Research

Potential role of specific antibodies in vaccine-induced protection against Aeromonas salmonicida subsp. salmonicida in rainbow trout (Oncorhynchus mykiss)

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Abstract

Furunculosis caused by infection with Aeromonas salmonicida subsp. salmonicida has now been a known threat to aquaculture for more than a century. Efficient prophylactic precautions against this disease are essential for continued growth of salmonid fish aquaculture. Ever since the introduction of successful oil-adjuvanted vaccines in the 1990’s, a number of studies have been published on the protective effects of these vaccines. While most of these studies mainly focus on vaccination of salmon (Salmo salar), rainbow trout (Oncorhynchus mykiss) are also highly susceptible to infection and are therefore vaccinated as well. In this study we have examined the levels of protection against infection with a Danish strain of A. salmonicida subsp. salmonicida in both non-vaccinated, as well as vaccinated rainbow trout. Both a commercial vaccine (AlphaJect 3000, PHARMAQ AS) as well as an experimental auto-vaccine was tested. For comparison, the isolated adjuvant used in the commercial vaccine, as well as the one used in the experimental vaccine was included in the experimental setup. The protective effects of the vaccines were tested by bacterial challenge 18 weeks post vaccination, and during the 18 weeks, the development of specific antibodies was monitored using ELISA assays. Both vaccines resulted in significantly increased survival during a 28 day challenge period. None of the two adjuvant systems provided increased protection. A significant increase in specific antibody levels was seen in both vaccinated groups during the 18 weeks between vaccination and challenge. Additionally, further analysis showed a significant correlation between the mean level of specific antibodies measured for each group and the final survival percentages of these groups. The positive correlation between specific antibodies and survival seems to indicate a prominent role of antibodies as a vaccine mediated protective mechanism.