Location: Endemic Poultry Viral Diseases ResearchTitle: Comparative genomic sequence analysis of the Marek’s disease vaccine strain SB-1 Author
Submitted to: International Marek's Disease Symposium Abstracts and Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 10/1/2010
Publication Date: 10/17/2010
Citation: Spatz, S.J., Karel, S. 2010. Comparative genomic sequence analysis of the Marek's desease vaccine strain SB-1. International Marek's Disease Symposium Abstracts and Proceedings. 1(1):141. Interpretive Summary:
Technical Abstract: Marek’s disease virus (MDV) is one of the most oncogenic herpesviruses known and induces a rapid onset T-cell lymphoma and demyelinating disease in chickens. Since the 1970s the disease has been controlled through mass vaccination with meleagrid herpesvirus type 1 (MeHV-1). Over time the efficacy of the vaccine has decreased, and in the 1980s a bivalent vaccine consisting of MeHV-1 and a non-oncogenic gallid herpesvirus type 3 (GaHV-3) strain known as SB-1 was introduced to control this costly pathogen. The complete DNA sequence (165,994 bp) of this GaHV-3 strain was determined using 454 pyrosequencing. A total of 524 open reading frames (ORFs) greater than 25 amino acids in length were examined for homology to protein sequences present in GenBank using BLAST (E-values <0.9). Of the 128 ORF hits, 75 ORFs showed homology to well-characterized alphaherpesviral proteins. Phylogenetically, this strain partitions in its own branch along with the GaHV-3 strain HPRS24 and shows more relatedness to MeHV-1 than gallid herpesvirus type 2 (GaHV-2, Marek’s disease virus). In comparing the two GaHV-3 genomes, 19 ORFs differ in the number of predicted amino acids; of these, eight (UL3.5, UL5, UL9, UL28, UL30, UL36, UL37 and UL50) encode well-characterized alphaherpesviral proteins. When comparing the GaHV-3 ORFs to their homologs in MeHV-1 and GaHV-2, a greater percentage of amino acid similarity was found with homologous ORFs in the genome of SB-1 than with those in the HPRS24 genome. Overall, twice as many of the 75 ORFs within the SB-1 genome showed greater sequence identities and similarities to homologous ORFs in the Marek’s disease genome than those within the HPRS24 genome. A sequence within the unique short region of the SB-1 genome exhibited significance sequence homology to long terminal repeat (LTR) sequences of avian retroviruses. This sequence was only found in the SB-1 genome and not the HPRS24 genome.