Characterization of a novel, virulent PRRSV-1 subtype 1 strain with intestinal tropism in China.

Porcine reproductive and respiratory syndrome virus (PRRSV) causes abortions in sows and abnormal respiratory symptoms in piglets. Recently, reports of PRRSV-1 infection in China are growing, however, data on the pathogenicity of PRRSV-1 subtype 1 are limited. In this study, a PRRSV strain, namely GXFS20220129, was isolated from the lung tissues of piglets exhibiting respiratory distress and diarrhea on a pig farm in southern China. Phylogenetic analysis revealed that the isolate belongs to lineage S1.1 within subtype 1 PRRSV-1, and is distinct from the major epidemic strains of PRRSV-1 in China. Sequence identity analysis showed that GXFS20220129 shares 77.4 %-90.1 % similarity with various PRRSV-1 subtypes, with the highest similarity (90.1 %) to the PRRSV-1 prototype strain LV. Compared to other subtype 1 PRRSV-1 strains, GXFS20220129 has 20 amino acid deletions (positions 274-293) and 18 amino acid deletions (positions 324-341) in the Nsp2 region. Piglets infected with GXFS20220129 exhibited transient fever, coughing, diarrhea, and weight loss, ultimately resulting in the death of 2 out of 4 piglets. Quantitative real-time PCR (qRT-PCR) showed comparable viral loads in the lung and intestinal tissues of infected piglets. Histopathological analyses revealed significant interstitial pneumonia and disruption of intestinal epithelial structures. Immunohistochemical analysis confirmed the presence of PRRSV N protein in both lung and intestinal tissues. These findings indicate that the GXFS20220129 strain is virulent and has a distinct intestinal tropism, causing severe clinical manifestations and mortality in piglets.