Immune Response And Protection In Gibel Carp, Carassius Gibelio, After Vaccination With β-Propiolactone Inactivated Cyprinid Herpesvirus 2

Gibel carp(Carassius gibelio) is one of the most important fish in freshwater aquaculture in China. Herpesviral haematopoietic necrosis(HVHN) of gibel carp(Carassius gibelio) is a newly emerged infectious disease and has caused huge economic losses in aquaculture operations. The causative pathogen has been identified as the cyprinid herpesvirus 2(CyHV-2). Vaccination has been proven to be an effective method in fish for preventing infectious diseases. This study was designed to investigate the method of inactiving virus, immunization dose of inactivated vaccine, the immune responses and protection in gibel carp. The aim of this study is to establish a technology for the prevention and control of the herpesviral haematopoietic necrosis(HVHN) of gibel carp. The contents and results of the study are listed as follows:1. Cell cultured cyprinid herpesvirus 2(CyHV-2) was inactivated with β-propiolactone, and the healthy gibel carp were immunized with different dose of the inactivated vaccine. Then, the periphery bloods from the gibel carp were collected at 7, 14, 21, 28 days post-immunization. At 30 days post-immunization, 500 μl of live CyHV-2 was injected intraperitoneally into the animals(1.0×107TCID50 ml-1 per animal) in each group for challenge test. Mortality was monitored over a period of 14 days, and the protective efficency was evaluated. The results demenstrated that the gibel carp immunized with 1.0×107TCID50 ml-1 inactivated vaccine obtained a relative survival of 71.4%.2. The healthy gibel carp were immunized intraperitoneally with β-propiolactone inactivated cyprinid herpesvirus 2(CyHV-2), and the immune response and protection in cultured gibel carp after vaccination were investigated, including blood cell counting and classification, phagocytic activity, lysozyme and superoxide dismutaseactivity, neutralizing antibody titration, and immune gene expression analysis in vaccinated gibel carp, etc. The results of blood cell counts indicated that the numbers of the red and white blood cells in the peripheral blood of immunized gibel carp increased significantly at day 4 and day 7 post-vaccination(p< 0.01). The percentage of neutrophils and monocytes in differential leukocyte count reached peak at day 4 and 7 post vaccination, respectively. At day 14 post vaccination, the percentage of lymphocytes was significantly higher than that in the control group, and reached a peak at day 21. The phagocytic percentage and phagocytic index peaked at day 4 post-vaccination,which were(33.56±2.96)% and 7.12±0.68, respectively. The lysozyme activity and superoxide dismutase activity were significantly increased compared to the control group(p < 0.01). The serum neutralizing antibody titer peaked(203.03±13.44) at day 21. The qPCR analysis revealed that the expression of the immune genes interlukin 11 and complement component C3 were significantly up-regulated in the immunized group.