Abstract:
At present all vaccines for fish are primarily delivered either by injection or immersion which introduces added stress and labor. A more attractive method of vaccine delivery is oral administration using an enteric protection system, Enteric Coated Antigen Microspheres (ECAMs), which can be utilized for a variety of antigenic forms. Relative efficacy of ECAMs was compared by inducing an antibody response in fish via injection (ip), immersion (im) or by ECAMs. Results showed that ECAMs were as effective as ip and im in inducing an antibody response to lipopolysaccharde and protein antigens. ECAMs were able to protect the protein antigen from gastric degradation. The ECAMs were employed to deliver a prototype vaccine for Renibacterium salmoninarum (Rs), the etiological agent of bacterial kidney disease. Upon characterization of the Rs antigens, one predominant cellassociated
and extracellular protein (ECP), p57 was identified. The p57 molecule is elaborated in high concentrations in infected fish and exhibits pathogenic activitiesin vitro which appear to suppress the immune response. Our studies have revealed that a 370C incubation of R. salmoninarum cells decreased the amount of p57 by the induction of an autoproteolytic activity. This activity was exploited to produce a prototype vaccine that was delivered by intraperitoneal injection (ip) and demonstrated a significant increase in mean time of death upon challenge by injection. A second experiment was conducted using a natural exposure (bath challenge) and the heat treated, p57 -Rs cells were delivered using ECAMs and ip administration. The results proved that the route of
immunization was critical with respect to natural exposure, as animals that received ECAMs with heat-treated p57 minus As cells demonstrated statistically significant reduction in the amount of ECP detected versus control. The decrease in ECP concentration is indicative of reduced Rs
infection. Those animals vaccinated by ip showed no difference. Finally, in order to assess immunological memory induced by
antigenic stimulation, an assay was developed that measured the production of cytokines induced by in vivo priming and subsequent in vitro exposure with the specific antigen.
