Abstract: Pseudorabies virus(PRV)’s prevalence brings huge economic losses to the domestic pig industry, however, many large-scale immunized pig herds broke out pseudorabies, and gE antybodies turned from negative to positive since 2011, causing PRV clinical symptoms infected pigs, and then resulting in “abortion storm”. Most scholars believed that national outbreak of PRV might be related to factors such as viral virulence and genetic variation. In this study, four pseudorabies viruses were successfully isolated from suspected PRV infected pigs by PK-15 cells, moreover, their TCID₅₀ and LD₅₀ were determined. Their main immunogenic genes and virulence-related genes gB, gC, gE and TK were amplified, sequenced and analyzed. The 4 pseudorabies viruses were affirmed, named as FJ01, FJ03, YK and MS2018 strain, respectively, whose titers were 10^-6.63, 10^-7.08, 10^-8.10, 10^-7.18 TCID_50s·0.1mL^-1, respectively, and the results of virulence test in Balb/c mice showed as 10^2.17, 10^2.72, 10^3.44, 10^3.51 TCID_50s, respectively. The virulence of FJ01 strain was the strongest. Their nucleotide and amino acid homologies were analyzed and evolutionary trees were established. The results showed that the genes of FJ01, FJ03 and MS2018 strains had higher homology with the mutants such as HNX, HNB and JS-2012 strains which were isolated in recent years. In evolutionary relationship, they belonged to a large branch, however, they belonged to different evolutionary branches from vaccine Bartha-K61,SA215, and foreign strains Becker and Kaplan with evident variations. YK had the closer affinity with foreign strains in evolutionary relationship, but the reason remained to be further explored.

Key words: pseudorabies virus, isolation and identification, virulence gene, sequence analysis