Efficacy of a novel oral bivalent vaccine with fucoidan as adjuvant against Aeromonas hydrophila and Edwardsiella tarda infections in Nile tilapia aquaculture.

Abstract

The emerging diseases caused by Aeromonas hydrophila and Edwardsiella tarda severely impact aquaculture and lead to economic losses. Vaccines, as a safe prophylaxis method, can only protect against specific infections. Therefore, the development of a multivalent vaccine is necessary to enhance protection and cost-effectiveness for sustainable aquaculture. In this study, a bivalent vaccine against A. hydrophila and E. tarda was developed using fucoidan as an adjuvant. The vaccines were administered via the oral route to assess their protective efficacy against challenges. A survival rate of 63 % and 73 % was observed in the orally vaccinated fish where fucoidan was utilized as an adjuvant. Other immunological parameters, such as serum lysozyme, catalase, superoxide dismutase, bactericidal activity, and total IgM production, were measured. TCRβ, IgM, MHCI, MHCII, IFNγ, and IL8 gene expressions were significantly altered in the vaccinated fish. The gut microbiome alterations were noticeable in the vaccinated fish. Although feed-based oral vaccines necessitate antigen stability to withstand degradation in the fish gut, fucoidan used as an adjuvant has enhanced vaccine efficacy in orally vaccinated groups, indicating the potential of fucoidan as a novel immunomodulator and vaccine adjuvant in aquaculture.