Immunological responses and protection in Chinese giant salamander Andrias davidianus immunized with inactivated iridovirus

Chinese giant salamander hemorrhage is a newly emerged infectious disease in China and has caused huge economic losses. The causative pathogen has been identified as the giant salamander iridovirus (GSIV). In this study, the immunological responses and protection in Chinese giant salamander immunized with β-propiolactone inactivated GSIV are reported. Red and white blood cell counting and classification, phagocytic activity, neutralizing antibody titration, immune-related gene expression and determination of the relative percent survival were evaluated after vaccination. The red and white blood cell counts showed that the numbers of erythrocytes and leukocytes in the peripheral blood of immunized Chinese giant salamanders increased significantly on days 4 and 7 post-injection (P < 0.01). Additionally, the differential leukocyte count of monocytes and neutrophils were significantly different compared to the control group (P < 0.01); the percentage of lymphocytes was 70.45 ± 7.52% at day 21. The phagocytic percentage and phagocytic index was 38.78 ± 4.33% and 3.75 ± 0.52, respectively, at day 4 post-immunization which were both significantly different compared to the control group (P < 0.01). The serum neutralizing antibody titer increased at day 14 post-immunization and reached the highest titer (341 ± 9.52) at day 21. The quantitative PCR analysis revealed that the immunization significantly up-regulated the expression of immune related genes TLR-9 and MyD88 the first two weeks after immunization. The challenge test conducted at day 30 post-injection demonstrated that the immunized group produced a relative survival of 72%. These results indicate that the inactivated GSIV could elicit significant non-specific and specific immunological responses in Chinese giant salamander that resulted in significant protection against GSIV induced disease.