title: Characterization of a thymidine kinase-deficient mutant of equine herpesvirus 4 and in vitro susceptibility of the virus to antiviral agents.
abstract: Equine herpesvirus 4 (EHV-4) is an important equine pathogen that causes respiratory tract disease among horses worldwide. A thymidine kinase (TK)-deletion mutant has been generated by using bacterial artificial chromosome (BAC) technology to investigate the role of TK in pathogenesis. Deletion of TK had virtually no effect on the growth characteristics of WA79DeltaTK in cell culture when compared to the parent virus. Also, virus titers and plaque formation were unaffected in the absence of the TK gene. The sensitivity of EHV-4 to inhibition by acyclovir (ACV) and ganciclovir (GCV) was studied by means of a plaque reduction assay. GCV proved to be more potent and showed a superior anti-EHV-4 activity. On the other hand, ACV showed very poor ability to inhibit EHV-4 replication. As predicted, WA79DeltaTK was insensitive to GCV. Although EHV-4 is normally insensitive to ACV, it showed >20-fold increase in sensitivity when the equine herpesvirus-1 (EHV-1) TK was supplied in trans. Furthermore, both ACV and GCV resulted in a significant reduction of plaque size induced by EHV-4 and 1. Taken together, these data provided direct evidence that GCV is a potent selective inhibitor of EHV-4 and that the virus-encoded TK is an important determinant of the virus susceptibility to nucleoside analogues.
authors.affiliation: Department of Veterinary Microbiology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
authors.forename: Walid
authors.initials: W
authors.lastname: Azab
authors.forename: Koji
authors.initials: K
authors.lastname: Tsujimura
authors.forename: Kentaro
authors.initials: K
authors.lastname: Kato
authors.forename: Jun
authors.initials: J
authors.lastname: Arii
authors.forename: Tomomi
authors.initials: T
authors.lastname: Morimoto
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Kawaguchi
authors.forename: Yukinobu
authors.initials: Y
authors.lastname: Tohya
authors.forename: Tomio
authors.initials: T
authors.lastname: Matsumura
authors.forename: Hiroomi
authors.initials: H
authors.lastname: Akashi
mesh_terms: D000212:Acyclovir / Q000494:pharmacology; D000818:Animals; D000998:Antiviral Agents / Q000494:pharmacology*; D002460:Cell Line; D015774:Ganciclovir / Q000494:pharmacology; D017353:Gene Deletion; D023141:Herpesvirus 4, Equid / Q000187:drug effects* / Q000235:genetics / Q000472:pathogenicity*; D006801:Humans; D008826:Microbial Sensitivity Tests; D013937:Thymidine Kinase / Q000172:deficiency*; D010948:Viral Plaque Assay; D014764:Viral Proteins / Q000235:genetics*
chemical_list: D000998:Antiviral Agents; D014764:Viral Proteins; D013937:Thymidine Kinase; D015774:Ganciclovir; D000212:Acyclovir