Molecular Screening and Cell Cultured–Based Isolation of Carp Edema Virus in Koi Carp ( Cyprinus carpio Koi) From Aquarium Shops in Tamil Nadu, India

This study aimed to explore the widespread occurrence of carp edema virus (CEV) in ornamental koi carp available at ornamental shops in Kolathur, Tamil Nadu. The affected koi carps showed various symptoms, such as ulcers, loss of scales, body and fin haemorrhage, fin necrosis, and gill hyperplasia. No known fish cell lines have been reported for the continuous culturing of CEV. To address this constraint, gill (ICG) and heart (SICH) cell lines derived from catla fish were used for the continuous in vitro cultivation of CEV. Virus-specific cytopathic effects (CPE) were similarly observed in all 12 consecutive passages in the infected cell lines. Furthermore, the in vitro replication efficacy of CEV in ICG and SICH cell lines was confirmed by PCR, and the viral copies were quantified using quantitative PCR (qPCR) at different passages. Initially, the levels of CEV copies were very low; however, they peaked by the 12th passage, indicating adaptation to the ICG and SICH cell lines. In addition, to study the virulence of the isolated CEV, filtrate from the pooled organ tissues of fish, as well as the supernatant of ICG culture of CEV infection, was injected into koi carp, and symptoms were observed and mortality was recorded. PCR and qPCR analyses were conducted to assess tissue tropism in various tissues experimentally CEV-infected koi carp. Based on the PCR and qPCR results, gill tissue was identified as the primary target organ for CEV infection. This study proves that CEV replication in fish cell lines supports future vaccine development.