Antiviral DNA vaccination in rainbow trout (Oncorhynchus mykiss) affects the immune response in the ovary and partially blocks its capacity to support viral replication in vitro

DNA vaccination has proved a very effective method for controlling viral infections in fish, especially those provoked by rhabdovirus such as viral hemorrhagic septicaemia virus (VHSV). Recently, an effective DNA vaccine against infectious pancreatic necrosis virus (IPNV) that codes for the viral polyprotein, and exerts its activity through a different mode of action than rhabdoviral vaccines has been developed. Despite their known protective capacity, whether DNA vaccines completely protect fish from viral replication or on the contrary allow residual replication levels that could give rise to asymptomatic carriers has never been clearly studied. This may be especially important in reproductive tissues in which transmission through seminal fluids takes place. In this context, we have determined in this study the effect that DNA vaccines against VHSV and IPNV have on the ovary immune response to then study how vaccination can affect the response to a posterior viral encounter. We have demonstrated that as VHSV and IPNV provoke very different immune responses in the ovary, the response to their corresponding vaccines also differs greatly. In the case of VHSV, we have also seen that vaccination significantly decreases the capacity of the virus to replicate in the ovary, but still permits some level of replication. This lower level of replication, however, provokes an immune unresponsiveness of the ovary to the virus.