Emergence of a novel porcine reproductive and respiratory syndrome virus strain inducing biphasic temperature fluctuations in Tianjin, northern China.

Porcine reproductive and respiratory syndrome virus (PRRSV) has imposed significant economic burdens on the global swine industry. The majority of PRRSV strains can induce high fever at various stages of pig development. However, the PRRSV strain that triggers the biphasic temperature phenomenon remains relatively rare. In this study, a novel PRRSV variant, designated SJ0107, was isolated from local pig farms in Tianjin, Northern China, in 2024. Recombination analysis reveals that SJ0107 is a recombinant PRRSV strain resulting from the interaction between lineage 1.8 and lineage 8.3, with four potential recombination breakpoints located in Nsp2 (nt 766/1997), Nsp4 (nt 5413), and Nsp9 (nt 7750). Animal challenge experiments conducted on four-week-old piglets demonstrated that SJ0107 can induce rare initial hypothermia symptoms within 5 days post-inoculation (dpi). Subsequently, the body temperature returned to normal, and high-grade fever symptoms emerged at 11 dpi, lasting for one week before normalizing again. Meanwhile, severe histopathological lung lesions were also detected in the pathological sections. In conclusion, the findings reveal that the SJ0107 strain undergoes a dual-phase temperature alteration, which not only complicates traditional diagnostic criteria reliant on persistent fever but also heightens the risk of misdiagnosis in the initial phases of infection. These insights underscore the necessity of revising surveillance protocols for emerging PRRSV variants that exhibit atypical pathogenic characteristics.