Characterization of an iridovirus detected from cultured turbot Scophthalmus maximus in Korea

Abstract

Juvenile turbot Scophthalmus maximus that became sick during an outbreak of disease at mariculture facilities at Go-Chang, Korea, in 2003, were examined to identify the cause of the disease. The fish had pale body color, an enlarged abdomen, protruding eyes, an enlarged spleen and kidney, and pale gills and/or liver. Histopathogical examination revealed basophilic enlarged cells in the kidney, spleen, gills, heart, stomach, intestine, liver, pancreas and skin. Hexagonal viral particles with a diameter of 136 to 159 nm were observed in the enlarged cells. A specific 1299 bp fragment of the major capsid protein (MCP) gene of the turbot iridovirus (TBIV) was amplified by PCR. Sequence homology was greater than 93.76% between the MCP gene in TBIV and the same gene in 5 viruses in the tentatively proposed genus Tropivirus (family Iridoviridae): red sea bream iridovirus, sea bass iridovirus, grouper sleepy disease iridovirus, African lampeye iridovirus and dwarf gourami iridovirus. These results suggest that the virus detected from turbot is similar to the proposed genus Tropivirus. KEY WORDS: Turbot · Scophthalmus maximus · Iridovirus · RSIV · MCP · Tropivirus Resale or republication not permitted without written consent of the publisherDis Aquat Org 64: [175][176][177][178][179][180] 2005 Korea. Juvenile turbot (mean weight 9.0 ± 1.9 g, mean length 7.9 ± 0.5 cm) began to show signs of disease in June 2003. Affected fish were lethargic and had a reduced appetite, pale body color, enlarged abdomen and protruding eyes. The key internal characteristics of the diseased fish were an extremely enlarged spleen and kidney, and pale gills and/or liver (Fig. 1).The fish farmers misdiagnosed the disease as hirame rhabdovirus (HRV) disease or viral hemorrhagic septicemia (VHS) disease, and increased the water temperature from 17-18°C to 20-23°C in an attempt to control the disease. The mortality increased rapidly when the water temperature was increased. Total mortality was about 50 to 70%. After sampling some of the diseased turbot, the remaining fish were killed, and all facilities were disinfected with sodium hypochlorite.Histology. The kidney, spleen, gills, heart, stomach, intestine, liver, pancreas, skin, eye and brain were removed from diseased fish and immediately fixed in 10% neutral buffered formalin (NBF). After fixation, standard histological procedures were used for tissue dehydration and paraffin embedding. Tissue sections were stained with haematoxylin and eosin (H&E).Electron microscopy. The spleens were fixed in 2.5% glutaraldehyde in 0.1 M phosphate buffer (pH 7.2) at 4°C. After several rinses with 0.1 M phosphate buffer, each sample was post-fixed with 1% OsO 4 for 1 h. Subsequently, the tissue was dehydrated in an ethanol series and embedded in Epon 812. Ultra thin sections were prepared using an RMC-MTX ultramicrotome (SIMS). Sections were stained with lead citrate and uranyl acetate. Stained grids were observed under a Hitachi-7000 electron microscope. DNA extraction. In preliminary investigati...

Systemic iridovirus from threespine stickleback Gasterosteus aculeatus represents a new megalocytivirus species (family Iridoviridae)

“…Megalocytivirus infections are characterized by a unique histopathologic change marked by the presence of large amphophilic to basophilic cytoplasmic inclusions in cytomegalic cells within multiple tissues (Gibson-Kueh et al 2003, Lee et al 2009). The megalocytiviruses have a broad host range, and closely related strains of the type species of the genus -infectious spleen and kidney necrosis virus (ISKNV) -have caused epizootics in wild and cultured freshwater and marine fish stocks, including numerous economically important food-fish species, in the temperate to tropical waters of Japan (Inouye et al 1992, Matsuoka et al 1996, Kawakami & Nakajima 2002, China (He et al 2000, Weng et al 2002, Shi et al 2004, Lu et al 2005, Wang et al 2007, Dong et al 2010, Korea (Jung & Oh 2000, YJ Kim et al 2002, Do et al 2005a, WS Kim et al 2005, Jeong et al 2006a, SE Asia (Miyata et al 1997, Chou et al 1998, Chao et al 2002, Sud thongkong et al 2002a, Gibson-Kueh et al 2003, and Australia (Lancaster et al 2003). Megalocytivirus epizootics have been diagnosed by histo pathology, electron microscopy, and molecular techniques in ornamental fish exports from both South America (Leibovitz & Riis 1980) and Asia (Armstrong & Ferguson 1989, Anderson et al 1993, Sudt hong kong et al 2002b, Go et al 2006, Lyu et al 2006, Jeong et al 2008a, 2008b, Weber et al 2009, Kim et al 2010, as well as in ornamental fish breeding facilities in the USA (Fraser et al 1993, Petty & Fraser 2...…”

Genetic variation and geographic distribution of megalocytiviruses

“…Kawakami and Nakajima (2002) reported that the disease caused by a megalocytivirus, termed red seabream iridovirus (RSIV), occurred in 31 cultured fish species (included within orders Perciformes, Pleuronectiformes, and Tetraodontiformes) in Japan. In a recent study, we also isolated a new megalocytivirus, turbot iridovirus (TBIV), from diseased turbot Scophthalmus maximus in Korea, indicating that megalocytiviruses have a broad host range (Kim et al, 2005;Oh et al, 2006). The viral genome of four megalocytiviruses, RSIV (Ehime-1 strain), ISKNV, rock bream iridovirus (RBIV) isolated from rock bream Oplegnathus fasciatus, and orange-spotted grouper iridovirus (OSGIV) isolated from orange-spotted grouper Epinephelus coioides have been completely sequenced (He et al, 2001;Kurita et al, 2002;Do et al, 2004;Lü et al, 2005).…”

Changes in Fish Viral Disease Outbreaks in the Coastal Area of Korea Due to Increasing Water Temperature, an Impact of Climate Change

“…12 , 1-4 16 VHS ( Fig. 2B; 2C) (Jung and Oh, 2000;Oh et al, 1999), RSIV (Do et al, 2005;, RSIV-like virus (Scophthalmus maximus) (Jeong et al, 2008;Kim et al, 2005;Lyu et al, 2006).…”