Viral Nervous Necrosis (VNN) an Emerging Disease Caused by Nodaviridae in Aquatic Hosts: Diagnosis, Control and Prevention: a Review

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Viral nervous necrosis (VNN) an emerging disease caused by Nodaviridae in aquatic hosts: Diagnosis, control and prevention: A review

Item Type article

Authors Zorriehzahra, M.J.; Adel, M.; Dadar, M.; Ullah, S.; Ghasemi, M.

DOI 10.22092/ijfs.2018.117849

Download date 29/09/2021 22:12:15

Link to Item http://hdl.handle.net/1834/40692 Iranian Journal of Fisheries Sciences 18(1) 30-47 2019 DOI: 10.22092/ijfs.2018.117849 Viral nervous necrosis (VNN) an emerging disease caused by Nodaviridae in aquatic hosts: Diagnosis, control and prevention: A review

Zorriehzahra M.J.1*; Adel M.1; Dadar M.2; Ullah S.3; Ghasemi M.4

Received: June 2016 Accepted: September 2016

Abstract Betanodavirus is one of the two genera making up the family Nodaviridae and is the etiological agent of viral nervous necrosis (VNN, also known as viral encephalopathy and retinopathy or VER). The virus infects a large range of host species in more than 50 species of marine and freshwater fish worldwide from different geographical areas and the known host range continues to expand as new species of fish are used for aquaculture. The disease is characterized by vacuolating necrosis of neural cells of the brain, retina and spinal cord and causes up to 100% mortality in larval and juvenile fish, and can cause significant losses in older fish. The lack of knowledge about control and prevention of the disease makes the problem serious and impedes development of management approaches. Therefore this review focuses on current knowledge and future perspectives of viral nervous necrosis in the aquaculture industry with special focus on the type of diagnosis, control and prevention of the disease.

Keywords: Viral nervous necrosis, Betanodavirus, Diagnosis, Control and prevention

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1-Aquatic Animal Health and Diseases Department, Iranian Fisheries Science Research Institute (IFSRI), Agricultural Research Education and Extension Organization (AREEO), Tehran, I.R. Iran. 2-Razi Vaccine and Serum Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Karaj, I.R. Iran. 3-Fisheries and Aquaculture Lab, Department of Animal Sciences, Quaid-i-Azam University, Islamabad, Pakistan. 4-Iranian Fisheries Science Research Institute (IFSRI), Inland Water Aquaculture Research Center, Bandar Anzali, I.R. Iran. *Corresponding author's Email: [email protected] 31 Zorriehzahra et al., Viral nervous necrosis (VNN) an emerging disease caused by…

Introduction strands known as RNA1 and RNA2. Viral nervous necrosis (VNN) is a RNA1 encodes RNA dependent RNA disastrous fish disease and one of the polymerase (RdRp), a mitochondrial main reasons for great economic losses enzyme, and is responsible for viral in marine fish and the aquaculture replication (Nopadon et al., 2009; Jia et industry. The agent of VNN is a virus al., 2015). On the other hand, RNA2 belonging to the genus Betanodavirus encodes the capsid protein (Wu et al., and family Nodaviridae (Peducasse et 2016). The existence of four genotypes al., 1999; Mu et al., 2013; Jia et al., characterized by high homology has 2015; Pascoli et al., 2016). Actually been approved on the basis of the viral the first documented nodavirus genome analysis, designated bar fin infection was detected in Japanese flounder nervous necrosis virus parrotfish (Oplegnathus fasciatus) in (BFNNV), tiger puffer NNV(TPNNV), Japan (Yoshikoshi and Inoue, 1990). striped jack NNV (SJNNV), and red Then the disease was reported in spotted grouper NNV (RGNNV) barramundi (Lates calcarifer) farmed in (Nishizawa et al., 1997; Shetty et al., Australia (Glazebrook et al., 1990), and 2012). The main target tissues are the then a year later in turbot, Scopthalmus nerve tissues especially the central maximus (Bloch et al., 1991), European nervous system (CNS) and the eye sea bass Dicentrarchus labrax (Breuil (retina). The characteristic lesions of et al., 1991), red spotted grouper, VNN are necrosis and vacuolation of Epinephalus akaara (Mori et al., 1992) the central nervous system and retina of striped jack, Pseudocaranx dentex the affected larvae and juvenile fishes (Mori et al., 1992) and several other showing abnormal swimming behavior species such as the golden grey mullet, (Liu et al., 2015). To date, the disease

Downloaded from jifro.ir at 15:23 +0430 on Wednesday April 17th 2019 Liza aurata (Zorriehzahra et al., 2005). has been reported in more than 120 Currently occurrence of VNN is species belonging to 30 families from reported in some African countries 11 different orders, mainly marine fish including: Tunisia (Chérif et al., 2009) being susceptible to infection (Munday and Algeria (Kara et al., 2014). It et al., 2002; Su et al., 2015; Costa et revealed that early unknown mortality al., 2016). On the other hand, several occurred in fry and juveniles of some freshwater fish species such as Chinese marine fish in decade of 1980-1990 in catfish (P. asotus); Australia catfish the world. Now this virus has been (Tandanus tandanus); Barramundi (L. recognized as a major problem and has calcarifer); Medaka (Oryzias latipes); been increasing in importance in Guppy (Poicelia reticulata) and Mediterranean and Asian marine Zebrafish (Danio rerio) showed aquaculture (Costa and Thompson, outbreaks of the disease (Hegde et al., 2016; Vendramin et al., 2016). 2003; Shetty et al., 2012). Affected fish Betanodavirus is non-enveloped and may reveal different clinical signs icosahedral with a diameter of 20–30 related to species, age and temperature nm, with two positive-sense RNA of the environment; an acute and sub- Iranian Journal of Fisheries Sciences 18(1) 2019 32

acute form characterized by atypical present in the retina and brain of the signs and a chronic form was observed infected fish, ultimately leading to for the first time only in affected fish in abnormal swimming, coloration, sight the Caspian Sea up to now and swim bladder control (Munday et (Zorriehzahra et al., 2016). The most al., 2002; Costa and Thompson, 2016,). specific and common symptoms In general, the clinical signs of VNN observed among the different species is are observed in the specific behavior of an abnormal swimming behavior, affected individuals. These behavioral lethargy and swim bladder changes include: loss of appetite, erratic hyperinflation that lead to abdominal swimming patterns like whirling, spiral, extension. The viral etiology has been looping swimming and belly up at rest, emphasized following the identification loss of equilibrium, minimized nervous of small, non-enveloped, RNA agents coordination, uncoordinated swimming definitively specified to the and alterations in pigmentations Nodaviridae family, genus (Nopadon et al., 2009). These signs are Betanodavirus. Although horizontal accompanied by some general sings transmission surely appears to be the such as anemia, lethargy and anorexia most common transmission route, (Munday et al., 2002). The infected vertical transmission has also been individuals also adopt a peculiar already proved in some species. stationary position, such as vertical According to the OIE protocol, position keeping caudal fin and head VER/VNN is officially diagnosed above the water surface. Some VNN through the isolation of the causative infected fish swim straight forward so agent in susceptible cell line and then swiftly that they are unable to identified with immunological or discontinue their speed and crash into

Downloaded from jifro.ir at 15:23 +0430 on Wednesday April 17th 2019 molecular methods such as FAT or by tanks’ walls and they experience real time RT-PCR or nested RT-PCR traumatic and harrowing lesions on (OIE, 2018). The control of the disease their jaws and nose (Maltese and Bovo, is intricate with difficulties in applying 2007; Binesh, 2014; Keawcharoen et biosecurity procedures, emphatic al., 2015). Other changes that coexist hygiene and preventive actions in open are hyperinflation of the swim bladder environments like the ocean and in (Mori et al., 1992; Hellberg et al., selecting brood fish free of pathogen. 2010; Kara et al., 2014; Vendramin et Furthermore, commercial vaccines are al., 2016) (Fig. 1). The presence or currently not available. absence of any of these signs or deviation in pigmentation change may Clinical signs and symptoms be due to species and water temperature The clinical sings of viral nervous (Binesh, 2014). necrosis are linked to the neuro- invasive nature of viruses of the family Nodaviridae, causing this disease, as well as the consequences of the lesions 33 Zorriehzahra et al., Viral nervous necrosis (VNN) an emerging disease caused by…

Figure 1: Clinical signs in VNN: hyperinflation of swim bladder (left) and abdominal extension (right) in infected Lisa aurata in the Caspian Sea (Zorriehzahra et al., 2014).

Virus isolation al., 1999; Iwamoto et al., 2001). These A number of cell lines are now observations were highly reproducible available for the culture of and formed the basis for a successful betanodaviruses (Qin et al., 2006). The virus titration system. Quantitative striped snakehead cell line (SSN-1) analysis using the cloned E-11 cell line originally developed by Frerichs et al., clearly revealed differences in the (1996) has been shown to be permissive optimal growth temperatures among the for 17 isolates of fish nodaviruses, 4 genotypic variants: 25 to 30° C for encompassing the RGNNV, SJNNV, strain SGWak97 (RGNNV), 20 to 25 TPNNV and BFNNV types (Iwamoto degrees C for strain SJNag93 (SJNNV), et al., 2000; Dalla Valle et al., 2001; 20 degrees C for strain TPKag93 Iwamoto et al., 2001; Chi et al., 2003). (TPNNV), and 15 to 20° C for strain Iwamoto et al., (2000) reported that six JFIwa98 (BFNNV) (Iwamoto et al., cell clones were derived from the SSN- 2001). Electron microscopy

Downloaded from jifro.ir at 15:23 +0430 on Wednesday April 17th 2019 1 cell line, which is composed of a demonstrated SnRV retrovirus particles mixed cell population and persistently only in A-6 and E-9 cells, but PCR infected with a C-type retrovirus amplification for the pool gene and (SnRV). These clones were susceptible LTR region of the proviral DNA to 4 piscine nodavirus strains belonging indicated the presence of the retrovirus to different genotypes SJNNV, in the other clones, including E-11. The RGNNV, TPNNV and BFNNV (striped cell clones obtained were more useful jack, redspotted grouper, tiger puffer for qualitative and quantitative analyses and bar fin flounder nervous necrosis of piscine nodaviruses than the SSN-1 viruses). Three clones, designated A-6, cell line. Further susceptible cell E-9, and E-11, were highly permissive cultures (GF-1) have been developed to nodavirus infection and production from the groupers Epinephelus coiodes (Iwamoto et al., 2000). The virus- (Chi et al., 1999; Mu et al., 2013) and induced cytopathic effects appeared as may be used for research and diagnostic cytoplasmic vacuoles and intensive purposes provided sensitivity is disintegration at 3 to 5 days post- regularly monitored (OIE, 2018). Lai et incubation (Frerichs et al., 1996; Chi et al., (2001) have developed another cell Iranian Journal of Fisheries Sciences 18(1) 2019 34

line from E. awoara (Lai et al., 2001), the eyes (Glazebrook et al., 1990; Le and Qin et al., (2006) have made other Breton et al., 1997; Grotmol et al., cell lines (GS) from the groupers, E. 1997; Nakai et al., 2009). A common coiodes that support grouper nervous finding in the CNS is gliosis (Shetty et necrosis viruses, but the lines have not al., 2012, Costa and Thompson, 2016). been tested for other types of fish Vacuolated cells and larger vacuoles nodaviruses (Qin et al., 2006). were mainly apparent in the In SSN-1 cells, the cytopathic effect telencephalon, the diencephalon and the appears on the 3rd day post infection cerebellum (Le Breton et al., 1997; Lai and is characterized by the appearance et al., 2001). In the nerve cells small of intracellular vacuolar lesions vacuoles and strong basophilic unevenly distributed throughout the cell inclusions are seen. The most monolayer (Iwamoto et al., 2000). prominent vacuolation is usually found These vacuolar lesions initially are in the grey matter of the optic tectum isolated and began assuming the form and cerebellum and there is often of vacuolized cellular aggregates after involvement of Purkinje cells (Starkey the passage of hours. Seventy-two et al., 2004; Shetty et al., 2012). hours post infection, their number and Vacuolation can also be seen in the size increase considerably and the white matter, adjacent to the ventricles. cellular monolayer is gradually replaced These vacuolations appear to be by cellular lysis until complete intracytoplasmic, but their exact destruction (Maltese and Bovo, 2007; position cannot always be determined Nishi et al., 2016). (Munday and Nakai, 1997; Su et al., 2015). Sections can be stained by Histopathology and immunohistochemistry (IHC) with the

Downloaded from jifro.ir at 15:23 +0430 on Wednesday April 17th 2019 immunohistochemistry avidin-biotin peroxidase complex The histological lesions of VNN technique using hydrogen peroxide and include severe degeneration, pyknosis, DAB as chromogen and substrate and shrinkage and basophilic cells in show strong positive reactions in the affected areas and vacuolation same layers (Le Breton et al., 1997). throughout the central nervous system The location of immunopositive cells is (CNS) of the fish and all retinal layers revealed by red or brown colour. This (Peducasse et al., 1999; Munday et al., demonstrated that the virus enters the 2002; Shetty et al., 2012). Infected CNS along nerves and blood vessels larvae have large vacuoles in the brain during the viremic stage of infection and retina, together with severe (Le Breton et al., 1997; Johansen et al., congestion of the blood vessels in the 2004; Shetty et al., 2012). brain. Larger fish also showed vacuoles and congestion in nervous tissue. Molecular diagnostic techniques Vacuolated cells and vacuoles are Many molecular methods have been mainly present in the bipolar and used in diagnosis of NNV. These ganglionic nuclear layer of the retina in methods were developed for the rapid, 35 Zorriehzahra et al., Viral nervous necrosis (VNN) an emerging disease caused by…

convenient and sensitive diagnosis of vertical transmission of this pathogen to the NNV pathogen in the fish and the larval offspring (Muroga, 1994). include: conventional or nested Some authors showed that nested RT– polymerase chain reaction (PCR) PCR is 10–100 times more sensitive (Muroga, 1994; Dalla Valle et al., than the previously reported RT–PCR 2000; Grotmol et al., 2000; Mu et al., methods (Thiery et al., 1999; Dalla 2013), real-time PCR (Starkey et al., Valle et al., 2000). 2004; Dalla Valle et al., 2005; Panzarin Moreover, since conventional PCR is et al., 2010; Hodneland et al., 2011; a non-quantitative technique, the actual Baud et al., 2015; Mekata et al., 2015) copy number of the viral template in and nucleic-acid sequence amplification samples cannot be determined (Starkey (NASBA) (Starkey et al., 2004). For et al., 2004; Dalla Valle et al., 2005). the first time during the nineties So, Dalla Valle and his colleagues Nishizawa et al. established NNV RT- described the setting up of two real- PCR detection method (Nishizawa et time, SYBR Green I-based, PCR al., 1995). With the development of this diagnostic assays targeting both RNA1 technology, the nucleic acid extraction and RNA2 of betanodavirus for its technique improved and now allows an quantitative detection in biological easy, fast, and high-quality RNA samples (Dalla Valle et al., 2005). The preparation, and the availability of more sensitivity of this technique was NNV genome sequences facilitating the compared with that of conventional RT- primer design and optimization (Mu et PCR assays previously developed for al., 2013). More recently, RT-PCR betanodavirus (Dalla Valle et al., 2000; assays with or without nested PCR have Grotmol et al., 2000; Mu et al., 2013) been developed as a powerful and with the results of routine virus

Downloaded from jifro.ir at 15:23 +0430 on Wednesday April 17th 2019 diagnostic tool alone or in combination isolation test (Delsert et al., 1997; with cell culture (Iwamoto et al., 2001; Iwamoto et al., 2001), to check for a Dalla Valle et al., 2005). The most used correlation between measured viral target is generally a portion of the coat RNA load and virus isolation response. protein gene (RNA2) of betanodavirus, Also, other quantitative real time a powerful and sensitive target for methods have been developed (Dalla identification of the infection Valle et al., 2005; Kuo et al., 2011; (Nishizawa et al., 1997; Grotmol et al., Lopez Jimena et al., 2012; Souto et al., 2000; Barke et al., 2002; Azad et al., 2015). They have been used as 2005). These PCR protocols have powerful tools to study transmission greatly improved test sensitivity, and development of this viral infection allowing better control of VNN in juveniles (Hodneland et al., 2011). infection through identification and NASBA is another useful method stamping out of infected spawners which consists of an isothermal method (Dalla Valle et al., 2005). For example, for nucleic acid amplification that is Striped jack (P. dentex) broodstocks particularly suited to RNA targets were screened for NNV to prevent (Deiman et al., 2002). The method Iranian Journal of Fisheries Sciences 18(1) 2019 36

amplifies a target-specific product al., 2015) and sometimes possesses an through oligonucleotide primers and the additional segment designated RNA3 co-ordinated activity of 3 enzymes: (Shetty et al., 2012). RNA1 encodes a reverse transcriptase, RNase H, and T7 non-structural protein, RNA-dependent RNA polymerase (Deiman et al., 2002; RNA polymeras (RdRP) and RNA2 Starkey et al., 2004). This method has encodes a capsid proteins (CP) of about been developed for the detection of 37-42 kDa (Jia et al, 2015). Using betanodavirus and the sensitivity of this molecular phylogenetic analyses based procedure was compared to a on partial sequences of the CP gene, the conventional single-tube RT–PCR betanodaviruses have been classified assay showing comparable results into four main clades: striped jack (Starkey et al., 2004). nervous necrosis virus (SJNNV), tiger puffer NNV (TPNNV), bar fin flounder Compare of methods and diagnostic NNV (BFNNV) and red spotted applications grouper NNV (RGNNV) (Nishizawa et The real-time PCR assays were more al., 1997; Aspehavg, 1999; Dalla Valle sensitive than the one step RT-PCR for et al., 2001; Gomez et al., 2004; Jia et betanodavirus (Dalla Valle et al., 2005; al., 2015). Hodneland et al., 2011; Panzarin et al., 2010; Baud et al., 2015, Mekata et al., Enzyme-linked Immunosorbent Assay 2015). This enhanced sensitivity can be (ELISA) exploited to reveal sub-clinical VNN Enzyme-linked immunosorbent assay is infections in carrier fish and to screen the rapid and sensitive test in order to out infected spawners to reduce or detect specific nodavirus antibodies as prevent the vertical transmission of the well as antigens from serum samples

Downloaded from jifro.ir at 15:23 +0430 on Wednesday April 17th 2019 virus (Costa and Thompson, 2016). It (Fenner et al., 2006; Costa and is important to point out that the real- Thompson, 2016; Jaramillo et al., time PCR can only detect the presence 2016). This method was used to of the viral genome, but is not able to identify sero-positive virus of fish of estimate its infectious potential (Dalla different ages especially from vectors Valle et al., 2005; Mekata et al., 2015). and broodstock in order to control Hence, PCR techniques will never vertical transmission of the disease replace the virus cultivation test and (Arimoto et al., 1993; Costa and both approaches should be used Thompson, 2016). The efficacy of this according to their specific benefits. assay was confirmed by Watanabe et al. Phylogenic analysis of NNV (2000) with the identification of The genome of NNV viruses consists of nodavirus antibodies from bar fin two single-stranded, positive-sense flounder broodstock and Arimoto et al. RNA molecules (RNA1 and RNA2) of (1996) from striped jack (Arimoto et about 3.0 and 1.4 kb in length, al., 1996). Also, Fenner et al. (2006) respectively, without poly(A) extension could detect 103–104 TCID50 units of at the 3’ end (Delsert et al., 1997; Jia et betanodavirus by antigen capture 37 Zorriehzahra et al., Viral nervous necrosis (VNN) an emerging disease caused by…

ELISA from infected tissues of juvenile VNN disease has a positive reaction to barramundi (L. calcarifer, Bloch) betanodavirus antigens in the optic (Fenner et al., 2006). In this assay 17% nerve, outer molecular and granular and 18% sera of wild and farmed layers of the brain and inner and outer European sea bass broodstock were nuclear layers of retina (Zorriehzahra et positive for nodavirus antibodies, al., 2014). respectively (Breuil et al., 1991). In a similar study, 9% sera of commercial Electron microscopy barramundi were positive for antibodies Virus particles observed with electron (Huang et al., 2001) by ELISA method. microscopy are icosahedral, non- enveloped with a commonly reported Immunofluorescence antibody test diameter of about 20-34 nm. Some (IFT) author showed that the virus has an Immunofluorescence antibody test electron-dense core of 13-21 nm (IFT) that uses fluorescent-labeled surrounded by a clear layer of about 5 antibodies to detect specific antigens nm (Glazebrook et al., 1990; Grotmol from target tissues including brain, et al., 1997; Chen et al., 2015; Xie et spinal cord and retina is a rapid, al., 2016b). The virions can be free in economical, powerful and important the cytoplasm of infected cell or technique for the screening of membrane-bound by endoplasmic Nodaviridae (Bigarré et al., 2009; Costa reticulum and may be present as and Thompson, 2016). In this assay by paracrystalline arrays (Glazebrook et preparing histopathological sections al., 1990). Cells containing virions have from CNS or other tissues such as eye, most often been recognized as neurons, swim bladder, spleen, kidney and liver astrocytes, oligodendrocytes and

Downloaded from jifro.ir at 15:23 +0430 on Wednesday April 17th 2019 staining with specialized microglia (Grotmol et al., 1997; immunofluorescence technique the Munday et al., 2002; Xie et al., 2016a). localized virus in target tissues is Virus particles in infected Atlantic indicated (Sanz and Coll, 1992). The halibut have been seen in endothelial binding of antibodies to target tissues, cells, pillar cells and lymphocytes cells or organisms can be visualized if attached to the endocardium, cardiac those antibodies are directly coupled to myocytes and epicardial cells by a fluorochrome or indirectly bound by a electron microscopy (Grotmol et al., fluorescent reagent ( Grist et al., 1981; 1997). Furusawa et al., 2006). Fluorochromes emit visible light (of an ‘emission’ Control and prevention wavelength) when exposed to light of a VNN could be very resistant in aquatic different (‘excitation’) wavelength, bodies and water environments and it usually in the ultraviolet range. The seems very difficult to eradicate when indirect fluorescent antibody test introduced to marine or aquaculture showed at least 20% of golden grey farms. Therefore, to recognize mullet (L. aurata) fish infected with pathways of virus transmission is very Iranian Journal of Fisheries Sciences 18(1) 2019 38

critical for control strategies. For this can inactivate the virus and prevent reason, broodstock and larval fish could spread of disease such as: ozone, acid be considered as viral repertoires and peroxygen, sodium hypochlorite and responsible asymptomatic carriers for benzalkonium chloride (Arimoto et al., horizontal transmission (Costa and 1993; Frerichs et al., 1996; Shetty et Thompson, 2016). Exclusion of virus- al., 2012). carrying animals from the production A vaccination method is essential to would be the best means of control in prevent the disease especially during the vertical transmission route. Thus, the primary stages and some the elimination or segregation of researchers reported effective infected spawners is the best way to procedures in controlling the disease prevent the introduction of the virus (Nakai et al., 2009; Xie et al., 2016a; into the hatchery (Munday et al., 2002; Vimal et al., 2014). Recombinant viral Costa and Thompson, 2016; Nakai et coat protein expressed in Escherichia al., 2009). Muroga et al. (1994) coli injected to fish (Sommerset et al., reported a successful control of VNN 2005) or injection of virus like particles by removal of infected striped jack (P. expressed in a baculovirus expression dentex) broodstock detected by PCR system were carried out by some (Muroga, 1994). In a similar study by researchers (Lin et al., 2001; Thiery et Breuil et al. (1991) the disease was al., 2006). Injection of the recombinant controlled by exclusion of serum protein in adult striped jack caused positive European sea bass (D. labrax) production of virus neutralizing broodstock (Breuil et al., 1991). Also antibodies (Munday et al., 2002), thus the use of disinfection of fertilized eggs vaccination seems to be a practical and by ozone has been recommended to appropriate way for the control of viral

Downloaded from jifro.ir at 15:23 +0430 on Wednesday April 17th 2019 control vertical transmission of nervous necrosis. Vaccinating broodfish betanodavirus in Atlantic halibut could reduce vertical transmission of (Hippoglossus hippoglossus) (Grotmol VNN and will be more acceptable by et al., 2000). Arimoto et al. (1993) the farmers (Kai et al., 2010). reported that 0.2 µg ml−1 ozone Unfortunately, no commercial vaccines disinfects fertilized eggs in striped jack are available at present. Also, feeding and also, 4 µg ml−1 was reported for of immunostimulant components could halibut by Grotmol et al. (1997). These be a beneficial way to increase results indicate that VNN transmitted immunity levels in larval fish against from the maternal sexual fluid was via VNN infection (Costa and Thompson, the surface of the eggs (Kai et al., 2016). 2010). Strict hygiene can help to control Horizontal transmission of VNN viral nervous necrosis within hatcheries infection may be: via contaminated (Munday et al., 2002; Bigarré et al., influent and rearing water, utensils, 2009; Shetty et al., 2012). No recycling vehicles and human activity (Nakai et of water and chemical sterilization of al., 2009). Some effective disinfectants seawater during each hatching cycle 39 Zorriehzahra et al., Viral nervous necrosis (VNN) an emerging disease caused by…

was successful to reduce VNN disease most important threat for the in a barramundi hatchery (Azad et al., development of mariculture in the 2005). Furthermore, applying Persian Gulf and Oman Sea in the near biosecurity measures and general future (Zorriehzahra et al., 2016). hygiene practices, such the UV Furthermore, the production of treatment, sanitary barriers, regular multivalent or recombinant vaccines monitoring and disinfection of tanks against VNN virus, the increase of and biological filters, disinfection of application of some immunostimulant utensils and decreasing stress factors drugs, the eco-epidemiological and density of larvae and juveniles are investigation on the global spreading of strongly recommended (OIE, 2018). VNN in the new regions and new VNN first occurred in 13 fish species susceptible hosts should be considered in 4 families about 23 years ago, in in future studies. 1993, but this transmissible viral disease is now recorded in more than 50 Acknowledgements species in 10 families (Munday et al., All the authors acknowledge their 2002; Costa and Thompson, 2016). thanks and support to their respective Also, unlike other viral diseases such as institutions and universities. Infectious hematopoietic necrosis (IHN), or Viral hemorrhagic septicemia References (VHS) that specially affects coldwater Arimoto, M., Mori, K., Nakai, T., fish, VNN virus can infect many Muroga, K. and Furusawa, I., different kinds of fish such as coldwater 1993. Pathogenicity of the causative fish (BFNNV genotype), warm water agent of viral nervous necrosis fish (RGNNV genotype) and other fish disease in striped jack,

Downloaded from jifro.ir at 15:23 +0430 on Wednesday April 17th 2019 such as ornamental fish (Nakai et al., Pseudocaranx dentex (Bloch & 2009; Costa and Thompson, 2016) and Schneider). Journal of Fish freshwater fish such as sturgeon fish Diseases, 16, 461-469. (Xylouri et al., 2007), tilapia (Bigarrè et Arimoto, M., Sato, J., Maruyama, K., al., 2009) and others (Pascoli et al., Mimura, G. and Furusawa, I., 2016). 1996. Effect of chemical and With regard to new intensive physical treatments on the mariculture systems being used in the inactivation of striped jack nervous Caspian Sea, Persian Gulf and Oman necrosis virus (SJNNV). Sea, the risk of viral and bacterial Aquaculture, 143, 15-22. infection could be high. This is true if Aspehavg, V., 1999. The phylogenetic we refer to recent mortality in some relationship of nervous necrosis species that were recorded by virus from Halibut. Bulletin researchers in that area (Zorriehzahra et European Association of Fish al., 2016). It could be summarized that Pathology, 19, 196. some worldwide emerging infectious Azad, I., Shekhar, M., diseases such as VNN could be the Thirunavukkarasu, A., Poornima, Iranian Journal of Fisheries Sciences 18(1) 2019 40

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