Background
Generally, the injection method is recommended as the best efficient method for vaccine application in fish. However, labor-intensive and difficult injecting to certain fish sizes is always considered as a limitation to the aquatic animals. To demonstrate the effectiveness of a novel oral delivery system for the piscine vaccine, the nano-delivery made from nano clay, halloysite nanotube (HNTs), and their modified forms, were loaded with killed vaccines and determined the ability of the system in releasing vaccines in the mimic digestive system. The efficaciousness of orally piscine vaccine nano-delivery was evaluated as the level of antibody production and level of disease prevention in Nile tilapia (Oreochromis niloticus).
Results
Unmodified HNTs (H) and modified HNTs [HNT-Chitosan (HC), HNT-APTES (HA), and HNT-APTES-Chitosan (HAC)] were successfully harboring streptococcal bivalent vaccine; inactivated S. agalactiae, designated as HF, HAF, HCF, and HACF, respectively. The releasing of loading antigens in the mimic digestive tract demonstrated a diverse pattern of proteins releasing depending on the types of HNTs. Remarkedly, HCF could properly release loading antigens in relevance to the increasing pH buffer. The oral vaccines revealed the greatest elevation of specific antibodies to S. agalactiae serotype Ia in HCF orally administered fish and to some extent in serotype III. The efficacy of streptococcal disease protection was determined by continually feeding with HF, HAF, HCF, and HACF coated feed pellets for 7 days with a week after week program. HCF showed significant RPS (75.00 ± 10.83%) among other tested groups [HF (18.75 ± 10.83%), HAF (37.50 ± 10.83%) and HACF (18.75 ± 10.83%)]. Interestingly, the HCF-treated group exhibited noticeable efficacy similar to the bivalent vaccine injected group (RPS 81.25 ± 0.00%).
Conclusions
This novel nano-delivery system for the fish vaccine was successfully developed and exhibited appropriated immune stimulation and promised disease prevention through oral administration. This delivery system would greatly support animals’ immune stimulation which conquers the limitation in vaccine application in aquaculture systems. Moreover, this delivery system would apply to carry diverse types of biologics including DNA, RNA, and subunit protein vaccines.