Emergence and etiological characteristics of novel genotype Ⅱ pseudorabies virus variant with high pathogenicity in Tianjin, China.

Pseudorabies (PR) is a highly infectious disease caused by pseudorabies virus (PRV). This study aimed to detect and identify recent outbreaks of genotype Ⅱ PRV, and further analysis it's etiological characteristics and pathogenicity. The brain tissues with suspected PRV infection were isolated and the main virulence-related genes of the isolated PRV strain were amplified and sequenced for phylogenetic analysis. In addition, the pathogenicity of the isolated PRV strain to 6-week-old mice and 9-days-old suckling piglets were evaluated. The results showed that a PRV strain was successfully isolated and named PRV TJbd2023 strain, which could proliferate in PK-15 cells and TCID of the 6th generation virus reached 10/0.1 ml. Phylogenetic trees and amino acids analysis were constructed based on full-length gE sequences, which showed that PRV TJbd2023 strain was clustered into genetype Ⅱ PRV variant with a characteristic 21-nucleotide insertion (encoding AASTPAA) in gC gene, and some amino acid point mutations were also found in other virulence-related genes, including gB protein RH and EK, gD protein RS, and gE protein TA. Animal experiments showed that TJbd2023 could cause acute neurological symptoms with 10/mL LD on KM mice, and intranasal inoculation of suckling piglets with 2 ml of TJbd2023 strain(10/0.1 ml) led to a mortality rate of 66.70 %. Emerging genotype Ⅱ PRV variant such as isolated in our research named TJbd2023 with high pathogenicity might be responsible for recent outbreaks of PRV and immunization failure of Bartha-K61 vaccine in Tianjin, China.