Published on 26 November 2024

Research project: vaccination of zoo birds against highly pathogenic avian influenza

Since 2021, all of Europe has been ravaged by the largest ever epidemic due to highly pathogenic avian influenza viruses of the H5N1 subtype. In addition to domestic poultry, many species of wild birds have succumbed to the virus, putting some populations locally at risk. As avian influenza is an ongoing problem and many of the wild species in zoos cannot be kept appropriately under close quarantine conditions, the plan is to protect these birds are to be protected by vaccination.

Use of an updated vaccines

Several years ago the IVI developed a vector vaccine based on a non-replicable vesicular stomatitis virus (VSV), in which an essential gene was removed and replaced with a gene from the H5N1 avian influenza virus. This vaccine conferred full protection against H5N1 in vaccinated chickens. The vaccine also allows the simple serological differentiation of vaccinated animals from H5N1-infected animals. The IVI has now adapted its existing vector vaccine using the HA antigen of H5N1 viruses (phylogenetic group 2.3.4.4b)) currently in circulation.

Protecting wild birds in zoos

In order to test this promising, innovative vaccine for the protection of zoo birds, a joint research project has been carried out by Bern Animal Park, Basel Zoo and the Institute of Virology and Immunology IVI. The aim was to show that endangered wild bird species kept in zoos can be protected effectively, thus guaranteeing their welfare.

Since August 2023, 348 birds representing 23 species have been vaccinated at Bern Animal Park and Basel Zoo. Five weeks after vaccination, each bird was given a booster, which was repeated after a year. The birds tolerated the vaccine well, with no side effects being observed. Serological tests show that they have produced enough antibodies to shield them against infection with highly pathogenic H5N1 viruses. This protection was still in force a full year after vaccination.

As avian influenza is an ongoing problem and many of the wild species in zoos cannot be kept appropriately under close quarantine conditions, zoos have an urgent need to protect these birds by vaccination. «The results of our research project show that the vaccine is effective and safe in zoo birds,» says Gert Zimmer, a virologist at the IVI and the University of Bern. He makes this appeal to the private sector and donors: «Now we need a company to produce the vaccine commercially in large quantities.»

• What are the key findings?

  • A safe, effective and DIVA*-compatible vaccine was developed on the basis of RNA replicon particles.
  • The vaccine contains the genetic information for the HA antigen of the currently-circulating H5N1 HPAI virus (clade 2.3.4.4b).
  • When used in a prime/boost vaccination protocol, the vaccines confer full protection against lethal H5N1 infection in chickens and prevent virus excretion.
  • In various wild bird species the vaccine induces high titres of H5N1-neutralising antibodies.
  • The vaccine induces long-lasting immunity and shows potential for cross-clade protection.
  • The vaccine allows simple serological differentiation between infected and vaccinated animals (DIVA principle).
  • The vaccine is also effective after mucosal application and therefore has potential for mass vaccination of large poultry flocks.

  * The DIVA principle refers to a veterinary vaccine that allows vaccinated animals to be differentiated from infected animals.

• What are the next steps?

  • Mucosal application of the vaccine will further be examined and optimised in  chicken vaccination studies.
  • In collaboration with the Friedrich-Löffler-Institut (the German Federal Research Institute for Animal Health), domestic geese are being immunised with the vaccine to investigate to what degree the vaccine can prevent the excretion and transmission of H5N1 viruses in this species.

Title and link (Nature Communication)
RNA replicon vaccination confers long-lasting protection against H5N1 avian influenza in 23 zoo bird species

Authors
Marion Stettler, Stefan Hoby, Christian Wenker, Fabia Wyss, Elisabeth Heiderich, Lisa Butticaz, Nicolas Ruggli, Karin Darpel & Gert Zimmer

More info
Influenza viruses – a global threat to humans and animals