Reduced loads of pre-existing Gill-associated virus (GAV) infection in juvenile Penaeus monodon injected with single or multiple GAV-specific dsRNAs

• Pre-existing GAV infection in juvenile shrimp is reduced by injection of dsRNAs.
• dsRNA target site is critical to the level of viral reduction achieved when using RNAi.
• Injection of 1 dsRNA may have the potential to abrogate vertical transmission of GAV.

The ability of RNA interference (RNAi) based on injected dsRNA was investigated here for its ability to reduce the severity of pre-existing subclinical Gill-associated virus (GAV) infections in farm stocks of juvenile Black Tiger shrimp (Penaeus monodon). Following tail muscle injection of single or multiple long dsRNAs targeted to sequences positioned across the GAV ORF1a/1b replicase genes, pleopods were sampled sequentially from individuals at regular intervals over a 2 week period to track changes in GAV RNA loads by quantitative real-time RT-PCR. Mean GAV RNA amounts showed statistically significant (P < 0.05) declines from Day 6 post-injection in shrimp injected with a cocktail of 5 GAV dsRNAs or a single dsRNA (dsGAV1) that targeted a ~ 1.2 kb sequence at the extreme 5′-terminus of the GAV genome. GAV RNA amounts were not reduced significantly among shrimp injected with another single dsRNA (dsGAV6) targeted to a sequence just downstream of the helicase motif in the ORF1b gene. Based on these encouraging data, it will be useful to determine whether the RNAi approach can reduce GAV infection loads sufficiently in P. monodon broodstock used in commercial hatcheries in Australia to restrict vertical transmission of GAV to seedstock.