DAO 66:129-134 (2005)  -  doi:10.3354/dao066129

Duration of protective antibodies and correlation with survival in Nile tilapia Oreochromis niloticus following Streptococcus agalactiae vaccination

David J. Pasnik1,*, Joyce J. Evans1, Phillip H. Klesius2

1Aquatic Animal Health Research Laboratory, United States Department of Agriculture, Agriculture Research Service, 118 Lynchburg Street, Chestertown, Maryland 21620, USA
2Aquatic Animal Health Research Laboratory, United States Department of Agriculture, Agriculture Research Service,PO Box 952, Auburn, Alabama 36832, USA

ABSTRACT: Streptococcus agalactiae is a major piscine pathogen that causes significant morbidity and mortality among numerous species of freshwater, estuarine and marine fishes. Considering the economic importance of fishes susceptible to S. agalactiae throughout the world, an efficacious S. agalactiae vaccine was developed using an extracellular product (ECP) fraction and formalin-killed whole cells of S. agalactiae. A vaccine study was conducted by intraperitoneal (i.p.) injection in Nile tilapia Oreochromis niloticus in order to determine the duration of protection and its correlation to antibodies specific for this pathogen. After 47, 90 or 180 d post-vaccination (DPV), the fish were i.p. challenged with approximately 2.0 × 104 S. agalactiae colony-forming units (CFU) fish–1 to determine the duration of protective immunity. The percent survival in control fish i.p.-injected with sterile TSB was 16, 16, and 4% on 47, 90 and 180 DPV, respectively, while the percent survival for the vaccinated fish was 67, 62 and 49%, respectively. The specific mean antibody concentration of the vaccinated fish was significantly higher than that of the control fish, with significant correlation between the ELISA optical density (OD) and protection. These results indicate that the specific antibody has a correlation with protection following immunization with the S. agalactiae vaccine and that the vaccine can confer protection against S. agalactiae up to 180 DPV.


KEY WORDS: Vaccine · Specific antibody response · Streptococcus agalactiae · Nile tilapia


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