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Title: Identifying the genetic basis of attenuation in Marek's disease virus

item HILDEBRANDT, EVIN - Michigan State University
item NIIKURA, MASAHIRO - Simon Fraser University
item Cheng, Hans

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/6/2011
Publication Date: 7/20/2011
Citation: Hildebrandt, E., Niikura, M., Cheng, H.H. 2011. Identifying the genetic basis of attenuation in Marek's disease virus [abstract]. American Society for Virology 30th Annual Meeting Scientific Program and Abstracts, University of Minnesota, July 16-20, 2011. P5-3 p. 258.

Interpretive Summary:

Technical Abstract: Marek’s disease virus (MDV) is an oncogenic alphaherpesvirus of chickens that induces lymphoid tumors in susceptible birds. This agronomically-important disease is controlled primarily through vaccines that prevent tumor formation but are non-sterilizing. Currently most efficacious vaccines consist of MDV attenuated by repeated cell passages. The goal of this project is to identify the genetic and molecular basis of in vitro attenuation utilizing next generation sequencing. To identify genetic changes, virulent MDV generated from a BAC clone was serially passed in chicken embryo fibroblast cells in triplicate. Birds were challenged with viral stocks at passages 50, 60, and 70 to determine disease incidence. In all three replicates, the virus was attenuated demonstrating mutations in the viral genome are the source of this phenotypic change. The rate at which attenuation occurred varied between the three viral lineages. One lineage was completely attenuated after 60 passages, another after 70 passages, and the third is expected to be after 80 passages. In all replicates, disease incidence quickly decreased from 80-100 percent to 0-20 percent within 10 passages. This rapid change suggests that the number of loci responsible for attenuation may be limited. Further bird trials are underway to validate these results and track the kinetics of attenuation in passages preceding complete attenuation. Bird trials conducted using viral defined mixtures of virulent and avirulent MDV will assist in correlating MD incidence to allele frequencies in virus populations before complete attenuation. Currently both DNA and RNA from the lowest passage of the completely attenuated viral stocks and the virulent parental virus strain have been submitted for sequencing. We are awaiting these results in order to identify shared changes in the genome and transcripts of the attenuated viruses compared to the virulent parental virus. Changes that appear likely candidates responsible for attenuation will be quantified in viral passages to determine allele frequencies. Furthermore, key polymorphisms will be introduced into the virulent BAC clone using recombineering for validation.