Avian Influenza

Avian Influenza



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 16 hemagglutinin and 9 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.

Pathogen reservoir

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.

Infection route

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.

Incubation time

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.

Situation in Austria

On 9.11.2022 we have confirmed an outbreak of avian influenza in Styria: Avian influenza virus, subtype H5N1, was detected in several animals (chickens and geese) in the district of Graz-Umgebung. This subtype is highly pathogenic (severely pathogenic) for birds and often leads to many deaths, especially in domestic poultry flocks. The cause of introduction is currently under investigation. In the current outbreak, human illnesses following infections with H5N1 in Europe have not been detected to date. A protection zone and a surveillance zone will be established around the outbreak farm. In these zones, poultry farms are subject to official veterinary controls.

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 unclear health problems in poultry farms, a veterinary examination should be carried out without fail. 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)

In the Austrian Animal Disease Radar, information on the international situation and spread of the most significant animal diseases and epizootics relevant to Austria is assessed and compiled. This enables potential risks for Austria to be identified and communicated at an early stage. The animal disease radar is published monthly.

Avian influenza: risk of transmission to humans low

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.

Avian influenza surveillance in Austria

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.

Surveillance for avian influenza in Austria

Technical information

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).


Institut für veterinärmedizinische Untersuchungen Mödling

Last updated: 10.11.2022

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