Porcine reproductive and respiratory syndrome virus (PRRSV) is an RNA virus that causes reproductive failure in sows and respiratory problems in piglets. PRRSV infection leads to substantial pig mortality and causing huge economic losses so that disease outbreaks caused by the new PRRSV strain from other regions have caused great concern in China. In this study, we analyzed the pathogenicity of the novel ORF5 RFLP 1-7-4-like PRRSV strain, named PRRSV-ZDXYL-China-2018-1 in pigs. The viral challenge test showed that PRRSV-ZDXYL-China-2018-1 infection can cause persistent fever, moderate dyspnea, serum viremia, and interstitial pneumonia in Piglets. The levels of viral loads in serum and PRRSV-specific antigen were also detected in lung tissues were used one-step Taq-Man RT-qPCR and Immunohistochemisitry, respectively. At 28dpi, the level of specific antibodies was increased among infected piglets. Importantly, the new virus appeared be a moderately virulent isolate with pathogenicity compared to HP-PRRSV strain LQ (JXA1-like strain). Histological examination revealed severe monocyte hemorrhage and interstitial pneumonia associated with monocyte infiltration in the lung tissue of pigs infected with PRRSV-ZDXYL-China-2018-1 and LQ-JXA1 strains. Immunohistochemistry (IHC) results showed positive brown-red epithelial cells and macrophages in pig lungs. Therefore, it is critical to establish an effective strategy to control the spread of PRRSV in China.
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