Effectiveness of different vaccine formulations against vibriosis caused by Vibrio vulnificus serovar E (biotype 2) in European eels Anguilla anguilla

Vibriosis due to Vibrio vulnificus serovar E (biotype 2) is one of the main causes of mortality in European eels cultured in Europe. The main objectiv e of this study was to develop a vaccine and a vaccination procedure agains t this pathogen. With this aim, we tested several vaccine formulations (ina ctivated whole-cells with and without toxoids-inactivated extracellular pro ducts-from capsulated and uncapsulated strains, attenuated live vaccines an d purified lipopolysaccharide [LPS]) on eels maintained under controlled la boratory conditions using different delivery routes (injection and immersio n). To study the immune response we estimated antibody titers and bacterici dal/bacteriostatic activity in mucus and serum. To evaluate protection, we calculated the relative percent survival (RPS) after intraperitoneal (i.p.) injection and bath challenge of the pathogen. The overall results indicate that: (1) capsular antigens seem to be essential for protective immunizati on; (2) vaccines confer the highest protection when administered by i.p. in jection; (3) booster is needed to achieve good protection by immersion; (4) enriching the vaccine with toxoids enhances protection to optimal levels ( RPS values around 70 to 100 %, depending on the delivery route); and (5) th e protective effect in serum and mucus depends on the route of administrati on and seems to be related to the production of specific antibodies.