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

The outbreaks of pseudorabies (PR) caused by the pseudorabies virus (PRV) variant strains have led to huge economic losses to the pig industry in China in recent years. In this study, a novel PRV variant strain named PRV/Gansu/China/2021 (GS-2021) was suc-cessfully isolated and identified from the brain tissue samples of PRV-suspected dead piglets at a Bartha-K61-vaccinated pig farm in Gansu Provinces, China, in 2021, and its biological characteristics, genetic features, evolutionary relationship and pathogenicity were further evaluated. The results showed that the PRV GS-2021 strain had different plaque sizes but no significant difference in replication kinetics with Bartha-K61 strain in vitro. In addition, sequence alignments revealed that the gB, gC, gD, and gE proteins of PRV GS-2021 strain shared highly homologous to those of the variant strains. However, glutamate was replaced by glycine at position 91 in the gE protein of the viral strain, alt-hough two aspartate insertions were detected at sites 48 and 498 in the gE protein of the virus. Phylogenetic analysis found that it was more closely related to endemic PRV strains, particularly the variant strains circulating in China, based on those 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 Bartha-K61 strain in mice through mortality, histopathology, and viral loads. Overall, our results suggested that the isolated PRV GS-2021 strain as a higher virulence variant, has prevalent in Gansu prov-ince of China before 2021 and these findings are important for continuously monitoring the epidemiological characterization and genetic evolution of PRV, which will provide a useful guidance for the design of novel vaccines and more efficacious control and preven-tion strategies of PR in the future.