Viral Diseases In Aquaculture Research Articles

Differentially expressed genes involved in immune pathways following Vibro parahaemolyticus challenge: A study on red swamp crayfish Procambarus clarkii

This study conducted a comprehensive analysis of the damage mechanism of Vibrio parahaemolyticus (V. parahaemolyticus) on crayfish, utilizing pathological section observations, biochemical indicator detection, and transcriptomics analysis. Histopathological examination showed fragmentation of the gill lamellae, spotted pigment deposition on the branchial membrane, degeneration of epithelial cells, and disruption of the normal structure of gill tissues. Biochemical tests indicated a significant decrease in the activity of antioxidant-related enzymes in crayfish injected with V. parahaemolyticus compared with the phosphate-buffered saline group. Transcriptomics analysis identified 2307 upregulated and 1721 downregulated differentially expressed genes (DEGs). Gene ontology enrichment analysis highlighted that DEGs were primarily involved in the regulation of lipid metabolic processes, cellular nitrogen compound biosynthesis and metabolic processes, and the negative regulation of neuron death. Kyoto Encyclopedia of Genes and Genomes pathway analysis revealed significant enrichment in N-glycan biosynthesis, fatty acid metabolism, and the mTOR signaling pathway. Gene set enrichment analysis indicated pathways related to immunity and oxidative stress, including oxidative phosphorylation and tyrosine metabolism. Quantitative reverse transcription–polymerase chain reaction results for selected genes involved in the oxidative phosphorylation pathway and immune-related genes corroborated the RNA-Seq trends, confirming the transcriptomics data's reliability. The findings suggest that infection with V. parahaemolyticus leads to excessive oxidative stress due to bacterial proliferation, overwhelming the crayfish's antioxidative defense. This causes a continuous increase in reactive oxygen species levels, leading to irreversible damage to the oxidative phosphorylation and innate immune systems. This study elucidated the mechanism of oxidative stress damage in crayfish following V. parahaemolyticus infection, providing valuable insights for reducing bacterial and viral diseases in aquaculture. A deeper understanding of pathogen affects the physiology and immune systems of aquatic organisms can help develop more effective prevention and control strategies, thereby improving the efficiency and sustainability of aquaculture.

Advances on genomes studies of large DNA viruses in aquaculture: A minireview

Genomic studies of viral diseases in aquaculture have received more and more attention with the growth of the aquaculture industry, especially the emerging and re-emerging viruses whose genome could contain recombination, mutation, insertion, and so on, and may lead to more severe diseases and more widespread infections in aquaculture animals. The present review is focused on aquaculture viruses, which is belonged to two clades, Varidnaviria and Duplodnaviria, and one class Naldaviricetes, and respectively three families: Iridoviridae (ranaviruses), Alloherpesviridae (fish herpesviruses), and Nimaviridae (whispoviruses). The viruses possessed DNA genomes nearly or larger than 100 kbp with gene numbers more than 100 and were considered large DNA viruses. Genome analysis and experimental investigation have identified several genes involved in genome replication, transcription, and virus-host interactions. In addition, some genes involved in virus genetic variation or specificity were also discussed. A summary of these advances would provide reference to future discovery and research on emerging or re-emerging aquaculture viruses.

The potent potential of Gentiana Macrophylla pall aqueous extract in protecting largemouth bass against Micropterus Salmoides Rhabdovirus: A promising application of herbal crude extract in the fight against MSRV

Due to variables such as insufficient host immune system, small size, and high operational costs, there are no commercially available vaccines and drugs against infection by Micropterus salmoides rhabdovirus (MSRV), which leads to serious financial losses in the aquaculture of largemouth bass (Micropterus salmoides). Since herbal extracts are abundant in a range of bioactive compounds and the extraction method is simple and inexpensive, they are more commercially available. In the present study, Gentiana macrophylla Pall (GMP) aqueous extracts rich in a variety of antiviral compounds were found to inhibit MSRV replication in vitro with a half-maximal inhibitory concentration (IC50) of 9.37 mg/L against MSRV, while achieving 99.85% inhibition at 50 mg/L. In addition, GMP was able to reduce MSRV-induced cytopathogenic effect (CPE) and nuclear damage, while decreasing MSRV-induced mitochondrial depolarization, as evidenced by an approximately 0.50-fold reduction in the proportion of JC-1 monomers. Administration of GMP-supplemented commercial diets to MSRV-infected fish significantly increased the expression of host antiviral-related genes while reducing viral load in the spleen and intestine (0.34- and 0.63-fold reduction on 9 day post-infection, respectively), increasing survival rates by up to 18%. In summary, GMP has been shown to have anti-MSRV activity and has the potential for commercial application as an additive against viral diseases in aquaculture based on its low cost and environmental friendliness.

Tetraselmis suecica and Porphyridium cruentum exopolysaccharides show anti-VHSV activity on RTG-2 cells

   The use of functional feed additives is an important approach to both, prevent and fight, viral diseases in aquaculture. In this regard, microalgae-derived products, and, more specifically, microalgal exopolysaccharides (EPSs), have attracted attention, since multiple biotechnological applications are being described for these molecules. Furthermore, depending on culture conditions, the composition and, therefore, properties of EPSs can vary. In the present study, the antiviral activity of EPSs from Tetraselmis suecica and Porphyridium cruentum cultured under autotrophic and heterotrophic conditions has been evaluated in vitro against Viral Haemorrhagic Septicaemia Virus (VHSV), an important pathogen in fish farming. Results showed that EPSs from both species have anti-VHSV activity. T. suecica EPSs from autotrophic cultures showed the strongest effect, since both, adsorption and post-adsorption phases of the VHSV multiplication cycle were affected. In contrast, both, autotrophic and heterotrophic P. cruentum EPSs showed anti-VHSV activity only after the adsorption phase. These results pave the way to use these EPSs to fight VHSV infections, and animate to evaluate the EPS antiviral activity against other viral pathogens relevant to the aquaculture industry.

Herbal active small molecule as an immunomodulator for potential application on resistance of common carp against SVCV infection.

Herbal immunomodulators are an important part of prevention and control on viral diseases in aquaculture because of their propensity to improve immunity in fish. The present study was conducted to evaluate the immunomodulatory effect and antiviral activity of a synthesized derivative (serial number: LML1022) against spring viremia of carp virus (SVCV) infection in vitro and in vivo. The antiviral data suggested that LML1022 at 100μM significantly inhibited the virus replication in epithelioma papulosum cyprini (EPC) cells, and may completely inhibit the infectivity of SVCV virion particles to fish cells by affecting the viral internalization. The results in the related stability of water environments also demonstrated that LML1022 had an inhibitory half-life of 2.3d at 15°C, which would facilitate rapid degradation of LML1022 in aquaculture application. For in vivo study, the survival rate of SVCV-infected common carp was increased 30% at least under continuous oral injection of LML1022 at 2.0mg/kg for 7d treatment. Additionally, pretreatment of LML1022 on fish prior to SVCV infection also obviously reduced the viral loads in vivo as well as an improved survival rate, showing that LML1022 was potential as an immunomodulator. As an immune response, LML1022 significantly upregulated the immune-related gene expression including IFN-γ2b, IFN-I, ISG15 and Mx1, indicating that its dietary administration may improve the resistance of common carp against SVCV infection.

Longitudinal analysis of changes in the gut microbiota of zebrafish following acute spring viremia of carp virus infection

The gut microbiota of vertebrates plays a critical role in resistance to invading pathogens. Spring viremia of carp (SVC) is one of the most severe viral diseases in aquaculture. The causative agent is the SVC virus (SVCV), resulting in devastating damage to cyprinid. Yet, knowledge regarding the relationship between the gut microbes and disease is still lacking, particularly the dynamic alteration of the gut microbiota in fish following SVCV infection. To understand the longitudinal effects of SVCV infection on the microbiota of the zebrafish intestine, an intraperitoneal injection zebrafish model mimicking acute SVCV infection in fish with typical virologic and pathologic features was used. Intestinal microbes from both control (CON) and SVCV-infected fish were characterized at various time points by 16S ribosomal RNA gene V3-V4 region sequencing. Viral load in spleen, kidney, and intestine and the total bacterial load in the gut were detected by qPCR.The results showed that SVCV infection was associated with alterations of the gut microbiota in zebrafish as indicated by both alpha and beta diversity indexes. Compared with the CON group, SVCV-infected fish had significantly reduced bacterial diversity at 4 to 6 days post-infection (dpi). It has been found that a number of bacteria were enriched in opportunistic pathogens and depleted of beneficial commensals, at the time of onset of obvious symptoms or even death and at the time of complete disappearance of symptoms. A noticeably higher relative abundance of opportunistic pathogens, such as Clostridium_XlVa, Vibrio, Aeromonas, Mycoplasmataceae_unclassified, and Rothia; and a lower relative abundance of beneficial symbionts were found in the gut microbiome at 4, 7, 10 days post-infection. Five biomarkers showed high accuracy for distinguishing SVCV-infected fish from CON with an area under the curve (AUC) up to 0.78, 0.80, 0.79, 0.89, and 0.84, respectively. The relative abundance of Enterobacteriaceae_unclassified showed a positive correlation with viral loads of SVCV and the relative abundance of Cetobacterium and Aeromonas were positively related to the bacterial load in the gut, while the same results were observed for the corresponding two phyla (Fusobacteria and Proteobacteria). SVCV causes long-term gut microbiome dysbiosis, which is linked to viral load in target organs and total intestinal bacterial count. The results of our study suggest the potential value of the gut microbiota as a diagnostic biomarker and therapeutic target for SVC, but further validation is required.

Identification of scale drop disease virus based on environment DNA in an aquaculture facility of Singapore

Scale drop disease virus (SDDV) is an emerging virus in Asian countries that infects barramundi, resulting in huge economic losses in aquaculture industries. Current methods of diagnosing viral diseases in aquaculture are time-consuming and rely on infected sick fish to confirm results. Delays in the management of outbreaks often occur due to the inefficiencies of conventional pathogen detection methods and difficulty in visually inspecting animals in aquaculture facilities. Environment DNA (eDNA) approaches on the other hand investigate the provenance of the genetic material in the environment, thus allowing the detection of specific pathogens even before animals become infected. SDDV was recently detected in the mucus and fin clips of infected fish, therefore it presents itself as an ideal viral candidate pathogen to test the viability of eDNA as an early monitoring tool for its detection and quantification from water samples. This study aimed to test for the first time, the viability of detecting SDDV using eDNA approach in an aquaculture research facility in Singapore with past reports of SDDV infected barramundi. Quantitative PCR (qPCR) and digital droplet PCR (ddPCR) targeting SDDV in water samples from several tanks over a period of 6 months were conducted to understand the association of abiotic and biotic variables with SDDV abundance. Both PCR techniques detected SDDV eDNA, with ddPCR outperforming qPCR as it was more sensitive for low virus copy numbers. SDDV was also detected in fingerling fin clips from tanks where higher levels of its genome were found. SDDV abundance was significantly associated with periods of higher rainfall and lower salinity (p < 0.05). Although SDDV abundance was more strongly associated to these cooler periods, temperature itself was not significantly associated with SDDV (p > 0.05). These findings demonstrated ddPCR as a more efficient technique to detect low levels of SDDV in aquatic environments. The eDNA approach offers an innovative way to identify viral diseases in aquaculture as generally very few options are available for farmers to pre-empt outbreaks. It also warrants future studies to better understand SDDV dynamics throughout the year and its association with the water physicochemical parameters and host microbiome.

Vibriosis Outbreaks in Aquaculture: Addressing Environmental and Public Health Concerns and Preventive Therapies Using Gilthead Seabream Farming as a Model System.

Bacterial and viral diseases in aquaculture result in severe production and economic losses. Among pathogenic bacteria, species belonging to the Vibrio genus are one of the most common and widespread disease-causing agents. Vibrio infections play a leading role in constraining the sustainable growth of the aquaculture sector worldwide and, consequently, are the target of manifold disease prevention strategies. During the early, larval stages of development, Vibrio species are a common cause of high mortality rates in reared fish and shellfish, circumstances under which the host organisms might be highly susceptible to disease preventive or treatment strategies such as vaccines and antibiotics use, respectively. Regardless of host developmental stage, Vibrio infections may occur suddenly and can lead to the loss of the entire population reared in a given aquaculture system. Furthermore, the frequency of Vibrio–associated diseases in humans is increasing globally and has been linked to anthropic activities, in particular human-driven climate change and intensive livestock production. In this context, here we cover the current knowledge of Vibrio infections in fish aquaculture, with a focus on the model species gilthead seabream (Sparus aurata), a highly valuable reared fish in the Mediterranean climatic zone. Molecular methods currently used for fast detection and identification of Vibrio pathogens and their antibiotic resistance profiles are addressed. Targeted therapeutic approaches are critically examined. They include vaccination, phage therapy and probiotics supplementation, which bear promise in supressing vibriosis in land-based fish rearing and in mitigating possible threats to human health and the environment. This literature review suggests that antibiotic resistance is increasing among Vibrio species, with the use of probiotics constituting a promising, sustainable approach to prevent Vibrio infections in aquaculture.

A review of the role of probiotics for the control of viral diseases in aquaculture

A review of the role of probiotics for the control of viral diseases in aquaculture

Review of Medicinal Plants and Active Pharmaceutical Ingredients against Aquatic Pathogenic Viruses.

Aquaculture offers a promising source of economic and healthy protein for human consumption, which can improve wellbeing. Viral diseases are the most serious type of diseases affecting aquatic animals and a major obstacle to the development of the aquaculture industry. In the background of antibiotic-free farming, the development and application of antibiotic alternatives has become one of the most important issues in aquaculture. In recent years, many medicinal plants and their active pharmaceutical ingredients have been found to be effective in the treatment and prevention of viral diseases in aquatic animals. Compared with chemical drugs and antibiotics, medicinal plants have fewer side-effects, produce little drug resistance, and exhibit low toxicity to the water environment. Most medicinal plants can effectively improve the growth performance of aquatic animals; thus, they are becoming increasingly valued and widely used in aquaculture. The present review summarizes the promising antiviral activities of medicinal plants and their active pharmaceutical ingredients against aquatic viruses. Furthermore, it also explains their possible mechanisms of action and possible implications in the prevention or treatment of viral diseases in aquaculture. This article could lay the foundation for the future development of harmless drugs for the prevention and control of viral disease outbreaks in aquaculture.

RNA Interference-Based Pesticides and Antiviral Agents: Microbial Overproduction Systems for Double-Stranded RNA for Applications in Agriculture and Aquaculture

RNA interference (RNAi)-based pesticides are pest control agents that use RNAi mechanisms as the basis of their action. They are regarded as environmentally friendly and are a promising alternative to conventional chemical pesticides. The effective substance in RNAi-based pesticides is double-stranded RNA (dsRNA) designed to match the nucleotide sequence of a target essential gene of the pest of concern. When taken up by the pest, this exerts an RNAi effect and inhibits some vital biochemical/biological process in the pest. dsRNA products are also expected to be applied for the control of viral diseases in aquaculture by RNAi, especially in shrimp farming. A critical issue in the practical application of RNAi agents is that production of the dsRNA must be low-cost. Here, we review recent methods for microbial production of dsRNAs using representative microorganisms (Escherichia coli, Pseudomonas syringae, Corynebacterium glutamicum, Chlamydomonas reinhardtii, and others) as host strains. The characteristics of each dsRNA production system are discussed.

Identification and characterization of type I and II IFN genes in obscure puffer (Takifugu obscurus)

Interferons (IFNs) play critical roles in the host defense against virus infection, and exhibit promising prospects for the prevention of viral diseases in aquaculture. Pufferfish is an important cultured fish in East Asia. However, the IFN genes haven’t been systematically analyzed in pufferfish until now. In this study, we identified three type I IFN genes (ToIFNd, ToIFNh and ToIFNc) and two type II IFN genes (ToIFNγ and ToIFNγrel) in obscure puffer, and compared their molecular characterizations and phylogenetic relationships. Then we revealed that the five IFN genes were constitutively expressed in all detected tissues with different tissue distribution patterns. Furthermore, the dynamic expression changes of the IFNs were analyzed after poly(I:C) stimulation, which implied that the IFNs played various roles in the antiviral responses of obscure puffer. Finally, we investigated the characteristic reactions and verified the key transcription factor binding sites of ToIFNd promoter, and analyzed the induction effects of ToIFNγ and ToIFNγrel. These results will be beneficial to understand the functional characteristics of IFNs in Takifugu.

Direct Amperometric Sensing of Fish Nodavirus RNA Using Gold Nanoparticle/DNA-Based Bioconjugates.

We describe the design of a simple and highly sensitive electrochemical bioanalytical method enabling the direct detection of a conserved RNA region within the capsid protein gene of a fish nodavirus, making use of nanostructured disposable electrodes. To achieve this goal, we select a conserved region within the nodavirus RNA2 segment to design a DNA probe that is tethered to the surface of nanostructured disposable screen-printed electrodes. In a proof-of-principle test, a synthetic RNA sequence is detected based on competitive hybridization between two oligonucleotides (biotinylated reporter DNA and target RNA) complimentary to a thiolated DNA capture probe. The method is further validated using extracted RNA samples obtained from healthy carrier Sparus aurata and clinically infected Dicentrarchus labrax fish specimens. In parallel, the sensitivity of the newly described biosensor is compared with a new real-time RT-PCR protocol. The current differences measured in the negative control and in presence of each concentration of target RNA are used to determine the dynamic range of the assay. We obtain a linear response (R2 = 0.995) over a range of RNA concentrations from 0.1 to 25 pM with a detection limit of 20 fM. The results are in good agreement with the results found by the RT-qPCR. This method provides a promising approach toward a more effective diagnosis and risk assessment of viral diseases in aquaculture.

Single-walled carbon nanotubes as drug carrier loaded with moroxydine hydrochloride against infectious spleen and kidney necrosis virus in mandarin fish

Infectious diseases of viral origin cause major aquatic production losses in different parts of the world. There are lots of limited therapeutic effects for large amounts of antiviral drugs because of several impenetrable barriers (cell, skin, and gastrointestinal tract). In this study, we selected moroxydine hydrochloride (Mor) for the treatment of infectious spleen and kidney necrosis virus (ISKNV) and choose single-walled carbon nanotubes (SWCNTs) as drug carrier by immersion bath on mandarin fish infected with ISKNV. The results showed that increasing Mor intake was observed by SWCNTs carrier and therapeutic dosage to kill ISKNV is significantly reduced. After 4 h treatment, the concentration of Mor was 103.48 μg/g in 40 mg/L Mor group, and 182.35 μg/g in 40 mg/L Mor-SWCNTs groups. Comparing with the same dosage in Mor group, the detention time of Mor was extended more than 48 h in Mor-SWCNTs group. After 11 d treatment, cumulative mortality was 11.51% and infection rate was 3.81% in 40 mg/L Mor-SWCNTs group. In the same dosage of Mor group, cumulative mortality was 43.34% and infection rate was 22.67%. Moreover, enzyme activities, complement (C3) content and immune-related genes expression were significantly increased in Mor and Mor-SWCNTs groups than control group, herein all these mentioned activities reached the highest level at 3 days post-treatment. Our results indicated that drug delivery with functionalized SWCNTs can improve the antiviral effect on mandarin fish and has a potential application value to control fish viral diseases in aquaculture.

Anti-betanodavirus activity of isoprinosine and improved efficacy using carbon nanotubes based drug delivery system

Viral nervous necrosis (VNN) disease has caused mass mortality in cultured marine and freshwater fish worldwide, resulting in enormous economic losses in the aquaculture industry. The causative agent of VNN is betanodavirus [also known as nervous necrosis virus (NNV)], which classified as a member of the Nodaviridae family. NNV mainly infects the central nervous system (CNS) of hosts, which is protected by an elaborate barrier system, limiting the number of drugs reaching the infected sites to tackle the infections. Therefore, it is important to develop alternative drugs and smart delivery technologies for treatment the NNV infection. In the study, the anti-NNV activity of an immunomodulatory antiviral drug, isoprinosine, was checked both in vitro and in vivo. Besides, single-walled carbon nanotubes (SWCNTs) were used as a carrier to improve the anti-NNV activity. Results showed that isoprinosine could effective protect SSN-1 cell from NNV infection, and the percentage of apoptosis was significantly decreased following isoprinosine treatment. Similarly, isoprinosine also showed a strong anti-NNV activity in zebrafish, and the IC50 (inhibitory concentration at half-maximal activity) values were 86.44 and 52.47 mg/L after exposure to isoprinosine for 3 and 5 days, respectively. The expression levels of IL-1β, IFN-γ and TNF-α were up-regulated following isoprinosine treatment, indicating that isoprinosine can improve the immune responses to against NNV infection. A smart delivery system (named as SWCNTs-I) based on SWCNTs, bovine serum albumin (BSA) and isoprinosine was constructed and characterized by transmission electron microscope, FTIR spectroscopy and UV–vis spectroscopy. SWCNTs-I was internalized inside the SSN-1 cells, and showed a systemic distribution in the zebrafish larvae. SWCNTs-I has a stronger anti-NNV activity than naked isoprinosine, and the mortality of larvae treated with SWCNTs-I was 39.3% during 7 days post infection, while that were 96.7% and 58% for the control and naked isoprinosine treatment groups, respectively. Results so far indicated that isoprinosine is a powerful anti-NNV drug, and drug delivery with SWCNTs has a potential application value to control fish viral diseases in aquaculture.

Synthesis and antiviral activity of a new arctigenin derivative against IHNV in vitro and in vivo

Viral diseases in aquaculture were challenging because there are few preventative measures and/or treatments. Our previous study indicated that imidazole arctigenin derivatives possessed antiviral activities against infectious hematopoietic necrosis virus (IHNV). Based on the structure-activity relationship in that study, a new imidazole arctigenin derivative, 4-(8-(2-ethylimidazole)octyloxy)-arctigenin (EOA), was designed, synthesized and its anti-IHNV activity was evaluated. By comparing inhibitory concentration at half-maximal activity (IC50), we found that EOA (IC50 = 0.56 mg/L) possessed a higher antiviral activity than those imidazole arctigenin derivatives in our previous study. Besides, EOA could significantly decrease cytopathic effect (CPE) and viral titer induced by IHNV in epithelioma papulosum cyprinid (EPC) cells. In addition, EOA significantly inhibited apoptosis induced by IHNV in EPC cells. Further data verified that EOA inhibited IHNV replication in rainbow trout, with reducing 32.0% mortality of IHNV-infected fish. The results suggested that EOA was more stable with a prolonged inhibitory half-life in the early stage of virus infection (1–4 days). Consistent with above results, EOA repressed IHNV glycoprotein gene expression in virus sensitive tissues (kidney and spleen) in the early stage of virus infection. Moreover, histopathological evaluation showed that tissues from the spleen and kidney of fish infected with IHNV exhibited pathological changes. But there were no lesions in any of the tissues from the control group and EOA-treaten group. In accordance with the histopathological assay, EOA could elicited anti-inflammation response in non-viral infected rainbow trout by down-regulating the expression of cytokine genes (IL-8, IL-12p40, and TNF-α). Altogether, EOA was expected to be a therapeutic agent against IHNV infection in the field of aquaculture.

Fish Red Blood Cells Modulate Immune Genes in Response to Bacterial Inclusion Bodies Made of TNFα and a G-VHSV Fragment.

Fish Red-Blood Cells (RBCs) are nucleated cells that can modulate the expression of different sets of genes in response to stimuli, playing an active role in the homeostasis of the fish immune system. Nowadays, vaccination is one of the main ways to control and prevent viral diseases in aquaculture and the development of novel vaccination approaches is a focal point in fish vaccinology. One of the strategies that has recently emerged is the use of nanostructured recombinant proteins. Nanostructured cytokines have already been shown to immunostimulate and protect fish against bacterial infections. To explore the role of RBCs in the immune response to two nanostructured recombinant proteins, TNFα and a G-VHSV protein fragment, we performed different in vitro and in vivo studies. We show for the first time that rainbow trout RBCs are able to endocytose nanostructured TNFα and G-VHSV protein fragment in vitro, despite not being phagocytic cells, and in response to nanostructured TNFα and G-VHSV fragment, the expression of different immune genes could be modulated.

Rainbow Trout Erythrocytes ex vivo Transfection With a DNA Vaccine Encoding VHSV Glycoprotein G Induces an Antiviral Immune Response

Fish red blood cells (RBCs), are integral in several biologic processes relevant to immunity, such as pathogen recognition, pathogen binding and clearance, and production of effector molecules and cytokines. So far, one of the best strategies to control and prevent viral diseases in aquaculture is DNA immunization. DNA vaccines (based on the rhabdoviral glycoprotein G [gpG] gene) have been shown to be effective against fish rhabdoviruses. However, more knowledge about the immune response triggered by DNA immunization is necessary to develop novel and more effective strategies. In this study, we investigated the role of fish RBCs in immune responses induced by DNA vaccines. We show for the first time that rainbow trout RBCs express gpG of viral hemorrhagic septicaemia virus (VHSV) (GVHSV) when transfected with the DNA vaccine ex vivo and modulate the expression of immune genes and proteins. Functional network analysis of transcriptome profiling of RBCs expressing GVHSV revealed changes in gene expression related to G-protein coupled receptor (GPCR)-downstream signaling, complement activation, and RAR related orphan receptor α (RORA). Proteomic profile functional network analysis of GVHSV-transfected RBCs revealed proteins involved in the detoxification of reactive oxygen species, interferon-stimulated gene 15 (ISG15) antiviral mechanisms, antigen presentation of exogenous peptides, and the proteasome. Conditioned medium of GVHSV-transfected RBCs conferred antiviral protection and induced ifn1 and mx gene expression in RTG-2 cells infected with VHSV. In summary, rainbow trout nucleated RBCs could be actively participating in the regulation of the fish immune response to GVHSV DNA vaccine, and thus may represent a possible carrier cells for the development of new vaccine approaches.

Broad-spectrum antiviral JL122 blocks infection and inhibits transmission of aquatic rhabdoviruses

The aquaculture industry is growing rapidly to meet the needs for global protein consumption. Viral diseases in aquaculture are quite challenging due to lack of treatment options as well as limited injection-delivery vaccines, which are costly. Thus, water-immersion antiviral treatments are highly desirable. This study focused on broad-spectrum, light-activated antivirals that target the viral membrane (envelope) of viruses to prevent viral-cell membrane fusion, ultimately blocking viral entry into cells. Of the tested small-molecules, JL122, a new broad-spectrum antiviral previously unexplored against aquatic viruses, blocked infection of three aquatic rhabdoviruses (IHNV, VHSV and SVCV) in cell culture and in two live fish challenge models. Importantly, JL122 inhibited transmission of IHNV from infected to uninfected rainbow trout. Further, the effective antiviral concentrations were not toxic to cells or susceptible fish. These results show promise for JL122 to become an immersion treatment option for outbreaks of aquatic enveloped viral infections.

Tilapia lake virus: a threat to the global tilapia industry?

AbstractTilapia lake virus (TiLV) is a recently described virus affecting wild and farmed tilapines. At present, it has been reported on three continents (Asia, Africa and South America) and the number of countries where the agent has been detected is likely to increase rapidly as a result of increased awareness, surveillance and availability of diagnostic methods. Any lack of openness regarding the TiLV status of a translocating live tilapia population destined for aquaculture may inadvertently contribute to the spread of the agent. Currently, there is no cure for viral diseases in aquaculture and while vaccines and selective breeding have proved successful in reducing the severity of some viral diseases, there are currently severe knowledge gaps relating to TiLV and no effective, affordable vaccines are yet available. This paper summarizes the published scientific information on TiLV and highlights important issues relating to its diagnosis, mitigation and control measures. While there have been no scientific studies on the socio‐economic impact of TiLV, it may pose a significant threat particularly to small‐scale fish farmers’ livelihoods and wild tilapine populations if left uncontrolled. To aid disease investigations, the authors propose case definitions for suspected and confirmed cases of TiLV infections.