Submersion Treatment of Chimeric MrN-VLPs Encapsulating Therapeutic Double-Stranded RNA Effectively Rescues Prawn Viral Infection.

One of the most successful applications to protect aquatic animals from viral infection is the use of RNA interference (RNAi) in the form of double-stranded RNA (dsRNA). However, its administration into animals is usually via injection route (laboratory scale) or mixing feed pellets with bacterial extracts (containing therapeutic compounds); the outcome of which remains to be improved. In this study, we encapsulated purified dsRNA into a virus-like particle (VLP) and delivered it into the prawn tissues by a submersion route using interiorly modified Macrobrachium rosenbergii nodavirus derived VLP with deca-arginine peptide (10R-MrN-VLP) to encapsulate a large scale (gram-level) of dsRNA against RNA2 gene of MrNV capsid. For tracing purposes of submersion administration, GFP plasmid-loaded VLP successfully delivered and expressed green fluorescent protein in prawn-targeted tissues. Delivery efficiency at 12-h submersion was about 50% of the prawn population and became 100% within 72 h, and they remained GFP-positive for up to 7 days during submersion. The protective effect of dsRNA-VLP submersion was tested with a large group (10,000) of post-larvae, which were naturally challenged with MrNV-positive dead prawn. Transcriptome analysis revealed up- and down-regulations of gene clusters involved in metabolism and signal transduction related to an antiviral immune system. The survival rate of prawn treated with dsRNA-VLP reached 80% at Day 7 post-MrNV challenge, significantly different from that of the MrNV-challenged group (control). PCR screening revealed an apparent decrease of MrNV genes and the copy number of MrNV in prawn sampling tissues. Together, we believe that the integration between the chimeric nanocontainer, RNAi technology and submersion application should be foreseen as one of the practical, powerful means to fight against prawn viral infection in field application.