Avian influenza, also known colloquially as bird flu, is an infectious disease caused by avian influenza viruses. It can occur in chickens, turkeys, ducks, geese, but also in other poultry, swans and other wild birds. A distinction can be made between two groups of avian influenza viruses, the so-called low-pathogenic ("less pathogenic") and the highly pathogenic ("highly pathogenic") influenza viruses. The highly pathogenic influenza viruses (e.g. H5N1) can cause severe illness in poultry, especially chickens or turkeys, which is usually fatal. Low pathogenic influenza viruses, on the other hand, often cause only minor or no signs of illness, as these viruses lack the properties to cause severe illness. However, low pathogenic influenza viruses can mutate into a highly pathogenic form.

Only the avian influenza viruses of subtypes H5 and H7 can occur in the highly pathogenic form. After infection with highly pathogenic avian influenza viruses, chickens and turkeys in particular show symptoms such as high fever, loss of appetite, weakness, listlessness and shortness of breath. Among other things, there is a drastic drop in laying performance. Sometimes the animals die suddenly without having shown any recognizable symptoms beforehand. The infected animals usually die. In ducks and geese, the symptoms are sometimes less pronounced so that the infection is not recognized immediately.

Although chickens and turkeys in particular become seriously ill, the symptoms of avian influenza are not unique to this disease and may also occur with other diseases. Livestock owners must therefore consult a veterinarian immediately if clinical abnormalities occur in the flock (e.g. sudden deaths, reduced feed and water intake, decline in laying performance, etc.).

If there are reasons to suspect an infection with avian influenza, the competent veterinary office must be informed immediately. The veterinary office then decides whether samples are to be taken from the animals and examined in the laboratory. If an infection with the avian influenza virus H5 or H7 is detected in the laboratory, the competent veterinary office must take the prescribed control measures. This applies to all holdings, regardless of the number of birds kept. For example, the poultry flock must be evacuated. The housing facility must then be cleaned and disinfected.

As a rule, a restricted zone with a radius of at least 10 kilometers is set up around the infected poultry farm for a period of at least 30 days. Numerous restrictions apply in the restricted zone. For example, kept birds may not be moved.

Due to the high risk of infection and the costly control measures, all poultry farmers are obliged 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 farmers: Poultry may only be fed and watered in places that are inaccessible to wild birds. Feed, litter and other objects with which poultry may come into contact must be kept out of the reach of wild birds.

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

Every poultry farmer is obliged to notify the competent veterinary office of their poultry husbandry.

In principle, highly pathogenic avian influenza viruses can be transmitted to humans. This usually only happens when there is intensive contact with infected animals. Contact with infected animals should therefore be avoided or only take place with suitable protective measures.