Molecular characterization and pathogenicity studies of Canadian infectious laryngotracheitis virus isolates
Date
2021-02-02
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Abstract
The extensive use of live-attenuated vaccines to control the upper respiratory tract viral infection in chicken known as infectious laryngotracheitis (ILT), has been associated with a surge in vaccine-related ILT outbreaks. It is documented that these ILT outbreaks are due to the regaining of virulence of the vaccine viruses due to multiple bird to bird passages following vaccination. These vaccine-originated infectious laryngotracheitis virus (ILTV) isolates are known as vaccine revertants. An additional concern is that the multiple live-attenuated vaccine ILTV and wild-type ILTV can recombine, resulting in ILTV strains with higher pathogenicity. To date, little is known about the molecular nature of the Canadian ILTV. The objectives of the present thesis work are to, 1) molecularly characterize the ILTV associated with ILT outbreaks in poultry flocks in Canada using a whole genome sequence approach and 2) study the pathogenicity of representative ILTV isolates in vivo. In achieving objective 1, It was found that most of the ILTV isolates of Canadian origin used in this study were genetically related to chicken embryo origin (CEO) live-attenuated vaccine ILTV strains. Evidence of recombination involving commonly used live-attenuated ILT vaccines was also detected in an ILTV isolate belonging to the British Columbia province. A second recombination event was found this time involving an ILTV isolate belonging to Alberta. This Alberta ILTV strain acted as a parental strain along with another live-attenuated ILT vaccine strain to give rise to an ILTV strain previously isolated in United States (US) territory. In objective 2, the pathogenicity of two wild-type and one CEO vaccine revertant ILTV isolates was compared, by infecting specific pathogen free chickens along with age-matched mock infected controls. We also used naïve contact chickens in order to determine the transmission potential of these ILTV isolates. It was found that the tested CEO vaccine revertant ILTV isolate can induce not only severe disease but also to transmit more efficiently than the wild-type ILTV isolates used for this study.
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Keywords
virology, infectious laryngotracheitis, poultry, herpesvirus, evolution, bioinformatics, vaccines, pathogenicity
Citation
Perez Contreras, A. P. (2021). Molecular characterization and pathogenicity studies of Canadian infectious laryngotracheitis virus isolates (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.