An oral delivery system for recombinant subunit vaccine to fish.

Oral vaccination is considered as the most desirable method for immunizing fish because it is non-stressful, user-friendly and is capable of easy administration to large numbers of fish. However, many publications have indicated that the current oral vaccines still lack the desired efficacy. Here we reported on an oral vaccine method to deliver recombinant subunit vaccine based on the food chain of fish, in that live Artemia nauplii are encapsulated with recombinant bacteria containing the antigen. The feasibility and efficacy of this method for delivering protein antigen was tested in a zebrafish model, where immunisation took place through feeding Artemia encapsulated with recombinant E. coli. By this oral vaccine method the antigen could be delivered to the hindgut as confirmed by immuno-histochemistry, and its efficacy was demonstrated by the ability to protect vaccinated fish significantly from a direct injection of a native Pseudomonas exotoxin and bacterial pathogen. Combined with the recombinant technology for producing desired protein antigens, this oral vaccine delivery method provides the capacity to deliver a variety of different antigens, including the option for delivery of multivalent vaccines by the oral route.