Proof of Principle Efficacy and Safety Optimisation of Tenacibaculum Vaccine Prototypes Against Tenacibaculosis in Atlantic Salmon
Abstract
Mouthrot, caused by the bacterium Tenacibaculum maritimum, is a major health and welfare problem in newly sea-transferred Atlantic salmon smolts (Salmo salar) in BC, Canada, and have caused large economical losses over the years. As there are currently no available vaccines against mouthrot, effective antibiotics are the only mitigation tool against the disease. Use of antibacterial treatment does, however, bring great concerns related to the possibility of bacterial resistance to antibiotics and that it negatively impacts the public perception of the industry. Therefore, the development of new mitigation tools are highly needed. The development of effective vaccines against pathogenic bacteria in the family Flavobactericeae, to which T. maritimum belongs, has proven to be difficult. However, a recent challenge study showed that a recombinant vaccine induced protection against T. maritimum isolate TmarCan15-1 in Atlantic salmon smolts. Moreover, results from the same study showed that the adjuvant used had a negative effect on the survival of the fish. The aim of this study was therefore to screen six recombinant protein-based vaccines formulated with different adjuvants to improve their efficacy and safety profile. Vaccine efficacy was evaluated by the immersion challenge of shedders to infect test- and control-vaccinated cohabitants in the Vaccine challenge. The vaccine safety profiles were evaluated prior to, and after, the vaccinated fish was exposed to infection. A Pre-challenge was performed prior to the Vaccine challenge to verify the immersion challenge dose, and to determine the shedders to cohabitant ratio to accommodate the tank size and number of fish to be used in the Vaccine challenge. Cohabitants were divided into eight treatment groups in the Vaccine challenge and intraperitoneal administered with either Control article 1 (saline with adjuvant control), Control article 2 (saline control), Test article 1, Test article 2, Test article 3, Test article 4, Test article 5 or Test article 6. Promising results were found for the safety profile of the two aqueous formulated vaccines, Test article 2 and 4, in addition to the oil-in-water formulated Test article 5. Test article 2 and 4 also showed a tendency towards efficacy compared to Control article 2, yet not significant. As the mortality in the control groups were too low, the efficacy of the vaccines was not possible to be determined. From this study, it is the two aqueous vaccine formulations which seem the most suitable for further investigation in the development of effective vaccines towards mouthrot in Atlantic salmon. Future studies should focus on optimising a challenge model able to demonstrate vaccine efficacy, which in turn will allow future trials to assess if the efficacy could be enhanced by e.i the route of administration.
Description
Postponed access: the file will be accessible after 2027-06-01