Iridovirus Infection Research Articles

8627 Viral Hormones: The Role Of Viral Insulin/IGF-1 Like Peptides In Host-Pathogen Interactions

Abstract Disclosure: A. Chuard: None. Viruses, encode proteins that are similar to host proteins to manipulate the host. Until our recent discovery of viral hormones, examples of viral mimicry were limited to immunomodulatory proteins and growth factors. We recently showed that six viruses in Iridoviridae family encode genes mimicking human insulin and IGF-1. We previously chemically synthesizing these viral insulin/IGF-1 like peptides (VILPs) and showed that VILPs can bind to human insulin and IGF-1 receptor and further stimulate post-receptor signaling. VILPs also stimulate glucose uptake and proliferation in mammalian cells and lower the blood glucose in mice. Originally, VILP-carrying viruses were isolated from fish; however, the role of VILPs in viral pathogenesis is not studied in depth. Here, we examined the effects of Grouper Iridovirus (GIV, one of the VILP carrying viruses) infection and GIV-VILP on host insulin/IGF signaling system using fish cells.To this end, we chemically synthesized GIV-VILP in its single chain (sc, IGF-1 like) and double chain (dc, insulin-like) forms. Stimulation of grouper kidney (GK) and AB9 zebrafish cells with these peptides, insulin and IGF-1, showed that IGF-1 was the most potent ligand in these cells indicating an abundance of IGF-1 receptor (IGF1R). Further, both forms of the VILPs were as potent as insulin in its activity on receptor phosphorylation and post-receptor signaling. Examining the viral kinetics, we also showed that GIV32 gene (encoding GIV VILP) is an early viral gene in both cell types. Virion analysis through mass spectrometry indicated that VILPs are not viral structural proteins. On the other hand, analysis of the supernatant from infected cells indicated that VILPs are secreted peptides during the viral cycle. Our results with supernatant transfer experiments from infected cells to uninfected cells support the same conclusion that VILPs are secreted. The secreted VILPs initiate autophosphorylation of IGF1R and/or insulin receptor (IR), consequently triggering downstream cellular signaling and metabolism. Through the use of specific inhibitors for each receptor, we illustrated that IR signaling is crucial for GIV viral replication. Surprisingly, inhibition of IGF1R increased viral replication and we are currently examining potential inhibitory effects of GIV VILP. Furthermore, VILPs appear to exert a biased effect on the AKT pathway compared to the Erk pathway. Furthermore, the inhibition of the AKT pathway significantly reduces GIV viral replication. In summary, our findings reveal that GIV-VILP is actively produced during infection and contributes to the viral replication. To our knowledge, VILPs are the first hormone-mimics characterized in viral replication. Elucidating the role of VILPs in host-pathogen interactions, we propose a novel viral pathogenesis mechanism where viruses mimic host hormones to manipulate the host's endocrine system. Presentation: 6/3/2024

Isolation, Identification and Genomic Analysis of Orange-Spotted Grouper Iridovirus Hainan Strain in China.

The orange-spotted grouper (Epinephelus coioides) is an important mariculture fish in China. However, in recent years, with the rapid development of aquaculture activities, outbreaks of viral diseases have affected the grouper aquaculture industry, causing severe economic losses. In the present study, we isolated and identified a virus from diseased, orange-spotted groupers from an aquaculture farm in Hainan Province, China. The isolated virus was identified as orange-spotted grouper iridovirus, hence named the orange-spotted grouper iridovirus Hainan strain (OSGIV-HN-2018-001). OSGIV-HN-2018-001 induces a cytopathic effect after the infection of mandarin fish (Siniperca chuatsi) brain clonal passage (SBC) cells. In addition, the cytoplasm of the OSGIV-HN-2018-001-infected SBC cells was found to contain a large number of hexagonal virus particles with a diameter of approximately 134 nm. Using the Illumina NovaSeq system, we assembled the sequence data and annotated the complete genome of OSGIV-HN-2018-001 (GenBank accession number: PP974677), which consisted of 110,699 bp and contained 122 open reading frames (ORFs). Phylogenetic tree analysis showed that OSGIV-HN-2018-001 was most closely related to ISKNV-ASB-23. The cumulative mortality rate of groupers infected with OSGIV-HN-2018-001 reached 100% on day 8. The spleens were enlarged and blackened after the dissection of the dying groupers. These results contribute to the understanding of the molecular regulatory mechanism of the iridovirus infection and provide a basis for iridovirus prevention.

Multi-epitope Vaccine Design against Grouper Iridovirus (GIV) Using Immuno-bioinformatics Approach

Grouper Iridovirus (GIV) infection induced cell death in grouper spleen cells and caused serious systemic diseases with more than 90% mortality. Therefore, effective strategies are critically needed to prevent economic losses and maintain the sustainability of grouper aquaculture. Using immuno-bioinformatics, this study aimed to create a multi-epitope vaccine (MEV) that would be effective against GIV. The GIV major capsid protein sequences were retrieved from the NCBI proteome database. Out of 284 epitopes, 17 CTL, 12 HTL, and 10 B-cell epitopes were predicted to be antigenic, non-allergenic, and non-toxic. 10 highly antigenic and overlapping epitopes were shortlisted. To generate full-length epitope vaccine candidates, the selected antigenic epitopes were fused with linkers and adjuvants. Four sets of different linker combinations (no linker, GGS, EAAK, GGGS, GPGPG, KK, and AAY) were tested and compared for their antigenicity, allergenicity, and toxicity using several servers. Molecular dynamics simulations with GROMACS were used on the modelled 3D structures to examine their stability. The results of vaccine candidate sequences screening and MD simulation predicted that the structure with GGS linker is relatively stable with a high antigenic index, non-allergenic, and non-toxic. The designed MEV in the present study could be a potential candidate for further vaccine production process against GIV.

First record of iridovirus (ISKNV) infections in Fourfinger threadfin from Kuwait

Following an initiative by the Govt. of Kuwait and the Kuwait Institute for Scientific Research (KISR), the institute started simultaneous efforts of domestication of locally caught fish and hatchery production of Fourfinger threadfin (FFT, Eleutheronema tetradactylum), locally called Sheem. A private farm and KISR are working together to optimize the conditions for growth and spawning performances under the environmental conditions of Kuwait. During these efforts, infectious spleen and kidney necrosis virus (ISKNV), an important fish pathogen from Iridoviridae, caused mortalities of the FFT sub-adults (150–200 g). We noticed that the mortality was associated with anorexia, haemorrhages of the snout, fin bases, and scale pockets. We also noticed that this was typical to one of the tanks that had consistently high ammonia (0.2–0.25 ppm) levels in the water, and all 35 sub-adults died within 4–5 days. Diagnostics (molecular and electron microscopy examinations) revealed ISKN iridovirus as the causative. We noticed viral particles of 150–200 nm in the tissue sections of the skin, gills, heart, liver, spleen, kidney, and intestine. The major capsid protein (MCP) gene sequence analysis confirmed the results, revealing 98 % similarity with the laminin-type epidermal growth factor-like protein gene of ISKNV. The present report is the first record of ISKNV infections in FFT and from Kuwait. The study aimed to decipher the cause of illness and mortality of cultured FFT.

Epinephelus coioides Sec3 promotes Singapore grouper iridovirus infection by negatively regulates immune response

Exocyst, a protein complex, plays a crucial role in various cellular functions, including cell polarization, migration, invasion, cytokinesis, and autophagy. Sec3, known as Exoc1, is a key subunit of the Exocyst complex and can be involved in cell survival and apoptosis. In this study, two subtypes of Sec3 were isolated from Epinephelus coioides, an important marine fish in China. The role of E. coioides Sec3 was explored during Singapore grouper iridovirus (SGIV) infection, an important pathogen of marine fish which could induce 90 % mortality. E. coioides Sec3 sequences showed a high similarity with that from other species, indicating the presence of a conserved Sec3 superfamily domain. E. coioides Sec3 mRNA could be detected in all examined tissues, albeit at varying expression levels. SGIV infection could upregulate E. coioides Sec3 mRNA. Upregulated Sec3 significantly promoted SGIV-induced CPE, and the expressions of viral key genes. E. coioides Sec3 could inhibit the activation of NF-κB and AP-1, as well as SGIV-induced cell apoptosis. The results illustrated that E. coioides Sec3 promotes SGIV infection by regulating the innate immune response.

Identification and functional characterization of interleukin-22 (IL-22) in orange-spotted grouper (Epinephelus coioides)

In mammals, IL-22 is considered as a critical cytokine regulating of immunity and homeostasis at barrier surfaces. Although IL-22 have been functional characterization in different species of fish, the studies about distinct responses of IL-22 in different organs/tissues/cell types is rather limited. Here, we identified and cloned IL-22 gene (named as Ec-IL-22) from grouper (Epinephelus coioides). Ec-IL-22 gene was detected in all orangs/tissues examined, and was induced in intestine, gill, spleen, head kidney, and primary head kidney/intestine leukocytes following the stimulation of LPS and poly (I:C), as well as Vibrio harveyi and Singapore grouper iridovirus infection (SGIV). In addition, the stimulation of DSS could induce the expression of Ec-IL-22 in intestine and primary leukocytes from intestine. Importantly, the treatment of recombinant Ec-IL-22 induced the mRNA level of proinflammatory cytokines in primary intestine/head kidney leukocytes. The present results improve the understanding of expression patterns and functional characteristics of fish IL-22 in different organs/tissues/cell types.

Fish ELOVL7a is involved in virus replication via lipid metabolic reprogramming

The elongation of very long chain fatty acids (ELOVL) proteins are key rate-limiting enzymes that catalyze fatty acid synthesis to form long chain fatty acids. ELOVLs also play regulatory roles in the lipid metabolic reprogramming induced by mammalian viruses. However, little is known about the roles of fish ELOVLs during virus infection. Here, a homolog of ELOVL7 was cloned from Epinephelus coioides (EcELOVL7a), and its roles in red-spotted grouper nervous necrosis virus (RGNNV) and Singapore grouper iridovirus (SGIV) infection were investigated. The transcription level of EcELOVL7a was significantly increased upon RGNNV and SGIV infection or other pathogen-associated molecular patterns stimulation in grouper spleen (GS) cells. Subcellular localization analysis showed that EcELOVL7a encoded an endoplasmic reticulum (ER) related protein. Overexpression of EcELOVL7a promoted the viral production and virus release during SGIV and RGNNV infection. Furthermore, the lipidome profiling showed that EcELOVL7a overexpression reprogrammed cellular lipid components in vitro, evidenced by the increase of glycerophospholipids, sphingolipids and glycerides components. In addition, VLCFAs including FFA (20:2), FFA (20:4), FFA (22:4), FFA (22:5) and FFA (24:0), were enriched in EcELOVL7a overexpressed cells. Consistently, EcELOVL7a overexpression upregulated the transcription level of the key lipid metabolic enzymes, including fatty acid synthase (FASN), phospholipase A 2α (PLA 2α), and cyclooxygenases −2 (COX-2), LPIN1, and diacylglycerol acyltransferase 1α (DGAT1α). Together, our results firstly provided the evidence that fish ELOVL7a played an essential role in SGIV and RGNNV replication by reprogramming lipid metabolism.

The antiviral role of largemouth bass STING against iridovirus infection

Stimulator of interferon gene (STING) plays a crucial role in the innate immune response against viral and bacterial pathogens. However, its function in largemouth bass iridovirus (LMBV) infection remains uncertain. Here, a STING homolog (MsSTING) from largemouth bass (Micropterus salmoides) was cloned and characterized. MsSTING encoded a 407-amino-acid polypeptide, which shared 84.08% and 41.45% identity with golden perch (Perca flavescens) and human (Homo sapiens) homologs, respectively. MsSTING contained four transmembrane domains and a conserved C-terminal domain. The mRNA level of MsSTING was significantly increased in response to LMBV infection in vitro. Subcellular localization observation indicated that MsSTING encoded a cytoplasmic protein, which co-localized predominantly with endoplasmic reticulum (ER) and partially with mitochondria. Moreover, its accurate localization was dependent on the N-terminal transmembrane motif (TM) domains. MsSTING was able to activate interferon (IFN) response, evidenced by the activation of IFN1, IFN3 and ISRE promoters by its overexpression in vitro. Mutant analysis showed that both the N-terminal and C-terminal domain of MsSTING were essential for its activation on IFN response. In addition, overexpression of MsSTING inhibited the transcription and protein levels of viral core genes, indicating that MsSTING exerted antiviral action against LMBV. Consistently, the inhibitory effects were significantly attenuated when the N-terminal or C-terminal domains of MsSTING was deleted. Furthermore, MsSTING overexpression upregulated the transcriptions of interferon-related genes and pro-inflammatory factors, including TANK-binding kinase 1(TBK1), interferon regulatory factor 3 (IRF3), interferon regulatory factor 7 (IRF7), interferon stimulated exonuclease gene 20 (ISG20), interferon-induced transmembrane protein 1(IFITM1), interferon γ (IFN-γ), tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β), and interleukin 6 (IL-6). Together, MsSTING exerted antiviral action upon LMBV infection through positive regulation the innate immune response.

Evaluation of the diagnostic assays detecting red sea bream iridovirus infection at different severity levels

Red sea bream iridovirus (RSIV) is a highly contagious viral infection that affects various fish species and poses a significant threat to the global aquaculture industry. Thus, accurate and timely diagnosis is paramount for sustainable management of fish health. This study rigorously evaluated the diagnostic efficacy of various polymerase chain reaction (PCR) assays, focusing on those recommended by the World Organization for Animal Health (WOAH) and the assays newly proposed by WOAH's Aquatic Animals Health Standards Commission. Specifically, this study assessed conventional PCR, nested PCR, modified 1-F/1-R, and real-time PCR assays using a 95% limit of detection (LoD95%), as well as diagnostic sensitivity (DSe) and specificity (DSp) tests across different RSIV severity grades (G0−G4). In previous studies, the LoD95% for the 1-F/1-R and 4-F/4-R conventional assays were 225.81 and 328.7 copies/reaction, respectively. The modified 1-F/1-R exhibited a lower LoD95% of 51.32 copies/reaction. Notably, the nested PCR had an LoD95% of 11.23 copies/reaction, and the real-time PCR assay had an LoD95% of 12.02 copies/reaction. The DSe varied across RSIV severity grades, especially in the lower G0−G2 grades. The nested PCR and modified 1-F/1-R assays displayed the highest DSe, making them particularly useful for early-stage screening and detection of asymptomatic carriers. In addition, the PCR assays did not cross-react with any other aquatic pathogens except RSIV. Our findings significantly advanced the diagnostic capabilities of RSIVD by suggesting that nested PCR and modified 1-F/1-R assays are particularly promising for early detection. We propose their inclusion in future WOAH guidelines for a more comprehensive diagnostic framework.

Interaction between Sea perch iridovirus (SPIV) infection and gut microbes in sea perch Lateolabrax japonicus

Sea perch iridovirus (SPIV) infection causes severe disease of fish and has led to economic loss of the sea perch Lateolabrax japonicus aquaculture industry. In this study, severe pathological damage of SPIV-infected sea perch was observed; the relationship of SPIV infection, gut microbial community structure, and gut transcripts of sea perch were explored. SPIV infection could inhibit normal immune function of the gut. The expression levels of immune genes such as MHC I, MHC II, TCR, BCR, and IgM were down-regulated during SPIV infection. Intestinal immunosuppression breaks the balance between mucosal immunity and gut microbes. Opportunistic pathogens such as Lawsonella, Corynebacterium, and Achromobacter expanded substantially following SPIV infection. The abundance of potential probiotics in aquatic animals such as Romboutsia declined following SPIV infection. Intestinal microbial lipopolysaccharide biosynthesis and bacterial secretion related functions increased in SPIV infection and correlated with the expression of intestinal lipopolysaccharide binding protein (LBP), TLR5, IL-1β and other genes. These results suggest that gut microbes can stimulate the innate immune system and trigger an acute inflammatory response through LPS. In conclusion, we analyzed the interaction between SPIV infection and gut microbes and provided a basis for further studies on the mechanism of SPIV pathogenesis and treatment.

Dual-specificity phosphatase 1 inhibits Singapore grouper iridovirus replication via regulating apoptosis in Epinephelus coioides

The dual-specificity phosphatase (DUSP) family plays key roles in the maintenance of cellular homeostasis and apoptosis etc. In this study, the DUSP member DUSP1 of Epinephelus coioides was characterized: the length was 2371 bp including 281 bp 5′ UTR, 911 bp 3′ UTR, and a 1125 bp open reading frame encoding 374 amino acids. E. coioides DUSP1 has two conserved domains, a ROHD and DSPc along with a p38 MAPK phosphorylation site, localized at Ser308. E. coioides DUSP1 mRNA can be detected in all of the tissues examined, and the subcellular localization showed that DUSP1 was mainly distributed in the nucleus. Singapore grouper iridovirus (SGIV) infection could induce the differential expression of E. coioides DUSP1. Overexpression of DUSP1 could inhibit SGIV-induced cytopathic effect (CPE), the expressions of SGIV key genes, and the viral titers. Overexpression of DUSP1 could also regulate SGIV-induced apoptosis, and the expression of apoptosis-related factor caspase 3. The results would be helpful to further study the role of DUSP1 in viral infection.

Dissecting the early and late endosomal pathways of Singapore grouper iridovirus by single-particle tracking in living cells

Iridoviruses are large DNA viruses that infect a wide range of invertebrates and lower vertebrates, causing serious threats to ecological security and aquaculture industry worldwide. However, the mechanisms underlying intracellular transport of iridovirus remain unknown. In this study, the transport of Singapore grouper iridovirus (SGIV) in early endosomes (EEs) and late endosomes (LEs) was explored by single-particle tracking technology. SGIV employs EEs to move rapidly from the cell membrane to the nucleus, and this long-range transport is divided into “slow-fast-slow” stages. SGIV within LEs mainly underwent oscillatory movements near the nucleus. Furthermore, SGIV entered newly formed EEs and LEs, respectively, possibly based on the interaction between the viral major capsid protein and Rab5/Rab7. Importantly, interruption of EEs and LEs by the dominant negative mutants of Rab5 and Rab7 significantly inhibited the movement of SGIV, suggesting the important roles of Rab5 and Rab7 in virus transport. In addition, it seems that SGIV needs to enter clathrin-coated vesicles to move from actin to microtubules before EEs carry the virus moving along microtubules. Together, our results for the first time provide a model whereby iridovirus transport depending on EEs and LEs, helping to clarify the mechanism underlying iridovirus infection, and provide a convenient tactic to investigate the dynamic infection of large DNA virus.

Evidence for infection influencing survival of the freshwater copepod Salmincola californiensis, a parasite of Pacific salmon and trout.

We explore apparent infection of Salmincola californiensis arising during investigations involving this lernaeopodid copepod parasitic on Pacific salmon and trout Oncorhynchus spp. We noted occasional unusual coloration of adult female copepods collected from the wild. These females were bright blue and pink in contrast to the cream white coloration characteristic of the copepod. We also observed that similar color patterns developed under laboratory settings when copepod eggs were held for hatching. In paired egg cases, we found consistent hatching failure of blue and pink eggs and patterns in apparent disease development that would be consistent with both vertical and horizontal transmission. Attempts to identify the cause of the apparent infection using genetic methods and transmission electron microscopy were inconclusive. Iridovirus infection was initially suspected, but bacterial infection is also plausible. This apparent reduced hatching success of S. californiensis warrants further exploration as it could reduce local abundances. Given the potential importance of a disease impacting this copepod, a parasite that itself affects endangered and commercially important Pacific salmon and trout, future research would benefit from clarification of the apparent infection through additional sequencing, primer development, visualization, and exploration into specificity and transmission.

Antiviral Effect and Mechanism of Edaravone against Grouper Iridovirus Infection.

Singapore grouper iridovirus (SGIV) is a virus with high fatality rate in the grouper culture industry. The outbreak of SGIV is often accompanied by a large number of grouper deaths, which has a great impact on the economy. Therefore, it is of great significance to find effective drugs against SGIV. It has been reported that edaravone is a broad-spectrum antiviral drug, most widely used clinically in recent years, but no report has been found exploring the effect of edaravone on SGIV infections. In this study, we evaluated the antiviral effect of edaravone against SGIV, and the anti-SGIV mechanism of edaravone was also explored. It was found that the safe concentration of edaravone on grouper spleen (GS) cells was 50 µg/mL, and it possessed antiviral activity against SGIV infection in a dose-dependent manner. Furthermore, edaravone could significantly disrupt SGIV particles and interference with SGIV binding to host cells, as well as SGIV replication in host cells. However, edaravone was not effective during the SGIV invasion into host cells. This study was the first time that it was determined that edaravone could exert antiviral effects in response to SGIV infection by directly interfering with the processes of SGIV infecting cells, aiming to provide a theoretical basis for the control of grouper virus disease.

Identification of circRNAs and circRNA-mRNA network of Epinephelus coioides during Singapore grouper iridovirus infection

Circular RNA (circRNA), one of the important non-coding RNA molecules with a closed-loop structure, plays a key regulatory role in cell processing. In this study, circRNAs of Epinephelus coioides, an important marine cultured fish in China, were isolated and characterized, and the network of circRNAs and mRNA was explored during Singapore grouper iridovirus (SGIV) infection, one of the most important double stranded DNA virus pathogens of marine fish. 10 g of raw data was obtained by high-throughput sequencing, and 2599 circRNAs were classified. During SGIV infection, 123 and 37 circRNAs occurred differential expression in spleen and spleen cells, indicating that circRNAs would be involved in the viral infection. GO annotation and KEGG demonstrated that circRNAs could target E. coioides genes to regulate cell activity and the activation of immune factors. The results provide some insights into the circRNAs mediated immune regulatory network during bony fish virus infection.

Molecular and functional characterization of viperin in golden pompano, Trachinotus ovatus

The radical S-adenosyl methionine domain-containing protein 2 (RSAD2), also known as viperin, plays a momentous and multifaceted role in antiviral immunity. However, the function of viperin is uninvestigated in golden pompano, Trachinotus ovatus. In the present study, a viperin homolog, named To-viperin, was cloned and characterized from golden pompano, and its role in response to grouper iridovirus (SGIV) and nervous necrosis virus (NNV) infection was investigated. The whole open reading frame (ORF) of To-viperin was composed of 1050 bp and encoded a polypeptide of 349 amino acids with 70.66%–83.51% identity with the known viperin homologs from other fish species. A variable N-terminal domain, a highly conserved C-terminal domain, and a conserved middle radical SAM domain (aa 61–271) with the three-cysteine motif CxxCxxC was found in To-viperin sequence. Expression analysis showed that To-viperin was constitutively expressed in all tested organs and was located mainly in the ER of golden pompano cells. Treatments with SGIV, poly I: C, or NNV could induce the up-regulation of viperin to varying degrees. The ectopic expression of To-viperin in vitro significantly reduced the viral titer of SGIV and NNV. Furthermore, To-viperin overexpression enhanced the expression of IFNc, IRF3, and ISG15 genes as well as, to a lesser extent, the IL-6 gene. In summary, our results suggested that the function of viperin is likely to be conserved in fish specise, as observed in other vertebrates, shedding light on the evolutionary conservation of viperin.

Grouper Atg14 promotes Singapore grouper iridovirus (SGIV) replication by inhibiting the host innate immune response

As one of the important members of the autophagy-related protein family, Atg14 plays a key role in the formation and maturation of autophagosomes. However, little is known about the potential roles of fish Atg14 and its roles in virus infection. In the present study, the homolog of Atg14 (EcAtg14) from the orange-spotted grouper (Epinephelus coioides) was cloned and characterized. The open reading frame (ORF) of EcAtg14 consists of 1530 nucleotides, encoding 509 amino acids, with a predicted molecular weight of 56.9 kDa. EcAtg14 was distributed in all tested tissues, with higher expression in liver, blood and spleen. The expression of EcAtg14 was increased in grouper spleen (GS) cells after Singapore grouper iridovirus (SGIV) infection. EcAtg14 was distributed in the cytoplasm of GS cells. Overexpression of EcAtg14 promoted SGIV replication in GS cells and inhibited IFN3, ISRE and NF-κB promoter activities. Co-immunoprecipitation results showed that there was an interaction between EcAtg14 and EcBeclin. EcAtg14 also promoted the synthesis of LC3-II in GS cells. These findings provide a basis for understanding the innate immune mechanism of grouper against viral infection.

Components of the Nucleotide Salvage Pathway Increase Frog Virus 3 (FV3) Replication.

Viruses are obligate intracellular parasites that alter host metabolic machinery to obtain energy and macromolecules that are pivotal for replication. Ranavirus, including the type species of the genus frog virus 3 (FV3), represent an ecologically important group of viruses that infect fish, amphibians, and reptiles. It was established that fatty acid synthesis, glucose, and glutamine metabolism exert roles during iridovirus infections; however, no information exists regarding the role of purine metabolism. In this study, we assessed the impact of exogenously applied purines adenine, adenosine, adenosine 5'-monophosphate (AMP), inosine 5'-monophosphate (IMP), inosine, S-adenosyl-L-homocysteine (SAH), and S-adenosyl-L-methionine (SAM) on FV3 replication. We found that all compounds except for SAH increased FV3 replication in a dose-dependent manner. Of the purines investigated, adenine and adenosine produced the most robust response, increasing FV3 replication by 58% and 51%, respectively. While all compounds except SAH increased FV3 replication, only adenine increased plaque area. This suggests that the stimulatory effect of adenine on FV3 replication is mediated by a mechanism that is at least in part independent from the other compounds investigated. Our results are the first to report a response to exogenously applied purines and may provide insight into the importance of purine metabolism during iridoviral infection.

Oral immunizations with Bacillus subtilis spores displaying VP19 protein provide protection against Singapore grouper iridovirus (SGIV) infection in grouper.

Disease caused by Singapore grouper iridovirus (SGIV) results in major economic losses in the global grouper aquaculture industry. Vaccination is considered to be the most effective way to protect grouper from SGIV. In this study, the spores of Bacillus subtilis (B.subtilis) WB600 were utilized as the vehicle that the VP19 protein was displayed on the spores surface. To further investigate the effect of oral vaccination, the grouper were orally immunized with B.s-CotC-19 spores. After challenged, the survival rate of grouper orally vaccinated with B.s-CotC-19 spores was 34.5% and the relative percent survival (RPS) was 28.7% compared to the PBS group. Moreover, the viral load in the tissues of the B.s-CotC-19 group was significantly lower than that of the PBS group. The histopathological sections of head kidney and liver tissue from the B.s-CotC-19 group showed significantly less histopathology compared to the PBS group. In addition, the specific IgM levels in serum in the B.s-CotC-19 group was higher than those in the PBS group. In the hindgut tissue, the immune-related gene expression detected by quantitative real-time PCR (qRT-PCR) exhibited an increasing trend in different degrees in the B.s-CotC-19 group, suggesting that the innate and adaptive immune responses were activated. These results indicated that the oral administration of recombinant B.subtilis spores was effective for preventing SGIV infection. This study provided a feasible strategy for the controlling of fish virus diseases.

Megalocytivirus and Other Members of the Family Iridoviridae in Finfish: A Review of the Etiology, Epidemiology, Diagnosis, Prevention and Control.

Aquaculture has expanded to become the fastest growing food-producing sector in the world. However, its expansion has come under threat due to an increase in diseases caused by pathogens such as iridoviruses commonly found in aquatic environments used for fish farming. Of the seven members belonging to the family Iridoviridae, the three genera causing diseases in fish comprise ranaviruses, lymphocystiviruses and megalocytiviruses. These three genera are serious impediments to the expansion of global aquaculture because of their tropism for a wide range of farmed-fish species in which they cause high mortality. As economic losses caused by these iridoviruses in aquaculture continue to rise, the urgent need for effective control strategies increases. As a consequence, these viruses have attracted a lot of research interest in recent years. The functional role of some of the genes that form the structure of iridoviruses has not been elucidated. There is a lack of information on the predisposing factors leading to iridovirus infections in fish, an absence of information on the risk factors leading to disease outbreaks, and a lack of data on the chemical and physical properties of iridoviruses needed for the implementation of biosecurity control measures. Thus, the synopsis put forth herein provides an update of knowledge gathered from studies carried out so far aimed at addressing the aforesaid informational gaps. In summary, this review provides an update on the etiology of different iridoviruses infecting finfish and epidemiological factors leading to the occurrence of disease outbreaks. In addition, the review provides an update on the cell lines developed for virus isolation and culture, the diagnostic tools used for virus detection and characterization, the current advances in vaccine development and the use of biosecurity in the control of iridoviruses in aquaculture. Overall, we envision that the information put forth in this review will contribute to developing effective control strategies against iridovirus infections in aquaculture.