Potential for spread of carp edema virus (CEV) trought vector fish species

Introduction: Carp edema virus (CEV) is poorly understood in terms of its potential for horizontal and/or vertical transmission in aquatic environments. Because of the need to identify species that can latently transmit CEV, we undertook a study to determine the degree of infection of species other than common carp (Cyprinus carpio) in natural waters and farm facilities. The aim of the study was to identify vector species and determine the routes of virus transmission in northwestern Poland. Materials and methods: 449 fish of 15 species were sampled for the study. The fish were collected in 2017-2018 from Lake Dąbie, Szczecin Lagoon, and three fish farms. Molecular analyses, which detected a fragment of the CEV gene encoding the P4a viral core protein, consisted of isolation of viral DNA, qualitative assessment of the purity of isolates obtained , and amplification of CEV genetic material by PCR reaction. The PCR reaction products were verified by real-time PCR. Results: The study revealed the presence of species that could potentially be involved in virus transmission between natural waters and carp culture centers in northwestern Poland. These species included roach, bleak, crucian carp, and tench. The results obtained suggest the need for mandatory virological testing for CEV in fish intended for stocking, which should limit the uncontrolled transmission of the virus in natural waters and its introduction into carp farms during the flooding of breeding ponds.