
- birds reluctant to move, eat or drink
- respiratory distress
- swollen and discoloured head, wattle or comb
- a dramatic drop in egg production.
Having skilled workers that can recognise the signs of AI and alert a poultry veterinarian for an accurate diagnosis are essential to preventing further spread of the virus. Owners of birds and backyard hen flocks should also check their birds every day for any changes in bird health and get advice immediately if they have any concerns.
It is important that any potential signs of bird flu are reported immediately to the relevant contacts, such as your local vet, agriculture department and the Emergency Animal Disease Watch Hotline on 1800 675 888. The quicker authorities are alerted to AI, the quicker its spread can be stopped and the quicker it can be eradicated.
What happens in the event of an AI outbreak?
State and territory governments are responsible for responding and managing AI outbreaks when they occur. AI is considered a notifiable emergency animal disease (EAD) in Australia, meaning that, in the event of an outbreak, there are strict EAD response steps in place to control and prevent further spread of the disease. These steps are outlined in the AUSVETPLAN avian influenza manual.
Once an AI infection has been confirmed, specialised emergency animal disease teams are activated to implement control measures on the infected farm and any at-risk farms nearby. These control measures may include quarantining the infected farm, movement restrictions, and disease tracing and surveillance activities. To eradicate and prevent further spread of AI, infected birds are depopulated (removed from their shed and euthanased) and disposed of using approved methods, and then the sheds are decontaminated. Nearby farms and those in surrounding areas are tested and monitored for the disease to ensure the virus has been contained.
In July and August 2020, cases of AI were confirmed at several poultry farms in Victoria. Agriculture Victoria responded to the outbreak with the set-out depopulation, disposal and decontamination procedures on the infected farms. Testing and disease monitoring activities were then conducted on infected farms, at-risk farms and surrounding areas to ensure the virus was no longer present .
Animal welfare risks associated with AI outbreaks
In the event of an AI outbreak, it is essential to comply with the state/territory government’s directions and control measures. Where large numbers of birds require depopulating, it is extremely important that these birds are all killed humanely. Humane killing means that birds are either killed instantly or rendered insensible until death ensues, without pain, suffering or distress. Methods such as ventilation shutdown are not humane and must never be used.
Animal welfare issues can also occur due to quarantine movement restrictions imposed over a large area. Unaffected poultry may not be able to be transported to slaughter leading to maximum stocking densities in sheds being exceeded and overcrowding occurring on farm. In addition, trucks supplying feed, litter and other supplies may also be delayed.
All those responsible for poultry must have contingency plans for EAD outbreaks and include details to ensure bird welfare is protected in the event of movement restrictions and that all birds can be killed humanely if required.
Preventing AI outbreaks
‘Biosecurity’ means protecting the environment, economy, human and animal health from pests and diseases. Good biosecurity practices are critical to preventing the occurrence and spread of emergency animal diseases such as AI. Commercial poultry farmers have well-developed biosecurity systems, however all bird keepers, particularly those with backyard hens, should also practice strict biosecurity measures.
Birds with access to the outdoors that may come into direct or indirect contact with wild waterfowl are at a higher risk of becoming infected with AI. Good biosecurity measures such as deterring and preventing wild waterfowl accessing areas near the shed or outdoor range area can greatly reduce the risk of AI occurring in free-range housing systems. To learn more about how the risk of AI can be managed in free-range housing systems click here.