Emergence and Characterization of Three Pseudorabies Variants with Moderate Pathogenicity in Growing Pigs

Pseudorabies virus (PRV) remains a critical threat for the global swine industry, with heightened attention due to the emergence of variant strains since late 2011 in China. Emergent viral variants generally undergo three to four years of adaptation to present new phenotypes. However, limited investigations have been performed on the evolution and pathogenicity of variant PRV strains in growing pigs after 2015. In this study, three PRV field strains, named SD1501, SD1701, and SD1801, were isolated and their genetic characteristics and pathogenicity on 9-week-old pigs were analyzed. Nucleotide identity and phylogenetic analyses based on the complete genome sequence, as well as major immunogenic and virulence-related genes revealed that all three isolates clustered closely with genotype II variant strains prevalent in China. The pathogenicity analysis demonstrated that the three isolates exhibited moderate pathogenicity in growing pigs with a TCID₅₀ of 10⁷. Infected pigs displayed transient fever and reduced appetite, with only one pig in each challenge group showing typical neurological symptoms and succumbing within 6 days post infection. These findings enrich the epidemiological data of PRV and provide direct evidence for the phenotypic variations caused by PRV infection, which enhances our understanding of PRV evolution in China and contributes to PRV control in the field.