Identification and characterization of novel live attenuated vaccine strains of infectious laryngotracheitis

Date
2013
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Publisher
University of Delaware
Abstract
Infectious laryngotracheitis (ILT) is an acute respiratory disease of chickens that can result in decreased egg production and increased mortality. A tissue culture origin vaccine (TCO), several chicken embryo origin vaccines (CEO), and three recombinant vaccines are currently used to control the disease. However, TCO vaccines may provide incomplete coverage, CEO vaccines are moderately pathogenic, and recombinant vaccines take several weeks to induce immunity. The objective of this study is to identify a live attenuated strain of ILTV that demonstrates both reduced pathogenicity and virulence through two approaches. Two ILTV field isolates (88-627 and 11-11349) were identified after an analysis of clinical submissions to the University of Delaware. One isolate (88-627) was chosen for further characterization. This isolate did not prove to be a potential vaccine candidate as it exhibited similar levels of pathogenicity to currently used CEO vaccines. In the second approach attempts were made to attenuate a CEO vaccine strain of ILTV through serial passage in tissue culture. After 20 passages in chicken embryo liver cells (CEL), strain UDCEOD1/CEL20 was evaluated in birds. UDCEOD1/CEL20 exhibited reduced levels of pathogenicity, and was able to elicit a protective immune response. The UDCEOD1/CEL20 genome was sequenced and found to be 153,694 nucleotides in length. Two single nucleotide polymorphisms (SNPs) were identified. One SNP resulted in a silent mutation in the glycoprotein J gene. The other SNP is located within both copies of the ILTV ICP4 gene. This SNP results in a threonine to alanine mutation that may be responsible for the observed decrease in virulence.
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