Abstract
Furunculosis caused by infection with Aeromonas salmonicida subsp. salmonicida has been a known threat to aquaculture for more than a century. Efficient prophylactic approaches against this disease are essential for continued growth of salmonid aquaculture. Since the introduction of successful oil-adjuvanted vaccines in the early 1990's, a number of studies have been published on the protective as well as adverse effects of these vaccines. Most studies focus on vaccination of salmon (Salmo salar). However, rainbow trout (Oncorhynchus mykiss) are also very susceptible to infection and are vaccinated accordingly. In this study we have examined the protection against infection with a Danish strain of A. salmonicida in both vaccinated and non-vaccinated rainbow trout. A commercial and an experimental auto-vaccine were tested. The protective effects of the vaccines were evaluated through an A. salmonicida challenge 18 weeks post vaccination. Both vaccines resulted in a significantly increased survival in the vaccinated fish during a 28 day challenge period relative to non-vaccinated fish (P = 0.01 and P = 0.001 for the commercial and experimental vaccine, respectively). Throughout the entire experiment, the presence of specific antibodies in plasma was monitored using ELISA. A significant increase in specific antibody levels was seen in fish vaccinated with both vaccines during the 18 weeks between vaccination and challenge. Within 3 days post challenge, a significant decrease in specific antibodies occurred in vaccinated fish. A positive correlation was found between mean levels of specific antibodies pre challenge and overall survival. This correlation, along with the observed depletion of antibodies during the initial phase of infection, suggests that specific antibodies play an essential role in vaccine mediated protection against A. salmonicida in rainbow trout.
Highlights
Aeromonas salmonicida subsp. salmonicida has been known as the causative agent of furunculosis since the first cases were described in the late 19th century [1]
The aims of this study were to assay the level of protection provided by the two different vaccines against infection with A. salmonicida, to investigate the development of specific antibody responses and to get an insight into the potential protection afforded by these antibody responses
Several studies on the effects of vaccination have been performed on salmon, possibly due to their economic role in modern aquaculture
Summary
Aeromonas salmonicida subsp. salmonicida (hereafter referred to as A. salmonicida) has been known as the causative agent of furunculosis since the first cases were described in the late 19th century [1]. With the emergence of modern aquaculture, this Gram-negative bacterium has developed into one of the most significant bacterial infections in cultured fish across the world, affecting a wide range of host species [2] This has resulted in substantial economic losses, in the production of salmonid species. Other experiments in Atlantic salmon have since demonstrated limited long-term effects of both oral and immersion vaccination when compared to intraperitoneal (i.p.) injection of adjuvanted vaccines [7]. Such short term protection will not meet the needs of modern aquaculture, since reduced long-term protection will result in an increased need for antibiotics during disease outbreaks, and an increase in disease related mortalities
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