Pathogenicity and genome-informed virulence features of Glaesserella parasuis serovar 13 in piglets

Glaesserella parasuis is an important swine pathogen that causes Glässer’s disease, a systemic disease associated with polyserositis, arthritis, meningitis, and pneumonia. Serovar 13 is generally considered highly pathogenic and has been linked to severe clinical disease in pigs; however, integrated evidence on its experimental pathogenicity and complete genomic characteristics remains limited. In this study, we systematically characterized G. parasuis serovar 13 strain W2, a clinical isolate recovered from the lung of a piglet with severe systemic disease, by combining a piglet challenge model, whole-genome sequencing, and comparative genomic analysis. W2 caused dose-dependent mortality after intraperitoneal challenge, disseminated to multiple tissues and body fluids, and induced dose-associated pulmonary injury, indicating marked pathogenic effects in this intraperitoneal challenge model. Sequencing results revealed that W2 contained a complete circular chromosome of 2.36 Mb without detectable plasmid replicons, and taxonomic analyses confirmed its placement within G. parasuis. Genome annotation identified multiple putative virulence-associated homologs mainly related to immune modulation, nutrient acquisition, adhesion, stress adaptation, and surface structure remodeling. Predicted prophage-like regions, genomic islands, and CRISPR array-like loci further suggested genomic plasticity in this strain. Antimicrobial resistance screening identified resistance-associated homologs but no definitive acquired resistance genes. Overall, W2 is a serovar 13 clinical isolate that exhibited marked pathogenic effects in a piglet intraperitoneal challenge model. Genome analysis identified multiple putative virulence-associated features, although their contributions to the observed phenotype remain to be established.