Cyprinid herpesvirus-3 (CyHV-3) is an etiological agent of a notifiable disease that causes high mortality
rates affecting both the common and koi carp Cyprinus carpio L. There is no current treatment strategy
to save CyHV-3 infected fish. RNA mediated interference (RNAi) is an emerging strategy used for
understanding gene function and is a promising method in developing novel therapeutics and antiviral
medications. For this study, the possibility of activating the RNAi pathway by the use of small interfering
(si)RNAs was tested to inhibit in vitro viral replication of CyHV-3 in common carp brain (CCB) cells. The
siRNAs were designed to target either thymidine kinase (TK) or DNA polymerase (DP) genes, which both
code for transcripts involved in DNA replication. The inhibition of viral replication caused by the siRNAs
was measured by a reporter gene, termed ORF81. Treatment with siRNA targeting either TK or DP genes
reduced the release of viral particles from infected CCB cells. However, siRNA targeting DP was most
effective at reducing viral release as measured by qPCR.