Investigation of the genetic differences between bovine herpesvirus type 1 variants and vaccine strains

Although an efficacious bovine herpesvirus type-1 (BHV-1) vaccine has been used for many years, BHV-1 vaccine-related abortion and respiratory disease have been occurring in a rising number of herds. To investigate whether isolates from BHV-1 vaccination with adverse effects are identical to the wild type virus or vaccine virus, regions of the thymidine kinase (TK) gene prone to mutation were examined. Two sets of PCR primers were used to investigate two unique polymorphisms of the TK gene in 35 BHV-1 isolates. The DNA polymorphisms in the TK gene were determined by Sanger sequencing of PCR amplicons and the sequence was analyzed with Geneious software. All BHV-1 isolates and vaccine were found to have TK genes that are different from the wild type virus. Over 50% of the sequenced BHV-1 isolate has TK genes that are different from vaccine strains, with 27% having genetic variation in region 1 of TK and 55% in region 2 of TK. This study suggests that BHV-1 isolates have genetic similarity with vaccine virus but have variation within TK genes, which may have resulted from mutations occurred within the vaccinated animals or from infection with a strain similar to the vaccine virus