Search Results (82)

We performed a diagnostic disease investigation on a wild smallmouth bass (Micropterus dolomieu) with skin ulcers that was collected from Lake Oahe, South Dakota, following reports from anglers of multiple fish with similar lesions. Gross and histologic lesions of ulcerative dermatitis, myositis, and lymphocytolysis within the spleen and kidneys were consistent with largemouth bass virus (LMBV) infection. LMBV was detected by conventional PCR in samples of a skin ulcer, and the complete genome sequence of the LMBV (99,184 bp) was determined from a virus isolate obtained from a homogenized skin sample. A maximum likelihood (ML) phylogenetic analysis based on the major capsid protein (MCP) gene alignment supported the LMBV isolate (LMBV-SD-2023) as a member of the species Ranavirus micropterus1, branching within the subclade of LMBV isolates recovered from North American largemouth (Micropterus salmoides) and smallmouth bass. This is the first detection of LMBV in wild smallmouth bass from South Dakota. The ultrastructure of the LMBV isolate exhibited the expected icosahedral shape of virions budding from cellular membranes. Viral nucleic acid in infected cells was visualized via in situ hybridization (ISH) within dermal granulomas, localized predominantly at the margin of epithelioid macrophages and central necrosis. Further sampling is needed to determine the geographic distribution, affected populations, and evolutionary relationship between isolates of LMBV. Full article

Red sea bream iridovirus is a serious threat to farmed fish, but little is known about how repeated freezing and thawing affect its stability. This study investigated the effects of repeated freeze–thaw cycles on RSIV infectivity by comparing quantitative polymerase chain reaction (qPCR), viability qPCR (vqPCR), and 50% tissue culture infectious dose (TCID₅₀) assays. While qPCR detected high amounts of viral DNA after multiple cycles, both viability qPCR and TCID₅₀ revealed a significant loss of infectivity unless serum was present. Correlation analysis showed a high degree of agreement between vqPCR and TCID₅₀, indicating their high compatibility for assessing viral infectivity. However, the correlations between qPCR and vqPCR, as well as between qPCR and TCID₅₀, were significantly lower, suggesting that qPCR alone may overestimate viral infectivity by detecting non-infectious viral DNA. These results demonstrate the critical role of serum in preserving RSIV infectivity and highlight the superior accuracy of vqPCR and TCID₅₀ in assessing viral infectivity compared with qPCR. This study emphasizes the importance of serum in storage media and suggests that combining vqPCR with TCID₅₀ is a more reliable measure of RSIV infectivity than qPCR alone. Full article

Large yellow croaker iridovirus (LYCIV) poses a significant threat to the large yellow croaker (Larimichthys crocea) aquaculture industry due to its rapid transmission and high lethality. Galectins, as evolutionarily conserved carbohydrate-binding lectins and pattern recognition receptors (PRRs) in the innate immune system, play crucial roles in immune responses. In this study, we characterized the beta-galactoside-binding lectin from large yellow croaker (LcβLectin) and explored its potential as a disease resistance gene against LYCIV. The full-length cDNA of LcβLectin was cloned and found to contain conserved elements, such as β-galactoside-binding motifs, HNPR, and WCEEHR domains. Using L. crocea head-kidney macrophages (LCM10), we demonstrated that recombinant LcβLectin significantly inhibits LYCIV-induced cytopathic effects and reduces macrophage apoptosis, highlighting its key role in viral defense. Moreover, the overexpression of LcβLectin in LCM10 cells followed by transcriptomic analysis revealed its substantial regulatory effects on key immune-related signaling pathways, including C-type lectin signaling, p53 signaling, and Toll-like receptor signaling pathways. Collectively, our findings suggest that LcβLectin enhances fish resistance to viral diseases by augmenting immune system function and activating immune-related pathways, providing valuable insights into the innate immune mechanisms of aquatic species and potential strategies for disease prevention in aquaculture. Full article

Commercial cricket production has been plagued by viral disease outbreaks that have decimated their potential outputs and profit margins. To date, no epidemiological studies have been performed to estimate the prevalence of major viruses affecting crickets raised in commercial settings. A cross-sectional study was performed to estimate the prevalence of three important viruses (Acheta domesticus densovirus [AdDV], Acheta domesticus volvovirus [AdVVV], and invertebrate iridovirus 6 [CrIV]). Samples were collected across age groups (2-, 4-, and 6-week-olds) and seasons (January, May, August, and October) to determine the effect that these variables had on the prevalence rates. Quantitative real-time PCR was performed and revealed the following high overall prevalence rates: 46.7, 100, and 100% for AdDV, AdVVV, and CrIV, respectively. Viral loads varied from 10^1–5 for AdDV, 10^2–7 for AdVVV, and 10^2–9 for CrIV. AdDV prevalence rates were statistically significant across age and season (age: χ² = 8.3, p = 0.015; season: χ² = 59.7, p < 0.001), with crickets more likely to be infected as they aged and during the colder winter months. CrIV followed similar trends when looking at changes in viral loads between ages and seasons. AdVVV experienced a spike in viral loads across all ages during the month of August. Understanding the epidemiology of these viruses is instrumental in determining best management practices for commercially raised crickets. Full article

Mandarin fish ranavirus (MRV) is a distinctive member among the genus Ranavirus of the family Iridoviridae. The persistently covert infection of MRV was previously observed in a natural outbreak of MRV, but the underlying mechanism remains unclear. Here, we show that mandarin fish peripheral B lymphocytes are implemented as viral reservoirs to maintain the persistent infection. When mandarin fish were infected with a sublethal dosage of MRV under a nonpermissive temperature (19 °C) and a permissive temperature (26 °C), all of the fish in the 19 °C group survived and entered the persistent phase of infection, characterized by a very low viral load in white blood cells, whereas some of the fish died of MRV infection in the 26 °C group, and the survival fish then initiated a persistent infection status. Raising the temperature, vaccination and dexamethasone treatment can reactivate the quiescent MRV to replicate and result in partial mortality. The viral reservoir investigation showed that IgM⁺-labeled B lymphocytes, but not CD3Δ⁺-labeled T lymphocytes and MRC-1⁺-labeled macrophages, are target cells for the persistent infection of MRV. Moreover, the reactivation of the quiescent MRV was confirmed through a non-TLR5 signal pathway manner. Collectively, we demonstrate the presence of the B cell-dependent persistent infection of ranavirus, and provide a new clue for better understanding the complex infection mechanism of vertebrate iridovirus. Full article

The threespine stickleback iridovirus (TSIV), a double-stranded DNA virus, was the first megalocytivirus detected in wild North American fishes. We report a second occurrence of TSIV in threespine stickleback (Gasterosteus aculeatus) from Stormy Lake, Alaska, and assemble a nearly complete genome of TSIV. The 115-kilobase TSIV genome contains 94 open reading frames (ORFs), with 91 that share homology with other known iridoviruses. We identify three ORFs that likely originate from recent lateral gene transfers from a eukaryotic host and one ORF with homology to B22 poxvirus proteins that likely originated from a lateral gene transfer between viruses. Phylogenetic analysis of 24 iridovirus core genes and pairwise sequence identity analysis support TSIV as a divergent sister taxon to other megalocytiviruses and a candidate for a novel species designation. Screening of stickleback collected from Stormy Lake before and after a 2012 rotenone treatment to eliminate invasive fish shows 100% positivity for TSIV in the two years before treatment (95% confidence interval: 89–100% prevalence) and 0% positivity for TSIV in 2024 after treatment (95% confidence interval: 0 to 3.7% prevalence), suggesting that the rotenone treatment and subsequent crash and reestablishment of the stickleback population is associated with loss of TSIV. Full article

Lateolabrax maculatus iridovirus (LMIV) is a variant strain of red sea bream iridovirus (RSIV), causing serious economic losses in aquaculture. Claudins (CLDNs) are major components of tight junctions (TJs) forming an important line of defense against pathogens. Our pilot miRNA-mRNA joint analysis indicated the degradation of CLDN3, as well as its interaction with miR-181a during LMIV infection. To elucidate the miR-181a/CLDN3/LMIV interactions, in vitro assays were carried out on LMB-L cells. We first confirmed that LMIV infection could decrease the expression of CLDN3, accompanied by the enhancement of permeability, suggesting the dysfunction of TJs. Contrary to the inhibition of CLDN3, the activation of miR-181a was proved, presenting a negative correlation between miR-181a and CLDN3 (Pearson r = −0.773 and p < 0.01). In addition, the influence of CLDN3 on LMIV replication was analyzed by knockdown and over-expression of CLDN3. When CLDN3 was silenced in LMB-L cells with siCLDN3-623 at 9 days post transfection (dpt), LMIV copies and titers were significantly up-regulated by 1.59-fold and 13.87-fold, respectively. By contrast, LMIV replication in LMB-L cells was reduced by 60% and 71%, post transfection with pcDNA3.1-CLDN3 over-expressed plasmid at 6 dpt and 9 dpt, respectively. Ultimately, the regulatory relationship between miR-181a and CLDN3 was further validated by dual luciferase reporter assays. Taking into account the above-described results, we proposed a “miR-181a/CLDN3/LMIV” regulatory relationship. This study provides a new insight for understanding the mechanism of LMIV replication. Full article

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. Full article

Haploid embryonic stem cells (ESCs), which combine the properties of haploidy and pluripotency, hold significant potential for advancing developmental biology and reproductive technology. However, while previous research has largely focused on haploid ESCs in freshwater species like Japanese medaka (Oryzias latipes), little is known about their counterparts in marine species. This study hypothesizes that haploid ESCs from marine fish could offer unique insights and tools for genetic and virological research. To address this, we successfully established and characterized a novel haploid ESC line, hMMES1, derived from marine medaka (Oryzias melastigma). The hMMES1 cells contain 24 chromosomes, exhibit core stem cell characteristics, and express key pluripotency markers. In vitro, hMMES1 cells form embryonic bodies (EBs) capable of differentiating into the three germ layers. In vivo, hMMES1 cells were successfully transplanted into marine medaka and zebrafish, resulting in the generation of interspecies and interordinal chimeras. Additionally, hMMES1 cells demonstrate high efficiency in transfection and transduction, and show susceptibility to major aquaculture viruses, nodavirus (NNV) and iridovirus (SGIV). These findings suggest that hMMES1 cells represent a valuable model for genetic manipulation and virological studies in marine fish species. Full article

The largemouth bass is a freshwater aquacultured fish species of great economic importance in China. With the rapid development of aquaculture industry and the increase in the aquaculture density of the fish, various infectious pathogens, including parasites, bacteria, and viruses, have been widely spread, which have caused huge losses to the aquaculture industry. Among them, largemouth bass iridovirus (LMBV) is one of the most harmful pathogens. In the present study, a virus strain named LMBV-GDSD was isolated from cultured largemouth bass and was successfully proliferated in FHM and EPC cells, with numerous viral particles observed in the infected cells under transmission electron microscopy analysis. The annotated complete genome of LMBV-GDSD was 99,285 bp and contained 102 ORFs. Based on genomic sequence alignment and phylogenetic analysis, the identified LMBV-GDSD belonged to the genus Ranavirus of Iridoviridae and was pathogenic to largemouth bass under regression infection experiments. In addition, the infection of LMBV-GDSD in largemouth bass could significantly up-regulate the expression of antiviral immune-related genes such as IRF3, IRF7, and Mx. It is thus providing valuable genetic data for a deeper understanding of the pathogenic mechanism of iridovirus in largemouth bass. Full article

Red seabream iridovirus (RSIV) is a major cause of marine fish mortality in Korea, with no effective vaccine available since its first occurrence in the 1990s. This study evaluated the efficacy of a formalin-killed vaccine against RSIV in rock bream under laboratory and field conditions. For the field trial, a total of 103,200 rock bream from two commercial marine cage-cultured farms in Southern Korea were vaccinated. Farm A vaccinated 31,100 fish in July 2020 and monitored them for 18 weeks, while farm B vaccinated 30,700 fish in August 2020 and monitored them for 12 weeks. At farm A, where there was no RSIV infection, the vaccine efficacy was assessed in the lab, showing a relative percentage of survival (RPS) ranging from 40% to 80%. At farm B, where natural RSIV infections occurred, cumulative mortality rates were 36.43% in the vaccinated group and 80.32% in the control group, resulting in an RPS of 54.67%. The RSIV-infectious status and neutralizing antibody titers in serum mirrored the cumulative mortality results. This study demonstrates that the formalin-killed vaccine effectively prevents RSIV in cage-cultured rock bream under both laboratory and field conditions. Full article

Groupers are valuable economic fish in the southern sea area of China, but the threat of disease is becoming more and more serious. Vibrio harveyi, V. parahaemolyticus, and Singapore grouper iridovirus (SGIV) are three important pathogens that cause disease in groupers, and infection with either a single one or a mix of these pathogens poses a serious threat to the healthy development of grouper culture. To enhance the rapid diagnosis and screening in the early stages, it is necessary to develop rapid detection methods of these pathogens. To simultaneously and rapidly detect the three pathogens, in this study, we utilized the TolC of V. harveyi, DNAJ of V. parahaemolyticus, and RAD2 of SGIV as the target genes and established a triple visual loop-mediated isothermal amplification (LAMP) method. This LAMP method showed a detection time as fast as 30 min and a high sensitivity of 100 fg/μL. Moreover, this method exhibited strong specificity and no cross-reaction with seven types of Vibrio and Staphylococcus aureus, as well as five common viruses in aquatic animals. Then, the LAMP products were enzymically cut, and three characteristic strips were used to identify the pathogen species. The results of the clinical trials demonstrated that the method could accurately and specifically detect V. harveyi, V. parahaemolyticus, and SGIV in grouper tissues. In summary, this study successfully established a triple visual LAMP rapid detection method for V. harveyi, V. parahaemolyticus, and SGIV. The method offers several advantages including simple equipment, easy operation, rapid reaction, high specificity, high sensitivity, and visual results. It is suitable for the early and rapid diagnosis of groupers infected with V. harveyi, V. parahaemolyticus, and SGIV, thereby providing useful technical support for further application in the large-scale disease surveillance of aquaculture animals. Full article

In September 2021, 14 smallmouth bass (SMB; Micropterus dolomieu) with skin lesions were collected from Green Bay waters of Lake Michigan and submitted for diagnostic evaluation. All the skin samples tested positive for largemouth bass virus (LMBV) by conventional PCR. The complete genome of the LMBV (99,328 bp) isolated from a homogenized skin sample was determined using an Illumina MiSeq sequencer. A maximum likelihood (ML) phylogenetic analysis based on the 21 core iridovirus genes supported the LMBV isolated from SMB (LMBV-WVL21117) as a member of the species Santee-Cooper ranavirus. Pairwise nucleotide comparison of the major capsid protein (MCP) gene showed that LMBV-WVL21117 is identical to other LMBV reported from the United States and nearly identical to doctor fish virus and guppy virus 6 (99.2%) from Southeast Asia, as well as LMBV isolates from China and Thailand (99.1%). In addition, ML phylogenetic analysis based on the MCP gene suggests three genotypes of LMBV separated by region: genotype one from the United States, genotype two from Southeast Asia, and genotype three from China and Thailand. Additional research is needed to understand the prevalence and genetic diversity of LMBV strains circulating in wild and managed fish populations from different regions. Full article

Frog virus 3 (FV3) in the genus Ranavirus of the family Iridoviridae causes mass mortality in both anurans and urodeles worldwide; however, the phylogenetic origin of FV3-like ranaviruses is not well established. In Asia, three FV3-like ranaviruses have been reported in farmed populations of amphibians and reptiles. Here, we report the first case of endemic FV3-like ranavirus infections in the Korean clawed salamander Onychodactylus koreanus, caught in wild mountain streams in the Republic of Korea (ROK), through whole-genome sequencing and phylogenetic analysis. Two isolated FV3-like ranaviruses (Onychodactylus koreanus ranavirus, OKRV1 and 2) showed high similarity with the Rana grylio virus (RGV, 91.5%) and Rana nigromaculata ranavirus (RNRV, 92.2%) but relatively low similarity with the soft-shelled turtle iridovirus (STIV, 84.2%) in open reading frame (ORF) comparisons. OKRV1 and 2 formed a monophyletic clade with previously known Asian FV3-like ranaviruses, a sister group of the New World FV3-like ranavirus clade. Our results suggest that OKRV1 and 2 are FV3-like ranaviruses endemic to the ROK, and RGV and RNRV might also be endemic strains in China, unlike previous speculation. Our data have great implications for the study of the phylogeny and spreading routes of FV3-like ranaviruses and suggest the need for additional detection and analysis of FV3-like ranaviruses in wild populations in Asian countries. Full article

Sturgeon farming is rapidly expanding in Europe, where Italy ranks first in farmed caviar production. A major threat to sturgeon health in captivity is infection with Acipenser European Iridovirus (AcIV-E), a viral disease definitively identified in 2016. Here we present data on the occurrence of AcIV-E in 482 sturgeons (age ≤ 12 months, species of the genus Acipenser and the species Huso huso) collected from sturgeon farms in northern Italy between January 2021 and December 2023. The health status of each specimen was determined by necroscopy and virological assay. Virological analysis was performed on gill samples and real-time PCR specific to the MCP gene of the iridovirus viral capsid. Molecular analysis revealed positivity to the virus in 204 samples (42.68% of the total), while anatomopathological examination of nearly all fish with positive real-time PCR disclosed swollen abdomen, hepatic steatosis, splenomegaly, and increased gill volume. Two challenges to timely diagnosis are the absence of pathognomonic symptoms and the inability to isolate the virus on cell monolayers. Continuous and widespread health monitoring is therefore crucial for disease management and to effectively control spread of the virus. Full article