[Thymidine kinase activity of virulent and vaccinal strains of Aujeszky's disease virus].

Studied was the timidine-kinase activity of the A2 virulent strain and the MK-25 and MK-35 vaccinal strains of the Aujeszky's disease virus via the infection of primary cell cultures of chick embryo fibroblasts and of pig kidney. It was found that the A2 strain substantially enhanced the induction of the timidine-kinase enzyme in the infected cell cultures, while the IUDR- and the BUDR-resistant vaccinal strains MK-25 and MK-35 showed 10 to 12 times lower activity. Strain MK-25 did not restore the high timidine-kinase activity of the parent A2 strain after 10 successive passages in primary chick embryo fibroblast cultures. The strongly reduced timidine-kinase activity of the two vaccinal strains (MK-25 and MK-35) could be used as a marker to control their properties. The virulent A2 strain of the Aujeszky's disease virus had a well manifested mutability when passing in cultures in the presence of IUDR.