Impacts of poultry vaccination on viruses of wild bird

• Transmission of viruses from farmed poultry to wild birds is not highly studied.
• Attenuated poultry vaccines can be transmitted from poultry to wild birds.
• Virulent poultry viruses may evolve under vaccine pressure and spread to wild birds.
• Poultry vaccines can contain viral contaminants that may spread to wild birds.
• Recombination could increase the risk of vectored vaccines spreading to wild birds.

Spillover of viruses from farmed poultry into wild birds is a relatively new area of study at the livestock–wildlife interface. These transmission events can threaten the health of wild birds. There is growing evidence of transmission of vaccine viruses from poultry to wild birds, including attenuated vaccine strains of Newcastle disease virus and infectious bronchitis virus, and also spread of virulent viruses that may have evolved under the pressure of vaccine use, such as Marek's disease virus. Viral contaminants of poultry vaccines, including reticuloendotheliosis virus, may also be transmitted to wild birds and result in disease. New, vectored vaccines are less likely to directly spread to wild birds but this risk may rise as a result of recombination.