Astragalus polysaccharide or β-glucan combined with inactivated vaccine markedly prevent CyHV-2 infection in Carassius auratus gibelio

Abstract

Herpesviral hematopoietic necrosis disease caused by cyprinid herpesvirus 2 (CyHV-2) results in huge economic losses for the gibel carp (Carassius auratus gibelio) aquaculture industry. A vaccination strategy is a feasible method to prevent CyHV-2 infection and the resulting economic losses. In this study, inactivators (including β-propiolactone, formaldehyde and binary ethylenimine) were used to prepare an inactivated vaccine. The optimal inactivated CyHV-2 vaccine (0.2% β-propiolactone inactivates CyHV-2 for 48 h) mixed with β-glucan, anisodamine, chitosan, and astragalus polysaccharide (APS) adjuvants were injected into gibel carp. The β-glucan and APS combined with inactivated vaccine significantly improved the relative immune protection rate of gibel carp against CyHV-2 infection. The highest specific antibody levels in β-glucan and APS groups were found in serum by ELISA assay and antibody neutralization titer. Furthermore, adjuvant addition groups produced better results for lysozyme, total superoxide dismutase, and complement C3 in serum. β-glucan and APS combined with vaccine treatment effectively enhanced mRNA expressions of important immune genes (IL-1β, IgM, IL-2 and IFN-γ2). Minimal tissue lesions (gill, spleen, and head kidney) and virus replication were seen in the β-glucan and APS groups by histopathological examination and expression analysis of CyHV-2 TK gene. These results indicated that the combination of inactivated vaccine and adjuvant β-glucan or APS is an effective method against CyHV-2 infection and provided a case study reference for prevention of fish viral diseases using inactivated vaccines.