Studies on the single-chain antibody (CRAb20) effectively protects chickens against very virulent infectious bursal disease virus

Infectious Bursal Disease Virus (IBDV) infection leads to the destruction of B lymphocytes in chicks, resulting in severe immunosuppression. In recent years, the prevalence of very virulent IBDV (vvIBDV) have significantly increased the complexity of preventing and controlling Infectious Bursal Disease (IBD). Anti-viral single chain antibody (scFv) has a small molecular weight, strong penetration, and can be efficiently expressed by genetic engineering. In this study, we utilized both a high-safety Lactobacillus expression system suitable for oral delivery and a high-expression Escherichia coli system to expressed scFv (CRAb20). Subsequently, we evaluated the in vitro neutralization effect of CRAb20 against vvIBDV and its protective efficacy in chicks. The results demonstrated that CRAb20 can significantly suppress the replication of IBDV in vitro. Importantly, oral administration of recombinant Lactobacillus expressing CRAb20 or intraperitoneal injection of recombinant CRAb20 can significantly mitigate the detrimental effects of vvIBDV on the bursa of Fabricius, improved the survival rate, and offered both prophylactic and therapeutic benefits against IBDV infection in chickens. These findings highlight the potential of scFv-based approaches as a promising strategy for controlling IBDV.