Emergence and persistence of Cyvirus cyprinidallo 2 (CyHV-2) in Prussian carp in Serbian lakes

Abstract

Between 2018 and 2021, significant die-offs of Prussian carp (Carassius gibelio) occurred in five lakes in eastern, central and northern Serbia. In all cases, Cyvirus cyprinidallo 2, formerly named Cyprinid herpesvirus 2 (CyHV-2) infection was suspected, based on initial diagnostic observations. To determine the cause of these mass mortalities, real-time PCR assays targeting CyHV-2, CyHV-3, and SVCV were conducted. CyHV-2 DNA was detected in the affected populations, while SVCV and CyHV-3 were negative in the assay. The CyHV-2 was also detected in asymptomatic Prussian carp. Sequence analysis of the CyHV-2 DNA polymerase and helicase genes revealed high similarity to previously reported strains from Serbia and other countries. The occurrence of these outbreaks in Prussian carp populations in lakes indicates the probable spread of the virus within freshwater ecosystems in Serbia, potentially impacting the degradation of aquatic habitats.