Evaluation of protective effects of heat-inactivated cyprinid herpesvirus-2 (CyHV-2) vaccine against herpesviral hematopoietic necrosis disease (HVHND) in goldfish (Carassius auratus)

Cyprinid herpesvirus-2 (CyHV-2) is an important virus that causes herpesviral hematopoietic necrosis disease (HVHND) leading to huge economic losses in goldfish (Carassius auratus). However, until now no proper pro-phylactic measure or treatment is available for CyHV-2 infection in goldfish. Hence, in this experiment, we developed a heat-inactivated CyHV-2 vaccine and evaluated its performance in goldfish. Initially, CyHV-2 was propagated in the fantail goldfish fin (FtGF) cell line and the titer of the viral inoculum was 107.8 TCID50/ml. Subsequently, various temperatures (40 degrees C, 50 degrees C, 60 degrees C, 70 degrees C, and 80 degrees C) were evaluated to achieve the complete inactivation of CyHV-2. Only the viral inoculum inactivated at 80 degrees C for 1 h did not show any cyto-pathic effect in the FtGF cell line after five blind passages. Hence the heat-inactivated CyHV-2 vaccine developed at 80 degrees C was further used for immunization trials in goldfish. The experimental goldfish were intraperitoneally immunized with 300 mu L of the heat-inactivated CyHV-2 vaccine. Subsequently, the kidney and spleen tissues were sampled at various time points post-vaccination (6th hr, 2nd day, 4th day, 6th day, 10th day, 16th day, and 30th day) to evaluate the expression of immune genes (IL-12, IL-10, IFN-gamma, CD8, and CD4). A significant upre-gulation of immune genes was observed at various time points in the kidney and spleen tissue of the vaccinated goldfish. Furthermore, in order to study the efficacy of the vaccine, the experimental fish were challenged with CyHV-2 (107.8 TCID50/ml) after the 30th day post-vaccination. The survival of the fish in the vaccine group (86.7%) was significantly higher compared to the non-vaccinated group (20%). Moreover, the relative per-centage survival of the vaccinated group was 83.34%. In spite of the single dose, the heat-killed vaccine developed in the present study elicited the immune response and offered better protection in goldfish against CyHV-2. However, further large-scale field performance evaluation studies are necessary to develop this vaccine on a commercial scale.

Automated summary

In this experiment, a heat-inactivated CyHV-2 vaccine was developed and evaluated in goldfish. The vaccine showed significant upregulation of immune genes and provided better protection against CyHV-2 in the challenged fish.