Characterising the process of attenuation by serial egg passaging of Infectious Bronchitis Virus (IBV) using genomic and phenotypic methods

Oade, Michael Steven (2020) Characterising the process of attenuation by serial egg passaging of Infectious Bronchitis Virus (IBV) using genomic and phenotypic methods. PhD thesis, University of Glasgow.

Abstract

Vaccines against infectious bronchitis virus (IBV) are produced by repeated passage of virulent IBVs in embryonated hens’ eggs. Although used as a standard method by industry to generate a vaccine, the mechanism behind attenuation remains unclear. Moreover, the genetic changes that occur during the process of attenuation by egg passage largely go unreported. RNA viruses such as IBV do not exist as clonal structures but rather a population of genetically related viruses that interact on a functional scale. The evolution of IBV is purportedly the influence of two factors; the generation of genetic diversity and selection of preexisting genetic variants. The origin of attenuating mutations as a result of serial egg passaging is a subject of debate.

A panel of egg-passaged isolates of IBV, four started using a virulent population and four started using the virulent population’s clone have previously been generated in the lab. The starting, intermediate and final attenuated viruses were deep sequenced using an array of high-throughput sequencing (HTS) techniques. The genetic differences occurring at both consensus- and subconsensus level between virulent and attenuated IBVs are reported here as is the order of mutational appearance; both are used to inform as to the evolutionary pathways leading to attenuation. The use of HTS to study the process of attenuation by egg passaging is novel to the field.

During this analysis, it was observed that the 3′ untranslated region (UTR) of IBV undergoes a proportionally higher rate of mutation compared to the rest of the genome. The involvement of the region in governing virus pathogenicity, to elude as to a possible mechanism of IBV attenuation, was studied by reverse genetics exchanging a virulent IBV’s 3′ UTR with that of a non-pathogenic IBV equivalent. Interestingly, this virus was shown to be non-pathogenic when introduced to birds.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: Q Science > QR Microbiology; Q Science > QR Microbiology > QR355 Virology
• Colleges/Schools: College of Medical Veterinary and Life Sciences > Institute of Biodiversity Animal Health and Comparative Medicine
• Supervisor's Name: Bickerton, Dr. Erica, Orton, Dr. Richard and Hammond, Prof. John
• Date of Award: 2020
• Depositing User: Mr Michael S Oade
• Unique ID: glathesis:2020-80241
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 16 Mar 2020 17:00
• Last Modified: 04 Apr 2023 11:22
• Thesis DOI: 10.5525/gla.thesis.80241
• URI: https://theses.gla.ac.uk/id/eprint/80241