Cyprinid herpesvirus 3 (CyHV-3)
infection in carp causes a fatal and highly contagious disease that results in huge economic losses in common and koi carp aquaculture worldwide. Thus the development of an effective
vaccine to protect carp stocks against the CyHV3 virus is imperative. In this study, we immunized common carps with
a DNA vaccine consisting of a plasmid that co-expresses the CyHV-3 envelope
protein ORF25 and the carp IL-1β gene in order to evaluate the adjuvant potential of IL-1β. Our result shows that
antibodies specific to ORF25 can be detected as early as one week after
intramuscular injection of the
DNA vaccine at low dosage. Moreover, the co-expression of IL-1β can enhance the potency of the
vaccine, as demonstrated by a higher antibody level after the third immunizations. Importantly, the
DNA vaccine reduced mortality in carps when they were immunized prior to a CyHV-3 challenge, as compared to negative control groups. However, despite being able to induce higher
neutralizing antibody titres, the co-expression of IL-1β in the
DNA vaccine did not significantly improve the overall survival of immunized fish following virus challenge. Furthermore, the
DNA vaccine can protect carps from tissue damage and histopathological alteration caused by
viral infection. These strongly suggests that the
vaccine can efficiently elicit protective immunity against CyHV-3
infection. In conclusion, the
DNA vaccine formulated with the pIRES-ORF25-IL-1β
DNA construct can protect carp against CyHV-3
infection and has potential applicability in the aquaculture industry.