Genotyping of Infectious Laryngotracheitis Virus (ILTV) Isolates from Western Canadian Provinces of Alberta and British Columbia Based on Partial Open Reading Frame (ORF) a and b

SIMPLE SUMMARY: Infectious laryngotracheitis virus is an economically important acute upper respiratory tract disease in chickens. To control the disease, there are two types of vaccines commercially available, the recombinant viral vector and the live attenuated vaccines. The live attenuated vaccines are effective in disease control, but because of their residual virulence, they can replicate, cause disease, and revert to their original virulent form. Strains of the virus can be categorized as vaccine-related or wild type related. Information is scarce on the type of strains that are circulating in Canada. This study aims to discriminate between wild type and vaccine strains associated with infectious laryngotracheitis cases in the provinces of Alberta and British Columbia between the years 2009–2018. To accomplish this objective, the sequencing of two specific partial genes was performed. As a result, 27 samples from Alberta, and 5 samples from British Columbia were successfully sequenced. From the total samples, ~85% were related to vaccine strains and the rest categorized as wild type. These results reinforce the concern on current practices surrounding vaccination and the need to implement better biosecurity measures. ABSTRACT: Infectious laryngotracheitis virus (ILTV) causes an acute upper respiratory disease in chickens called infectious laryngotracheitis (ILT). Live attenuated vaccines are effective in disease control; however, they have residual virulence, which makes them able to replicate, cause disease and revert to the original virulent form. Information is scarce on the molecular nature of ILTV that is linked to ILT in Canada. This study aims to determine whether isolates originating from ILT cases in Western Canada are a wild type or vaccine origin. Samples submitted for the diagnosis of ILT between 2009–2018 were obtained from Alberta (AB, n = 46) and British Columbia (BC, n = 9). For genotyping, a Sanger sequencing of open reading frame (ORF) a and b was used. A total of 27 from AB, and 5 from BC samples yielded a fragment of 1751 base pairs (bp). Three of the BC samples classified as group IV (CEO vaccine strains) and 2 as group V (CEO revertant). Of the AB samples, 22 samples clustered with group V, 3 with group VI (wild type), and 2 with group VII, VIII, and IX (wild type). Overall, 17 non-synonymous single nucleotide polymorphisms (SNPs) were detected. Further studies are underway to ascertain the virulence and transmission potential of these isolates.