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Influenza Virus Propagation in Embryonated Chicken Eggs
Published on: March 19, 2015
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Evolution of avian encephalomyelitis virus during embryo-adaptation
Rüdiger Hauck1, C Gabriel Sentíes-Cué2, Ying Wang3
1Department of Population Health and Reproduction, School of Veterinary Medicine, University of California, Davis, United States.
Veterinary Microbiology
|May 24, 2017
Summary
Embryo-adaptation of avian encephalomyelitis virus (AEV) vaccines can lead to disease outbreaks in layer pullets. Specific genetic mutations indicate embryo-adaptation, appearing by the fifth passage in experimental settings.
Area of Science:
- Veterinary Virology
- Avian Pathology
- Molecular Epidemiology
Background:
- Wild-type avian encephalomyelitis virus (AEV) typically causes neurological signs in young chicks but not adult pullets.
- Embryo-adapted AEV strains can cause disease (AE) in chickens of all ages following intracutaneous infection.
- Recent outbreaks of AE in layer pullets after vaccination prompted an investigation into potential vaccine embryo-adaptation.
Purpose of the Study:
- To determine if inadvertently embryo-adapted vaccines were responsible for recent avian encephalomyelitis outbreaks in layer pullets.
- To investigate the process and genetic markers of AEV embryo-adaptation.
Main Methods:
- Virus isolation from commercial vaccines and field samples.
- Serial passaging of AEV strains in chicken embryos.
- Quantification of viral load using RT-qPCR.
- Partial VP2 gene sequencing and whole-genome analysis.
- Sanger sequencing of brain and nerve tissues from field isolates and passaged strains.
Main Results:
- Initial vaccine and field isolates were not embryo-adapted; full adaptation occurred after seven passages.
- Viral load remained consistent throughout the passaging process.
- Partial and whole-genome sequencing identified specific genetic markers (SNPs) distinguishing wild-type and embryo-adapted strains.
- Mutations associated with embryo-adaptation were first detected in the fifth passage.
Conclusions:
- Inadvertent embryo-adaptation of AEV vaccines is a plausible cause for recent outbreaks in vaccinated layer pullets.
- Specific genetic mutations, particularly single nucleotide polymorphisms (SNPs), can serve as indicators of AEV embryo-adaptation.
- The fifth passage appears to be a critical stage for the emergence of embryo-adaptation markers.
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