Wi-Sik Kim

Toll-like receptors and interferon associated immune factors in viral haemorrhagic septicaemia virus-infected olive flounder (Paralichthys olivaceus)

Pattern recognition receptor (PRR) toll-like receptors (TLRs), antiviral agent interferon (IFN) and the effector IFN stimulated genes (ISGs) play pivotal role in antiviral innate immunity of a host. The present in-vivo experiment was conducted to investigate the role of these innate immune factors in early phase as well as during recovery of viral haemorrhagic septicaemia virus (VHSV) infection by quantitative real-time reverse transcriptase polymerase chain reaction. A less lethal VHSV infection was generated in olive flounder (Paralichthys olivaceus) and was sampled at 3, 6, and 12h post infection (hpi), and 1, 2, 4, and 7 days post infection (dpi). At 3 hpi, the VHSV N gene was detected in three out of five fish and all five fish showed a relative fold increase of TLR 2, TLR 7, interleukin 8 (IL 8), IFN regulatory factor 3 (IRF 3), IRF 7, and ISG 15. Viral copies rapidly increased at 12 hpi then remained high until 2 dpi. When viral copy numbers were high, a higher expression of immune genes IL 1β, IRF 3, IRF 7, Type I IFN, ISG 15 and Mx was observed. Viral copies were drastically reduced in 4 and 7 dpi fish, and also the immune response was considerably reduced but remained elevated, except for ISG 15 which found equal to control in 7 dpi fish. A high degree of correlation was observed between immune genes and viral copy number in each of the sampled fish at 12 hpi. A fish with ascites sampled at 7 dpi displayed high viral copy but under-expressed immune genes except for Mx. When viral copies were high at 1 and 2 dpi, both TLR 2 and TLR 7 were down-regulated, perhaps indicating immune suppression by the virus. The quick and prolonged elevated expression of the immune genes indicates their crucial role in survival of host against VHSV.

Atypical Aeromonas salmonicida infection in the black rockfish, Sebastes schlegeli Hilgendorf, in Korea.

Cultured black rockfish, Sebastes schlegeli, suffered mass mortalities during winter 2008 and spring 2009 in Korea, showing clinical signs of ulcer lesions and haemorrhages over their body surface. The aetiological agent was identified as Aeromonas salmonicida (strains RFAS-1, -2 and -3), which is a non-pigmented, slow-growing bacterium. Phenotypes of RFAS strains showed variation, while 16S rRNA, gyrB, rpoD, dnaJ and recA gene sequences of all the strains were affiliated to A. salmonicida. In particular, vapA gene sequences of the strains were most closely related to one of the five subspecies of A. salmonicida subsp. masoucida (=KCCM 40239(T) ). LD(50) values of RFAS-1 for intraperitoneal and intramuscular injection were 1.5 × 10(5.25) and 1.5 × 10(6.4) cfu/rockfish, respectively. However, A. salmonicida strains KCCM 40239(T) and SAS-1, which originate from masou and chum salmon, respectively, were not pathogenic to black rockfish. RFAS strains, possessing A-layer protein on their surface, exhibited β-haemolytic activity against rockfish erythrocytes and capability to survive in rockfish serum, which seem to be associated with virulence.

Temperature-dependent viral replication and antiviral apoptotic response in viral haemorrhagic septicaemia virus (VHSV)-infected olive flounder (Paralichthys olivaceus).

The olive flounder (Paralichthys olivaceus) shows a high rate of mortality to viral haemorrhagic septicaemia virus (VHSV) in the winter and spring but has zero mortality over 20 °C. In this experiment, we studied the effect of rearing temperature on viral replication, viral transcription and antiviral apoptotic immune response in VHSV-infected olive flounder by real-time polymerase chain reaction. Olive flounder were given intra-peritoneal injections of VHSV (10(7.8) TCID(50)/ml) and were reared at 15 °C or 20 °C. Five fish were randomly sampled for head kidney at 3, 6 and 12 h post-infection (hpi) and 1, 2, 4 and 7 days post-infection (dpi). Total RNA extracted from the tissue was reverse transcribed and used as template for real-time PCR. In the 15 °C group, the number of viral gRNA copies peaked after 2 dpi and remained high through 7 dpi, while in the 20 °C group, the copy number was at the highest at 1 dpi but drastically declined at later stages. Viral mRNA levels in the 15 °C group gradually increased starting at 3 hpi to reach their maximum value at 12 hpi and remained high until 2 dpi, whereas the other group showed much lower copy numbers that were undetectably low at 4 and 7 dpi. Type II IFN expression increased as the viral copies increased and the 20 °C group showed quicker and stronger expression than the 15 °C group. The MHC class I and CD8 expression was high in both the groups at early stage of infection (3-6 hpi) but at later stages (2-7 dpi) in 15 °C group expression reduced below control levels, while they expressed higher to control in 20 °C group. The expression of granzyme in 15 °C fish showed a single peak at 2 dpi, but was consistently expressing in 20 °C fish. Individuals expressed very high levels of perforin expressed very high levels of caspase 3. In 15 °C fish, TNFα, FasL and p53 expressed significantly higher than 20 °C only at initial stages of infection (3-6 hpi). Caspase 3 expression found to be low in 15 °C fish whereas it was significantly elevated in 20 °C group. Interestingly individual fish with high caspase 3 expression contained very low viral RNA. Thus, from our experiment, we can conclude that an effective apoptotic immune response in VHSV-infected olive flounder plays a crucial role in the survival of the host at higher temperatures.

Change in infectivity titre of nervous necrosis virus (NNV) in brain tissue of sevenband grouper, Epinephalus fasciatus Thunberg, with Poly(I:C) administration.

Viral nervous necrosis (VNN) has become a serious disease in over 30 species of cultured marine fish worldwide over the last 20 years (Muroga 2001; Munday, Kwang & Moody 2002). The causative agents of VNN are nervous necrosis viruses (NNVs) belonging to the genus Betanodavirus of the family Nodaviridae (Schneemann et al. 2005), which are classified into five genotypes: striped jacked NNV (SJNNV), tiger puffer NNV (TPNNV), barfin flounder NNV (BFNNV), redspotted grouper NNV (RGNNV) and turbot NNV (Nishizawa et al. 1995, 1997; Johansen et al. 2004). Although VNN in the larval stage occurs by vertical transmission of NNV, it can be prevented by selection of NNV-free spawners as well as disinfection of eggs and rearing water during seed production (Mushiake et al. 1994; Mori, Mushiake & Arimoto 1998; Watanabe, Nishizawa & Yoshimizu 2000). However, there are still problems at the grow-out stages in sea cages because of horizontal transmission of NNV through the rearing sea water sourced from the environment. Under these circumstances, several kinds of NNV vaccines have been developed (Húsgarð et al. 2001; Tanaka et al. 2001; Yuasa et al. 2002; Sommerset et al. 2005; Yamashita et al. 2005; Thiéry et al. 2006; Kai & Chi 2008), although no vaccine has been marketed. It was recently demonstrated that Poly(I:C) immunization of sevenband grouper, Eepinephelus septemfasciatus Thunberg, with live NNV confers protection against VNN (Nishizawa et al. 2009, 2011). The process of ‘Poly(I:C) immunization’ involves immunization of fish with a pathogenic live virus following administration of polyinosinicpolycytidylic acid [Poly(I:C)], a synthetic doublestranded RNA that induces interferon and a transient, non-specific antiviral state. As a result, the fish in an antiviral state survive the initial immunization with live virus. Moreover, the fish that survive the infection with the live virus mount a specific protective immune response against the injected pathogenic virus. The efficacy of Poly(I: C) immunization has also been confirmed experimentally in Japanese flounder, Paralichthys olivaceus, with viral haemorrhagic septicemia virus (VHSV) and rainbow trout, Oncorhynchus mykiss, with infectious hematopoietic necrosis virus (Kim et al. 2009; Takami et al. 2010). Thus, it is conceivable that Poly(I:C) immunization will eventually be applicable to a wide range of fish species and virus diseases. We previously demonstrated that the degree of NNV infection must be similar to that of a fatal dose in order for fish to mount a specific protective immune response against the virus, and Poly(I:C) administration to achieve an antiviral state could protect fish from such intense viral infection. Correspondence T Nishizawa, Department of Aqualife Medicine, Chonnam National University, Yeosu 550749, Korea (e-mail: jjnishi@chonnam.ac.kr)

Inactivated vaccine against viral hemorrhagic septicemia (VHS) emulsified with squalene and aluminum hydroxide adjuvant provides long term protection in olive flounder (Paralichthys olivaceus).

Viral hemorrhagic septicemia (VHS) in olive flounder (Paralichthys olivaceus) remains an unsolved health problem in Korean aquaculture. Vaccination plays a significant role in modern aquaculture, and the duration of protection provided is of vital importance. Here, we have demonstrated the efficacy, duration of protection and safety of an inactivated vaccine emulsified with squalene (5%) and aluminum hydroxide (0.5%). The inactivated VHS vaccine provided a moderate protection of 37% and 47% relative percent survival (RPS) at 4 and 10 weeks post vaccination (wpv). Addition of squalene and aluminum hydroxide into inactivated VHS vaccine clearly enhanced the level of protection showing 58% and 83% RPS at 4 and 10 wpv, respectively, indicating the need for adjuvants to enhance the efficacy. The vaccinated fish showed significant protection at 3, 6, 12, 18, 24, and 40 wpv (except week 57) than non-vaccinated fish to an intraperitoneal challenge of 10(7.1)TCID₅₀/fish at 15 °C, with RPS of 60%, 64%, 71%, 55%, 52% and 50% (45% at 57 week), respectively, covering the duration of natural outbreak. Fish challenged at 18 wpv at 6 °C showed 56% RPS and protection at a low temperature. The antibody titer was high at 3 wpv with an OD of 1.08 ± 0.13, but decreased gradually and was undetectable by 24 wpv. The vaccine formulation was safe without injection site reactions, adhesions, or pigmentation observed at 6, 12, 18, or 24 wpv. Inflammatory reactions were observed in the spleen intestine at 6 and 12 wpv but were similar as control by 24 wpv. These results confirm that this vaccine is efficient and safe for olive flounder and could offer an appropriate strategy to prevent VHS without causing side effects.

A survey of fish viruses isolated from wild marine fishes from the coastal waters of southern Korea

A survey was conducted to investigate viral infection in 253 wild marine fishes harvested in the southern coastal area of Korea from 2010 to 2012. The fish that were captured by local anglers were randomly bought and sampled for virus examination. The samples were tested for presence of virus by virus isolation with FHM, FSP, and BF-2 cells and molecular methods (polymerase chain reaction and sequencing). Of the 253 fish sampled, 9 fish were infected with virus. Aquabirnaviruses (ABVs), Viral hemorrhagic septicemia virus (VHSV), and Red seabream iridovirus (RSIV) were detected in 7, 1, and 1 fish, respectively. Molecular phylogenies demonstrated the detected viruses (ABV, VHSV, and RSIV) were more closely related to viruses reported of the same type from Korea and Japan than from other countries, suggesting these viruses may be indigenous to Korean and Japanese coastal waters.

Complete Genome Sequence of Viral Hemorrhagic Septicemia Virus Isolated from an Olive Flounder in South Korea

ABSTRACT Viral hemorrhagic septicemia virus (VHSV) is a seriously problematic pathogen in olive flounder (Paralichthys olivaceus) aquaculture farms in South Korea. Here, we report the complete genome sequence of VHSV which was isolated from spleen and kidney tissues of dead fish at an aquaculture farm in 2005. This genome sequence will be useful for virus diagnostics and in comparative analyses with other virus genotypes.

Monitoring of viruses in chum salmon ( Oncorhynchus keta ) migrating to Korea

It is important to investigate the prevalence of salmonid pathogens because they can affect the amount of release of salmonid fry and the migration rate of adult salmonids. In this study, routine surveys were conducted for investigating virus distribution in migrating chum salmon spawners (Oncorhynchus keta) and their offsprings at the Namdae River, Yangyang, Korea, during 2006-2008. Anterior kidneys were removed from chum salmon spawner individuals, homogenized with minimal essential medium, and centrifuged to make supernatants for conducting RT-PCR. Five offspring were pooled to for conducting RT-PCR. Infectious pancreatic necrosis virus (IPNV), infectious hematopoietic necrosis virus (IHNV) and viral hemorrhagic septicemia virus (VHSV) were the target viruses for monitoring. In 2006, only spawners were investigated, and 27.5% of fish (22/80) were found to be IHNV-positive by nested PCR. In 2007, 65.6% of pooled fry (21/32) were IHNV-positive, and 9.4% (3/32) were IPNV-positive by one-step PCR. When nested PCR was conducted, 84.4% (27/32) were IHNV-positive, and 28.1% (9/32) were IPNV-positive. However, only 1.3% of spawners (1/80) were IHNV-positive by nested PCR. In 2008, 25% (8/32) of pooled fry were IHNV-positive by one-step PCR, but 59.4% (19/32) were IHNV-positive and 12.5% (4/32) were IPNV-positive by nested PCR. All of the samples tested were VHSV-negative. Although all viruses detected in this study were from chum salmon, phylogenetic analysis showed that they possibly originated from rainbow trout or clustered with the rainbow trout isolates. More extensive long-term studies are needed to clarify the origins of these viruses and their potential effects on chum salmon migration in Korea.

Morphologic and Genetic Evidence for Mixed Infection with Two Myxobolus Species (Myxozoa: Myxobolidae) in Gray Mullets, Mugil cephalus, from Korean Waters

The present study was performed to trace the decisive evidence for mixed infection of 2 Myxobolus species, M. episquamalis and Myxobolus sp., in the gray mullet, Mugil cephalus, from Korean waters. Mullets with whitish cyst-like plasmodia on their scales were collected near a sewage plant in Yeosu, southern part of Korea, in 2009. The cysts were mainly located on scales and also found in the intestine. The spores from scales were oval in a frontal view, tapering anteriorly to a blunt apex, and measured 7.2 µm (5.8-8.0) in length and 5.3 µm (4.7-6.1) in width. Two polar capsules were pyriform and extended over the anterior half of the spore, measuring 3.5 µm (2.3-4.8) in length and 2.0 µm (1.5-2.2) in width. In contrast, the spores from the intestine were ellipsoidal, 10.4 µm (9.0-11.9) in length and 8.4 µm (7.3-10.1) in width. The polar capsules were pyriform but did not extend over the anterior half of the spore, 3.7 µm (2.5-4.5) in length and 2.2 µm (1.8-2.9) in width. The nucleotide sequences of the 18S rDNA gene of the 2 myxosporean spores from scales and intestine showed 88.1% identity to each other and 100% identity with M. episquamalis and 94.5% identity with M. spinacurvatura from mullet, respectively. By the above findings, it is first confirmed that mullets from the Korean water are infected with 2 myxosporean species, M. episquamalis and Myxobolus sp.

Hirame rhabdovirus (HIRRV) as the cause of a natural disease outbreak in cultured black seabream (Acanthopagrus schlegeli) in Korea

In 2015, a high mortality rate of about 40xa0% was observed in black seabream (Acanthopagrus schlegeli) on a farm on the southern coast of Korea. Most of the diseased fish showed a hemorrhage of the mouth, pale liver, petechial hemorrhaging in the internal fat, and an enlarged spleen. Other than Alella sp., no parasites or bacteria were isolated from the diseased fish, and all of the tissue filtrates produced cytopathic effects (CPEs) in FHM and CHSE-214 cells. A polymerase chain reaction analysis revealed that the cell culture supernatants with CPE expressed specific 730-bp fragments for the hirame rhabdovirus (HIRRV) phosphoprotein gene. The nucleotide sequences showed a minimum of 95.8xa0% identity to five other known isolates of HIRRV, including CA-9703 and 8401-H from olive flounder (Paralichthys olivaceus) in Korea and Japan. An experimental challenge was conducted in which the virus was delivered by injection, and the cumulative mortalities of black seabream challenged with this new HIRRV isolate at 104.8 TCID50/fish and 103.8 TCID50/fish were 100xa0% and 20xa0%, respectively. This fulfilled Koch’s postulates and confirmed that HIRRV was the cause of disease and mortality for both the natural and experimental infection of black seabream.