Mass mortality caused by cyprinid herpesvirus 2 (CyHV-2) in prussian carp (carassius gibelio) in China

From 2011 to 2012, hematopoietic necrosis associated with Cyprinid herpesvirus 2 (CyHV-2) caused serious mortality of farmed Prussian carp (Carassius gibelio) in Central China. Signs of diseased fish included lethargy and inappetence, gill hemorrhages, haemorrhagic spots on body surface. Internal gross pathology included hyperaemia, hepatic hypertrophy and splenomegaly. The spleen showed extensive necrosis of the white pulp and arteries in both the kidney and spleen. Large numbers of viral particles, approximately 90-170nm in diameter with a spherical shape, were observed by electron microscopy. PCR assays with CyHV-2 specific primers were used to detect the virus in DNA extracted from the infected cell supernatant and tissue homogenates of diseased fish brain, liver, spleen and kidney. Sequencing of the PCR product showed more than 98% nucleotide identity with the published sequence of CyHV-2. Experimental infection with healthy Prussian carp using filtrates of tissues by intramuscular injection caused 100% mortality and presented similar clinical signs to those seen in wild infected fish, in which the presence of the virus was regarded as the cause of the high mortalities.