Identification of a novel strain of carp edema virus affecting Songpu mirror carp in Liaoning, China

Abstract

Carp edema virus disease (CEVD), also referred to as koi sleepy disease (KSD), is a viral infectious disease caused by the carp edema virus (CEV). It is primarily characterized by lethargy, generalized edema, and gill hyperplasia and necrosis. The disease has a widespread distribution and is associated with high mortality, leading to significant economic losses within the carp aquaculture industry. This study aims to identify the pathogenic agents affecting Songpu mirror carp (Cyprinus carpio Songpu) from a carp farm experiencing elevated mortality rates in Liaoning Province, China, which experienced elevated mortality in late May 2018. Bacterial and parasitic infections were systematically excluded, and the presence of CEV infection in Songpu mirror carp was confirmed through nested PCR identification. The isolate was named CEV L-3 strain. The p4a partial gene sequence obtained was analyzed, which revealed that L-3 strain exhibits the highest homology compared with the UK isolate R083, which is classified within the IIa genotype. It was observed that the L-3 strain demonstrates a closer phylogenetic relationship to M141 from the UK and 112–2015 from Poland. Additionally, the gills were identified as the target organ of the L-3 strain by real-time PCR, which exhibited the highest viral load, followed by the kidney and spleen. This study has identified a novel strain of CEV which is prevalent in China, thereby paving the way for further research into the epidemiological characteristics, diagnostics and viral biological properties of CEVD.