Introduction: Poultry vaccines are used to immunize chickens against different diseases. Inactivated vaccines have been widely used to protect poultry against diseases such as infectious bursal disease (IBD). IBD is one of the most important viral immunosuppressive diseases in the poultry industry. This viral disease targets the immune organs. This study was aimed to evaluate the effect of an inactivated IBDV antigen on inducing the humoral immune response in Specific-Pathogen-Free (SPF) chickens. Methods: An infectious strain of bursal disease virus (IBDV) was isolated from an affected chicken bursa of Fabricius. Serological diagnostic tests and molecular experiments were carried out to identify the isolate. Different concentrations of formalin, beta propiolacton (BPL) and binary ethylenimine (BEI) were used for inactivation of IBDV. The samples of IBDV antigen were adjuvanted separately with ISA-70. Three-week-old SPF chickens were divided into four groups. Groups 1, 2, and 3 received 0.5 ml of the adjuvanted antigens subcutaneously and group 4 received PBS as negative control. Blood samples from each group were collected 4 weeks post-inoculation and the targets were measured by ELISA and serum neutralization test (SNT). Results: The lowest concentrations that could fully inactivate the infectivity of IBD virus were 2.5 mM for BEI, 0.15% for BPL and 0.1% for formalin. Examination of the inactivated samples with 0.1% formalin showed a decrease in antigenicity after 12 months. Treatment with 2.5 mM BEI and 0.15% BPL showed no apparent adverse effect on IBDV infectivity and showed a reliable inactivation. In the SPF chickens of all experimental groups, the antibody titers raised against IBDV were detected by ELISA. Conclusion: In the group which the virus was inactivated using BEI, the antigenicity stability was much better than others. Hence, BEI-inactivated IBDV is suggested for preparing more immunogenic, efficient and stable vaccines against IBD.

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