Preferential suppression of yellow head virus (YHV) envelope protein gp116 in shrimp that survive challenge with YHV

In silico screening of chalcones and flavonoids as potential inhibitors against yellow head virus 3C-like protease

Yellow head virus (YHV) is one of the most important pathogens in prawn cultivation. The outbreak of YHV could potentially result in collapses in aquaculture industries. Although a flurry of development has been made in searching for preventive and therapeutic approaches against YHV, there is still no effective therapy available in the market. Previously, computational screening has suggested a few cancer drugs to be used as YHV protease (3CL^pro) inhibitors. However, their toxic nature is still of concern. Here, we exploited various computational approaches, such as deep learning-based structural modeling, molecular docking, pharmacological prediction, and molecular dynamics simulation, to search for potential YHV 3CL^pro inhibitors. A total of 272 chalcones and flavonoids were in silico screened using molecular docking. The bioavailability, toxicity, and specifically drug-likeness of hits were predicted. Among the hits, molecular dynamics simulation and trajectory analysis were performed to scrutinize the compounds with high binding affinity. Herein, the four selected compounds including chalcones cpd26, cpd31 and cpd50, and a flavonoid DN071_f could be novel potent compounds to prevent YHV and GAV propagation in shrimp. The molecular mechanism at the atomistic level is also enclosed that can be used to further antiviral development.

Nidoviruses of Fish and Crustaceans

Viruses with diverse virion architectures demarcated into four families in the order Nidovirales have been discovered in vertebrate mammalian and fish species, as well as in invertebrate crustacean and mosquito species. The order is unified by nidoviruses sharing intermediate (12.7 kb) to very long (31.7 kb) (+) ssRNA genomes, each possessing a long 5′-terminal gene encoding overlapping ORF1a and ORF1b reading frames that contain a diversity of functionally related enzymes and that are translated in toto using a −1 ribosomal frameshift mechanism, as well as by semiconserved strategies for transcribing a nested set of 3′-coterminal subgenomic mRNAs that translate the viral proteins. The nidovirus that is most important to an aquaculture species is yellow head virus (YHV), which causes disease in shrimp farmed throughout the Eastern Hemisphere and is classified in the genus Okavirus, family Roniviridae. Fathead minnow nidovirus, genus Bafinivirus, subfamily Torovirinae, family Coronaviridae, also causes disease in minnows grown for the baitfish industry in the United States. Virions similar in morphology to okaviruses and bafiniviruses have also been detected in several crab species. Of these, however, only Eriocheir sinensis ronivirus, which causes disease in the Chinese mitten crab, an important freshwater aquaculture species in China, has been shown to possess a ~22 kb ssRNA genome that supports its being a nidovirus, but its taxonomic classification awaits genome sequence analysis. This chapter provides an overview of the structure, replication and biology of these viruses with a particular focus on YHV disease characteristics, diagnostic methods and disease prevention strategies.

Protection from yellow head virus (YHV) infection in Penaeus vannamei pre-infected with Taura syndrome virus (TSV)

Pacific white shrimp Penaeus vannamei that were pre-exposed to Taura syndrome virus (TSV) and then challenged with yellow head virus (YHV) acquired partial protection from yellow head disease (YHD). Experimental infections were carried out using specific-pathogen-free (SPF) shrimp which were first exposed per os to TSV; at 27, 37 and 47 d post infection they were then challenged by injection with 1 × 104 copies of YHV per shrimp (designated the TSV-YHV group). Shrimp not infected with TSV were injected with YHV as a positive control. Survival analyses comparing the TSV-YHV and YHV (positive control) groups were conducted, and significant survival rates were found for all the time groups (p < 0.001). A higher final survival was found in the TSV-YHV group (mean 55%) than in the positive control (0%) (p < 0.05). Duplex reverse transcription quantitative PCR was used to quantify both TSV and YHV. Lower YHV copy numbers were found in the TSV-YHV group than in the positive control in pleopods (3.52 × 109 vs. 1.88 × 1010 copies µg RNA-1) (p < 0.001) and lymphoid organ (LO) samples (3.52 × 109 vs. 1.88 × 1010 copies µg RNA-1) (p < 0.01). In situ hybridization assays were conducted, and differences in the distribution of the 2 viruses in the target tissues were found. The foci of LO were infected with TSV but were not infected with YHV. This study suggests that a viral interference effect exists between TSV and YHV, which could, in part, explain the absence of YHD in the Americas, where P. vannamei are often raised in farms where TSV is present.

Viral disease emergence in shrimp aquaculture: origins, impact and the effectiveness of health management strategies

Shrimp aquaculture has grown rapidly over several decades to become a major global industry that serves the increasing consumer demand for seafood and has contributed significantly to socio-economic development in many poor coastal communities. However, the ecological disturbances and changes in patterns of trade associated with the development of shrimp farming have presented many of the pre-conditions for the emergence and spread of disease. Shrimp are displaced from their natural environments, provided artificial or alternative feeds, stocked in high density, exposed to stress through changes in water quality and are transported nationally and internationally, either live or as frozen product. These practices have provided opportunities for increased pathogenicity of existing infections, exposure to new pathogens, and the rapid transmission and transboundary spread of disease. Not surprisingly, a succession of new viral diseases has devastated the production and livelihoods of farmers and their sustaining communities. This review examines the major viral pathogens of farmed shrimp, the likely reasons for their emergence and spread, and the consequences for the structure and operation of the shrimp farming industry. In addition, this review discusses the health management strategies that have been introduced to combat the major pathogens and the reasons that disease continues to have an impact, particularly on poor, small-holder farmers in Asia.