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Histopathology revealed severe vacuolar degeneration and neuronal necrosis and in the olfactory lobe of infected fish (A). In retina, vacuolar degeneration was clearly observable in the inner nuclear and outer nuclear layers (B). Marked hyperplastic change in the gas glandular epithelium (C) and homogenous pale pink intranuclear inclusion body was occasionally seen in the hyperplastic gas glandular epithelium (D). Immunohistochemistry showed diffuse positive nodavirus antigens in the inner nuclear layer of retina (E) and the Purkinje cells of cerebellum (F). Nodaviral RNA was in situ detectable in the inner and outer nuclear layers of retina (G) and cerebellum using in situ hybridization (H).
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The present study characterized viral nervous necrosis in sea cage-reared adult spotted coralgroupers (Plectropomus maculatus). Histopathological study showed extensive vacuolation and neuronal necrosis of the olfactory bulb and the optic lobe of the forebrain and the inner and outer nuclear layer of retina. Mild necrosis was observed in the spinal...
Citations
... Betanodavirus is non-enveloped and icosahedral with a diameter of 20-30 nm, with two positive-sense RNA strands known as RNA1 and RNA2. RNA1 encodes RNA-dependent RNA polymerase (RdRp), a mitochondrial enzyme responsible for viral replication (Nopadon et al., 2009), and RNA2 encodes the capsid protein. The first nodavirus infection was detected in Japanese parrotfish (Oplegnathus fasciatus) (Yoshikoshi and Inoue, 1990). ...
Viral Nervous Necrosis (VNN) caused by Betanodavirus is a devastating disease in aquatic animals. The virus infects both marine and freshwater fish worldwide. Vacuolating necrosis of neural cells of the brain, the retina of the eye, and the spinal cord of the infected fish are the primary histological lesions of the condition. It causes up to 100% mortality in larvae and juvenile fish and can cause significant death in adult fish. The present study detected viral nervous necrosis in larvae and fry of Asian sea bass (Lates calcarifer) with progressive mortality of up to 95% in one week during the Northeast monsoon when the mean water temperature was 27 to 29°C. Histopathological examination of the moribund fish revealed extensive vacuolation and gliosis in the olfactory bulb, the optic lobe of the forebrain, and the inner and outer layer of the retina. Furthermore, tissues of the brain and the retina had intracellular inclusion bodies suggesting viral etiology, further justified by the negative results of the bacterial and parasitic examinations. The Reverse Transcriptase Polymerase Chain Reaction (RT-PCR) test additionally confirms the etiology diagnosis using specific primers designed previously. The histopathology and RT-PCR results suggest that the mortalities of Asian sea bass were due to the VNN. The present finding is the first report of the VNN associated with mass mortalities in Asian seabass cultured in Sri Lanka. These crucial findings emphasize the need for quarantine and control strategies to prevent the spread of the virus and outbreak of the disease.
... The virus has a single-stranded bipartite positive sense RNA genome. Although adults can be affected, hatchery-reared larvae and juveniles are primarily affected by VNN outbreaks, which can cause high mortalities of up to 100% [54]. The virus was first isolated in cell culture from seabass fry using striped snakehead cell line [55]. ...
Aquaculture, being the fastest growing food production sector, has now become vital to the socioeconomic development of many countries. In India, aquaculture plays a significant role in food production, ensuring nutritional security, boosting agricultural exports, and generating job opportunities. The production of farmed fish has greatly expanded qualitatively and quantitatively in both freshwater and marine water regimes to fulfill the ever-growing demand. However, the occurrence of diseases is the main obstacle to sustainable aquaculture production, which has an impact on the socioeconomic status of fish farmers of the country. Viral diseases inflict irreparable damage to the aquaculture enterprise causing large-scale economic losses and ecological problems. Recently, there has been a spike in the incidence of new emerging viral diseases in diverse species of aquaculture species. Prophylactics by far being the only feasible method of viral disease control, the development of viral vaccines is highly imperative. A precise understanding of the disease pathology, etiological agent, and species susceptible to the specific diseases are highly essential in this perspective. The chapter highlights the emerging and reemerging viral diseases in the Indian aquaculture sector.
... According to the reports of NNV from East and Southeast Asia, erratic swimming and resting on the bottom of nets, lethargy, skin darkening, vacuolization of the eye and muscle around it, as well as inflammation and necrosis of the brain, kidney and liver, and mortalities were listed as clinical and pathological signs associated with this virus (Abdullah et al., 2017;Juniar et al., 2018;Nopadon et al., 2009). ...
East and Southeast Asia have the largest share of mariculture production in Asia, and most of this is cage farming. An increase in marine fish consumption in the region has led to an expansion of marine cage culture over the last decade, which has resulted in an increase in the incidence of infectious diseases within this sector. Knowledge about pathogens, their distribution and clinical signs can help establish appropriate preventive and control strategies. We systematically reviewed the literature for infectious diseases affecting fish in marine cage culture in East and Southeast Asia, using two scientific databases, Scopus and Aquaculture Compendium, as well as two government‐based databases, quarterly aquatic animal disease reports published by the Network of Aquaculture Centres in Asia‐Pacific, and the fish health data published by the World Animal Health Information System (OIE). We also discussed the transmission routes of pathogens and potential environmental triggers for outbreaks when the information was available. Our review revealed that Vibrio spp., followed by parasitic monogeneans, trematodes and copepods are the most commonly reported pathogens in the literature. There were a few reports of viral pathogens, such as iridoviruses and nervous necrosis virus, but these were more commonly reported in the government surveillance documents. The results of this review can help inform surveillance programmes, improve the early detection of disease on farms and identify pathogens of concern for developing preventive and control strategies.
... Some studies indicate that pathological changes first developed in the olfactory lobes and then spread to the abnormal brain tissue, medulla oblongata, spinal cord and finally to the retina (82-83-84-85). Direct entry of VNN into the nerve cell through axonal transport to the brain stem via cranial nerves is another hypothesis (84)(85)(86). The central nervous system (CNS) including the brain, spinal cord, and retina are the main target organs in which the virus actively replicates (16, 26, 69) (Fig. 4). ...
... These authors suggest that the viral antigens first appear in the nervous tissues, where the virus has the highest persistence and the other organs are not generally believed to play an important role in the disease pathogenesis (92). Although the swim bladder hyperinflation has been described in most of the infected fish with clinical signs of VNN, this is not considered to be a target organ for betanodavirus because no marked histopathological changes have been observed (85). In addition, the distribution of VNN in other tissues varies with fish species and age. ...
Viral Nervous Necrosis (VNN) causes viral encephalopathy and retinopathy (VER), a hazardous and devastating disease of many species of cultured and marine fish worldwide. It caused by betanodaviruses a serious concern especially in the fry and young fish. This virus infects most of the cultured fishes causing severe mortality. Our current review focuses chiefly on recent studies performed on VNN disease. Recent outbreaks have been reported in China, Indonesia, Singapore and India, affecting the mariculture and aquaculture industry. It also decreased dramatically Mullet stocks in the Caspian Sea. The four main genotypes of VNN were found in all continentals’ except South America. The economic loss due to the virus is mainly due to mortality and spread of infection both vertically and horizontally. Our investigation in recent years suggest that more research and epidemiological surveys should be conducted, especially in critical areas were mariculture farms are planned to be established. Therefore, finding new rapid diagnosis tools, Monitoring and Surveillance program, and effective vaccines, Control, Prevention and Eradication in the comprehensive program should be considered globally.
Keywords: Viral Nervous Necrosis, fish, Mariculture
... Although PCR is widely used, it also has limitations as it requires complex procedures and specialized equipment, and it cannot be used on the spot. Other methods, such as electron microscopic observation of infected tissues (Nopadon et al., 2009), enzyme-linked immunosorbent assay (ELISA) (Arimoto et al., 1992;Shieh and Chi, 2005;Nuñez-Ortiz et al., 2016), and immuno-fluorescence antibody test (IFAT) (Nguyen et al., 1996;Mladineo, 2003), require well-trained personnel and expensive instruments. They are also laboratorybased and do not meet the requirements for real-time detection. ...
Nervous necrosis virus (NNV) has infected more than 50 fish species worldwide, and has caused serious economic losses in the aquaculture industries. However, there is no effective antiviral therapy. The development of a rapid and accurate point-of-care diagnostic method for the prevention and control of NNV infection is urgently required. Commonly used methods for NNV detection include the cell culture-based assay, antibody-based assay and polymerase chain reaction (PCR)-based assay. However, these methods have disadvantages as they are time-consuming and complex. In the present study, we developed a simple and sensitive aptamer-based lateral flow biosensor (LFB) method for the rapid detection of red-spotted grouper nervous necrosis virus (RGNNV). An aptamer is a single-stranded nucleotide, which can specifically bind to the target and has many advantages. Based on a previously selected aptamer, which specifically bound to the coat protein of RGNNV (RGNNV-CP), two modified aptamers were used in this study. One aptamer was used for magnetic bead enrichment and the other was used for isothermal strand displacement amplification (SDA). After amplification, the product was further tested by the LFB, and the detection results were observed by the naked eye within 5 min with high specificity and sensitivity. The LFB method could detect RGNNV-CP protein as low as 5 ng/mL or 5 × 103 RGNNV-infected GB (grouper brain) cells. Overall, it is the first application of a LFB combined with aptamer in the rapid diagnosis of virus from aquatic animals, which provides a new option for virus detection in aquaculture.
... The neurotropism of betanodaviruses has been repeatedly demonstrated (see reviews [74,144,163]) and viral replication seems to be almost entirely restricted to nerve tissue, preferentially brain and retina [157,162,164]. Histopathological studies have demonstrated the vacuolation of nerve cells in the olfactory lobe and cerebellum (Purkinje cell layer and the underlying granule cell layer) [10,82,119,120,125,135,161,165,166]. Megalocells and small nerve cell nuclei were also infected in the preoptic area, thalamus, medulla oblongata and spinal cord, whereas only a few small nerve cells were infected in the olfactory bulb and optic tectum [57,93,109,119,158,[166][167][168]. ...
... Histopathological studies have demonstrated the vacuolation of nerve cells in the olfactory lobe and cerebellum (Purkinje cell layer and the underlying granule cell layer) [10,82,119,120,125,135,161,165,166]. Megalocells and small nerve cell nuclei were also infected in the preoptic area, thalamus, medulla oblongata and spinal cord, whereas only a few small nerve cells were infected in the olfactory bulb and optic tectum [57,93,109,119,158,[166][167][168]. ...
The outbreaks of viral encephalopathy and retinopathy (VER), caused by nervous necrosis virus (NNV), represent one of the main infectious threats for marine aquaculture worldwide. Since the first description of the disease at the end of the 1980s, a considerable amount of research has gone into understanding the mechanisms involved in fish infection, developing reliable diagnostic methods, and control measures, and several comprehensive reviews have been published to date. This review focuses on host–virus interaction and epidemiological aspects, comprising viral distribution and transmission as well as the continuously increasing host range (177 susceptible marine species and epizootic outbreaks reported in 62 of them), with special emphasis on genotypes and the effect of global warming on NNV infection, but also including the latest findings in the NNV life cycle and virulence as well as diagnostic methods and VER disease control.
... Some studies indicate that pathological changes first developed in the olfactory lobes and then spread to the abnormal brain tissue, medulla oblongata, spinal cord and finally to the retina (82-83-84-85). Direct entry of VNN into the nerve cell through axonal transport to the brain stem via cranial nerves is another hypothesis (84)(85)(86). The central nervous system (CNS) including the brain, spinal cord, and retina are the main target organs in which the virus actively replicates (16, 26, 69) (Fig. 4). ...
... These authors suggest that the viral antigens first appear in the nervous tissues, where the virus has the highest persistence and the other organs are not generally believed to play an important role in the disease pathogenesis (92). Although the swim bladder hyperinflation has been described in most of the infected fish with clinical signs of VNN, this is not considered to be a target organ for betanodavirus because no marked histopathological changes have been observed (85). In addition, the distribution of VNN in other tissues varies with fish species and age. ...
Viral Nervous Necrosis (VNN) Virus causes viral encephalopathy and retinopathy (VER), a hazardous and devastating disease of many species of cultured and marine fish worldwide. It caused by betanodaviruses a serious concern especially in the fry and young fish. This virus infects most of the cultured fishes causing severe mortality. Our current review focuses chiefly on recent studies performed on VNN disease. Recent outbreaks have been reported in China, Indonesia, Singapore and India, affecting the marinculture and aquaculture industry. It also decreased dramatically Mullet stocks in the Caspian Sea. The four main VNN viral genotypes were found in all continentals’ exception South America. The economic loss due to the virus is mainly due to mortality and spread of infection both vertically and horizontally. Our investigation in recent years suggest that more research and epidemiological surveys should be conducted, especially in critical areas were marinculture farms are planned to be established. Therefore, finding new rapid diagnosis tools, Monitoring and Surveillance program, and effective vaccines, Control, Prevention and Eradication in the comprehensive program should be considered globally.
... Quantitative RT-PCR (qRT-PCR), in situ hybridization (ISH), and immunohistochemistry (IHC) have been used to detect Betanodavirus from organs and tissues of various fish species (Comps et al., 1996;Chi et al., 2001;Grove et al., 2006;Cha et al., 2007;Nopadon et al., 2009;David et al., 2010;Lopez-Jimena et al., 2011;Kim et al., 2018a, b). However, viral replication and underlying mechanism of infection with the host has not yet fully understood. ...
Nervous necrosis virus (NNV) belongs to the genus Betanodavirus of family Nodaviridae. Its genome consists of two RNA segments, RNA1 and RNA2. Several studies have investigated NNV detection by in situ hybridization (ISH), but these have typically focused on the detection of the RNA2 gene. In this study, we localized both RNA1 and RNA2 NNV segments in viral-infected cells by ISH, using labeled RNA probes (RNA-ISH). Also, immunocytochemistry (ICC) assay was carried out for localization of viral particle by targeting the coat protein. Further, viral quantification assays were performed by quantitative RT-PCR and viral infectivity (TCID50) in SSN-1 cells. Viral segments were observed by RNA-ISH at 6 h post infection (hpi), while NNV particles were detected at 24 hpi by ICC. Use of double labeling RNA-ISH revealed the co-expression of the two viral segments in the same area of the cells, while RNA1 was also detected separately. Comparison of the level of viral genomic segments and viral infectivity revealed significantly more copies of RNA1 at each time points than copies of RNA2 and greater NNV titers. The results suggest that RNA1 might be expressed in the early stages of replication, with RNA2 expressed later. The virions then assemble through initially expressed viral genomic segments. Even though infectious particles displayed very efficient packaging, the RNA1 segment was still over-produced.
... However, this technique offers advantage of studying viral expression or localization of target gene at cellular level. Several studies have investigated NNV genome using ISH based on RNA2 segment which forms DNA-RNA hybrid [6,8,[12][13][14]. Unfortunately, currently there is no information about the status of RNA1 segment in NNV infected cells or tissue. ...
... The main reported clinical sings of VNN are anorexia, abnormal colouration, hyperinflation of swim bladder and a whirling swimming pattern [21]. Although, nodavirus distribution is observed in many organs [28] but the main target organ for nodavirus is the central nervous system (CNS), including the brain, spinal cord and retina [19,21,26]. The characteristic lesions of VNN are necrosis and vacualtion of CNS and retina of the affected fish. ...
... Therefore, the clinical sings relate to the lesions present in the brain and retina, i.e. there are abnormalities of movement, swim bladder control, sight and colouration [21,26]. It is notable that an age related susceptibility has been reported to VNN, larval and juvenile stages are more susceptible than adult fish to the disease and mortality rates of up to 100 % have been reported in larvae and juvenile fish., whereas adult fish are more resistance and survive for a longer time after infection [19,21,25,26,28]. ...
