In vivo inhibition of the Ostreid Herpesvirus-1 (OsHV-1) replication in juveniles of the Pacific oyster Crassostrea gigas by a specific RNAi targeting the viral DNA polymerase gene

The global industrial farming of the Pacific oyster (Crassostrea gigas) has faced significant losses in production and a major negative social impact due to the occurrence of massive mortalities putatively attributed to the Ostreid Herpesvirus-1 (OsHV-1). Therefore, therapies based on RNA interference (RNAi), including the small hairpin RNAs (shRNA), have become promising and powerful alternatives against viral infections. A large open reading frame (ORF) in the OsHV-1 genome encodes a DNA polymerase gene. Since this polymerase is essential for viral replication, it is an ideal target for silencing OsHV-1. Thus, this study aimed to investigate the effect of silencing the OsHV-DNA polymerase gene using an shRNA in C. gigas in vivo on viral replication. The shRNA targeting the viral DNA polymerase was injected into OsHV-1 inoculated juveniles of C. gigas. The results demonstrate that silencing the viral DNA polymerase retarded the mortality of OsHV-1 experimentally infected oysters by 60 h. Furthermore, a decrease in the apoptotic levels (19%) was detected in the gills of DNApol-silenced organisms, compared to those levels observed in experimentally infected organisms. In addition, it was found that the viral load from DNApol-silenced organisms decreased in comparison to the infected oysters. These results suggest that the DNA polymerase gene was silenced, preventing viral DNA replication. Therefore, shRNA may be a promising approach for the future control of OsHV-1 infection in the Pacific oyster.