As commercial aquaculture operations grow and intensify , growers continue to adopt vaccination programs to prevent losses from disease . Oral vaccination can significantly reduce costs of these programs while allowing for low stress vaccine delivery to small fish. This study evaluates the ability of a novel alginate-based oral vaccine particle to stimulate immunity and provide protection against the causative agent of furunculosis, Aeromonas salmonicida .
A formalin-killed A. salmonicida vaccine was produced and used to vaccinate juvenile rainbow trout via four routes: intraperitoneal (i.p. )injection (IP), anal intubation (AL), immersion (BA), and the experimental oral vaccine particle (OV). Control groups included a particle containing no bacterin (CP), and an i.p. injection with sterile PBS (PB). All treatment groups received a booster 2 weeks after the initial vaccination. Specific antibodies in serum were measured at 0, 2, 4, 6, 8, and 13 weeks post vaccination . After 13 weeks, fish were challenged with A. salmonicida via immersion and monitored for 28 days. The OV group had an antibody titer peak at 4 weeks, but then steadily declined . The IP group maintained the highest titers, followed by the AL group. In the pathogen challenge, cumulative percent mortality (CPM) of the PB group (82%) was significantly higher than all treatments except for the OV group (48%) which was not significantly different from any treatments. Other groups, including CP, showed significant protection and their CPM ranged from 30-35%.
The oral vaccine particle successfully stimulated an antibody response and both groups fed the alginate-particle showed resistance to A. salmonicida in a pathogen challenge. The anal vaccination demonstrated the ability of killed vaccines to stimulate gut associated lymphoid tissue (GALT) which can provide protection against pathogens. Interestingly, the control particle without vaccine provided equal protection to other vaccine treatments. The reason for this is not clear but may be due to an adjuvant effect of the alginate particle. The oral vaccine stimulated a specific antibody response, which provides evidence for oral delivery of vaccines but adjustments to particle formulation, dose and delivery strategy requires further research.