Histopathological study and PCR detection of white spot syndrome virus from infected Procambarus clarkii

In May 2016, a severe infectious disease occurred among the farmed Procambarus clarkii in Qianjiang, Hubei Province. Histological examination, virus isolation, nested-PCR. artificial infection experiment and phylogenetic analysis were performed to explore its causes and the epidemic law. Principal symptoms included darkening of the body, reduction in vigour, low feeding. Histopathologically, hepatopancreas, intestines, muscle, gill showed varying degrees of degeneration, necrosis and inflammatory cellinvasion. Pathologic changes were the same as the white spot syndrome virus (WSSV) infected arthropod. PCR detection results also showed that tissues of dying P. clarkii were positive to WSSV, the positive rates of PCR was 55.56%(15/27), while those were negative to monodon baculovirus disease (MBV) and infectious hypodermal and hematopoietic necrosis (IHHNV). P. clarkii that died in oral infection was positive for the presence of WSSV by Nested-PCR.The sequenced amplification products shared 100% identity with white spot syndrome virus isolate EG3, complete genome (GenBank access number: KR083866.1). Phylogenetic analysis showed that the isolate was belonging to WSSV. The hepatopancreas, intestine and muscle tissue of the diseased P. clarkii were fed to the healthy P. clarkii. The results showed that a cumulative mortality of 100% was observed in the infected P. clarkii, while no death in control group. Therefore WSSV was determined to be the pathogen of the P. clarkii.