Characterization and Morphology of the Bluegill Virus

Abstract

SUMMARYAn enveloped, ether-sensitive, acid-labile virus isolated from Lepomis macrochirus, the bluegill, is described. Virus replication is limited to teleostean cell lines and achieves highest titres in centrarchid cells. As determined by the uptake of tritiated nucleotides and the effect of 6-azauridine and actinomycin D on replication, the virus genome is RNA. The virus has no haemagglutinin or neuraminidase nor does it share antigens with prototypes of orthomyxoviruses, paramyxoviruses or arenaviruses. Thin-section electron microscopy reveals a virion 8o to Ioo nm in diam. associated with the cell surface and intracellular vacuoles. The virus appears to mature by budding and exhibits a prolonged replication cycle and significant cellassociated infectivity. The time sequence of replication indicates that the prolonged cycle is due to maturation rather than to delayed synthesis of RNA and protein.The bluegill virus (BGV) represents a novel, hitherto undescribed, type of teleostean virus. I N T R O D U C T I O NIn I969 a virus and a chlamydial-like agent were isolated in association with epitheliocystis in the bluegill (Lepomis macrochirus) (Hoffman et al. I969). The unique cytopathic effect of the virus and its resistance to antibiotics distinguished it from the chlamydial agent. Preliminary electron microscopy revealed a virus morphologically distinguishable from any known teleostean virus. Serial passage was accomplished in BF-2 cells derived from L. macrochirus. It seemed desirable to confirm the agent as a teleostean virus, to determine its biophysical characterization and to relate it to known virus families. METHODS Virus and cells.The original isolate of the bluegill virus (BGV) was provided by K. Wolf of the National Fish Health Research Laboratory, Kearneysvilte, W. Va. BGV was propagated in BF-2 cells between passages 39 and 5o. The cells were grown at 24 °C in Eagle's minimal essential medium with iO°/o foetal calf serum (MEM-Io). Cells used in the susceptibility testing (Table t) were cultivated at the temperature and in the medium recommended by the American Type Culture Collection (ATCC) or the cell line's originator.Replication curve. The replication curve was determined by assaying virus liberated from confluent monolayers of BF-2 cells infected with BGV at a multiplicity of infection (m.o.i.) equal to ten. The virus inoculum was allowed to adsorb for I h after which it was decanted and the cell sheet washed three times with Hanks' basic salt solution (HBSS). The cells

Fish Viruses and Viral Infections

“…Neither hemagglutination nor neuraminidase activities are detectable in virus preparations. No antigenic relationships were detected in serological assays using antisera against two orthomyxoviruses, a paramyxovirus, an atypical paramyxovirus, and an arenavirus (Beckwith, 1974(Beckwith, , 1975.…”

“…Hoffman et al (1969) reported that the bluegill virus was 70-80 nm in diameter, was rather uniform in electron density, and resembled a myxovirus. Beckwith (1974Beckwith ( , 1975, however, reported that the virus was pleomorphic, varying from 80 to 250 nm in diameter, and contained electron-dense granules -20 nm in diameter. Beckwith suggested that the bluegill virus resembled an arenavirus or an atypical paramyxovirus.…”

“…Later attempts to reisolate the virus from the Leetown population were unsuccessful, as were attempts to detect the virus in other feral bluegill populations (Beckwith, 1974(Beckwith, , 1975. Beckwith (1974) and Hoffman et al (1969) could detect no pathology associated with infection and were unable to induce pathological changes by experimental infection.…”

“…Cytochemical staining and uridine uptake studies suggest that the viral genome contains single-stranded RNA, and the sensitivity to ether indicates that the virus contains lipid essential to infectivity (Beckwith, 1974(Beckwith, , 1975. Viral structural proteins have not been characterized, nor has the potential association of carbohydrate with the mature virion been assessed.…”

“…Beckwith suggested that the bluegill virus resembled an arenavirus or an atypical paramyxovirus. Membrane filtration studies indicated a particle diameter of 75-220 nm (Beckwith, 1974(Beckwith, , 1975.…”