Danish sea reared rainbow trout suffer from furunculosis despite vaccination - How can applied research help to solve the problem?

Despite vaccination by intraperitoneal injection with oil-adjuvanted vaccines against vibriosis and furunculosis, sea reared rainbow trout in Denmark often develop furunculosis and occasionally vibriosis during warm summer periods. This implies an excessive use of antibiotics and has also decreased some fish farmer’s confidence in the commercially available vaccine.

This vaccine comprises Aeromonas salmonicida subspecies salmonicida and Vibrio anguillarum serotypes O1 and O2a bacterins emulsified with mineral oil. The bacterin antigens are based on bacteria isolated from Atlantic salmon cultured outside Denmark. Vaccination and challenge trials performed under experimental conditions suggest that the commercial vaccine provides good protection against challenge with Aeromonas salmonicida when the fish are exposed to the bacteria by injection.

However, the protection is far less significant when the fish are challenged by cohabitation with infected donor fish followed by elevation of the water temperature. The results demonstrate the importance of optimizing the challenge procedure for evaluation of vaccine efficacy under experimental conditions.

In terms of Vibrio anguillarum the commercial vaccine failed to protect the fish against an serotype O2 isolate from diseased fish, suggesting that tailoring the antigen composition to Danish/local bacterial variants is needed. Serological examination of the vaccine induced antibody response in the fish is in progress aiming at evaluating the contribution of the humoral immune response to protection as well as at development of an in vitro tool for evaluation of vaccine potency.