Pathogenicity and antigenic characterization of a novel highly virulent lineage 3 porcine reproductive and respiratory syndrome virus 2.

Background/purpose: Porcine reproductive and respiratory syndrome virus (PRRSV) is a pathogen with a negative economic impact on the global swine industry. In 2019, a suspected highly pathogenic strain, NPUST-108-929/2019 (108-929), was isolated from a pig farm in Pingtung with an outbreak of high mortality and analyzed. The characteristics of PRRSV 108-929 have barely been studied.

Methods: This study was to evaluate pathogenicity through animal challenge experiments using PRRSV 108-929 and antigenic characterization of this novel PRRSV.

Results: This PRRSV strain is PRRSV 2, belonging to lineage 3 based on open reading frame 5 sequence analysis. Four putative N-linked glycosylation sites (N32, N35, N44 and N51) are located on glycoprotein 5. Experimental results revealed that high fever occurred at 3 days postinoculation (dpi) in the high-titer inoculation (HIN) group (2 × 10⁴ TCID₅₀/mL), 8 dpi in the high-titer contact (HC) group, 4 dpi in the low-titer inoculation (LIN) group (2 × 10³ TCID₅₀/mL) and 9 dpi in the low-titer contact (LC) group. All pigs in each PRRSV 108-929 challenge and contact group showed severe clinical signs, such as high fever (>40.5 °C) and significant weight loss. Deaths occurred only in the HIN group; the survival rate was 60 %. All the piglets except the control group piglets showed high viremia titers (6.04-8.28 log¹⁰ copies/μL).

Conclusion: The pathogenic characteristics of PRRSV 108-929 suggest that it is a highly virulent PRRSV strain at both the farm and laboratory levels.