4Lomniczi B, Blan-Kenship M L, Ben-Porat T T. Deletions in the genomes of pseudorabies virus vaccine strains and existence of four isomers of the genomes [J]. J Virol, 1984, 49 (3): 970-979.
5Petrovskis E A, Timmins J G, Gierman T M, et al. Deletions in vaccine strains of pseudorabies virus and their effect on synthesis of glycoprotein gp63 [J]. J Virol, 1986, 60(3): 1166-1169.
6Klupp B G, Lomniczi B,Visser N, et al. Mutations affecting the UL21 gene contribute to avirulence of pseudorabies virus vaccine strain Bartha [J]. Virology, 1995, 212(2): 466-473.