Carp edema virus – a new threat to Ukrainian carp farming

Purpose. To conduct monitoring studies on the diagnosis of the emerging Carp Edema Virus in carp farms from different geographical zones of Ukraine, to investigate the circulation of the virus in full-system farms and to assess the consequences of infection for different age groups of carp and other sensitive species. Methodology. Gill samples of common carp (C. carpio), koi carp (C. carpio koi), silver and bighead carp hybrid (H. molitrix × H. nobilis) and grass carp (C. idella) from 16 regions of Ukraine were examined for the presence of a specific sequence of the CEV virus p4a gene fragment by nested PCR. Findings. 34 gill samples from different age groups of common carp (24), silver and bighead carp hybrids (7) and grass carp (3) were analyzed. 19 samples from 14 regions of Ukraine were positive for the virus. Among the positive samples, clinical signs of the disease, such as gill discoloration, gill tissue necrosis, atypical lethargic behavior and sunken eyes, were present in 11 samples. When the virus was detected in broodstock, larvae or fry of carp, CEV was almost guaranteed to retain its presence in older age groups of fish, including broodstock individuals. In addition to the CEV, 4 isolates of the SVCV were identified during the studies, 3 in common carp and 1 in silver and bighead carp hybrids. Cyprinid herpesvirus type 3 (CyHV-3) was not identified in any of the analyzed samples. Originality. It was shown that the disease caused by CEV is widespread throughout Ukraine. The most characteristic signs of the disease are specific (lethargic) behavior of fish and necrosis of gill tissue, and the course of infection can also be asymptomatic. In addition to common carp and koi carp, a hybrid of silver carp was also susceptible to the virus, mortality can reach 15-20%. In full-system carp farms, the CEV virus can be identified in all age groups of carp during the growing season. For the first time, a case of CEV infection has been recorded, which caused significant mortality among ornamental koi carp in Ukraine. Practical Value. Data on epizootic monitoring of the emerging CEV and its spread in carp farms from different geographical zones of Ukraine are presented. Clinical signs of CEV infection and a method for diagnosing the virus, which can be used by specialists to identify the disease, are described. The virus circulates among different age groups of carp in full-system farms, therefore monitoring of the disease should be carried out at different stages of the production cycle. The consequences of CEV infection for fish farms are assessed, the ways of virus transmission and the reasons for its rapid spread in Ukraine are analyzed. Keywords: carp poxvirus, CEV, diagnostics, Ukraine, disease spread.