Elimination of a NADC30/NADC34/JX recombinant PRRSV strain from a 5,000-sow breeding herd: a longitudinal intervention study.

Porcine reproductive and respiratory syndrome (PRRS) remains one of the most economically devastating diseases affecting the global swine industry. This case report describes the successful elimination of a recombinant porcine reproductive and respiratory syndrome virus (PRRSV) strain from a 5000-sow PRRS-naïve breeding herd in China. The emergent strain was identified as a recombinant of NADC30-like, NADC34-like, and JX (FJ09) strains based on GP5 gene sequencing and phylogenetic analysis, with GenBank accession number PZ303389. Following the initial detection of PRRSV in week 3 of 2025, a systematic elimination program was implemented, including mass vaccination with modified live virus (MLV) vaccine in sows, feedback exposure in gilts, transition to inactivated vaccine in piglets, and strict biosecurity measures such as McREBEL practices in farrowing houses. Longitudinal monitoring was conducted using serological (IDEXX PRRS antibody ELISA) and virological (PCR on processing fluid, colostrum, and environmental samples) assays. The elimination timeline spanned approximately 52 weeks, with processing fluid testing negative for PRRSV RNA by week 37 and the entire herd achieving PRRSV-negative status by week 52. Self-reared replacement gilts were resumed at week 20 of 2026 after 20 consecutive weeks of negative monitoring. Production performance analysis revealed that the outbreak primarily affected weaning numbers for 18 weeks, with the most significant decline occurring between weeks 9-14, while total born numbers remained relatively unaffected. This case demonstrates that a well-designed elimination program combining gradual virus exposure, strategic vaccination, and strict biocontainment can successfully eliminate recombinant PRRSV from large breeding herds without resorting to depopulation-repopulation. These findings provide valuable reference for similar PRRS control and elimination efforts in the field.