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 significant (P < 0.001) protection against a virus injection challenge can be attained in subyearling rainbow trout Oncorhynchus mykiss (145–160 g, 8- to 10-months-old) 6 weeks after a single intramuscular injection with doses as low as 1 μg. Complete protection was also reproducibly demonstrated at higher vaccine doses; however, no protection was observed with a 0.1-μg dose. Virus-neutralizing antibody titers were detected in fish that had been vaccinated with different doses of the DNA vaccine and then sham-infected; there appeared to be a dose-dependent effect, with higher titers obtained with higher doses of vaccine. The DNA-vaccinated animals that survived virus challenge had significantly (P < 0.05) higher neutralizing antibody titers than sham-infected, DNA-vaccinated control fish. Additionally, the titers detected in the IHN survivors exhibited a significant (P < 0.05) dose-dependent effect, with the highest titers being present in fish that received the highest vaccine doses.