• Korean Journal of Fisheries and Aquatic Sciences
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• v.48 no.4
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• pp.403-410
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• 2015

Viral nervous necrosis (VNN) is a serious disease of sevenband grouper Epinephelus septemfasciatus in Korean aquaculture farms. However, we suggest the following preventative methods for hatcheries: 1) disinfecting rearing water, 2) selecting spawners via ELISA and PCR, 3) selecting eggs via PCR, 4) disinfecting fertilized eggs, and 5) proper facilities management. When these methods are implemented, nervous necrosis virus (NNV)-free fish are produced because vertical and horizontal transmission is prevented. However, horizontal transmission of NNV through rearing seawater sourced from the environment during grow-out stages in sea cages can still occur. Live NNV vaccines with a low rearing temperature or Poly(I:C) immunization are very effective at preventing horizontal transmission of NNV in rearing farms. Furthermore, even after VNN is contracted, fish mortality can be reduced by administering Poly(I:C).

• Journal of fish pathology
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• v.25 no.2
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• pp.111-116
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• 2012

Prevalence of viral nervous necrosis (VNN) in sevenband grouper Epinephelus septemfasciatus farms was investigated during the period of 2006-2008. The outbreak of the VNN was observed from August (water temperature: $24-26^{\circ}C$) to September or October ($20-25^{\circ}C$). The viral infection resulted in acute or chronic mortality of the host, where the mortality rate of juvenile fish was higher than that of the adult fish. Phylogenetic analysis based on partial RNA2 coat protein gene nucleotide sequences revealed that all the isolates from sevenband grouper were classified into the genotype redspotted grouper nervous necrosis virus (RGNNV). In conclusion, VNN of juvenile and adult sevenband groupers during the summer season (July to October, water temperature: about $24^{\circ}C$) was caused by virus belonging to the genotype RGNNV.

• Journal of fish pathology
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• v.14 no.2
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• pp.91-95
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• 2001

Mass mortalities occurred among red drum larvae, 20 to 30 days old, culturing at hatcheries on southern costal area. No specific external signs were observed except abnormal swimming and spinal deformity. It was, however, suspected as a viral etiology due to high mass mortalities so that histopathological and molecular biological study was performed to evaluate the agent. Both vacuoles and necrosis were observed on nerve cells of brain and eye by H-E staining, and viral particles were observed on electronmicroscopic examination. On the other hand, DNA fragment, approximately 426 bps, was amplified with RT-PCR. The above results were able to diagnosis the etiological agent of mass moralities in red drum larvae as VNN(viral nervous necrosis)virus.

• Proceedings of the Korean Society of Fisheries Technology Conference
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• 2001.05a
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• pp.511-512
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• 2001

VNN(viral nervous necrosis)는 종묘단계 및 양성장의 해산어 양식장에서 발생하는 바이러스성 질병으로 외견적으로 척추만곡, 이상유영, 체색흑화와 조직학적으로는 뇌와 망막에 공포 및 괴사를 형성하고, 또한 매우 높은 폐사율을 나타내는 질병으로 보고되어 있다. 이러한 질병은 성공적인 종묘의 생산 및 보급을 위해서 반드시 해결해야 할 사항이다. (중략)

• Korean Journal of Fisheries and Aquatic Sciences
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• v.35 no.3
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• pp.237-241
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• 2002

This study was performed both to explore the host of nervous necrosis virus (NNV) between mariculturing fish species and to examine the phylogenic position of the NNV in Korea. NNV was confirmed on the basis of histopathological and molecular biological examination, then VNN infection was Preyed from either moribund or dead fishes including red drum, Sciaenops ocellatus; oblong rock fish, Sebastes oblongus and flounder, Paralichthys olivaceus. As a result of sequencing for a part of ms, virus from red drum was showed $98\%, $97\%, $86\% and $74\% homology with oblong rock fish, grouper, Japanese flounder and striped jack, respectively. On the other hand, NNV from oblong rock fish was demonstrated $96\%, $85\% and $72\% homology with grouper, Japanese flounder and striped jack, respectively. NNV from red drum and oblong rock fish was exhibited phylogenically distant from the representative NNV, SJNNV originated from striped jack. On the contrary, the viruses appeared to be similar species with Taiwan NNV isolated from culturing grouper.

• Journal of fish pathology
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• v.12 no.2
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• pp.107-113
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• 1999

The pathogenicity of the fish nodavirus causing viral nervous necrosis (VNN) of sevenband grouper, Epinephelus septemfasciatus was examined in sevenband grouper and other marine fish by intramuscular injection. Sevenband groupers of 27~104 g in body weight were highly susceptible to the fish nodavirus, but yellowtail (537 g in body weight), red seabream (207 g), rock bream (43 g), flounder (41 g), tiger puffer (27 g) and rockfish (94 g) of the sizes used to this experiment were not. The pathogenicity of the viral agent to the sevenband grouper was high without regard to fish sizes at rearing water temperature over $20^{\circ}C$, but not at $15^{\circ}C$. Therefore, susceptibility of sevenband grouper to the viral agent causing VNN was thought to be water temperature-dependent rather than fish size (age-dependent). Compared to the infectivity of the viral agent to sevenband grouper with artificial infection methods, fish were successfully affected by intramuscular, intraperitoneal, oral, dipping and cohabitation administrations although there were slight differences in mortalities among infection methods. And survival sevenband grouper after infection with the fish nodavirus was resistant to the reinfection for a long time.

• Journal of Microbiology and Biotechnology
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• v.25 no.10
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• pp.1761-1767
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• 2015

Sevenband grouper, Epinephelus septemfasciatus, is becoming an important aquaculture species in Korea. However, viral nervous necrosis disease is a large problem causing mass mortality in sevenband grouper aquaculture. Recombinant protein vaccines are one of the best methods to reduce these economic losses. However, the cell-based expression method mainly produces inclusion bodies and requires additional procedures. In this study, we expressed a recombinant viral coat protein of sevenband grouper nervous necrosis virus (NNV) using a cell-free protein synthesis system. The purified recombinant NNV coat protein (rNNV-CP) was injected into sevenband grouper at different doses followed by a NNV challenge. Nonimmunized fish in the first trial (20 μg/fish) began to die 5 days post-challenge and reached 70% cumulative mortality. In contrast, immunized fish also starting dying 5 days postchallenge but lower cumulative mortality (10%) was observed. Cumulative morality in the second trial with different doses (20, 4, and 0.8 μg/fish) was 10%, 40%, and 50%, respectively. These results suggest that rNNV-CP can effectively immunize sevenband grouper depending on the dose administered. This study provides a new approach to develop a recombinant vaccine against NNV infection for sevenband grouper.

• Journal of fish pathology
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• v.26 no.3
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• pp.163-171
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• 2013

Polymerase chain reaction (PCR) is the most rapid and widely used method to detect viral pathogens. However, this method does not provide histopathologic nature of the virus. In situ hybridization (ISH) with oligonucleotide probes is attractive because it is a rapid method for detection and identification of viral pathogens at sites of tissue infection. In order to understand the histopathologic characterictics of Red sea bream iridovirus (RSIV), viral-hemorrhagic septicemia (VHS) virus and viral nervous necrosis (VNN) virus to cultured olive flounder, we her applied ISH method to various kinds of olive flounder tissues with PCR-positive for these three viruses. We found that these viruses showed different tissue tropism and were detected from different cell types. Our results suggest that ISH is useful not only in rapid detection of viral pathogens but also in understanding the histopathologic characters of specific viral pathogens.

• Korean Journal of Ichthyology
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• v.29 no.3
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• pp.157-164
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• 2017

In 2015, a nervous necrosis virus (NNV) was isolated from sevenband grouper, Epinephelus septemfasciatus, maintained in land-based aquaculture system at below $12^{\circ}C$ in winter. Mortality was up to 30% in brood fish, over 4 kg of body weight. Moribund fish showed clinical sings typical of viral encephalopathy and retinopathy (VER), also called viral nervous necrosis (VNN), such as uncoordinated, corkscrew-like swimming behavior, belly-up at rest, darkening of body, cloudy eyeball and hyperinflation of the swim bladder. Aetiology of the disease was confirmed by gross observation of clinical signs, histopathology and molecular diagnosis. Histological studies revealed severe vacuolation and necrosis in the brain. Molecular diagnosis by revere transcription-polymerase chain reaction (RT-PCR) specific to batanodavirus yielded a positive result. The nucleotide sequences of the PCR-amplified fragment were 99.48~100% similar to barfin flounder nervous necrosis virus (BFNNV) genotype and most closely aligned with Pacific cod betanodavirus (PCNNV). This is the first report of natural batanodavirus, NNV infection in sevenband grouper reared in low water temperature during winter (below $12^{\circ}C$) in Korea.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.46 no.5
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• pp.582-588
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• 2013

The impact of global warming on aquatic systems has been a priority research area in the past decade. However, the possibility that increased temperatures will cause shifts in viral disease outbreaks has not been well addressed. In the present study, with increasing water temperature (WT) in the coastal area of Korea, we estimated the possibility of changes in fish viral diseases. From the present time, WT may rise between 0.62 and $1.7^{\circ}C$ by 2050, and the effect on aquaculture could be more adverse than benefitial. Red seabream iridovirus disease (RSIVD) and viral nervous necrosis (VNN) cause high mortality above 22 and $24^{\circ}C$, respectively, and outbreaks could commence earlier and persist for prolonged periods. Nevertheless, the period of occurrence of viral hemorrhagic septicemia (VHS), which outbreaks at a lower WT (< $18^{\circ}C$), could be shorter than the current infectious period. Thermal stress in fish causes reductions in growth and immunocompetence; thus, increases in summer WT can lead to the development of new viral diseases. WT has a strong influence on fish population dynamics; therefore, entry of new viruses and changes in the prevalence of infection can be expected if carrier fishes are introduced or migrate to Korean waters.