Comparative Molecular Characterization of Three Gallid alphaherpesvirus Type 3 Strains 301B/1, HPRS24, and SB-1

Marek's disease (MD) is a highly contagious lymphoproliferative disease of chickens caused by Gallid alphaherpesvirus type 2. Gallid alphaherpesvirus type 3 (GaHV-3) strain 301B/1 was previously shown to be an effective MD vaccine with synergistic efficacy when used as a bivalent vaccine with turkey herpesvirus. Since the nucleotide sequences of only two GaHV-3 strains have been determined, we sought to sequence the 301B/1 genome using Illumina MiSeq technology. Phylogenomic analysis indicated that 301B/1 is more closely related to other GaHV-3 strains (SB-1 and HPRS24) than to virulent or attenuated strains of GaHV-2. One hundred and twenty-six open reading frames (ORFs) have been identified within the 301B/1 genome with 108 ORFs showing a high degree of similarity to homologs found in the genomes of SB-1 and HPRS24; 14 ORFs are highly homologous (> 90% identity) with the corresponding ORFs within the SB-1 genome. The R-LORF8 and R-LORF9 genes are the most dissimilar to the collinear genes found in the SB-1 genome but are highly homologous (99%-100% identity) with those within the HPRS24 genome. Overall the 301B/1 genome is most similar to the SB-1 virus genome (99.1%) and to a lesser degree with the HPRS24 virus genome (97.7%). However, six 301B/1 ORFs (UL47, UL48, UL52, pp38, ICP4, and US10) have been identified that contain nonsynonymous substitutions relative to homologs found in the SB-1 genome. Notably, unlike the avian retrovirus long terminal repeat sequences found within the SB-1 genome, none were identified within the 301B/1 genome.