Identification and ultrastructural characterization of a novel virus from fish

During routine investigations on fish, a virus (isolate DF 24/00) with nove l morphological features and hitherto undescribed morphogenesis was isolate d from a white bream (Blicca bjoerkna L.; Teleostei, order Cypriniformes). Cell-free virions consist of a rod-shaped nucleocapsid (120-150 x 19-22 nm) similar to that seen in baculoviruses. The virion has a bacilliform shape (1170-200 x 75-88 nm) reminiscent of rhabdoviruses with an envelope contain ing coronavirus-like spikes (20-25 nm). DF 24/00 replicated well in various fish cell lines. Inhibitor studies with 5-iodo-2'-deoxyuridine indicated t hat the viral genome consists of RNA and chloroform sensitivity correlated with ultrastructural demonstration of enveloped virions. The buoyant densit y of the virus determined in sucrose was 1.17-1.9 g/ml. Preliminary biochem ical characterization revealed the presence of six antigenic glycoproteins, three of which contain sugars with concanavalin-A specificity. Ultrastruct urally, morphogenesis of virus progeny was detected only in the cytoplasm. Nucleocapsids were observed to bud through membranes of the endoplasmic ret iculum and/or Golgi apparatus into dilated vesicles. Egress of mature virio ns occurs primarily by exocytosis and, only very rarely, by budding directl y at the plasma membrane. Morphologically similar viruses had previously be en isolated from grass carp (Ctenopharyngodon idella), blue crab (Callinect is sapidus), European shore crab (Carcinus maenas) and shrimp (Penaeus mono don). To date, none of them has been classified. In summary, the first char acterization of a new virus that might represent a member of a novel virus family that has morphological features resembling those found in rhabdo-, c orona- and baculoviruses; is presented.