Aujeszky's disease virus strains with peculiar features

Aujeszky's disease (AD) virus strains isolated from weak colostrum-deprived piglets were investigated for virulence in rabbits. Most of them (5 out of 9 investigated) proved avirulent. As clinical symptoms of AD were not observed during this period on the farms of origin, one can assume that the strains had a particular affinity for the pig fetus. It is proposed that the strains may be a result of recombination between the attenuated strains MK-35 (gI-) now in use as a live vaccine and MK-35 (gI+), used as a live vaccine until 3 years ago, as well as between the vaccine strain and a wild-type strain of AD virus, followed by the acquisition of tropism for the reproductive system. Virulent as well as avirulent strains were isolated in the same herd. The evaluation of a highly immunogenic killed AD vaccine in this complicated situation is recommended.