• Development and Reproduction
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• v.21 no.4
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• pp.371-378
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• 2017

Interferon-stimulated gene 15 (ISG15) is known to interfere with viral replication and infection by limiting the viral infection of cells. Interferon-stimulated gene 15 (ISG15) interferes with viral replication and infectivity by limiting viral infection in cells. It also plays an important role in the immune response. In this study, tissue-specific expression of ISG15 in healthy rock bream samples and spatial and temporal expression analysis of rock bream ISG15 (RbISG15) were performed following rock bream iridovirus (RSIV) infection. RbISG15 expression was significantly higher in the eye, gill, intestine, kidney, liver, muscle, spleen, and stomach, but low in the brain. There were particularly high levels of expression in the liver and muscle. RbISG15 expression was also examined in several tissues and at various times following RSIV infection. ISG15 expression increased within 3 h in the whole body and decreased at 24 h after infection. In addition, temporal expression of several tissues following RSIV infection showed a similar pattern in the muscle, kidney, and spleen, increasing at 3 h and decreasing at 72 h. These results suggest that ISG15 plays an important role in the immune response of rock bream. Overall, this study characterizes the response of RbISG15 following RSIV infection.

• Journal of fish pathology
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• v.34 no.1
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• pp.1-7
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• 2021

Red sea bream iridovirus (RSIV), belonging to the genus Megalocytivirus, is the predominant cause of mortality in marine fishes in Korea, including rock bream (Oplegnathus fasciatus). Rockfish (Sebastes schlegelii) are the host fish for RSIV, exhibiting no clinical signs or mortality. Cohabitation challenges, which mimicked natural transmission conditions, were performed to evaluate viral transmission between rock bream and rockfish, and to determine the pathogenicity and viral loads. In cohabitation challenge, artificially RSIV-infected rock bream were the viral donor, and healthy rockfish were the recipient. The results showed that although the donor rock bream had 95-100 % cumulative mortality (>10⁸ viral genome copies/mg of spleen 7-14 days after viral infection), the recipient rockfish did not die, even when the viral genome copies in the spleen were >10⁵ copies/mg. These results indicated asymptomatic infections. Notably, in a reverse-cohabitation challenge (artificially RSIV-infected rockfish as the viral donor and healthy rock bream as the recipient), RSIV horizontally infected from subclinical rockfish to rock bream (10⁷ viral genome copies/mg of spleen 21 days after cohabitation) with 10-20% cumulative mortality. These results suggest that an asymptomatic, infected rockfish can naturally transmit the RSIV without being sacrificed.

• Journal of fish pathology
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• v.34 no.2
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• pp.149-159
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• 2021

Genus Megalocytivirus cause red sea bream iridoviral disease (RSIVD) and scale drop disease (SDD). Based on the phylogeny of the major capsid protein (MCP) and adenosine triphosphatase (ATPase) genes, megalocytiviruses except for SDD virus (SDDV) could be three different genotypes, red sea bream iridovirus (RSIV), infectious spleen and kidney necrosis (ISKNV), and turbot reddish body iridovirus (TRBIV). In this study, primary cells derived from the caudal fin of rock bream (Oplegnathus fasciatus) grew at 25℃ in Leibovitz's medium supplemented with 10% (v/v) fetal bovine serum and primocin (100 ㎍/mL). Rock bream fin (RBF) cells exhibited susceptibility to infections by different genotypes of megalocytiviruses (RSIV, ISKNV and TRBIV) with the appearance of cytopathic effects with an increase in the viral genome copy number. Furthermore, compared to grunt fin (GF) cells, even though 10 times lower number of RSIV genome copies were inoculated in RBF cells, viral genome copy number produced on RBF cells were 44 times higher than that of GF cells at 7 d post-inoculation. As the isolated RBF cells are sensitive to different genotypes of megalocytiviruses (RSIV, ISKNV and TRBIV), they can be used for future studies regarding in vitro viral infection and subsequent diagnosis.

• Journal of Microbiology and Biotechnology
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• v.15 no.4
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• pp.873-879
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• 2005

Red sea bream iridovirus (RSIV) obtained from infected rock bream was propagated by Bluegill fry-2 (BF-2) cell culture. The virus titer was determined as $10^{5.5}\;TCID_{50}/ml$ on confluent BF-2 cell monolayers. The integrin binding site of ORF 055L of infectious spleen and kidney necrosis virus (ISKNV) was selected for the construction of a primer to obtain the RSIV ORF 055L gene. The genes were amplified using RSIV gene lyzate by PCR. The homologies of the ORF 055L sequence of RSIV with ISKNV and rock bream iridovirus (RBIV) were approximately $96\%$ and $100\%$, respectively. DNA vaccine was constructed by cloning the ORF 055L of RSN into pcDNA 3.1 (+), containing a cytomegalovirus (CMV) promoter. For antibody production, pcDNA-055 DNA vaccine was injected to BALB/c mice. The production of antibodies against pcDNA-055 DNA vaccine was confirmed by the Western blot analysis. The antibodies produced by the pcDNA-055 DNA vaccine showed efficacy to neutralize the RSIV in the neutralization test in BF-2 cell culture.

• Journal of fish pathology
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• v.37 no.1
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• pp.25-36
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• 2024

In this study, we analyzed the phylogenetic classification, epitope prediction, and pathogenicity of red sea bream iridovirus (RSIV) isolated from rock bream between 2019 and 2023. Phylogenetics based on genes encoding MCP and ATPase indicated that all five RSIV isolates belonged to RSIV subtype II. The deduced amino acid sequence of the MCP for the amplicons (1362 bp) obtained from RSIV isolates had a length of 453 amino acids. Among these, the amino acid sequences of the RSIV-19, 21, 22, and 23 isolates showed 100% identity, while the RSIV-20 isolate showed 99.78% identity with one residue difference at position 306. As a result of antigenicity analysis based on amino acid sequence, the antigenicity score of the RSIV-20 isolate was 0.6386 and the other RSIV isolates were 0.6365. Additionally, the prediction of their antigenic determinants resulted in a total of 17 identical antigenic plots. When each RSIV was inoculated into rock bream, no significant differences were observed with 100% cumulative mortality in all groups. This study provides data on the potential for genetic variation of RSIV isolated in the same marine area over the past five years, and the antigenicity and pathogenicity results of each isolate are expected to be useful information for selecting future vaccine strains.

• Journal of fish pathology
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• v.36 no.2
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• pp.229-238
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• 2023

In this study, the correlation between clinical changes and RSIV genome copy number was investigated to determine the quantitative criteria for the characteristics of RSIV infection. The rock bream (Oplegnathus fasciatus) was intraperitoneally injected with three different doses (1.0×10¹, 1.0×10³ and 1.0×10⁵ viral genome copies/fish) as low, medium, and high doses, respectively. The clinical signs (spleen enlargement, death) observation and real-time PCR were conducted at 5, 10 and 14 days post-injection. During the experiment, spleen index as a quantitative indicator for spleen enlargement was continuously increased in the medium- (up to 2.26) and high-dose (up to 4.99) challenge groups, respectively. Notably, when the spleen index was over 1.5, 2.0, 2.5 and 3.0, a positive correlation was revealed with average viral genome copy numbers of 2.51, 3.37, 4.97 and 5.43×10⁷ viral genome copies/mg, respectively. Moreover, the threshold of spleen index over 1.5 was 1.0×10⁶ viral genome copies/mg, while the thresholds of spleen index over 2.0 and dead was 2.51×10⁷ viral genome copies/mg and the thresholds of spleen index over 2.5 and 3 was 3.98×10⁷ viral genome copies/mg. These findings suggest the possibility of quantitatively analyzing the characteristics and development process of RSIV infection.

• Journal of fish pathology
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• v.23 no.1
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• pp.85-98
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• 2010

Ministry of Agriculture, Fisheries and Food (MAFF) and National Fisheries Research and Development Institute (NFRDI) have inspected the hatchery-reared seeds of 22 marine species and 11 freshwater species for aquatic animal diseases in stock enhancement program in 2009. Results showed that total 12 local selfgovernments have been restocking the sea with cultured juveniles. Gyeongsangnam-do, Jeollanam-do, Jejudo and Chungcheongnam-do have a preference for marine species seeds to freshwater species. On the contrary, freshwater species were released mostly in Gyeonggi-do, Jeollabuk-do and Chungcheongbuk-do. In the marine species group, abalone was the most abundant as 24.5%, and then sea cucumber (15.2%), olive flounder (11.5%), swimming crab (5.6%), black sea bream and rockfish (6.8%), rock bream (5.1%), black rockfish (4.6%) and scorpionfish (4.5%) were followed. Crucian carp was the most abundant as 19.4%, and then eel (17.0%), Korean bullhead (12.3%), melanian snail (12.0%), catfish (8.4%) were followed in the freshwater species group. The total number of inspection cases in this study were 1,080 and disqualification cases were 19 by detection of aquatic animals pathogens such as red sea bream iridovirus (RSIV), koi herpesvirus (KHV) or white spot syndrome virus (WSSV).