Efficacy of double-stranded RNA against white spot syndrome virus (WSSV) non-structural (orf89, wsv191) and structural (vp28, vp26) genes in the Pacific white shrimp Litopenaeus vannamei.

White spot syndrome virus (WSSV) is a major pathogen in shrimp aquaculture. RNA interference (RNAi) is a promising tool against viral infections. Previous works with RNAi showed different antiviral efficacies depending on the silenced gene. This work evaluated the antiviral efficacy of double-stranded (ds) RNA against two non-structural ( orf89 , wsv191 ) WSSV genes compared to structural ( vp26 , vp28 ) genes to inhibit an experimental WSSV infection. Gene orf89 encodes a putative regulatory protein and gene white spot virus ( wsv ) 191 encodes a nonspecific nuclease; whereas genes vp26 and vp28 encode envelope proteins, respectively. Molecules of dsRNA against each of the WSSV genes were intramuscularly injected (4 μg per shrimp) into a group of shrimp 48 h before a WSSV challenge. The highest antiviral activity occurred with dsRNA against orf89 , vp28 and vp26 (cumulative mortalities 10%, 10% and 21%, respectively). In contrast, the least effective treatment was wsv191 dsRNA (cumulative mortality 83%). All dead animals were WSSV-positive by one-step PCR, whereas reverse-transcription PCR of all surviving shrimp confirmed inhibition of virus replication. This study showed that dsRNA against WSSV genes orf89 , vp28 and vp26 were highly effective to inhibit virus replication and suggest an essential role in WSSV infection. Non-structural WSSV genes such as orf89 can be used as novel targets to design therapeutic RNAi molecules against WSSV infection. [ABSTRACT FROM AUTHOR]