Detection and Analysis of Carp Edema Virus (CEV) in Farmed Carp and Koi

The carp edema virus (CEV) disease were caused by CEV, which may result in high losses in carp culture. In 2014, it had spread into China according to the report of the first CEV case confirmed in Beijing region. To investigate the epidemic status of CEV in farmed carps, select suitable method for CEV survey, and explore its pathogenic mechanism, from May to September in 2016, 13 samples were collected and detected CEV using Nest-PCR methods developed by Japanese researchers, and Nest-PCR methods and Real-time PCR method developed by UK researchers. The results showed that 3 koi samples and 2 common carp samples of CEV positive were found. Real-time PCR and Nest-PCR could be well used to detect CEV in koi samples, but Nest-PCR could not detect CEV well in common carp. In positive samples, there were no clinical signs and death in case 3 and case 10 of farmed fish, and case 3 harboured higher copy numbers of CEV-specific DNA than that of case 7, case 8 and case 13 with signs of disease. Based on the above information, surveillance programs need to carry out urgently to avoid further spread of CEV according to the epidemic status of CEV. And Real-time PCR method was more suitable for CEV survey than Nest-PCR method. In addition, the farmed carps did not always occurred CEV disease in optimum temperature when the farmed fish carried CEV or the CEV mass reproduction in fish body. Therefore, the environmental stress was the crucial factor leading to the occurrence of the CEV disease, avoiding environmental stress was an effective measure to reduce the occurrence of the CEV disease.