Oral vaccination of fish againstVibrio anguillarumusing alginate microparticles

Abstract The 800  g supernatant fraction of a Vibrio anguillarum bacterin was encapsulated in alginate microparticles to protect the vaccine against degradation in the anterior part of the digestive tract. Microparticles can be optimised for different fish species with respect to differences in the digestive tract. Two types of microparticles were tested in carp (stomachless) and trout (stomach-containing). For oral vaccination, alginate microparticles with or without antigen were added to food or food containing non-encapsulated antigen was used. Uptake of antigen in the hindgut, development of immunological memory and mucosal immune responses were studied. After feeding with encapsulated antigen a better uptake was observed compared to feeding with the same amount of non-encapsulated antigen. Antibody titres were measured 3 weeks after oral vaccination and 3 weeks after an intramuscular booster given 10 weeks after oral vaccination. Best memory formation in carp was found when fish were fed with encapsulated antigen in microparticles of type I, whereas type II microparticles gave better results in trout. The presence of mucosal plasma cells after repeated oral vaccination of carp with encap-sulated antigen was studied with ELISPOT using a mucus-IgM-specific monoclonal antibody. Specific mucosal plasma cells appeared to be present mainly in gut and gills after oral vaccination and absent after intramuscular injection. These results indicate that oral vaccination with encapsulated antigens evokes systemic memory and induces mucosal immune responses in fish. Consequently, oral vaccination appears to be a promising method to control bacterial diseases.