Vaccination of swine with thymidine kinase-deficient mutants of pseudorabies virus.

A mutant of pseudorabies virus (PRV) deficient in thymidine kinase (TK-) activity was isolated and characterized. The mutant grew well in cell culture and did not revert to the thymidine kinase-positive phenotype. The PRV-TK- was not virulent when inoculated intranasally into 3-to 4-week-old pigs and could not be reactivated from the ganglia of these pigs by explantation and cocultivation with susceptible cells several weeks after virus inoculation. Pigs that had been exposed to PRV-TK- were immune to challenge exposure with a virulent strain of PRV. Furthermore, the challenge virus was not recovered from the ganglia of most of these pigs, indicating that colonization of the ganglia by a super-infecting virulent PRV strain was considerably reduced by vaccination.