Gene silencing of VP9 gene impairs WSSV infectivity on Macrobrachium rosenbergii

RNAi-Based Therapy: Combating Shrimp Viral Diseases

Shrimp aquaculture has become a vital industry, meeting the growing global demand for seafood. Shrimp viral diseases have posed significant challenges to the aquaculture industry, causing major economic losses worldwide. Conventional treatment methods have proven to be ineffective in controlling these diseases. However, recent advances in RNA interference (RNAi) technology have opened new possibilities for combating shrimp viral diseases. This cutting-edge technology uses cellular machinery to silence specific viral genes, preventing viral replication and spread. Numerous studies have shown the effectiveness of RNAi-based therapies in various model organisms, paving the way for their use in shrimp health. By precisely targeting viral pathogens, RNAi has the potential to provide a sustainable and environmentally friendly solution to combat viral diseases in shrimp aquaculture. This review paper provides an overview of RNAi-based therapy and its potential as a game-changer for shrimp viral diseases. We discuss the principles of RNAi, its application in combating viral infections, and the current progress made in RNAi-based therapy for shrimp viral diseases. We also address the challenges and prospects of this innovative approach.

Potential dsRNAs can be delivered to aquatic for defense pathogens

The use of antibiotics to facilitate resistance to pathogens in aquatic animals is a traditional method of pathogen control that is harmful to the environment and human health. RNAi is an emerging technology in which homologous small RNA molecules target specific genes for degradation, and it has already shown success in laboratory experiments. However, further research is needed before it can be applied in aquafarms. Many laboratories inject the dsRNA into aquatic animals for RNAi, which is obviously impractical and very time consuming in aquafarms. Therefore, to enable the use of RNAi on a large scale, the methods used to prepare dsRNA need to be continuously in order to be fast and efficient. At the same time, it is necessary to consider the issue of biological safety. This review summarizes the key harmful genes associated with aquatic pathogens (viruses, bacteria, and parasites) and provides potential targets for the preparation of dsRNA; it also lists some current examples where RNAi technology is used to control aquatic species, as well as how to deliver dsRNA to the target hydrobiont.

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.

Temporal changes in transcriptome profile provide insights of White Spot Syndrome Virus infection in Litopenaeus vannamei

Shrimp aquaculture is severely affected by WSSV. Despite an increasing effort to understand host/virus interaction by characterizing changes in gene expression (GE) following WSSV infection, the majority of published studies have focussed on a single time-point, providing limited insight on the development of host-pathogen interaction over the infection cycle. Using RNA-seq, we contrasted GE in gills of Litopenaeus vannamei at 1.5, 18 and 56 hours-post-infection (hpi), between WSSV-challenged and control shrimps. Time course analysis revealed 5097 differentially expressed genes: 63 DEGs were viral genes and their expression in WSSV group either peaked at 18 hpi (and decreased at 56 hpi) or increased linearly up to 56 hpi, suggesting a different role played by these genes during the course of infection. The remaining DEGs showed that WSSV altered the expression of metabolic, immune, apoptotic and cytoskeletal genes and was able to inhibit NF-κB and JAK/STAT pathways. Interestingly, GE changes were not consistent through the course of infection but were dynamic with time, suggesting the complexity of host-pathogen interaction. These data offer novel insights into the cellular functions that are affected during the course of infection and ultimately provide a valuable resource towards our understanding of the host-pathogen dynamics and its variation with time.

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.

Meta-analysis of antiviral protection of white spot syndrome virus vaccine to the shrimp

Currently, white spot syndrome virus (WSSV) is one of the most serious pathogens that impacts shrimp farming around the world. A WSSV vaccine provides a significant protective benefit to the host shrimp. Although various types of vaccines against WSSV have emerged, the immune effects among them were not compared, and it remains unclear which type of vaccine has the strongest protective effect. Meanwhile, due to the lack of effective routes of administration and immunization programs, WSSV vaccines have been greatly limited in the actual shrimp farming. To answer these questions, this study conducted a comprehensive meta-analysis over dozens of studies and compared all types WSSV vaccines, which include sub-unit protein vaccines, whole virus inactivated vaccines, DNA vaccines and RNA-based vaccines. The results showed that the RNA-based vaccine had the highest protection rate over the other three types of vaccines. Among the various sub-unit protein vaccines, VP26 vaccine had the best protective effects than other sub-unit protein vaccines. Moreover, this study demonstrated that vaccines expressed in eukaryotic hosts had higher protection rates than that of prokaryotic systems. Among the three immunization modes (oral administration, immersion and injection) used in monovalent protein vaccines, oral administration had the highest protection rate. In natural conditions, shrimp are mostly infected by the virus orally. These results provide a guide for exploration of a novel WSSV vaccine and help facilitate the application of WSSV vaccines in shrimp farming.

Long dsRNAs promote an anti-viral response in Pacific oyster hampering ostreid herpesvirus 1 replication

Double stranded RNA-mediated genetic interference (RNAi) is a widely used reverse genetic tool for determining the loss-of-function phenotype of a gene. Here, the possible induction of an immune response by long dsRNA was tested in a marine bivalve, i.e. Crassostrea gigas, as well as the specific role of the subunit 2 of the nuclear factor κB inhibitor (IκB2). This gene is a candidate of particular interest for functional investigations in the context of massive mortality oyster events as Cg-IκB2 mRNA levels exhibited significant variation depending on the amount of ostreid herpesvirus 1 (OsHV-1) DNA detected. In the present study, dsRNAs targeting Cg-IκB2 and Green Fluorescence Protein genes were injected in vivo into oysters before being challenged by OsHV-1. Survival appeared close to 100% in both dsRNA injected conditions associated with a low detection of viral DNA and a low expression of a panel of 39 OsHV-1 genes as compared to infected control. Long dsRNA molecules, both Cg-IκB2- and GFP-dsRNA, may have induced an anti-viral state controlling the OsHV-1 replication and precluding the understanding of the Cg-IκB2 specific role. Immune-related genes including Cg-IκB1, Cg-Rel1, Cg-IFI44, Cg-PKR, and Cg-IAP appeared activated in dsRNA-injected condition potentially hampering viral replication and thus conferring a better resistance to OsHV-1 infection. We revealed that long dsRNA-mediated genetic interference triggered an anti-viral state in the oyster, emphasizing the need of new reverse genetics tools for assessing immune gene function and avoiding off-target effects in bivalves.