Characterization of a ranavirus isolated from cultured largemouth bass (Micropterus salmoides) in China

During June through October 2008, numerous cultured largemouth bass (Micropterus salmoides) died in the Foshan area of Guangdong Province, China. Affected fish had ulcerations on the skin and muscle. Epithelioma papillosum cyprini (EPC) cell cultures inoculated with filtrates of muscle homogenates from the diseased fish developed the cytopathic effect (CPE) 5 days after inoculation at the primary passage. Transmission electron microscopy of the ulcerative muscle tissue and the infected EPC cells revealed a cytoplasmic, icosahedral virion that averaged 145 nm in diameter. Intramuscular injection of the virus (≥ 107.82 TCID50 ml−1) resulted in clinical signs of the disease and caused 100% mortality of healthy largemouth bass. In addition, the mandarinfish (Siniperca chuatsi) was susceptible to the virus after intramuscular injection of the virus (0.2 ml of 109.82 TCID50 ml−1), and the mortality was 20%. However, no death or clinical signs were found in grass carp (Ctenopharyngodon idella), bighead carp (Aristichthys nobilis), Nile tilapia (Oreochromis niloticus), crucian carp (Carassius carassius), common carp (Cyprinus carpio), and fancy carp (C. carpio) after experimental infection. DNA fragments of the viral major capsid protein (MCP) and DNA methyltransferase (MTase) were amplified and sequenced. Subsequent multiple alignment and phylogenetic analysis revealed that the virus is identical to doctor fish virus (DFV) and closely related to largemouth bass virus (LMBV).