Submitted to: Western Poultry Disease Conference
Publication Type: Proceedings
Publication Acceptance Date: December 9, 2009
Publication Date: April 18, 2010
Citation: Spatz, S.J., Gimeno, I.M., Witter, R.L., Heidari, M. 2010. The genomes of Marek’s disease virus exist as quasispecies at defined intervals during serial passage-induced attenuation. Western Poultry Disease Conference. 1(1):90-91. Technical Abstract: Virulent strains of Gallid Herpesvirus-2, the causative agent of Marek’s disease (MD), are attenuated through extensive serial passage in avian fibroblasts. To identify the genes involved in attenuation, a single vv+ strain (648A) was passaged 100 times and the pathotype and genotype of every tenth passage was determined. Using second generation sequencing, mutations that accumulated and predominated in late passages were identified in cis-acting regions involved in replication and cleavage/packaging, in genes encoding known virulence factors vLipase, vIL8, RLORF4 and vTR, and in the promoter of the major transactivator, ICP4. Numerous single nucleotide polymorphisms were also identified and their genomic frequency fluctuated among the passages. Although the appearance of these mutations corresponded well with the loss of virulence, few genetic changes were absolute, present in 100% of the sequences within a passage. This indicates that the DNA virus Gallid Herpesvirus-2 exists as a collection of quasispecies in vitro.