Avian influenza, commonly known as bird flu, is an infectious disease caused by avian influenza viruses. It can affect chickens, turkeys, ducks, and geese, as well as other poultry, swans, and other wild birds. Avian influenza viruses can be divided into two groups: the so-called low-pathogenic (“less pathogenic”) and high-pathogenic (“highly pathogenic”) influenza viruses. Highly pathogenic influenza viruses (such as H5N1) can cause severe disease in poultry—especially in chickens and turkeys—which is usually fatal. Low-pathogenic influenza viruses, on the other hand, often cause only mild or no signs of illness at all, as these viruses lack the properties necessary to trigger severe disease. However, low-pathogenic influenza viruses can mutate into the highly pathogenic form.

Only avian influenza viruses of the H5 and H7 subtypes can occur in the highly pathogenic form. Following infection with highly pathogenic avian influenza viruses, chickens and turkeys in particular exhibit symptoms such as high fever, loss of appetite, weakness, lethargy, and difficulty breathing. Among other things, this leads to a drastic decline in egg production. Sometimes the animals die suddenly without having shown any prior recognizable symptoms. In most cases, the infected animals die. In ducks and geese, the symptoms are sometimes less pronounced, so that the infection is not immediately recognized.

Although chickens and turkeys are particularly susceptible to severe illness, the symptoms of avian influenza are not specific to this disease and may also occur in other illnesses. Livestock owners must therefore consult a veterinarian immediately if clinical abnormalities occur in their flock (e.g., sudden deaths, reduced feed and water intake, decline in egg production, etc.).

If there are grounds to suspect an infection with avian influenza, the responsible veterinary office must be notified immediately. The veterinary office will then decide whether to collect samples from the animals and have them tested in a laboratory. If an infection with the H5 or H7 avian influenza virus is confirmed in the laboratory, the responsible veterinary authority must implement the prescribed control measures. This applies to all poultry operations, regardless of the number of birds kept. For example, the poultry flock must be culled. The facility must then be cleaned and disinfected.

A restricted zone with a radius of at least 10 kilometers is generally established around the infected poultry farm for a period of at least 30 days. Numerous restrictions apply within the restricted zone. For example, poultry may not be moved out of the area.

Due to the high risk of infection and the extensive control measures required, all poultry farmers are required to protect their animals from infection with avian influenza and to strictly adhere to so-called biosecurity measures. This also applies to small hobby farms.

Certain biosecurity measures are mandatory for all poultry keepers: Poultry may only be fed and watered in areas that are inaccessible to wild birds. Feed, bedding, and other items with which poultry may come into contact must be stored out of reach of wild birds.

Other important biosecurity measures include cleaning and disinfecting clothing and shoes before entering the poultry house. Alternatively, disposable protective clothing (coveralls, shoe covers) may be used. Disposable protective clothing must be disposed of immediately after use. Equipment and vehicles should also be cleaned and disinfected before being brought into the poultry house.

Every poultry farmer is required to register their poultry operation with the responsible veterinary office.

In principle, highly pathogenic avian influenza viruses can be transmitted to humans. This generally occurs only through close contact with infected animals. Contact with infected animals should therefore be avoided or should only take place with appropriate protective measures in place.