Comparison of pathogenicity and host responses of emerging porcine reproductive and respiratory syndrome virus variants in piglets.

Porcine reproductive and respiratory syndrome virus (PRRSV) is a highly variable virus with genetic diversity. This study comparatively examines the pathogenicity and immunological impact of two emergent PRRSV strains, SD53 and HuN4, in piglets. Our results indicate that SD53 strain induces milder clinical syndromes and less severe tissue damage than HuN4, despite similar replication rates. Hematological tests showed less perturbations in peripheral blood cell profiles after SD53 infection, suggesting a less systemic impact. The neutrophil-to-lymphocyte ratio was notably lower in SD53-infected piglets, suggesting a less intense inflammatory reaction. Moreover, SD53 infection led to lower levels of pro-inflammatory cytokines, further supporting a less pronounced inflammatory profile. Both strains induced the production of PRRSV-specific antibodies. However, transcriptomic analysis of lung and lymph node tissues from infected piglets disclosed a more moderate up-regulation of core genes, including IMPORTANCE: The high mutation rate of porcine reproductive and respiratory syndrome virus (PRRSV) poses significant challenges to its accurate diagnosis and the implementation of effective control measures. This research explores the pathogenic profiles of two emerging PRRSV stains: the NADC30-like strain SD53 and the highly pathogenic strain HuN4. Our investigation reveals that SD53 initiates distinct immunopathological responses