Vaccination of market-size eels against vibriosis due to Vibrio vulnificus serovar E

Abstract

Vaccination with Vulnivaccine at eel farms has been previously shown to protect cultured eels against vibriosis caused by Vibrio vulnificus serovar E for more than 1 year. The reported protocol included an initial vaccination by triple prolonged immersion at the glass-eel stage together with one optional oral booster at the elver stage. However, eels at the market-size stage (around 150 g body weight) can suffer stress-related vibriosis after handling and transport to the selling facilities, which implies a serious risk for consumer health. The main objective of this work was therefore to develop an effective re-vaccination procedure, useful for preventing stress-related vibriosis and zoonosis in market-size eels. To this end, eels, primed 2 years before, were reimmunised by prolonged immersion with a very low dose of Vulnivaccine, a procedure commercially applicable to large fish. The protection, the immune response in plasma, skin mucus and bile as well as the bactericidal activity of the collected body fluids were evaluated in reimmunised and control animals (non-reimmunised) during a 30-day period. Reimmunisation significantly increased antibody titres in plasma, mucus and bile, as well as the bactericidal activity of these fluids, and reduced the mortality rate after bath challenge with the pathogen. In conclusion, the prolonged immersion in a very high dilution of Vulnivaccine can protect market-size eels against stress-related vibriosis and, consequently, significantly reduce additional risks of zoonosis.