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 Project: 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. Other than poultry, many species of wild birds have also been affected by the 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 these animals by vaccination. Therefore, the IVI recently submitted an application for approval for the use of a vaccine developed at the IVI against avian influenza in various species of wild birds kept in free-ranging corrals and aviaries that may come into contact with H5N1-infected wild birds. This project was authorised by the Federal Office for the Environment (FOEN) in April 2023, such that the vaccination trial can begin at the Bern Animal Park and Basel Zoo in late summer 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. This vaccine was developed at the IVI and was found to completely protect vaccinated chickens against lethal infection with H5N1. The vaccine also allows easy discrimination between vaccinated and infected animals using serological tests. Since the vaccine involves a genetically modified organism (GMO), the IVI had to submit an application for experimental release of the GMO to the Federal Office for the Environment (FOEN).

Approval of experimental release of a genetically modified vaccine

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

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 19.04.2023

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