Location: Endemic Poultry Viral Diseases ResearchTitle: Virulence determination of Marek's disease virus that changed multiple nucleotides in virulence-related open reading frames.
Submitted to: American Society for Virology Meeting
Publication Type: Proceedings
Publication Acceptance Date: 3/16/2023
Publication Date: N/A
Technical Abstract: Marek's disease (MD) is a highly infectious lymphoproliferative disease with significant economic impacts. Gallid alphaherpesvirus 2, better known as Marek's disease virus (MDV) has been categorized based on virulence rank as three pathotypes, virulent, very virulent, and very virulent plus. A comparative genomics study suggested that single nucleotide polymorphisms (SNPs) in eight open reading frames (ORF), UL22, UL36, UL37, UL41, UL43, R-LORF-8, R-LORF7, and ICP4, were most significantly associated with the different pathotypes of MDV. We validated these SNPs by substituting the nucleotides in the suggested eight ORFs in the genome of vv+MDV strain 686 with unique nucleotides observed in vMDV strains. All modifications resulted in nonsynonymous amino acid substitutions of the MDV genome. Initial pathogenicity studies indicated that these substitutions of SNPs showed reduced MD incidence and increased survival of challenged birds compared to those of the parental virus. In this study, the pathotype of the modified viruses were evaluated by the best fit pathotyping method to rank the modified viruses with reference pathotype viruses. The modified genome of the vv+MDV 686 virus resulted in the reduction of its pathotype/ virulence similar to the vvMDV Md5 strain, but these changes in eight ORFs alone were not sufficient to reduce to the vMDV pathotype.