Submitted to: International Aquatic Animal Health Symposium Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: June 20, 2006
Publication Date: September 2, 2006
Citation: Pasnik, D.J., Evans, J.J., Klesius, P.H., Panangala, V.S., Shoemaker, C.A., Shelby, R.A. 2006. Protective antibody responses following vaccination with Streptococcus agalactiae in Nile tilapia, Oreochromis niloticus. 5th International Symposium on Aquatic Animal Health Proceedings. San Francisco, CA. September 2-6, 2006. p 210. Technical Abstract: Experiments using Nile tilapia, Oreochromis niloticus, were conducted to further characterize a highly efficacious Streptococcus agalactiae vaccine containing extracellular products [ECP] and formalin-killed whole cells. One study assessed the efficacy of stored reconstituted S. agalactiae vaccine, which failed to significantly (p = 0.19) prevent mortality among vaccinates. Significantly lower (p < 0.0001) anti-S. agalactiae antibody levels were produced among fish administered stored ECP than fresh ECP. Western blot immunostaining revealed bands around 55 kDa in freshly-prepared ECP fractions but not in the stored fractions. The duration of protection and its correlation to S. agalactiae-specific antibodies was also evaluated. Fish were injected with fresh vaccine and challenged with S. agalactiae 47, 90, or 180 days post-vaccination (DPV), and mortalities among vaccinates were significantly lower (p < 0.05) than for controls at each time point. Specific antibody levels among vaccinates were significantly higher (p < 0.05) than among controls, with significant correlation (r2 = 0.5712 to 0.8828 though 180 DPV) between increased antibody levels and protection. Fingerling tilapia were also administered serum from S. agalactiae-immune fish and challenged with S. agalactiae. Passively-immunized fish had significantly higher (p < 0.0001) pre-challenge antibody levels than controls and significantly less (p < 0.0001) mortalities post-challenge. A highly significant (r2 = 0.5892; p < 0.0001) correlation between increased pre-challenge specific serum antibody OD levels and survival post-challenge was demonstrated. The results of these studies illustrate a strong correlation between protection and ECP-specific antibody production and also the immunogenicity of the 55 kDa ECP antigen.