Efficacy of intraperitoneal and oral administration of a lectin-adjuvanted microencapsulated scaffold vaccine on immune response in Nile tilapia (Oreochromis niloticus) infected with Streptococcus iniae.

Streptococcus iniae, an emerging pathogen, significantly impacts the productivity of marine and freshwater aquaculture by causing streptococcosis. Vaccination is a promising strategy to address this challenge. This study investigates an innovative vaccination approach utilizing a biomaterial-based scaffold encapsulated with a lectin adjuvant to combat S. iniae in Nile tilapia (Oreochromis niloticus). The scaffold was prepared via ion gelation using chitosan and alginate, and it was adjuvanted with lectin. The fish were administered with both injection and oral routes, by the formulated vaccine. Both the i.p. and oral vaccinated groups exhibited significantly higher levels of lysozyme, myeloperoxidase, and superoxide dismutase compared to the control group (P < 0.05). Furthermore, increased levels of specific antibody Immunoglobulin M (IgM) were observed, along with notable fold changes in adaptive immune genes in the spleen and head kidney. The treatment group vaccinated with the encapsulated vaccine adjuvanted with lectin demonstrated high survival rates in both routes. These findings highlight the potential of this scaffold-based vaccine delivery and adjuvant for its long-term efficacy both i.p. and oral administration as a novel and effective approach for aquaculture. This strategy could also be applied for the delivery of other vaccines and therapeutics in aquatic species.