Recombinant Bacillus subtilis Displaying DHAV-1 VP1 Protein as a Dual-Function Probiotic: Evaluation of Immunological Efficacy, Growth Performance, Antioxidant Capacity, and Intestinal Health in Cherry Valley Ducks.

Duck hepatitis A virus type 1 (DHAV-1) demonstrates extremely high lethality in 3-week-old ducklings, while causing subclinical infections in adult ducks with latent pathogenicity. Our previous research developed a vaccine-functional probiotic preparation targeting DHAV-1-recombinant Bacillus subtilis RV. In the present study, we conducted a 28-day oral immunization trial in Cherry Valley ducks to evaluate the immunoprotective effects and probiotic functions of this engineered strain. Results showed that B. subtilis RV induced humoral and mucosal immune responses in ducklings, producing high levels of specific IgG and intestinal secretory IgA, demonstrating immune-enhancing capabilities. During DHAV-1 challenge tests, it significantly reduced viral loads in various organ tissues. Additionally, B. subtilis RV improved the growth performance and antioxidant capacity of ducklings. Furthermore, this engineered probiotic enhanced intestinal health by improving intestinal structure, increasing tight junction protein expression, and modulating gut microbiota composition. This study evaluates a novel vaccine-functional probiotic preparation, providing a new strategy for DHAV-1 prevention and control.