Detection of Cyprinid herpesvirus 2 (CyHV-2) in symptomatic ornamental types of goldfish (Carassius auratus) and asymptomatic common carp (Cyprinus carpio) reared in warm-water cage culture

Cyprinid herpesvirus 2 (CyHV-2) is the agent of herpesviral haematopoietic necrosis (HVHN), a serious disease affecting two fish species of the Carassius genus, i.e. goldfish (C. auratus) and Prussian Carp (C. gibelio). In Poland, no asymptomatic vectors of CyHV-2 and no farms in which the virus would cause mortalities have been identified. In 2016 and 2017, mass mortalities of ornamental varieties of C. auratus were observed in a cage culture submerged in a channel receiving post-cooling water from the Dolna Odra power plant (north-western Poland). End-point PCRs and sequencing of the mA marker confirmed the presence of CyHV-2 DNA in the gills and pool (kidney, liver, gut and spleen) samples collected from four ornamental types of goldfish, i.e. Veiltail, Wakin, Red Cap Oranda and Ranchu imported from Thailand and UK. Further analysis revealed that the obtained sequences represent a new type of a 295-bp mA sequence (RSD-PL, GenBank accession no. KX852452.1), which had the greatest similarity to the AMS-8 and FR types of CyHV-2 identified in diseased fish imported from Israel and Asia, respectively. Additionally, our study identified common carp (Cyprinus carpio) individuals reared in neighbouring cages as asymptomatic carriers of CyHV-2. The virus was not detected in fish, i.e. ide (Leuciscus idus), perch (Perca fluviatilis), pumpkinseed (Lepomis gibbosus) and common bleak (Alburnus aimus), collected from the environment of the power plant discharge channel. Identification of CyHV-2 is the first case reported in Poland and the only one in which blood, gills and pool samples of common carp were CyHV-2-positive. Our study identified the cause of mortalities of ornamental goldfish in cage culture, but also shed a new light on issues concerning the species-specificity of CyHV-2.