Immune gene expression and protective effects in goldfish (Carassius auratus L.) immunized with formalin-inactivated cyprinid herpesvirus-2 (CyHV-2) vaccine.

The goldfish hematopoietic necrosis viral disease (GHNVD) has led to worldwide economic losses in goldfish aquaculture. The present study has focused on the development of an inactivated vaccine for the cyprinid herpesvirus (CyHV-2) and to check the immunogenicity of the vaccine in the host. The fantail goldfish fin (FtGF) cell line was used in the propagation of the CyHV-2 and the viral titer obtained were of 107.8 TCID50/ml. Followed by the virus was inactivated using 0.1% formalin for 2 days. Various concentrations of formalin-inactivated CyHV-2 (1%, 0.7%, 0.5%, 0.3% and 0.1%) were studied in the FtGF cell line. Morphological changes were observed in the FtGF cell line in all other concentrations of formalin except 0.1% formalin-inactivated CyHV-2 vaccine. The goldfishes were intraperitoneally injected with 300 μl of vaccine and various immune gene responses were studied for a period of 30 days. The gene expression of the adaptive markers CD8, CD4, IFN-ϒ, the cytokines (IL-10, IL-12) was studied in kidney and spleen tissues. Formalin-inactivated CyHV-2 vaccine showed a significant up-regulation of the genes CD8 and IFN-ϒ by the 6th hr post-vaccination onwards. The experimental fish were challenged intraperitoneally with CyHV-2 virus of concentration 107.8 TCID50/ml after 30 days of post-vaccination. A significant difference in cumulative mortality rate was observed for the vaccinated fishes from the unvaccinated fishes. The relative percent survival for formalin immunized fish was 74.03%. Our results have proven that the formalin-inactivated vaccines were efficient and it resulted in triggering the immune gene expression in goldfish. The development and further enhanced studies for this vaccine will lead to a promising low-cost commercial vaccine for CyHV-2 viral infection.