Pathogenicity of NADC34-like PRRSV HLJDZD32-1901 isolated in China

Porcine reproductive and respiratory syndrome virus (PRRSV) causes a substantial economic loss to the swine industry. Recently, NADC34-like PRRSV was reported in the USA, China and Peru and consistently attributed to a large number of abortions in the clinic. In the USA, the pathogenicity of NADC34-like PRRSV in piglets is highly variable. However, the pathogenicity of NADC34-like PRRSV in China is unclear. In this study, an NADC34-like PRRSV strain, HLJDZD32-1901, was isolated in primary alveolar macrophage (PAM) cells from a sow blood sample collected from an abortive farm in China. HLJDZD32-1901, with no recombination, has a 100-aa deletion in the NSP2 protein corresponding to positions 328-427 in the VR2332 strain. Phylogenetic analysis based on open reading frame 5 (ORF5) indicated that HLJDZD32-1901 belongs to sublineage 1.5. Animal experiments showed that the weight loss of HLJDZD32-1901-infected piglets was significantly different from that of control piglets at 8-14 dpi. In addition, the challenge group had obvious histopathological lesions, including interstitial pneumonia and enlarged lymph nodes, and increased viremia and viral loads in three tissues. However, piglets in the challenge group had only mild clinical symptoms, with no death or fever. Our results showed that NADC34-like PRRSV HLJDZD32-1901 is a mildly pathogenic strain in piglets. However, we speculate that HLJDZD32-1901 may be a highly pathogenic strain in pregnant sows based on clinical morbidity.