Detection and phylogenetic analysis of epidemic carp edema virus in Beijing, China (2021–2022)

Carp edema virus (CEV) is the causative agent of carp edema virus disease (CEVD), also known as koi sleepy disease (KSD), which is a highly pathogenic viral infection of koi and common carp. Initially identified in Japan in 1974, the spread of CEVD has escalated in recent years with the increasing global trade of koi, and has been documented throughout Europe and Asia, thereby negatively impacting koi aquaculture. Between 2021 and 2022, an infectious disease outbreak occurred in koi farms across various regions of Beijing. Following clinical diagnosis, histopathological examination, and molecular testing, CEV was identified as the causative agent of the epidemics. Using the detection method designed by the Centre for Environment, Fisheries and Aquaculture Science(CEFAS), 11 positive samples were detected by PCR, including nine that were verified by nested PCR. Subsequently, nested PCR and phylogenetic analysis confirmed that CEV was the main pathogen of koi farms. Additionally, increased water temperature was positively correlated to the mortality rate of CEV-infected koi, indicating that temperature is an important factor influencing the incidence of CEV infection. The findings of this study provide valuable references for the development of new strategies for the diagnosis and prevention of CEVD.