The pathogens causing avian influenza (avian influenza or avian plague) are influenza viruses. They are divided into types A, B and C. Influenza virus A has different subtypes, which result from different surface antigens (neuraminidase, N and haemagglutinin, H). As a result of genetic changes, new variants of influenza viruses are constantly emerging. To date, there are 16 hemagglutinin and 9 neuraminidase subtypes.
The obligation to keep poultry on farms with more than 350 birds will cease to apply on March 16, 2022. As a result of the now reduced risk of introduction, the compulsory stabling of poultry farms, which has been mandatory since November 2021, will be suspended by an amendment to the Avian Influenza Ordinance. However, due to a still existing but reduced risk situation, the other measures to increase biosecurity in the designated risk areas will continue to be prescribed.
Poultry farmers:inside should pay special attention to compliance with biosecurity measures, such as feeding in covered areas. Direct and indirect contacts between poultry and wild birds should be prevented at all costs. In case of unclear health problems on poultry farms, a veterinary examination should be carried out without fail. Mandatory reporting of wild waterfowl and birds of prey found dead to the local competent veterinary authority (official veterinarian) is also important for early detection.
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: Not dangerous for humans
The pathogens of avian influenza can be transmitted from birds to humans in very rare cases. However, no human infection has ever been detected in Austria. Currently, the H5N1 subtype, which AGES has also detected in Austria, is rampant in birds throughout Europe. This subtype is highly infectious for a number of bird species, including most domestic poultry. According to the European Center for Disease Control (ECDC), the virus is poorly adapted to humans, and transmission from birds to humans is therefore a rare event: although isolated human cases have occurred, no lasting human-to-human transmission has been observed. Almost all human infections are due to very close contact with infected or sick birds or their feces in domestic settings. In the United Kingdom, avian influenza infection was recently detected in a human for the first time. According to U.K. health authorities, the infected person had very close, regular contact with a large number of infected birds that he or she had kept in and around his or her home for an extended period of time. The person is well, and there is no evidence that the infection has spread to others. Laboratory tests revealed low levels of the H5 virus type. According to health authorities, this is a very rare event due to the special circumstances at this farm. In any case, the recommended increased protective measures should be followed when handling poultry and wild birds: Poultry keepers:inside should enter all sheds and enclosures where poultry are kept only after thoroughly cleaning and disinfecting footwear or wearing protective clothing and overshoes used exclusively there. Waterfowl and birds of prey found dead must be reported to the competent district administrative authority (official veterinarian). Such animals should not be touched and should be left at the place where they were found; recovery and further examinations will be arranged by the authority.
Avian influenza surveillance in Austria
In 2020, a total of 3,655 blood samples were tested for avian influenza virus. All samples were negative. The Europe-wide surveillance programme consists of an active (commercial poultry) and a passive (wild birds) part. In the active surveillance programme 2020, slaughter blood from 1,240 laying hens from 124 farms (of which 61 were free-range), from 440 parent hens from 44 parent farms, from 530 turkeys for fattening from 53 farms, from 1,407 geese and ducks from 75 farms and from 64 ostriches from 8 farms were sent for serological testing. No antibodies to AI virus were detected. 158 poultry samples additionally tested for the AI virus genome were also negative. During passive surveillance in 2020, 187 samples from wild birds found dead were tested for the avian influenza A virus genome. Non-pathogenic AI virus was detected in 4 dead wild birds.
Avian influenza last occurred in poultry in Austria in 2016/17: HPAIV H5N8 was detected in two farms. The two outbreaks (10.11.2016, 17.01.2017) in Vorarlberg and Burgenland had in common with Lake Constance and Lake Neusiedl the immediate proximity to the lake and positive wild bird findings in the immediate vicinity. HPAIV H5N8 was also detected in wild birds in the lake regions of Salzburg and Upper Austria, but there were no cases of disease introduction into 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).