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Diseases of Aquatic Organisms

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DAO 53:1-9 (2003)  -  doi:10.3354/dao053001

Characterization of a novel ranavirus isolated from grouper Epinephelus tauvina

Q. W. Qin1,2,*, S. F. Chang3, G. H. Ngoh-Lim3, S. Gibson-Kueh3, C. Shi1, T. J. Lam1,2

1Tropical Marine Science Institute and
2Department of Biological Sciences, The National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260
3Central Veterinary Laboratory, Agri-food and Veterinary Authority, 60 Sengkang East Way, Singapore 548596

ABSTRACT: A large icosahedral virus was isolated from diseased grouper Epinephelus tauvina. The virus grew well in several cultured fish cell lines, with stable and high infectivity after serial passages in grouper cell line (GP). The virus was sensitive to both acid and heat treatments. Virus replication was inhibited by 5-iodo-2-deoxyuridine (IUDR), indicative of a DNA-containing genome. The virus infectivity was reduced with ether treatment, suggesting that the virus was lipid-enveloped. Electron micrographs showed abundant cytoplasmic icosahedral virons in the virus-infected GP cells. The size of the intracellular nucleocapsid was 154 nm between the opposite sides, or 176 nm between the opposite vertices with an inner electron-dense core of 93 nm. Virus particles were released through budding from plasma membranes with a size of 200 nm in diameter. SDS-PAGE of purified virus revealed 20 structural protein bands and a major capsid protein (MCP) of 49 kDa. A DNA fragment of ~500 nucleotides was successfully amplified by polymerase chain reaction (PCR) using the primers from conserved regions of the MCP gene of frog virus 3 (FV3), the type species of Ranavirus. Subsequent multiple alignment and phylogenetic analysis showed that the newly isolated grouper virus was closely related to largemouth bass virus (LMBV), FV3 and Regina ranavirus (RRV). Our data suggests that the virus isolate is a novel member of genus Ranavirus, family Iridoviridae. We tentatively name the virus as Singapore grouper iridovirus (SGIV). SGIV was able to cause serious systemic disease capable of killing 96% of grouper fry.

KEY WORDS: Fish virus · Iridovirus · Ranavirus · Iridoviridae · Grouper · Epinephelus tauvina

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