Histopathology and Detection of Cyprinid Herpesvirus Infection in Two Koi Farms in Tianjin City (China)

Abstract

Koi herpesvirus (KHV) is the etiologic agent of koi herpesvirus disease (KHVD) causing mass mortalities in common carp (Cyprinus carpio carpio), koi (Cyprinus carpio koi), and ghost carp (Cyprinus carpio goi) populations. In this study, we report new outbreaks of the koi herpesvirus (KHV) disease in a koi carp farm in Tianjin city, northern China. From June to September 2017, severe mortalities of koi juvenile and broodstock occurred in ornamental fish, and infected koi carp which showed signs of lethargy and loss of appetite, and clinical signs including sunken eyes, gill necrosis, and excessive secretion of mucus. Histopathologically, the gills showed hyperplasia and degeneration of epithelial cells and fusion of the lamellae, and foci necrosis was found in gills, liver, kidney, and spleen. In addition, KHV and Carp edema virus (CEV) were detected in the diseased koi fish by diagnostic PCR tests for the viruses. The results showed that the nucleotide sequences of thymidine kinase (TK), DNA polymerase (SphI-5), and four open reading frame (ORF 25, ORF 56, ORF 72, ORF 81) genes confirmed the highest identity with other KHV strains such as KHV-I, KHV-U and KHV-J, but the CEV was negative. The phylogenetic tree showed KHV-TJ1708 and KHV-TJ1709 clustered with the Asian strain KHV-J (AP008984). Results of the present study confirmed the prevalence of Carp herpes disease (KHVD) in China koi populations by means of clinical examination, histopathology and molecular technique. These data will provide a reference for diagnosis, quarantine, and surveillance of KHV in China.