Recombinant infectious hematopoietic necrosis virus and viral hemorrhagic septicemia virus glycoprotein epitopes expressed in Aeromonas salmonicida induce protective immunity in rainbow trout (Oncorhynchus mykiss).

Fragments of the glycoprotein genes of viral hemorrhagic septicemia virus (VHSV) and infectious hematopoietic necrosis virus (IHNV) were cloned into a bacterial broad-host-range expression vector under the control of the plac promoter. Western blot (immunoblot) analysis with monoclonal antibodies specific to the glycoproteins demonstrated the inducible expression of the fusion proteins in Escherichia coli. Aeromonas salmonicida is the causative agent of furunculosis in salmonid fish. It was confirmed that an avirulent strain of A. salmonicida, A440, which contains a deletion in the structural gene for the paracrystalline surface protein array, will provide protective immunity against furunculosis when used as a live attenuated vaccine. The plasmid-encoded viral epitopes were then mobilized into A440 for use as a shuttle system for the expression of fragments of the glycoprotein genes of IHNV and VHSV. Vaccination of rainbow trout with A440 containing the viral epitopes resulted in the development of protective immunity against both VHSV and IHNV. This indicates that the use of cloned fragments of the glycoproteins and the use of A. salmonicida as a shuttle system constitute a feasible approach to fish vaccine development.