In vivo studies on Aujeszky's disease virus mutants

We report the construction and in vivo analysis of three recombinant Aujeszky's disease virus (ADV) strains containing mutations at three different loci of the genome. Mutant vE16lac was generated by deleting of 2976 bp DNA fragment which covers 1851 bp of the right arm of UL component, the UL-US junction, the "a" element of the internal repeat (IR) region and a putative LAT promoter. Mutant vRRlac was generated by deletion of a 1805 bp fragment from the coding region of the large and small subunits of ribonucleotide reductase gene (rr). The third mutant, vTKlac, was constructed using insertional mutagenesis of the thymidine kinase gene (tk). In the constructed mutants a lacZ gene expression cassette was either inserted into the target gene (vTKlac) or replaced the deleted DNA segment (vE16lac, vRRlac). Constructed recombinant viruses were analyzed by infecting pigs and monitoring the virus excretion from nasal fluid and disease symptoms. Tissue specimens were collected for virus isolation and pathological examination. Strains vTKlac and vRRlac retained the ability to establish an infection, but showed reduced replication efficiency in the respiratory tract and were unable to attack the central nervous system (CNS) of pigs. Thus, both deletions induce significant attenuation of the virus measured by decrease of virulence in infected pigs. Strain vE16lac showed disease symptoms similar to that of wild type and could be detected in the CNS of pigs.