The dose-dependent effect on protection and humoral response to a DNA vaccine against infectious hematopoietic necrosis (IHN) virus in subyearling rainbow trout

A dose-response study that used the DNA vaccine pIHNw-G against infectious hematopoietic necrosis virus (IHNV) showed that complete and highly signifi cant (P < 0.001) protection against a virus injection challenge can be atta ined in subyearling rainbow trout Oncorhynchus mykiss (145-160 g, 8- to 10- months-old) 6 weeks after a single intramuscular injection with doses as lo w as 1 <mu>g. Complete protection was also reproducibly demonstrated at-hig her vaccine doses; however, no protection was observed with a 0.1-mug dose. Virus-neutralizing antibody titers were detected in fish that had been Vac cinated With different doses of the DNA vaccine and then sham-infected; the re appeared to be a dose-dependent effect, with higher titers obtained with higher doses of vaccine. The DNA-vaccinated animals that survived virus ch allenge had significantly (P < 0.05) higher neutralizing antibody titers th an sham-infected, DNA-vaccinated control fish. Additionally, the titers det ected in the IHN survivors exhibited a significant (P < 0.05) dose-dependen t effect, with the highest titers being present in fish that received the h ighest Vaccine doses.