Isolation and Characterization of a Pseudorabies Virus Variant Strain in Gansu Province, China, 2021

The outbreaks of pseudorabies (PR) caused by pseudorabies virus (PRV) variant strains have led to huge economic losses in the pig industry in China in recent years. In this study, a variant PRV strain named PRV/Gansu/China/2021 (GS-2021) was successfully isolated and identified from brain tissue samples of PR-suspected dead piglets at a Bar-tha-K61-vaccinated pig farm in Gansu Province, China in 2021. Its biological characteris-tics, genetic features, evolutionary relationship, and pathogenicity were further evaluated. The results indicate that the PRV GS-2021 strain had different plaque sizes but no signifi-cant difference in replication kinetics from the Bartha-K61 strain in vitro. In addition, se-quence alignments revealed that the gB, gC, gD, and gE proteins of the PRV GS-2021 strain share high homology with those of the Chinese variant strains. However, glutamate is re-placed by glycine at position 91 and two aspartate insertions are detected at sites 48 and 496 in the gE protein of the virus. Phylogenetic analysis revealed that it was more closely related to endemic PRV strains, particularly the variant strains circulating in China, based on the gB, gC, gD, and gE genes and complete genome sequence. Moreover, we further discovered that the PRV GS-2021 strain exhibited a higher pathogenicity than the Bar-tha-K61 strain in mice through analyses of mortality, histopathology, and viral loads. Overall, our results suggest that the isolated PRV GS-2021 strain, as a variant with higher virulence and pathogenicity, was prevalent in Gansu Province, China before 2021. These findings are important for continuously monitoring the epidemiological characterization and genetic evolution of PRV, providing useful guidance for the design of novel vaccines and more efficacious control and prevention strategies for PR in the future.