White spot syndrome virus envelope protein VP28 is involved in the systemic infection of shrimp

Recombinant snakehead rhabdovirus-mediated expression of white spot syndrome virus (WSSV) VP28 confers protection against WSSV in Penaeus vannamei

White spot syndrome virus (WSSV) is a major pathogen responsible for significant economic losses in global shrimp aquaculture. In this study, we developed a recombinant snakehead rhabdovirus (rSHRV) expressing the WSSV VP28 envelope protein (designated rSHRV-AVP28) and evaluated its potential as a vaccine candidate for Penaeus vannamei. The VP28 gene was successfully inserted between the N and P genes of the SHRV genome, and the rescued virus demonstrated plaque formation and intracellular VP28 expression, although the antigen was not incorporated into viral particles. Vaccination with rSHRV-AVP28 significantly reduced cumulative mortality to ∼30 % upon WSSV challenge, compared to 100 % mortality in both buffer- and vector-control groups. Quantitative PCR revealed a 10,000-fold reduction in WSSV viral load in the rSHRV-AVP28 group, with surviving shrimp exhibiting viral titers below 104 copies/mg of muscle tissue. These results demonstrate that rSHRV-AVP28 effectively induces protective immunity in shrimp, highlighting the potential of rhabdovirus-based vectors as novel delivery platforms for crustacean vaccines.

Viral circular RNA-encoded protein, ceVP28, divulges an antiviral response in invertebrates

Invertebrates mostly use innate immunity to counteract pathogenic infections. In this study, shrimp was used as a model organism to explore the functions of circular RNAs (circRNAs) derived from white spot syndrome virus (WSSV). We identified four viral circRNAs, termed circWSSV147, circWSSV326, circWSSV458, and circVP28, from transcriptomic data of WSSV-infected shrimp. CircVP28, which contains an internal ribosome entry site, was further characterized to determine its potential as a template for protein translation. We observed the presence of a truncated, circRNA-encoded VP28 (ceVP28) in infected shrimp. Both ceVP28 and its parental counterpart, VP28, share the same host cell binding partner Rab7, which is a host receptor for WSSV. Coadministration of recombinant ceVP28 protein and WSSV to penaeid shrimps reduced both viral copy numbers and mortality upon WSSV challenges. These findings uncovered a host defense mechanism by which a protein encoded by a viral circRNA modulates virus-receptor interactions, resulting in blocking of viral entry.

Newly developed mRNA vaccines induce immune responses in Litopenaeus vannamei shrimps during primary vaccination

White spot syndrome virus (WSSV) causes highly destructive infection in crustacean aquaculture, often resulting in 100% mortality within a week. However, there is lack of studies addressing the safety issues of WSSV vaccines in shrimps. In this study, WSSV VP28 mRNA vaccines were developed using codon deoptimization approach. These vaccines were administered to Litopenaeus vannamei shrimps at various dosages to access their safety and the shrimps' immune responses using quantification PCR (qPCR). The findings of this study indicate that the expression level of codon deoptimized VP28 mRNA vaccines are lower compared to the wild type VP28 vaccines, as observed through a comparison of bioinformatic predictions and experimental results. Additionally, the total haemocyte count (THC) in shrimps injected with codon deoptimized VP28 vaccine was higher than those injected with wild type VP28 vaccines. Furthermore, the expression of immune-related genes differed between codon deoptimized and wild type VP28 vaccines. In summary, the results suggest that 0.01 μg codon deoptimized VP28-D1 mRNA vaccine is the most promising WSSV mRNA vaccine, displaying low pathogenicity and expression in shrimps. To the best of our knowledge, this research represents the first attempt to attenuate WSSV using codon deoptimization method and development of a potential mRNA vaccine for shrimp purpose. The study addresses an important gap in shrimp vaccine research, offering potential solutions for WSSV control in shrimps.

VP28 interacts with PmRab7 irrespective of its nucleotide state

In shrimp aquaculture, white spot syndrome virus (WSSV) infections severely impact production. Previous research highlighted the crucial role of the Penaeus monodon Rab7 (PmRab7) protein in WSSV entry, specifically its interaction with the viral envelope protein VP28. PmRab7 exists in two conformations: GDP-bound (inactive) and GTP-bound (active). This study, using ELISA and isothermal titration calorimetry (ITC), reveals that the PmRab7-VP28 interaction occurs irrespective of the nucleotide binding state of PmRab7. Comparing the binding affinity between VP28 and different PmRab7 conformations, including wild-type (WT, 22.5 nM), a fast nucleotide exchange (L129F, 128 nM), a GDP-bound form (T22N, 334 nM), and a favorably GTP-bound form (Q67L, 1990 nM), PmRab7-WT exhibits the strongest binding affinity, especially at a lower temperature (25 °C). The binding of PmRab7-WT and VP28 in the presence of excess nucleotide (WT with excess GDP, 924 nM, and WT with excess GTP, 826 nM) shows a 2-fold higher binding affinity than in the absence (WT, 1920 nM) indicating that the addition of excess nucleotide for PmRab7-WT enhanced the affinity for VP28. Together, these findings support the potential of PmRab7-WT as a promising therapeutic candidate for WSSV control in shrimp. Furthermore, from an industrial point of view, the ITC platform developed to study the VP28-PmRab7 interactions provides a high-throughput method for screening additives for shrimp feed that can inhibit this interaction.

Alleviating effects of Gracilaria verrucosa supplement on non-specific immunity, antioxidant capacity and immune-related genes of pacific white shrimp (Litopenaeus vannamei) provoked with white spot syndrome virus

Our work evaluated the possible underlying roles of dietary dried seaweed (Gracilaria verrucosa; GV) on the inherent immune response, antioxidant capacity, immune-related gene expression, and protection of whiteleg shrimp (Litopenaeus vannamei) contra white spot syndrome virus (WSSV). Three hundred and sixty healthy L. vannamei (15.26 g ± 1.29 g) were graded into four supplemental groups ( Triplicate/group) and fed with diets including 0 (control), 2, 4, and 8 g GV (kg diet) -1 for 21 days. Following the feeding period, each group of shrimp received an intramuscular WSSV injection (1.4 × 106 copies/ml). Hemolymph and gills samples were collected before and after the challenge with WSSV. Notably, the administration of dietary GV significantly enhanced the innate immune parameters of pacific white shrimp including total hemocyte count (THC), phagocytosis, phenoloxidase activity, reactive oxygen species (ROS) production, and lysozyme activity before and after challenge with WSSV. Additionally, dietary supplementation of 4, and 8 g of GV (kg diet)-1 remarkably elevated ACP, AKP, SOD, GPx, and catalase activities along with a decrease in the MDA level in gills of shrimp before and post-WSSV challenge. In response to the GV supplement, significant upregulation of expression of ALF1, CRU1, PEN4, and CTL with downregulation of TRAF6, STAT, TLR1, and NOS genes was recorded in the gills tissue before and post-challenge with WSSV, especially at a dose of 8.0 GV g kg - 1. Dietary inoculated shrimp with GV revealed notably higher survival percentages after being challenged with WSSV. Conclusively, these data indicate that Gracilaria verrucosa can be recommended as a valuable supplemented seaweed to stimulate the innate immunity and enhance the health of Litopenaeus vannamei against viral infection.

Complete genome of the new bacilliform virus that causes Milky Hemolymph Syndrome in Chionoecetes bairdi (Rathbun, 1924)

The genome of a new member of the Nimaviridae family has been sequenced. The Chionoecetes bairdi bacilliform virus (CbBV) causes Milky Hemolymph Syndrome (MHS) in Chionoecetes bairdi populations of the Pacific coast of Kamchatka. The CbBV genome is represented by double-stranded DNA with a length of 245,567 nucleotides containing 120 ORFs. Of these, 85 proteins had significant matches in the NCBI database, and 57 genes encoded capsid, envelope, tegument and nonstructural proteins. Comparative analysis of the genomes of CbBV and a number of representatives of the class nuclear arthropod large DNA viruses (NALDVs) made it possible to isolate 49 evolutionarily conserved orthologue core genes. Among them, 5 were multicopy genes, and 44 were single-copy genes. There were ancestral genes characteristic of all Naldaviricetes - per os infectivity complex genes, one DNA polymerase gene and one thymidylate synthase gene. Phylogenetic analysis of representatives of the Nimaviridae family revealed that the CbBV and Chionoecetes opilio bacilliform virus (CoBV) form an independent clade within the family separate from the clade containing WSSV strains. This is supported by data on the order and arrangement of genes in the genomes of nimaviruses that were identical within each clade but differed between them. In addition, a high identity of the genomes and proteomes of CbBV and CoBV (approximately 99%) was shown, and their identity with WSSV strains was no more than 33%. The data on the structure of the genome of the new virus that causes MHS in C. bairdi indicate that it belongs to the family Nimaviridae, genus Whispovirus. Thus, the CbBV infecting the commercially important species of Tanner crab in populations of the Pacific coast of Kamchatka is the second "wild" representative of replicating nimaviruses whose genome has been characterized after the CoBV that causes MHS in C. opilio in populations of the Sea of Japan. The discovery of a new member of the family that infects decapods indicates the prevalence of nimaviruses in marine ecosystems. The information obtained is important for understanding the evolution of representatives of the class of nuclear arthropod large DNA viruses. The discovery of a new nimavirus that causes MHS in Chionoecetes crabs, in contrast to the white spot syndrome (WSS) caused by WSSV strains, makes it relevant to identify two variants and possibly species within the family, namely, WSSV and Milky Hemolymph Syndrome virus (MHSV).

Experimental Infection Models and Their Usefulness for White Spot Syndrome Virus (WSSV) Research in Shrimp

White spot syndrome virus (WSSV) is marked as one of the most economically devastating pathogens in shrimp aquaculture worldwide. Infection of cultured shrimp can lead to mass mortality (up to 100%). Although progress has been made, our understanding of WSSV's infection process and the virus-host-environment interaction is far from complete. This in turn hinders the development of effective mitigation strategies against WSSV. Infection models occupy a crucial first step in the research flow that tries to elucidate the infectious disease process to develop new antiviral treatments. Moreover, since the establishment of continuous shrimp cell lines is a work in progress, the development and use of standardized in vivo infection models that reflect the host-pathogen interaction in shrimp is a necessity. This review critically examines key aspects of in vivo WSSV infection model development that are often overlooked, such as standardization, (post)larval quality, inoculum type and choice of inoculation procedure, housing conditions, and shrimp welfare considerations. Furthermore, the usefulness of experimental infection models for different lines of WSSV research will be discussed with the aim to aid researchers when choosing a suitable model for their research needs.

Vertical transmission and prevalence of white spot syndrome virus (WSSV) in the wild spawning population of the Indian white shrimp, Penaeus indicus

White spot disease, caused by white spot syndrome virus (WSSV), has historically been the most devastating disease in shrimp aquaculture industry across the world. The mode of virus transmission is the most crucial stage in the dynamics and management of virus infection. This study explored the mechanism of vertical transmission of WSSV in Indian white shrimp, Penaeus indicus, potential native species for domestication and genetic improvement, using quantitative real time PCR (q RT PCR), light and electron microscopy, and in situ hybridization. Wild brooders of P. indicus (n = 2576) were sampled along the South east coast of India, during 2016 to 2021. Of these ∼ 58 % of the brooders were positive for WSSV, and almost 50 % of infected wild brooders were at the various stages of reproductive maturation. WSSV-PCR positive brooders (n = 200) were analysed for vertical WSSV transmission. The q RT PCR studies of reproductive tissues revealed that 61 % (n = 13) of spermatophore, 54 % (n = 28) of immature ovaries and 48 % (n = 27) of ripe ovaries were infected with WSSV. The lowest level of infection was recorded in females with ripe ovaries (6.84 × 101 ± 9.79 × 100 ng genomic DNA) followed by fertilized eggs (1.59 × 102 ± 3.69 × 101 ng genomic DNA), and larvae (nauplius and zoea). The histology of gravid females with high WSSV copies showed pyknotic and karyorrhectic germinal vesicle with degenerated cortical rods. Conversely, the gravid females with low WSSV copies showed fully developed ovary without characteristic signs of WSSV infection. Transmission electron microscopic studies clearly established the presence of WSSV particles in both ovaries and spermatophores. When subjected to in situ hybridization, WSSV-specific signals were observed in connective tissues of spermatophore, although gravid ovary and fertilized eggs were failed to produce WSSV specific signals. The present study provides the first molecular and histological evidence for trans-ovarian vertical transmission of WSSV. Development of disease-free base population being the cornerstone and first step in establishing the breeding program, the present findings could be a basis for development of such programs.

Immune-stealth VP28-conjugated heparin nanoparticles for enhanced and reversible anticoagulation

Heparins are a family of sulfated linear negatively charged polysaccharides that have been widely used for their anticoagulant, antithrombotic, antitumor, anti-inflammatory, and antiviral properties. Additionally, it has been used for acute cerebral infarction relief as well as other pharmacological actions. However, heparin's self-aggregated macrocomplex may reduce blood circulation time and induce life-threatening thrombocytopenia (HIT) complicating the use of heparins. Nonetheless, the conjugation of heparin to immuno-stealth biomolecules may overcome these obstacles. An immunostealth recombinant viral capsid protein (VP28) was expressed and conjugated with heparin to form a novel nanoparticle (VP28-heparin). VP28-heparin was characterized and tested to determine its immunogenicity, anticoagulation properties, effects on total platelet count, and risk of inducing HIT in animal models. The synthesized VP28-heparin trimeric nanoparticle was non-immunogenic, possessed an average hydrodynamic size (8.81 ± 0.58 nm) optimal for the evasion renal filtration and reticuloendothelial system uptake (hence prolonging circulating half-life). Additionally, VP28-heparin did not induce mouse death or reduce blood platelet count when administered at a high dosein vivo(hence reducing HIT risks). The VP28-heparin nanoparticle also exhibited superior anticoagulation properties (2.2× higher prothrombin time) and comparable activated partial thromboplastin time, but longer anticoagulation period when compared to unfractionated heparin. The anticoagulative effects of the VP28-heparin can also be reversed using protamine sulfate. Thus, VP28-heparin may be an effective and safe heparin derivative for therapeutic use.

Effects of geniposide on innate immunity and antiviral activity of Scyllaparamamosain

In this study, we examined the impact of geniposide on the innate immunity of the mud crab Scylla paramamosain, specifically in relation to WSSV infection. Through the use of in vitro cell culture experiments, we assessed the effects of geniposide on various parameters of hemocyte activity in S. paramamosain. Our findings revealed that high doses of geniposide inhibited hemocyte growth, with an optimal dose of 100 mg/kg determined. Additionally, we observed that geniposide increased the total hemocyte counts in S. paramamosain following WSSV infection. Geniposide also enhanced the enzymatic activities in hemolymph following treatment. The enzymes affected by geniposide encompassed ACP (acid phosphatase), POD (phenol oxidase catalase), PO (phenoloxidase), SOD (superoxide dismutase), CAT (catalase), and LZM (lysozyme). Furthermore, the activities of ACP, POD, PO, and LZM were also observed to increase subsequent to infection with WSSV. Notably, geniposide was found to enhance the phagocytosis of V. alginolyticus within the hemocytes. Geniposide can reduce hemocyte apoptosis rates after treatment, as well as hemocytes infected with WSSV. Furthermore, geniposide treatment significantly up-regulated the expression level of Myosin, but expression levels of Astakine, C-type lectin (CTL), STAT, JAK, proPO, minichromosome maintenance protein (MCM7), caspase-3 and crustin were down-regulated in the hemocytes. Additionally, geniposide treatment inhibited WSSV replication in hemocytes of S. paramamosain, and enhanced the survival rates of mud crabs following WSSV infection. These experimental results provide evidence that geniposide can improve the immune response by regulating humoral immunity and cellular immunity, and enhance pathogen resistance in S. paramamosain.

Use of brome mosaic virus-like particles in feed, to deliver dsRNA targeting the white spot syndrome virus vp28 gene, reduces Penaeus vannamei mortality

Numerous strategies have been investigated to combat viral infections in shrimp, specifically targeting the white spot syndrome virus (WSSV) that has caused outbreaks worldwide since the 1990s. One effective treatment involves intramuscular application of dsRNA-mediated interference against the viral capsid protein VP28. However, this approach presents challenges in terms of individual shrimp management, limiting its application on a large scale. To address this, our study aimed to evaluate the efficacy of oral delivery of protected dsRNA using chitosan nanoparticles or virus-like particles (VLPs) synthesized in brome mosaic virus (BMV). These delivery systems were administered before, during, and after WSSV infection to assess their therapeutic potential. Our findings indicate that BMV-derived VLPs demonstrated superior efficiency as nanocontainers for dsRNA delivery. Notably, the treatment involving vp28 dsRNA mixed in the feed and administered simultaneously to shrimp already infected with WSSV exhibited the highest survival rate (48%), while the infected group had a survival rate of zero, suggesting the potential efficacy of this prophylactic approach in commercial shrimp farms.

Single von Willebrand factor C-domain protein confers host defense against white spot syndrome virus by functioning as a pattern recognition receptor in Macrobrachium nipponense

The single von Willebrand factor C-domain proteins (SVWCs), also known as Vago, are primarily found in arthropods. Their expression was induced by nutritional status, bacterial and viral infections. Despite the prominence of SVWCs in antiviral immunity, the detailed molecular mechanisms remain poorly explained. SVWC has been proposed to elicit antiviral activities through its function as an interferon analog. In contrast, herein, we illustrate that an SVWC homolog from Macrobrachium nipponense (MnSVWC) confers host defense against white spot syndrome virus (WSSV) and covert mortality nodavirus (CMNV) as a pattern recognition receptor (PRR). qRT-PCR analyses demonstrated that the expression of MnSVWC was enhanced upon WSSV infection in all detected tissues, including gills, nerve cords, and hemocytes. Coating WSSV with recombinant MnSVWC (rMnSVWC) promoted the phagocytic activity of hemocytes and subsequent clearance of invasive WSSV from the prawn. On the other hand, the knockdown of MnSVWC with RNAi improved the proliferation ability of WSSV and CMNV in the prawn. Analysis of ELISA and Co-immunoprecipitation (Co-IP) showed that rMnSVWC could bind WSSV by interacting with the vesicle proteins VP26 and VP28. Co-IP analysis verified the interaction between MnSVWC and calmodulin, which implies a vesicle protein-SVWC-calmodulin-clathrin-dependent mechanism underlying the hemocyte-mediated phagocytosis against WSSV. Subsequently, MnSVWC was recognized to activate the expression of transcription factor STAT and an interferon-stimulating gene Viperin, illustrating its involvement in modulating humoral immunity via activation of the JAK/STAT pathway after WSSV infection. These findings indicate that MnSVWC could bind to WSSV as a PRR and participate in the promotion of hemocyte-mediated phagocytosis and the activation of the JAK/STAT pathway in prawns.

The effect of white spot syndrome virus (WSSV) envelope protein VP28 on innate immunity and resistance to white spot syndrome virus in Cherax quadricarinatus

VP28 is the most abundant membrane protein of WSSV, and the recombinant protein VP28 (VP26 or VP24) was constructed for the immune protection experiment in this study. Crayfish were immunized by intramuscular injection of recombinant protein V28 (VP26 or VP24) at a dose of 2 μg/g. The survival rate of crayfish immunized by VP28 showed a higher value than by VP26 or VP24 after WSSV challenge. Compared with the WSSV-positive control group, the VP28-immunized group could inhibit the replication of WSSV in crayfish, increasing the survival rate of crayfish to 66.67% after WSSV infection. The results of gene expression showed that VP28 treatment could enhance the expression of immune genes, mainly JAK and STAT genes. VP28 treatment also enhanced total hemocyte counts and enzyme activities including PO, SOD, and CAT in crayfish. VP28 treatment reduced the apoptosis of hemocytes in crayfish, as well as after WSSV infection. In conclusion, VP28 treatment can enhance the innate immunity of crayfish and has a significant effect on resistance to WSSV, and can be used as a preventive tool.

Review: Recent Applications of Gene Editing in Fish Species and Aquatic Medicine

Gene editing and gene silencing techniques have the potential to revolutionize our knowledge of biology and diseases of fish and other aquatic animals. By using such techniques, it is feasible to change the phenotype and modify cells, tissues and organs of animals in order to cure abnormalities and dysfunctions in the organisms. Gene editing is currently experimental in wide fields of aquaculture, including growth, controlled reproduction, sterility and disease resistance. Zink finger nucleases, TALENs and CRISPR/Cas9 targeted cleavage of the DNA induce favorable changes to site-specific locations. Moreover, gene silencing can be used to inhibit the translation of RNA, namely, to regulate gene expression. This methodology is widely used by researchers to investigate genes involved in different disorders. It is a promising tool in biotechnology and in medicine for investigating gene function and diseases. The production of food fish has increased markedly, making fish and seafood globally more popular. Consequently, the incidence of associated problems and disease outbreaks has also increased. A greater investment in new technologies is therefore needed to overcome such problems in this industry. To put it concisely, the modification of genomic DNA and gene silencing can comprehensively influence aquatic animal medicine in the future. On the ethical side, these precise genetic modifications make it more complicated to recognize genetically modified organisms in nature and can cause several side effects through created mutations. The aim of this review is to summarize the current state of applications of gene modifications and genome editing in fish medicine.

Inhibition of White Spot Syndrome Virus (WSSV) in Pacific White Shrimp (Litopenaeus vannamei) Using Polyamine-Modified Carbon Quantum Dots

White spot syndrome virus (WSSV), an enveloped double-stranded DNA virus, is the causative agent of white spot syndrome (WSS), which has been linked to cultured shrimp mass mortality in many countries. Therefore, the development of anti-WSSV agents is among the top priorities of the aquaculture sector. Here, we describe the preparation of polyamine-modified carbon quantum dots (polyamine CQDs) for the treatment of WSSV. Moreover, in vivo experiments were conducted in shrimp to confirm the anti-WSSV effect of the proposed CQD-based strategy.

Functional Peroral Infectivity Complex of White Spot Syndrome Virus of Shrimp

White spot syndrome virus (WSSV) is a major cause of disease in shrimp cultures worldwide. The infection process of this large circular double-stranded DNA virus has been well studied, but its entry mechanism remains controversial. The major virion envelope protein VP28 has been implicated in oral and systemic viral infection in shrimp. However, genetic analysis of viral DNA has shown the presence of a few genes related to proteins of per os infectivity factor (PIF) complex in baculoviruses. This complex is essential for the entry of baculoviruses, large terrestrial circular DNA viruses, into the midgut epithelial cells of insect larvae. In this study, we aimed to determine whether a PIF complex exists in WSSV, the components of this complex, whether it functions as an oral infectivity complex in shrimp, and the biochemical properties that contribute to its function in a marine environment. The results revealed a WSSV PIF complex (~720 kDa) comprising at least eight proteins, four of which were not identified as PIF homologs: WSV134, VP124 (WSV216), WSSV021, and WSV136. WSV134 is suggested to be a PIF4 homolog due to predicted structural similarity and amino acid sequence identity. The WSSV PIF complex is resistant to alkali, proteolysis, and high salt, properties that are important for maintaining infectivity in aquatic environments. Oral infection can be neutralized by PIF-specific antibodies but not by VP28-specific antibodies. These results indicate that the WSSV PIF complex is critical for WSSV entry into shrimp; the complex's evolutionary significance is also discussed. IMPORTANCE White spot disease, caused by the white spot syndrome virus (WSSV), is a major scourge in cultured shrimp production facilities worldwide. This disease is only effectively controlled by sanitation. Intervention strategies are urgently needed but are limited by a lack of appropriate targets. Our identification of a per os infectivity factor (PIF) complex, which is pivotal for the entry of WSSV into shrimp, could provide new targets for antibody- or dsRNA-based intervention strategies. In addition, the presence of a PIF complex with at least eight components in WSSV, which is ancestrally related to the PIF complex of invertebrate baculoviruses, suggests that this complex is structurally and functionally conserved in disparate virus taxa.

Monoclonal antibodies (mAbs) and single chain variable fragment (scFv) antibodies targeting envelope protein VP28 of white spot syndrome virus provide protection against viral infection

White spot syndrome virus (WSSV) is extremely pathogenic and causes huge economic losses in the shrimp farming industry. Neutralizing antibodies against WSSV is expected to be an effective means of preventing infection with the virus. In the present study, eight monoclonal antibodies (mAbs) against VP28 were developed by immunizing BALB/c mice with WSSV-VP28 recombinant protein. Among them, three mAbs named 3B7, 2G3 and 5D2 were determined to be able to delay the mortality of WSSV-infected shrimp in vivo neutralization assay, suggesting their neutralizing ability against WSSV infection. Immunoblotting results showed that the three mAbs reacted specifically with native VP28 of WSSV, and could also recognize the virions in the gills of WSSV-infected shrimp by IFA. Furthermore, the single chain variable fragment (scFv) genes specific for WSSV-VP28 were cloned from the three hybridoma cells and expressed in Escherichia coli. After purification and refolding, three biologically active scFv recombinant proteins were all capable of recognizing the native VP28 of WSSV and delayed the mortality of WSSV-infected shrimp, indicating their neutralizing capacity against WSSV. Subsequently, the eukaryotic expression plasmids of three scFv genes were constructed and the transcriptional properties of expression vectors in shrimp were analyzed. Animal experiments also proved that the scFv eukaryotic expression plasmids were able to partially neutralize WSSV infection. Thus, the production of neutralizing mAb and recombinant scFv antibodies against WSSV has a promising therapeutic potential in prevention and treatment of white spot disease of shrimp.

Integrative omics analysis highlights the immunomodulatory effects of the parasitic dinoflagellate hhematodinium on crustacean hemocytes

Parasitic dinoflagellates in genus Hematodinium have caused substantial economic losses to multiple commercially valuable marine crustaceans around the world. Recent efforts to better understand the life cycle and biology of the parasite have improved our understanding of the disease ecology. However, studies on the host-parasite interaction, especially how Hematodinium parasites evade the host immune response are lacking. To address this shortfall, we used the comprehensive omics approaches (miRNA transcriptomics, iTRAQ-based proteomics) to get insights into the host-parasite interaction between hemocytes from Portunus trituberculatus and Hematodinium perezi in the present study. The parasitic dinoflagellate H. perezi remodeled the miRNome and proteome of hemocytes from challenged hosts, modulated the host immune response at both post-transcriptional and translational levels and caused post-transcriptional regulation to the host immune response. Multiple important cellular and humoral immune-related pathways (ex. Apoptosis, Endocytosis, ECM-receptor interaction, proPO activation pathway, Toll-like signaling pathway, Jak-STAT signaling pathway) were significantly affected by Hematodinium parasites. Through modulation of the host miRNome, the host immune responses of nodulation, proPO activation and antimicrobial peptides were significantly suppressed. Cellular homeostasis was imbalanced via post-transcriptional dysregulation of the phagosome and peroxisome pathways. Cellular structure and communication was seriously impacted by post-transcriptional downregulation of ECM-receptor interaction and focal adhesion pathways. In conclusion, H. perezi parasites could trigger striking changes in the miRNome and proteome of crustacean hemocytes, and this parasite exhibited multifaceted immunomodulatory effects and potential immune-suppressive mechanisms in crustacean hosts.

Identification of a TRIM32 from Penaeus monodon is involved in autophagy and innate immunity during white spot syndrome virus infection

Many tripartite motif (TRIM) family proteins played an important role in regulating innate immune and autophagy pathway and were important for host defenses against viral pathogens. However, the role of TRIM proteins in autophagy and innate immunity during virus infection was seldom studied in crustaceans. In this study, a novel TRIM32 homolog was identified from Penaeus monodon (named PmTRIM32). PmTRIM32 was significantly upregulated by rapamycin stimulation and WSSV infection. RNA interference experiments showed that PmTRIM32 could restrict WSSV replication and lead P. monodon more resistance to WSSV challenge. Autophagy could be induced by WSSV or rapamycin challenge and has been proved to play a positive role in restricting WSSV replication in P. monodon. The autophagy activity induced by WSSV or rapamycin challenge could be obviously inhibited by silence of PmTRIM32 in P. monodon. Further studies revealed that PmTRIM32 positively regulated the expression of nuclear transcription factor (NF-κB) and it mediated antimicrobial peptides. Moreover, Pull-down and in vitro ubiquitination assay demonstrated that PmTRIM32 could interact with WSSV envelope protein and target it for ubiquitination in vitro. Collectively, this study demonstrated that PmTRIM32 restricted WSSV replication and was involved in positively regulating autophagy and NF-κB pathway during WSSV infection in P. monodon.

Evaluation of the antiviral activity of naringenin, a major constituent of Typha angustifolia, against white spot syndrome virus in crayfish Procambarus clarkii

White spot syndrome virus (WSSV) is a serious pathogen threatening global crustacean aquaculture with no commercially available drugs. Herbal medicines widely used in antiviral research offer a rich reserve for drug discovery. Here, we investigated the inhibitory activity of 13 herbal medicines against WSSV in crayfish Procambarus clarkii and discovered that naringenin (NAR) has potent anti-WSSV activity. In the preliminary screening, the extracts of Typha angustifolia displayed the highest inhibitory activity on WSSV replication (84.62%, 100 mg/kg). Further, NAR, the main active compound of T. angustifolia, showed a much higher inhibition rate (92.85%, 50 mg/kg). NAR repressed WSSV proliferation followed a dose-dependent manner and significantly improved the survival of WSSV-challenged crayfish. Moreover, pre- or post-treatment of NAR displayed a comparable inhibition on the viral loads. NAR decreased the transcriptional levels of vital genes in viral life cycle, particularly for the immediately early-stage gene ie1. Further results showed that NAR could decrease the STAT gene expression to block ie1 transcription. Besides, NAR modulated immune-related gene Hsp70, antioxidant (cMnSOD, mMnSOD, CAT, GST), anti-inflammatory (COX-1, COX-2) and pro-apoptosis-related factors (Bax and BI-1) to inhibit WSSV replication. Overall, these results suggest that NAR may have the potential to be developed as preventive or therapeutic agent against WSSV.

Feasibility Study on the Use of Fly Maggots (Musca domestica) as Carriers to Inhibit Shrimp White Spot Syndrome

The shrimp aquaculture industry has encountered many diseases that have caused significant losses, with the most serious being white spot syndrome (WSS). Until now, no cures, vaccines, or drugs have been found to counteract the WSS virus (WSSV). The purpose of this study was to develop an oral delivery system to transport recombinant proteinaceous antigens into shrimp. To evaluate the feasibility of the oral delivery system, we used white shrimp as the test species and maggots as protein carriers. The results indicated that the target protein was successfully preserved in the maggot, and the protein was detected in the gastrointestinal tract of the shrimp, showing that this oral delivery system could deliver the target protein to the shrimp intestine, where it was absorbed. In addition, the maggots were found to increase the total haemocyte count and phenoloxidase activity of the shrimp, and feeding shrimp rVP24-fed maggots significantly induced the expression of penaeidins 2. In the WSSV challenge, the survival rate of rVP24-fed maggots was approximately 43%. This study showed that maggots can be used as effective oral delivery systems for aquatic products and may provide a new method for aquatic vaccine delivery systems.

Dual VP28 and VP37 dsRNA encapsulation in IHHNV virus-like particles enhances shrimp protection against white spot syndrome virus

Accumulative evidence of using double stranded (ds) RNA encapsulated into virus like particle (VLP) nanocarrier has open feasibility to fight against shrimp viral infection in aquaculture field. In this study, we co-encapsulated VP37 and VP28 dsRNA into hypodermal and hematopoietic necrosis virus (IHHNV) like particle and investigated its protection against white spot syndrome virus (WSSV). Five micrograms of each dsRNA were used as starting materials to load into VLP, while the loading efficiency was slightly different, i.e, VP37 dsRNA had somewhat a better load into VLP's cavity. It was apparent that co-encapsulation of dual dsRNA showed a superior WSSV silencing ability than the single dsRNA counterpart as evidence by the lower WSSV gene expression and its copy number in the gill tissues. Besides, we also demonstrated that co-encapsulated dual dsRNA into IHHNV-VLP stimulated the increased number of hemocytes and the corresponding PO activity as well as up-regulated proPO gene expression in hemocytes to resist viral invasion after an acute stage of WSSV infection. This synergistic action of dual dsRNA encapsulated into IHHNV-VLPs could thus act to delay time of shrimp death and reduced shrimp cumulative mortality greater than the single, naked dsRNA treatment and positive control groups. The obtaining results would encourage the feasibility to use it as a new weapon to fight WSSV infection in shrimp aquaculture.

Identification of a Shrimp E3 Ubiquitin Ligase TRIM50-Like Involved in Restricting White Spot Syndrome Virus Proliferation by Its Mediated Autophagy and Ubiquitination

Most tripartite motif (TRIM) family proteins are critical components of the autophagy machinery and play important roles in host defense against viral pathogens in mammals. However, the roles of TRIM proteins in autophagy and viral infection have not been studied in lower invertebrates, especially crustaceans. In this study, we first identified a TRIM50-like gene from Penaeus monodon (designated PmTRIM50-like), which, after a white spot syndrome virus (WSSV) challenge, was significantly upregulated at the mRNA and protein levels in the intestine and hemocytes. Knockdown of PmTRIM50-like led to an increase in the WSSV quantity in shrimp, while its overexpression led to a decrease compared with the controls. Autophagy can be induced by WSSV or rapamycin challenge and has been shown to play a positive role in restricting WSSV replication in P. monodon. The mRNA and protein expression levels of PmTRIM50-like significantly increased with the enhancement of rapamycin-induced autophagy. The autophagy activity induced by WSSV or rapamycin challenge could be inhibited by silencing PmTRIM50-like in shrimp. Further studies showed that rapamycin failed to induce autophagy or inhibit WSSV replication after knockdown of PmTRIM50-like. Moreover, pull-down and in vitro ubiquitination assays demonstrated that PmTRIM50-like could interact with WSSV envelope proteins and target them for ubiquitination in vitro. Collectively, this study demonstrated that PmTRIM50-like is required for autophagy and is involved in restricting the proliferation of WSSV through its ubiquitination. This is the first study to report the role of a TRIM family protein in virus infection and host autophagy in crustaceans.

Metabolic responses of whiteleg shrimp to white spot syndrome virus (WSSV)

Outbreaks of white spot syndrome virus (WSSV) have caused serious damage to penaeid shrimp aquaculture worldwide. Despite great efforts to characterize the virus, the conditions that lead to infection and the infection mechanisms, there is still a lack of understanding regarding these complex virus-host interactions, which is needed to develop consistent and effective treatment methods for WSSV. In this study, we used a gas chromatography - mass spectrometry (GC-MS)-based metabolomics approach to compare the metabolite profiles of gills, haemolymph and hepatopancreas from whiteleg shrimp (Penaeus vannamei) exposed to WSSV and corresponding controls. The results revealed clear discriminations between metabolite profiles of WSSV-challenged shrimp and controlled shrimp in each tissue. The responses of shrimp gills to WSSV infection were characterized by increases of many fatty acids and amino acids in WSSV-challenged shrimp compared to the controls. Changes in haemolymph metabolite profiles include the increased levels of itaconic acid, energy-related metabolites, metabolites in glutathione cycle and decrease of amino acids. The WSSV challenge led to the decreases of several fatty acids and amino acids and increases of other amino acids, lactic acid and other organic compounds (levulinic acid, malonic acid and putrescine) in hepatopancreas. These alterations of shrimp metabolites suggest several immune responses of shrimp to WSSV in a tissue-specific manner, including upregulation of osmoregulation, antimicrobial activity, metabolic rate, gluconeogenesis, glutathione pathway in control of oxidative stress and shift from aerobic to anaerobic metabolism in shrimp which indicates the Warburg effect. The findings from this study provide a better understanding of molecular process of shrimp response against WSSV invasion which may be useful for development of disease management strategies.

Molecular identification of white spot syndrome virus (WSSV) and associated risk factors for white spot disease (WSD) prevalence in shrimp (Penaeus monodon) aquaculture in Bangladesh

White spot disease has caused significant economic losses in the shrimp farming industry of Bangladesh over the last two decades. The responsible virus, WSSV, may show severe disease with significant mortality depending on farm management and environmental and seasonal changes. Data on farm management and environmental parameters were collected from the southwest region of Bangladesh in 2018, and WSSV infection was confirmed by the species-specific gene VP28 using conventional PCR, real-time PCR and sequencing. Through bivariate analysis, nine significant risk factors for WSD were identified, viz. farm age, presence of nursery pond, reservoir of PL, weed in farm area, control of weed, stocking density, stocking frequency, ammonia and oxygen concentration. This study detected 46 WSSV-infected shrimp farms by conventional PCR, whereas real-time PCR identified 47 WSSV-positive out of 49 farms. WSSV prevalence was highest in the Khulna region, with 100% positivity in all seasons. WSSV loads ranged from 5.62 × 10⁹ to 2.01 × 10¹⁵ copies/g of shrimp tissue. The VP28 gene sequence confirmed that 15 representative samples were 100% identical to the 2018 WSSV strain of India. The relationships among risk factors, prevalence and severity of disease, and origin of WSSV strains could be impactful for WSD management.

Dietary Bacillus amyloliquefaciens enhance survival of white spot syndrome virus infected crayfish

Bacillus amyloliquefaciens, which is closely related to Bacillus subtilis, produces a series of metabolites that can inhibit the growth of fungi and bacteria. Here, we investigated the effect of B. amyloliquefaciens used as a probiotic on the innate immunity of the crayfish Procambarus clarkii when challenged with white spot syndrome virus (WSSV). Dietary B. amyloliquefaciens supplement significantly reduced the mortality of WSSV-challenged crayfish and reduced copy numbers of WSSV. The quantitative reverse transcription-polymerase chain reaction results showed that B. amyloliquefaciens supplement increased the expression of several immune-related genes, including Toll-like receptor, NF-κB and C-type-lectin. Further analysis showed that B. amyloliquefaciens supplement also had an effect on three immune parameters, including total hemocyte count, phenoloxidase activity and superoxide dismutase activity. In both infected and uninfected crayfish, B. amyloliquefaciens supplement significantly decreased hemocyte apoptosis. Our results showed that B. amyloliquefaciens can regulate innate immunity of crayfish and reduce the mortality following WSSV challenge. This study provides a novel insight into the potential for therapeutic or prophylactic intervention with B. amyloliquefaciens to regulate crayfish immunity and protect against WSSV infection, and also provides a theoretical basis for the use of probiotics as aquatic feed additives.

WSSV proteins and DNA genome released by ultrasonic rupture can infect crayfish as effectively as intact virions

Proteins and nucleic acids from ultrasonically ruptured white spot syndrome virus (WSSV) can infect crayfish and cause death as effectively as intact WSSV virions. In this study, ultrasound was used to rupture the virus and the resulting suspension was filtered through a 50 nm membrane. Analysis by PCR and SDS-PAGE showed that both viral genes (VP19, VP26, VP28 and DNA polymerase) and proteins (VP15, VP19, VP26 and VP28) were present in the filtered solution. Electron microscopy showed that there were no intact virions in the filtered solution. When crayfish were injected with the filtered solution or with intact WSSV, the mortality in each group was 100 %. The same result was seen when crayfish were challenged orally with the filtered solution and intact WSSV. The filtered solution of ultrasonically ruptured virus, which contains viral proteins and residual DNA genome, can thus infect the host as effectively as intact virions. When the solution of viral proteins and residual DNA genome was digested with DNase I and then injected into crayfish, the survival rate was 100 %. We also found that, although viral proteins (except VP15) in the solution of ruptured virus were destroyed by treatment with DNase I, DNase I did not destroy the structural proteins of intact virions. A remaining viral protein in the DNase I-treated solution protects the DNA genome from degradation and we concluded that this protein is VP15, which is a DNA-binding protein. Our study highlights the extreme danger in producing vaccines from proteins obtained by ultrasonic rupture of viruses sincethe viral DNA genome is difficult to degrade and, if present, will lead to viral infection.

Antigenic properties of VP15 from white spot syndrome virus in kuruma shrimp Marsupenaeus japonicus

White spot syndrome virus (WSSV) is known as one of the most lethal pathogenic viruses in shrimp causing massive damage to shrimp aquaculture industries. To date, no effective treatment or prevention has been found. In this study, five recombinant viral proteins VP15, VP19, VP24, VP26, and VP28 were expressed and purified in E. coli, which were employed as candidates against WSSV in Kuruma shrimp Marsupenaeus japonicus. In vivo antiviral assay in this study newly revealed that VP15 of major nucleocapsid protein, being known as a DNA-binding protein provided the substantial protection against the viral infection when pre-injected into shrimps. Furthermore, we also verified the immunogenic effects of purified VP15 and VP19 proteins produced in a silkworm-bacmid expression system. Taken together, our study identified VP15 as an effective candidate against WSSV infection in the Kuruma shrimp. It is interesting to uncover why and how VP15 is involved in the immune memory in shrimp in the future study.

Synthesis and evaluation of polyamine carbon quantum dots (CQDs) in Litopenaeus vannamei as a therapeutic agent against WSSV

White spot syndrome virus (WSSV) is the causative agent of white spot syndrome (WSS), a disease that has led to severe mortality rates in cultured shrimp all over the world. The WSSV is a large, ellipsoid, enveloped double-stranded DNA virus with a wide host range among crustaceans. Currently, the main antiviral method is to block the receptor of the host cell membrane using recombinant viral proteins or virus antiserum. In addition to interference with the ligand-receptor binding, disrupting the structure of the virus envelope may also be a means to combat the viral infection. Carbon quantum dots (CQDs) are carbonaceous nanoparticles that have many advantageous characteristics, including small size, low cytotoxicity, cheap, and ease of production and modification. Polyamine-modified CQDs (polyamine CQDs) with strong antibacterial ability have been identified, previously. In this study, polyamine CQDs are shown to attach to the WSSV envelope and inhibit the virus infection, with a dose-dependent effect. The results also show that polyamine CQDs can upregulate several immune genes in shrimp and reduce the mortality upon WSSV infection. This is first study to identify that polyamine CQDs could against the virus. These results, indeed, provide a direction to develop effective antiviral strategies or therapeutic methods using polyamine CQDs in aquaculture.

Epitope mapping of the White Spot Syndrome Virus (WSSV) VP28 monoclonal antibody through combined in silico and in vitro analysis reveals the potential antibody binding site

White Spot Syndrome Virus (WSSV) infecting shrimp is an enveloped double-stranded DNA virus. The WSSV is a member of the genus Whispovirus. The envelope protein VP28 is the most investigated protein of WSSV. In the present study, the epitope mapping of the monoclonal antibody (MAb) C-33 was carried out. Based on the epitope mapping results, an antigen-antibody interaction model was derived. Peptide scanning and confirmation of epitopes of MAb C-33 were carried out using the sequence data. The MAb was reactive to the epitope of both recombinant VP28 and the whole virus. The results of the study indicated the presence of an epitope region. The epitope region is found positioned within two peptides, covering 13 amino acids. Framework and CDR (complementarity determining regions) of heavy and light chain (VH & VL) sequences showed identity to germline immunoglobulin sequences. The Web Antibody Modelling (WAM) selected for further evaluation based on a comparative analysis of WAM and Rosetta server-generated models of the Fv region. The docking study using WAM generated model revealed that the residues from LEU98 to GLY105 are active in antibody binding. The findings of this study could form a structural basis for further research in VP28 based diagnostics and therapeutics or vaccine discovery.

VP19 is important for the envelope coating of white spot syndrome virus

VP19 is a major envelope protein of white spot syndrome virus (WSSV), an important pathogen of farmed shrimp. However, the exact function of VP19 in WSSV assembly and infection is unknown. To understand the function of VP19, the gene was knocked down by RNA interference. We found that the dsRNA specific for vp19 gene dramatically reduced the replication of WSSV genomic DNA in infected animals. Further investigation by transmission electron microscopy showed that inhibition of VP19 prevented envelope coating of progeny virions, resulting in a high amount of immature virus particles without outer layer (envelope) in the host cells. This finding was further confirmed by SDS-PAGE analysis, which showed the loss of VP19 and other envelope proteins from the improperly assembled virions. These results suggest that VP19 is essential for WSSV envelope coating.

Alternative PCR primers for genotyping of Brazilian WSSV isolates

White spot syndrome virus (WSSV) is one of the major challenges faced by global shrimp farming in recent decades. The characterization of WSSV genetic variability has been used to determine viral dispersion and is a promising method to determine the association between genotype and virulence. The major variable regions that have been used as markers to differentiate the WSSV genomes include the VNTR loci inside ORF94, ORF75, ORF125, and insertions/deletions interspersing ORF14/15 and ORF23/24. The primers used to amplify these regions were described at least 10 years ago, but some of them do not work efficiently to identify new WSSV variants. The objective of this work was to develop improved PCR primers for WSSV genotyping based on sequence alignments that include new sequences described in recent years. We validated these new primers in a pilot study to verify the genetic variability of the WSSV in Rio Grande do Norte state (northeast Brazil), and efficiency was compared to that of other previously described primers. We confirmed that the primers we developed were more efficient for genotype Brazilian WSSV isolates, enabling us to genotype a larger number of samples. In addition, our results also introduce new data about the genetic characterization of the WSSV isolates that occur in the northeastern region of Brazil.

The Improvement and Application of Lentivirus-Mediated Gene Transfer and Expression System in Penaeid Shrimp Cells

This study first reported the improvement and application of lentivirus-mediated gene transfer and expression system in shrimp cells. After modified by the inclusion of two envelope proteins (VP19 and VP28) of shrimp white spot syndrome virus (WSSV) into the envelope of the packaged lentivirus, and insertion of a truncated promoter of immediate-early gene 1 (Pie1-504) of shrimp WSSV virus into the lentiviral reporter plasmid, the second-generation lentiviral expression system (pLVX-PEF1α-IRES-mCherry, psPAX2, and PMD2.G) was found to behave better in the mitosis-arrested shrimp cells than the similarly modified retrovirus expression system did. Results from the insect sf9 cells indicated that the inclusion of VP19 and VP28 into the envelope of packaged lentiviruses could significantly improve the tropism or infectivity of the modified lentiviruses to insect cells in a cumulative way. Notably, the VP28 contributed about 86% of the total increase of the tropism. In the shrimp primary lymphoid cells infected by modified lentivirus IV with both VP19 and VP28 included, the infection efficiency was up to 11% (non-confocal) and 19% (confocal) and no background fluorescent signal was observed. However, background fluorescent signal was observed in the shrimp primary Oka organ cells although only under a confocal microscope. In the lentivirus IV-infected Oka organ cells, the actual infection efficiencies were calculated up to 8% (non-confocal) and 19% (confocal), significantly higher than those of commercial intact lentivirus I of 0 (non-confocal) and 3% (confocal). The insertion of WSSV promoter (Pie1-504) had interrupted the effective expression of reporter plasmid encoding lentiviral construct of pLVX-PEF1α-Pie1-504-IRES-mCherry in the HEK293T cells, but markedly increased its efficiencies up to 14% (non-confocal) and 26% (confocal) in the Oka organ cells. This improved lentivirus expression system will provide us a useful tool for efficient gene transfer and expression in shrimp cells.

Crustacean Genome Exploration Reveals the Evolutionary Origin of White Spot Syndrome Virus

White spot syndrome virus (WSSV) is a crustacean-infecting, double-stranded DNA virus and is the most serious viral pathogen in the global shrimp industry. WSSV is the sole recognized member of the family Nimaviridae, and the lack of genomic data on other nimaviruses has obscured the evolutionary history of WSSV. Here, we investigated the evolutionary history of WSSV by characterizing WSSV relatives hidden in host genomic data. We surveyed 14 host crustacean genomes and identified five novel nimaviral genomes. Comparative genomic analysis of Nimaviridae identified 28 "core genes" that are ubiquitously conserved in Nimaviridae; unexpected conservation of 13 uncharacterized proteins highlighted yet-unknown essential functions underlying the nimavirus replication cycle. The ancestral Nimaviridae gene set contained five baculoviral per os infectivity factor homologs and a sulfhydryl oxidase homolog, suggesting a shared phylogenetic origin of Nimaviridae and insect-associated double-stranded DNA viruses. Moreover, we show that novel gene acquisition and subsequent amplification reinforced the unique accessory gene repertoire of WSSV. Expansion of unique envelope protein and nonstructural virulence-associated genes may have been the key genomic event that made WSSV such a deadly pathogen.IMPORTANCE WSSV is the deadliest viral pathogen threatening global shrimp aquaculture. The evolutionary history of WSSV has remained a mystery, because few WSSV relatives, or nimaviruses, had been reported. Our aim was to trace the history of WSSV using the genomes of novel nimaviruses hidden in host genome data. We demonstrate that WSSV emerged from a diverse family of crustacean-infecting large DNA viruses. By comparing the genomes of WSSV and its relatives, we show that WSSV possesses an expanded set of unique host-virus interaction-related genes. This extensive gene gain may have been the key genomic event that made WSSV such a deadly pathogen. Moreover, conservation of insect-infecting virus protein homologs suggests a common phylogenetic origin of crustacean-infecting Nimaviridae and other insect-infecting DNA viruses. Our work redefines the previously poorly characterized crustacean virus family and reveals the ancient genomic events that preordained the emergence of a devastating shrimp pathogen.

A new crustin homologue (SpCrus6) involved in the antimicrobial and antiviral innate immunity in mud crab, Scylla paramamosain

Crustins play important roles in defending against bacteria in the innate immunity system of crustaceans. In present study, we identified a crustin gene in Scylla paramamosain, which was named as SpCrus6. The ORF of SpCrus6 possessed a signal peptide sequence (SPS) at the N-terminus and a WAP domain at the C-terminus. And there were 5 Proline residues, 5 Glycine and 4 Cysteine residues between SPS and WAP domain in SpCrus6. These features indicated that SpCrus6 was a new member of crustin family. The SpCrus6 mRNA transcripts were up-regulated obviously after bacteria or virus challenge. These changes showed that SpCrus6 was involved in the antimicrobial and antiviral responses of Scylla paramamosain. Recombinant SpCrus6 (rSpCrus6) showed strong inhibitory abilities against Gram-positive bacteria (Bacillus megaterium, Staphylococcus aureus, and Bacillus subtilis). But the inhibitory abilities against four Gram-negative bacteria (Vibrio parahemolyticus, Vibrio alginolyticus, Vibrio harveyi and Escherichia coli) and two fungi (Pichia pastoris and Candida albicans) were not strong enough. Besides, rSpCrus6 could strongly bind to two Gram-positive bacteria (B. subtilis and B. megaterium) and three Gram-negative bacteria (V. alginolyticus, V. parahemolyticus, and V. harveyi). And the binding levels to S. aureus and two fungi (P. pastoris and C. albicans) were weak. The polysaccharides binding assays' results showed rSpCrus6 had superior binding activities to LPS, LTA, PGN and β-glucan. Through agglutinating assays, we found rSpCrus6 could agglutinate well three Gram-positive bacteria (S. aureus, B. subtilis and B. megaterium). And the agglutinating activities to Gram-negative bacteria and fungi were not found. In the aspect of antiviral functions, rSpCrus6 could bind specifically to the recombinant envelop protein 26 (rVP26) of white spot syndrome virus (WSSV) but not to recombinant envelop protein 28 (rVP28), whereas GST protein could not bind to rVP26 or rVP28. Besides, rSpCrus6 could suppress WSSV reproduction to some extent. Taken together, SpCrus6 was a multifunctional immunity effector in the innate immunity defending response of S. paramamosain.

Quantitative analysis of the dose-response of white spot syndrome virus in shrimp

White spot syndrome virus (WSSV) is an important cause of mortality and economic losses in shrimp farming. Although WSSV-induced mortality is virus dose dependent and WSSV infection does not necessarily lead to mortality, the relationships between virus-particle dose, infection and mortality have not been analysed quantitatively. Here, we explored WSSV dose-response by a combination of experiments, modelling and meta-analysis. We performed dose-response experiments in Penaeus vannamei postlarvae, recorded host mortality and detected WSSV infection. When we fitted infection models to these data, two models-differing in whether they incorporated heterogeneous host susceptibility to the virus or not-were supported for two independent experiments. To determine the generality of these results, we reanalysed published data sets and then performed a meta-analysis. We found that WSSV dose-response kinetics is indeed variable over experiments. We could not clearly identify which specific infection model has the most support by meta-analysis, but we argue that these results also are most concordant with a model incorporating varying levels of heterogeneous host susceptibility to WSSV. We have identified suitable models for analysing WSSV dose-response, which can elucidate the most basic virus-host interactions and help to avoid underestimating WSSV infection at low virus doses.

RNAi screening identifies a new Toll from shrimp Litopenaeus vannamei that restricts WSSV infection through activating Dorsal to induce antimicrobial peptides

The function of Toll pathway defense against bacterial infection has been well established in shrimp, however how this pathway responds to viral infection is still largely unknown. In this study, we report the Toll4-Dorsal-AMPs cascade restricts the white spot syndrome virus (WSSV) infection of shrimp. A total of nine Tolls from Litopenaeus vannamei namely Toll1-9 are identified, and RNAi screening in vivo reveals the Toll4 is important for shrimp to oppose WSSV infection. Knockdown of Toll4 results in elevated viral loads and renders shrimp more susceptible to WSSV. Furthermore, Toll4 could be a one of upstream pattern recognition receptor (PRR) to detect WSSV, and thereby leading to nuclear translocation and phosphorylation of Dorsal, the known NF-κB transcription factor of the canonical Toll pathway. More importantly, silencing of Toll4 and Dorsal contributes to impaired expression of a specific set of antimicrobial peptides (AMPs) such as anti-LPS-factor (ALF) and lysozyme (LYZ) family, which exert potent anti-WSSV activity. Two AMPs of ALF1 and LYZ1 as representatives are demonstrated to have the ability to interact with several WSSV structural proteins to inhibit viral infection. Taken together, we therefore identify that the Toll4-Dorsal pathway mediates strong resistance to WSSV infection by inducing some specific AMPs.

The TLR pathway mediated antiviral immune response is well identified in mammals, yet, Toll pathway governing this protection in invertebrates remains unknown. In the present study, we uncover that a shrimp Toll4 from a total of nine Tolls in L. vannamei confers resistance to WSSV thought inducing the NF-κB transcription factor Dorsal to inspire the production of some antimicrobial peptides (AMPs) with antiviral activity. The anti-LPS-factor (ALF) and lysozyme (LYZ) family are identified as the Toll4-Dorsal pathway targeted genes with the ability to interact with viral structural proteins in response to WSSV infection. These results suggest that the Toll receptor induces the expression of AMPs with antiviral activity could be a general antiviral mechanism in invertebrates and Toll pathway established antiviral defense could be conserved during evolution.

White spot syndrome virus (WSSV) suppresses penaeidin expression in Marsupenaeus japonicus hemocytes

Penaeidins are a unique family of antimicrobial peptides specific to penaeid shrimp and have been reported mainly function as anti-bacterial and anti-fungal. In order to investigate whether penaeidins could also respond to virus or not, we examined the effect of WSSV on MjPen-II (penaeidin in kuruma shrimp, Marsupenaeus japonicus) expression. In the control group, MjPen-II transcript level can be detected in almost all test tissues but was expressed most strongly in hemocytes. After WSSV infection, MjPen-II transcript level was significantly downregulated in hemocytes. Moreover, the proportion of MjPen-II+ hemocytes was not significantly different between non-infected and WSSV-infected shrimp, but the number of MjPen-II+ highly expressing hemocytes decreased after infection. In addition, MjPen-II was observed in the cytoplasm of granule-containing hemocytes. These results suggest that WSSV suppresses MjPen-II expression in hemocytes.

A novel white spot syndrome virus-induced gene (MjVIG1) from Marsupenaeus japonicus hemocytes

cDNA of a newly recognized white spot syndrome virus (WSSV)-induced gene (MjVIG1) was characterized from Marsupenaeus japonicus hemocytes; this gene encodes a protein that lack similarity to any known characterized protein. To identify this novel gene, we mainly conducted transcript level analysis, immunostaining and flow cytometry after WSSV infection. MjV1G1 transcript levels were also measured after Yellow head virus (YHV) and Vibrio parahaemolyticus infection tests. In non-infected and WSSV-infected shrimp, MjVIG1 was observed in granule-containing hemocytes. In addition, the MjVIG1 transcript level and ratio of MjVIG1-positive hemocytes both significantly increased, and number of MjVIG1-positive hemocytes slightly increased after WSSV infection. In contrast, MjVIG1 transcript level did not change after YHV and V. parahaemolyticus infection. These results indicated that MjVIG1 might be a WSSV-specific induced gene in M. japonicus hemocytes.

C-terminal domain of WSSV VP37 is responsible for shrimp haemocytes binding which can be inhibited by sulfated galactan

Viral envelope proteins play an important role in facilitating the attachment of viruses to the surface of host cells. Here, we investigated the binding of White Spot Syndrome Virus (WSSV) VP37 to haemocytes of whiteleg shrimp, Litopenaeus vannamei. Three versions of recombinant VP37 proteins, including full length VP37 (VP37_(1-281)), C-terminal domain VP37 (VP37_(111-281)) and C-terminal domain disrupted VP37 (VP37_(1-250)) were individually expressed and tested for their haemocytes binding ability. Through an ELISA-based binding assay, we found that VP37_(111-281) bound to shrimp haemocytes in a similar way to VP37_(1-281), while VP37_(1-250) exhibited a significantly weaker binding. This suggests that the C-terminal domain of VP37 is required for the binding of VP37 to shrimp haemocytes. Furthermore, we found that the binding of VP37 to shrimp haemocytes was impaired by pre-incubation of VP37 with sulfated galactan (SG), a sulfated polysaccharide derived from red seaweed (Gracilaria fisheri). Previously, it has been shown that a type of sulfated polysaccharide, heparin, is also present in L. vannamei. To investigate the role of heparin as a receptor for VP37, the binding of VP37 to porcine heparin, whose structure is similar to that found in L.vannamei, was investigated in a Surface Plasmon Resonance (SPR) system. The results showed that VP37 bound strongly to heparin with binding affinity (K_D) of 1.0 μM and the binding was significantly blocked by SG. These findings have lead us to propose that the attachment of WSSV might be mediated by the interaction between VP37 and a heparin-like molecule presented on the shrimp cells.

Shrimp hemocyte homeostasis-associated protein (PmHHAP) interacts with WSSV134 to control apoptosis in white spot syndrome virus infection

Hemocyte homeostasis-associated protein (PmHHAP) was first identified as a viral-responsive gene, due to a high upregulation in transcription following white spot syndrome virus (WSSV) infection. Functional studies using RNA interference have suggested that PmHHAP is involved in hemocyte homeostasis by controlling apoptosis during WSSV infection. In this study, the role of PmHHAP in host-viral interactions was further investigated. Yeast two-hybrid assay and co-immunoprecipitation revealed that PmHHAP binds to an anti-apoptosis protein, WSSV134. The viral protein WSSV134 is a late protein of WSSV, expressed 24 h post infection (hpi). Gene silencing of WSSV134 in WSSV-infected shrimp resulted in a reduction of the expression level of the viral replication marker genes VP28, wsv477, and ie-1, which suggests that WSSV134 is likely involved in viral propagation. However, co-silencing of PmHHAP and WSSV134 counteracted the effects on WSSV infection, which implies the importance of the host-pathogen interaction between PmHHAP and WSSV134 in WSSV infection. In addition, caspase 3/7 activity was noticeably induced in the PmHHAP and WSSV134 co-silenced shrimp upon WSSV infection. Moreover, PmHHAP and WSSV134 inhibited caspase-induced activation of PmCasp in vitro in a non-competitive manner. Taken together, these results suggest that PmHHAP and WSSV134 play a role in the host-pathogen interaction and work concordantly to control apoptosis in WSSV infection.

Circulatory white spot syndrome virus in South-West region of Bangladesh from 2014 to 2017: molecular characterization and genetic variation

White Spot Syndrome Virus (WSSV), the etiological agent of White Spot Disease (WSD) is a major impediment for shrimp aquaculture in the worldwide. A critical threshold level of WSSV load in infected shrimp is an important trait for disease manifestation and WSSV transmission in cultured shrimp and subsequently make outbreaks. The present study investigated 120 naturally infected cultured shrimp samples by SYBR Green based qPCR assay for WSD diagnosis and quantification of WSSV load. Among them, 94 samples resulted a variable count of WSSV load ranging from 2.1 × 10⁸ to 2.64 × 10¹⁴ copies/g of shrimp tissue. The severity of WSSV infection was assessed based on the established critical threshold load of WSSV in shrimp tissue. Compared to the established critical threshold value of WSSV load in shrimp tissue, our findings showed the horrifying scenario of the severity of WSSV infection in cultured shrimps of Bangladesh that was found to be above the critical limit to initiate an outbreak in the Bangladeshi shrimp aquaculture industry. The latest phylogenetic pattern was altered from the former monophyletic history among WSSVs of Bangladesh due to a variation at 500th nucleotide of VP28 coding gene. Viruses characterized from recent outbreaks in 2015 and 2017 displayed amino acid substitution at position 167 (G→E) on the surface of VP28 protein which has demonstrated the probable replacement of indigenous virus pool. Therefore, it is imperative to take initiative for the management and prevention of WSSV outbreak to sustain shrimp aquaculture in South-West region of Bangladesh.

Novel Insights into Antiviral Gene Regulation of Red Swamp Crayfish, Procambarus clarkii, Infected with White Spot Syndrome Virus

White spot syndrome virus (WSSV), one of the major pathogens of Procambarus clarkii, has caused severe disruption to the aquaculture industry of P. clarkii in China. To reveal the gene regulatory mechanisms underlying WSSV infection, a comparative transcriptome analysis was performed among WSSV-infected susceptible individuals (GS), viral resistant individuals (GR), and a non-infected control group (GC). A total of 61,349 unigenes were assembled from nine libraries. Subsequently, 515 and 1033 unigenes exhibited significant differential expression in sensitive and resistant crayfish individuals compared to the control group (GC). Many differentially expressed genes (e.g., C-type lectin 4, Peroxinectin, Prophenoloxidase, and Serine/threonine-protein kinase) observed in GR and GS play critical roles in pathogen recognition and viral defense reactions after WSSV infection. Importantly, the glycosaminoglycan biosynthesis-chondroitin sulfate/dermatan sulfate pathway was identified to play critical roles in defense to WSSV infection for resistant crayfish individuals by upregulating the chondroitin sulfate related genes for the synthesis of WSSV-sensitive, functional chondroitin sulfate chains containing E units. Numerous genes and the key pathways identified between resistant and susceptible P. clarkii individuals provide valuable insights regarding antiviral response mechanisms of decapoda species and may help to improve the selective breeding of P. clarkii WSSV-resistance.

Vaccination with multimeric recombinant VP28 induces high protection against white spot syndrome virus in shrimp

To improve the efficacy of WSSV protection, multimeric (tetrameric) recombinant VP28 (4XrVP28) was produced and tested in comparison with those of monomeric VP28 (1XrVP28). In vitro binding of either 1XrVP28 or 4XrVP28 to shrimp hemocyte surface was evident as early as 10 min after protein inoculation. Similar results were obtained in vivo when shrimp were injected with recombinant proteins that the proteins bound to the hemocyte surface could be detected since 5 min after injection. Comparison of the WSSV protection efficiencies of 1XrVP28 or 4XrVP28 were performed by injection the purified 1XrVP28 or 4XrVP28 (22.5 μg/shrimp) and WSSV inoculum (1000 copies/shrimp) into shrimp. At 10 dpi, while shrimp injected with WSSV inoculum reached 100% mortality, shrimp injected with 1XrVP28 + WSSV or 4XrVP28 + WSSV showed relative percent survival (RPS) of 67% and 81%, respectively. PCR quantification revealed high number of WSSV in the moribund shrimp of WSSV- and 1XrVP28+WSSV-injected group. In contrast, lower number of WSSV copies were found in the survivors both from 1XrVP28+WSSV- or 4XrVP28+WSSV- injected groups. Histopathological analysis demonstrated the WSSV infected lesions found in the moribund from WSSV-infected group and 1XrVP28+WSSV-injected group, but less or none in the survivors. ELISA demonstrated that 4XrVP28 exhibited higher affinity binding to rPmRab7, a WSSV binding protein essential for WSSV entry to the cell than 1XrVP28. Taken together, the protection against WSSV in shrimp could be improved by application of multimeric rVP28.

An optimized double-antibody sandwich ELISA for quantitative detection of WSSV in artificially infected crayfish

Developing a rapid, accurate and quantitative method for detecting white spot syndrome virus (WSSV) is extremely urgent and critical for reducing the risk of white spot disease outbreaks. In the present work, an optimized double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) was developed for quantitative detection of WSSV. The method employed rabbit polyclonal antibodies against WSSV as the capture antibody and previously produced anti-WSSV monoclonal antibodies as the detector antibody. A standard curve of the log concentration of WSSV versus OD value was established, which was linear in the concentration range of 120-7680ng/mL, and the linear regression equation was y=0.166x-0.151. Viral proteins in different tissues of crayfish (Procambarus clarkia) post artificial infection with WSSV were quantitatively measured using the DAS-ELISA. WSSV proliferated quickly within 60h post infection and gradually slowed down afterwards. According to the linear regression relationship, the viral proteins in hemolymph, gut and gonad were firstly able to be quantified at 24h post infection with the concentrations of 186, 158 and 128ng/mL, respectively. These three tissues also contained higher viral proteins than the gill, heart, hepatopancreas and muscle during the entire infection period. The viral protein concentration in gut reached the highest level of 6220ng/mL at 72h post infection. Real time quantitative PCR was also used to detect the dynamic change of viral copies in crayfish hemolymph post WSSV infection, with similar results for both assays. The developed DAS-ELISA could detect WSSV propagation from initial to moribund stage in infected crayfish and demonstrated potential application for diagnosis of WSSV.

Delivery of viral recombinant VP28 protein using chitosan tripolyphosphate nanoparticles to protect the whiteleg shrimp, Litopenaeus vannamei from white spot syndrome virus infection

The VP28 gene of white spot syndrome virus was amplified by PCR using gene specific primer set and cloned into pRSET B vector to produce recombinant VP28 (r-VP28) in E. coli GJ1158. The chitosan tripolyphosphate nanoparticles (CS/TPP) were prepared by ionic gelation process and characterized. The purified r-VP28 protein was encapsulated by CS/TPP nanoparticles. The encapsulation efficiency of CS/TPP nanoparticles was found to be 84.8% for r-VP28 protein binding with CS/TPP nanoparticles. The in vitro release profile of encapsulated r-VP28 was determined after treating with protease and chitosanase. The different types of feed were formulated and named as normal feed with PBS, Feed A coated with crude r-VP28, Feed B with purified r-VP28 and Feed C with CS/TPP encapsulated r-VP28 (Purified). Tissue distribution and clearance of r-VP28 at different time intervals were examined in shrimp fed with different types of feed by ELISA and the results showed the presence of r-VP28 protein in different organs. Various immunological parameters were assessed in experimental shrimp. The mRNA expression of five immune-related genes was analysed by qPCR in order to investigate their response to all types of feed in shrimp. A cumulative percentage mortality was also recorded in treated shrimp challenged with WSSV.

The Roles of β-Integrin of Chinese Shrimp (Fenneropenaeus chinensis) in WSSV Infection

Our previous study demonstrated that an integrin β subunit of Chinese shrimp (Fenneropenaeus chinensis) (FcβInt) plays an important role in white spot syndrome virus (WSSV) infection. In the present work, in order to further elucidate the potential role of FcβInt in WSSV infection, the recombinant extracellular domain of β integringene of F. Chinensis (rFcβInt-ER) was expressed in Escherichia coli BL21 (DE3), and the eukaryotic expression plasmid PcDNA3.1-FcβInt-ER (PFcβInt-ER) was also constructed. Far-western blotting was performed to determine the binding specificity of rFcβInt-ER to WSSV envelope proteins, and results showed that rFcβInt-ER was able to specifically interact with rVP31, rVP37, rVP110 and rVP187. Moreover, the blocking effects of mouse anti-rFcβint-ER antibodies were both detected in vivo and in vitro. The ELISA and Dot-blotting in vitro assays both showed that mouse anti-rFcβInt-ER antibodies could partially block the binding of WSSV to the hemocyte membrane of F. chinensis. In the in vivo assays, the mortality of shrimp injected with WSSV mixed with anti-rFcβInt-ER antibodies was delayed, and was lower than in the control group. While the shrimp were intramuscularly injected with PFcβInt-ER, transcripts of PFcβInt-ER could be detected in different shrimp tissues within 7 days, and the mortality of shrimp injected with PFcβInt-ER was also delayed and lower compared with the control group post WSSV challenge. Furthermore, gene silencing technology was also used to verify the effect of FcβInt in WSSV infection, and results showed that the expression levels of the WSSV immediate early gene iel, early gene wsv477, and late gene VP28 and the mortality of F. Chinensis were all significantly decreased in the FcβInt knock-down hemocyctes compared to the control group. Taken together, these results suggest that FcβInt plays important roles in WSSV infection.