Identification and pathogenicity analysis of a novel highly virulent strain of spring viraemia of carp virus and production of its structural proteins by the mammalian expression system

Abstract

Spring viraemia of carp virus (SVCV), a highly pathogenic fish rhabdovirus, caused an acute hemorrhagic and highly contagious disease in cyprinids. In this study, a new strain of SVCV was isolated from diseased zebrafish in Yangling, Shaanxi Province, China, and named SVCV-CG01. Tissue filtrates of diseased fish were detected by Nest PCR using the specific 714 bp and 606 bp fragments from the glycoprotein gene of SVCV. The genes encoding for the N, P, M and G protein were amplified, and the fragments were inserted into pMD-19T vectors to determine the genome of SVCV. Based on phylogenetic analysis of G protein gene, the isolated virus was classified into the Ia genogroup. The titer of the new strain at 48 h and 72 h was approximately 108 and 109 times higher than that of the 0504 strain, respectively. The virus could produce typical cytopathic effects (CPE) and induce apoptosis in EPC cells at 48 and 72 h post infection (hpi). Healthy zebrafish were injected with different doses of SVCV and mass mortality of fish was detected after 4 d infection, with a cumulative death rate of 100% from 107 TCID50 group at 7 d post infection (dpi). Using cultured mammalian 293T cells, an average transfection efficiency of the four structural proteins was 49.1% and 69.6% at 24 and 48 h post transfection (hpt), respectively. This study could be served as a reference for the research on the molecular epidemiology, evolution and pathogenicity of fish viruses.