First report of cyprinid herpesvirus 2 isolated from the golden crucian carp in China

In this study, a virus strain designated GCC2021 was isolated from the golden crucian carp (Carassius auratus red var. male x Cyprinus carpio L. mirror female) in Jiangsu Province, China. GCC2021 was propagated in the Gibel carp brain (GiCB) cell line with a typical cytopathic effect. Healthy golden crucian carp was injected with GCC2021 virus solution intraperitoneally, and the symptoms of the artificially infected fish were consistent with those of the naturally diseased golden crucian carps. The mortality was 6.67 +/- 3.33% (kidney homogenate group) and 4.44 +/- 1.93% (cell culture virus group). The histopathological results indicated systemic inflammation and changes in multiple organs. Electron microscopy observation using ultra-thin sections of the diseased fish kidney revealed a number of spherical particles with capsid that were approximately 110-120 nm in diameter, and the mature virus particle was about 170-220 nm in diameter. The helicase (Hel) gene of GCC2021 was amplified using PCR and sequenced. PCR amplification showed positive results for GCC2021 in the diseased fish, artificially infected fish, and infected GiCB cells. Sequence analysis of the amplification products showed 99.68% identity with the helicase gene of CyHV-2 SY-C1 strain. Phylogenetic analysis of the CyHV-2 ORF25B non-coding region revealed that the isolate clustered with CyHV-2 1301 strain, SY strain, and SY-C1 strain. CyHV-2 copies in different tissues were determined using digital PCR. Viral loads were detected in the liver, spleen, kidney, brain, intestine, and gill, with the highest in the kidney and lowest in the brain. In this study, it was provided solid evidence that CyHV-2 could infect golden crucian carp.