Submitted to: Annual Eastern Fish Health Workshop
Publication Type: Abstract Only
Publication Acceptance Date: February 23, 2004
Publication Date: March 22, 2004
Citation: PASNIK, D.J., EVANS, J.J., KLESIUS, P.H., SHOEMAKER, C.A. POTENCY AND SHELF-LIFE OF A STREPTOCOCCUS AGALACTIAE VACCINE IN NILE TILAPIA (OREOCHROMIS NILOTICUS). ANNUAL EASTERN FISH HEALTH WORKSHOP. 2004. Technical Abstract: Group B streptococcal infections have been associated with significant morbidity and mortality in freshwater, estuarine, and marine fish species. Currently, no commercial fish vaccines are available for the prevention of disease caused by the emerging group B streptococcal fish pathogen, Streptococcus agalactiae. Thus an effective vaccine for S. agalactiae could help decrease the associated mortalities due to S. agalactiae infection. Juvenile Nile tilapia (Oreochromis niloticus) were used to test the efficacy of a killed vaccine composed of formalin-killed S. agalactiae cells and concentrated extracellular products. Previous studies had shown that fresh vaccine provided significant protection against S. agalactiae challenge. The objective of this project was to determine whether vaccine stored at 4ºC for one year could confer the same protective benefits as fresh vaccine. Tilapia were inoculated with one year-old vaccine by intraperitoneal (IP) injection, and control tilapia were inoculated IP with tryptic soy broth (TSB). All fish were then held at approximately 32ºC. At 31 days post-inoculation, fish were challenged IP with 1.7 x 104 CFU S. agalactiae/fish and monitored for clinical signs and mortality for 14 days. Blood was also sampled from control and vaccinated fish on Days 0 and 31 for ELISA. In our previous studies, inoculation with fresh vaccine significantly helped prevent development of clinical signs and reduced the post-challenge mortalities, yielding a relative percent survival of 80. The vaccine held for one year failed to produce the same effects, resulting in an RPS of 29 and allowing the development of clinical signs. ELISA results indicated that the one year-old vaccine induced significantly increased antibody production in vaccinates as compared to the TSB controls. However, this level of antibody production was significantly lower than found in our studies using fish injected with fresh S. agalactiae vaccine. Decreased antibody production in fish administered the one year-old vaccine may account for the decreased relative percent survival. This study suggest that the shelf-life of the vaccine is less than one year when stored at 4ºC, indicating that a fresh preparation of the vaccine should be utilized to obtain the full benefits of this S. agalactiae vaccine. Because it would be desirable to have this vaccine available for multiple tilapia production cycles, other vaccine preparations (lyophilized) or storage considerations (freezing) should be assessed.