The pathogens causing avian influenza (avian influenza or avian plague) are influenza viruses. Influenza viruses are divided into types A, B and C. Influenza virus A has different subtypes based on different surface antigens (neuraminidase, N and hemagglutinin, H). New variants of influenza viruses are constantly emerging as a result of gene changes. To date, there are 18 hemagglutinin and 11 neuraminidase subtypes. Avian influenza is caused by influenza virus A subtypes H5 or H7.

Avian influenza was first observed in Italy in 1878. The pathogens occur worldwide.

All poultry species, as well as many species of ornamental and wild birds, are susceptible to avian influenza viruses. Wild waterfowl are the natural reservoir of the pathogen.

Avian influenza is highly contagious for poultry. The virus is excreted with feces, saliva and tear fluid. If there is a lot of dust, indirect airborne infection is also possible.

Humans and other mammals (including pigs, cats, dogs, foxes, badgers, martens, otters, or minks) can also become infected with avian influenza viruses through intensive contact with infected poultry. Transmission through food is not possible.

1-3 days

In avian influenza, highly pathogenic avian influenza (HPAI) and low pathogenic avian influenza (LPAI) can be distinguished. The distinction between highly pathogenic and low-pathogenic AI types refers to the severity of the disease in birds: while low-pathogenic AI types cause no or only mild symptoms, highly pathogenic AI types cause severe courses of disease and high mortality rates.

Low-pathogenic viruses can spontaneously mutate to a highly pathogenic form, causing avian influenza outbreaks with high animal losses. In particular, chickens, turkeys, and numerous wild bird species can contract avian influenza with severe disease progression. Ducks, geese, and some wild bird species show no or only mild symptoms but are important for pathogen spread. In mammals, infection with avian influenza viruses is often asymptomatic or with mild flu-like symptoms. In exceptional cases, however, the infection can lead to severe and even fatal disease.

Since November 2022, we have confirmed numerous outbreaks of avian influenza in wild birds, but also in individual poultry farms and hobby farms in several provinces in Austria. To minimize the risk of further transmission to poultry flocks, protection and surveillance zones have been established. Due to the easing of the situation, a relaxation of the compulsory stabling can be decreed nationwide as of April 22, 2023.

However, the all-clear cannot be given. Since there is a certain risk of infection, the classification "increased risk" remains. Since the end of 2020, an increased incidence of the disease has been observed throughout Europe, even in the summer months.

Poultry farmers should pay particular attention to the observance of biosecurity measures: Direct and indirect contacts between poultry and wild birds should be prevented at all costs. In case of health problems of the animals in poultry farms, a veterinary examination should definitely be carried out and avian influenza should be excluded. For early detection and prevention of further spread, all wild waterfowl and birds of prey found dead must be reported to the locally competent district administrative authority (official veterinarian). In view of the above, we would also like to point out that every poultry holding must be reported to the competent district administrative authority.

Information from the Ministry of Health on avian influenza

Notification of poultry keeping in the Consumer Health Information System (VIS)

No human infection with avian influenza viruses has ever been detected in Austria. While the H5N1 subtype currently occurring in Europe is highly infectious to many avian species, the European Centre for Disease Prevention and Control (ECDC) points to the poor adaptation of the virus to humans. However, sporadic evidence of avian influenza infections in people with animal contact in other regions of the world but also in Europe shows that transmission from animals to humans is possible. Almost all human infections are due to close direct contact with infected or diseased poultry or indirectly via their feces. Human-to-human transmission has not yet been observed worldwide.

Use of appropriate protective equipment and adherence to hygiene measures may reduce the risk to persons who have direct or indirect contact with domestic poultry or wild birds potentially infected with avian influenza.

Waterfowl or birds of prey found dead must be reported to the competent district administrative authority (official veterinarian). Such animals should not be touched and left at the site where they were found. Recovery and further investigations will be arranged by the authority.

The Europe-wide surveillance program consists of an active part (commercial poultry) and a passive part (wild birds).

In the active part of the surveillance program, a total of 3,524 poultry blood samples were tested for avian influenza virus in Austria in 2021. Slaughter blood from 1,284 laying hens from 128 farms (of which 61 were free-range), from 470 parent chicken birds from 47 parent farms, from 530 fattening turkeys from 53 farms, from 1,170 geese and ducks from 59 farms, and from 70 ostriches were submitted for serological testing. Antibodies to AI virus could not be detected in any of the samples, so all samples were negative.

In the passive part of the surveillance program in 2021, 419 samples from wild birds found dead were tested for avian influenza virus. Highly pathogenic avian influenza viruses of subtypes H5N8, H5N5, and H5N1 were detected in 44 of these dead wild birds.

In the course of clarification investigations, 376 samples were examined for the AI virus genome. The highly pathogenic AI virus (HPAIV) of subtypes H5N8 and H5N1 was detected in 3 hobby farms.

At the National Reference Laboratory for Avian Influenza, we examine samples (organs, swabs, carcasses) for direct virus detection using real-time RT - PCR, sequencing and with egg culture and haemagglutination test (HA). Indirect detection by determination of antibodies is performed by ELISA and haemagglutination inhibition test (HAH).

Hemagglutination test: Certain viruses such as influenza viruses bind erythrocytes to their surface by means of hemagglutinin. This causes the blood to clump together (agglutinate). The amount of virus can be determined by means of dilution series.

Hemagglutination inhibition test: Special antibodies can prevent the agglutination/clumping caused by the virus. In this way, antibody titers and specific individual virus strains can be determined.

ELISA: Enzyme-linked immunosorbent assay is an antibody-based detection method, antibodies bind to an antigen and are visualized by an enzymatic color reaction.

Real-time RT polymerase chain reaction (PCR) and sequencing: AI virus gene segments are detected and it can be directly typed whether an H5 or H7 type is present. By means of sequencing the pathotype of the virus strain (high or low pathogenic) can be determined.

Egg culture: A potentially infectious vaccination solution is prepared from the samples, with which guaranteed virus-free chicken eggs are inoculated. These eggs are incubated for at least five days. If highly pathogenic avian influenza viruses are present, the embryos in the eggs die and the virus in the allantios can be identified by haemagglutination (HA).