Antiviral Activity of Ribavirin against Tilapia tilapinevirus in Fish Cells

A New Cell Line from the Brain of Red Hybrid Tilapia (Oreochromis spp.) for Tilapia Lake Virus Propagation

Tilapia lake virus (TiLV) presents a substantial threat to global tilapia production. Despite the development of numerous cell lines for TiLV isolation and propagation, none have been specifically derived from red hybrid tilapia (Oreochromis spp.). In this study, we successfully established a new cell line, RHTiB, from the red hybrid tilapia brain. RHTiB cells were cultured for 1.5 years through over 50 passages and demonstrated optimal growth at 25 °C in Leibovitz-15 medium supplemented with 10% fetal bovine serum at pH 7.4. Morphologically, RHTiB cells displayed a fibroblast-like appearance, and cytochrome oxidase I gene sequencing confirmed their origin from Oreochromis spp. Mycoplasma contamination testing yielded negative results. The revival rate of the cells post-cryopreservation was observed to be between 75 and 80% after 30 days. Chromosomal analysis at the 25th passage revealed a diploid count of 22 pairs (2n = 44). While no visible cytopathic effects were observed, both immunofluorescence microscopy and RT-qPCR analysis demonstrated successful TiLV propagation in the RHTiB cell line, with a maximum TiLV concentration of 107.82 ± 0.22 viral copies/400 ng cDNA after 9 days of incubation. The establishment of this species-specific cell line represents a valuable advancement in the diagnostic and isolation tools for viral diseases potentially impacting red hybrid tilapia.

Effects on viral suppression and the early-immune expression of ribavirin against spring viremia of carp virus in vitro

Spring viremia of carp virus (SVCV) is a globally distributed virus that causes severe clinical symptoms and high mortality in fish belonging to the families Cyprinidae and Siluridae. To protect the host against viral infection, understanding the relatedness between viral susceptibility and antiviral mechanisms must be crucial. Thus, we evaluated the viral suppression efficacy of ribavirin by measuring the transcription levels of viral and immune genes in vitro. The results showed that following ribavirin treatment after SVCV infection (MOI 0.1), ribavirin inhibited SVCV replication in epithelioma papulosum cyprini (EPC) cells and completely inhibited viral gene (G and N) expression at concentrations above 10 μg/mL at 48 h post-infection. Ribavirin does not directly damage SVCV particles but inhibits early viral replication. In the absence of SVCV infection, the immunological dynamics triggered by ribavirin resulted in upregulated pattern recognition receptors and proinflammatory cytokine-related genes (i.e., PI3K, MYD88, IRAK1, RIG-І, MAVS, Mx1, TNF-α, and NF-κB). Furthermore, EPC cells treated with ribavirin following SVCV infection showed upregulation of PI3K, MYD88, IRAK1, RIG-І, TNF-α, and NF-κB genes within 24 h post-SVCV infection, suggesting that ribavirin positively inhibits the SVCV infection in vitro.

Structural and functional analysis of the minimal orthomyxovirus-like polymerase of Tilapia Lake Virus from the highly diverged Amnoonviridae family

Tilapia Lake Virus (TiLV), a recently discovered pathogen of tilapia fish, belongs to the Amnoonviridae family from the Articulavirales order. Its ten genome segments have characteristic conserved ends and encode proteins with no known homologues, apart from the segment 1, which encodes an orthomyxo-like RNA-dependent-RNA polymerase core subunit. Here we show that segments 1-3 encode respectively the PB1, PB2 and PA-like subunits of an active heterotrimeric polymerase that maintains all domains found in the distantly related influenza polymerase, despite an unprecedented overall size reduction of 40%. Multiple high-resolution cryo-EM structures of TiLV polymerase in pre-initiation, initiation and active elongation states, show how it binds the vRNA and cRNA promoters and performs RNA synthesis, with both transcriptase and replicase configurations being characterised. However, the highly truncated endonuclease-like domain appears inactive and the putative cap-binding domain is autoinhibited, emphasising that many functional aspects of TiLV polymerase remain to be elucidated.

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.

Tilapia lake virus causes mitochondrial damage: a proposed mechanism that leads to extensive death in fish cells

Background

Tilapia lake virus (TiLV), also known as Tilapinevirus tilapiae, poses a significant threat to tilapia aquaculture, causing extensive mortality and economic losses. Understanding the mechanisms and pathogenesis of TiLV is crucial to mitigate its impact on this valuable fish species.

Methodology

In this study, we utilized transmission electron microscopy to investigate the ultrastructural changes in E-11 cells following TiLV infection. We also examined the presence of TiLV particles within the cells. Cellular viability and mitochondrial functions were assessed using MTT and ATP measurement assays and mitochondrial probes including JC-1 staining and MitoTracker™ Red.

Results

Our findings provide novel evidence demonstrating that TiLV causes cytotoxicity through the destruction of mitochondria. Transmission electron micrographs showed that TiLV particles were present in the cytoplasm of E-11 cells as early as 1 h after infection. Progressive swelling of mitochondria and ultrastructural damage to the cells were observed at 1, 3 and 6 days post-infection. Furthermore, losses of mitochondrial mass and membrane potential (MMP) were detected at 1 day after TiLV inoculation, as determined by mitochondrial probes. The results of the MTT assay also supported the hypothesis that the cell deaths in E-11 cells during TiLV infection may be caused by the disruption of mitochondrial structure and function.

Conclusions

Our study reveals the significant role of mitochondrial disruption in contributing to cellular death during the early stages of TiLV infection. These findings advance the understanding of TiLV pathogenesis and further enhance our knowledge of viral diseases in fish.

The Modulation of Immune Responses in Tilapinevirus tilapiae-Infected Fish Cells through MAPK/ERK Signalling

Tilapia lake virus (TiLV) is a novel RNA virus that has been causing substantial economic losses across the global tilapia industry. Despite extensive research on potential vaccines and disease control methods, the understanding of this viral infection and the associated host cell responses remains incomplete. In this study, the involvement of the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway in the early stages of TiLV infection was investigated. The results showed a distinct pattern of ERK phosphorylation (p-ERK) upon TiLV infection in two fish cell lines, E-11 and TiB. Specifically, the p-ERK levels in the TiB cells decreased substantially, while the p-ERK levels in the E-11 cells remained constant. Interestingly, a large number of cytopathic effects were observed in the infected E-11 cells but none in the infected TiB cells. Furthermore, when p-ERK was suppressed using the inhibitor PD0325901, a significant reduction in the TiLV load and decrease in the mx and rsad2 gene expression levels were observed in the TiB cells in days 1–7 following infection. These findings highlight the role of the MAPK/ERK signalling pathway and provide new insights into the cellular mechanisms during TiLV infection that could be useful in developing new strategies to control this virus.

In vitro and in vivo evaluation of the antiviral activity of arctigenin, ribavirin, and ivermectin against viral hemorrhagic septicemia virus infection

Viral hemorrhagic septicemia virus (VHSV) causes a severe and often lethal infection in olive flounder (Paralichthys olivaceus) in Korea, resulting in mass mortality and substantial economic loss. As a potential prevention strategy for infectious viral diseases, this study aimed to evaluate the antiviral activity of three compounds (arctigenin [ARG], ribavirin [RBV], and ivermectin [IVM]) against VHSV infection in vitro and in vivo. In epithelioma papulosum cyprini cells, the expression of both VHSV glycoprotein (G) and nucleoprotein (N) genes were significantly suppressed by the three compounds in a dose-dependent manner (P < 0.05). Also, cell morphology and viability were maintained at the following concentrations: ARG 1.5 mg/L, RBV 2.5 mg/L, and IVM 10 mg/L. The fish that were treated with RBV (8.33 mg/kg) and IVM (0.25 mg/kg) before VHSV infection and those treated with IVM (0.25 mg/kg) after VHSV infection showed significant improvements in the survival rate, a reduction in the viral shedding rate, and downregulation of viral gene expression compared to those seen in fish with naïve VHSV infections. Furthermore, among the innate immune genes studied, persistent expression of Mx and upregulation of tumor necrosis factor-α gene expression in VHSV-infected fish treated with RBV and IVM revealed that these compounds might induce an immunostimulatory effect as one of their antiviral activities. Overall, this study supports the use of RBV and IVM as antiviral agents to control VHSV infections in olive flounder.