Influenza A virus

  • Wild birds, particularly waterfowl, are considered to be a natural reservoir for the influenza A virus.
  • Highly pathogenic bird flu viruses cause classical avian flu in chickens and turkeys leading to 100% mortality.
  • Bird flu viruses possess a zoonotic potential and in rare cases may lead to serious illnesses in humans with a fatal outcome.
  • Pigs may serve as a host for porcine, avian and human influenza viruses. Novel influenza A viruses having pandemic potential may result from the adaptation and exchange of gene segments.

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Research: Application for approval of vaccination of birds kept in zoos against highly pathogenic avian influenza (H5N1) using a non-replicating viral vector



In the past two years (2021 and 2022), Europe has been hit by the largest epidemic of highly pathogenic avian influenza even seen, with several thousand outbreaks at poultry farms. Various species of wild bird including several endangered species have also been affected by the highly pathogenic H5N1 virus, posing a serious threat to some wild bird populations in certain regions. In February 2022, an H5N1 outbreak occurred in the pelican corral located close to the River Aare at Bern Animal Park.

Protecting wild birds in zoos

Since avian influenza is a persistent problem and as it is impossible to closely quarantine all of the wild bird species kept in zoos according to animal welfare standards, it is planned to protect the animals by vaccination. Therefore, the IVI recently submitted an application for approval of a propagation-incompetent vector vaccine that has been developed at the IVI. The vaccine will be tested in various wild bird species kept in free-ranging corrals and aviaries that may come into contact with H5N1-infected wild birds. The vaccination trial at Bern Animal Park and Basel Zoo is scheduled for autumn 2023.

An effective vector vaccine

The viral vector vaccine to be used in this experimental release trial is based on a non-replicating vesicular stomatitis virus (VSV), from which one essential gene has been removed and replaced by a gene from the H5N1 avian influenza virus. The vector vaccine has been experimentally tested at the IVI and was found to completely protect chickens against lethal infection with H5N1. The vaccine also allows easy discrimination between vaccinated and infected animals using serological tests. Since the vaccine contains a genetically modified organism (GMO), the IVI has submitted an application for experimental release of the GMO to the Federal Office for the Environment (FOEN). The application has been published in the Federal Gazette and by the municipalities of Bern and Basel, where the trials will take place.

More about the application “Approval of experimental release of a genetically modified vaccine”

Authorising authority: Federal Office for the Environment (FOEN), 3003 Bern

Authorisation procedure: The procedure is based on Article 11 of the Gene Technology Act of 21 March 2003 (GTA, SR 814.91) and on Articles 17 et seq. and 36 et seq. of the Release Ordinance of 10 September 2008 (RO, SR 814.911).

The non-confidential files will be available for anyone to view at the following addresses during normal office hours from 14 December 2022 to 30 January 2023 inclusive:

B/CH/22/01 (B22001): Application 

Which virus is behind the flu?

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While all eyes are focused on the SARS-CoV-2 pandemic, another virus currently circulating in Europe hits the poultry industry seriously. Hundreds of thousands of birds had to be culled this winter in order to control this epizootic. The pathogen responsible for this animal disease is an influenza virus. Other influenza viruses cause disease in pigs or “flu” in humans. What is the relationship between these different influenza viruses?

Interview with Dr Gert Zimmer, a virologist at the Institute of Virology and Immunology (IVI) and the University of Bern (PDF, 214 kB, 24.02.2022)

NEWS from IVI on cases in Switzerland 


Last modification 14.12.2022

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