Submitted to: Aquaculture America Conference
Publication Type: Abstract Only
Publication Acceptance Date: 12/13/2005
Publication Date: 2/16/2006
Citation: Evans, J.J., Klesius, P.H., Shoemaker, C.A. 2006. Therapeutic and prophylactic immunization against streptococcus iniae infection in hybrid striped bass morone chrysops x m. saxatilis. Aquaculture America Conference 2006. Las Vegas, Nevada. February 13-16, 2006. page 97.
Technical Abstract: Therapeutic and prophylactic immunization with three Streptococcus iniae vaccine preparations: formalin-killed whole cells (FKC), concentrated extracellular products (greater than 2 kDa) (ECP), and a combination of killed cells and extracellular products (FKC+ECP) were tested in naturally infected hybrid striped bass, Morone chrysops x Morone saxatilis. Fish (mean weight, 10.0 g) were intraperitoneal (IP) or intramuscular (IM) vaccinated with each of the vaccine preparations, tryptic soy broth (TSB-control) or non-injected (control) to evaluate therapeutic effects (Trial 1). Survivors of the ECP and FKC+ECP immunization and an another lot of non-injected control fish were immersion challenged with 1.47 × 106 CFU mL-1 of S. iniae at 44 days post immunization and mortality assessed 14 days post challenge to evaluate vaccine efficacy (Trial 2). Hybrid striped bass (1.0g) IM injected with S. iniae ECP vaccine at an aquaculture facility and immersion challenged as in trial 2 twelve weeks post immunization was also conducted to evaluate vaccine efficacy (Trial 3). The ECP and FKC+ECP preparations, regardless of injection route, significantly (P<0.001) increased survival in asymptomatic fish providing a therapeutic effect (see figures). Hybrid bass IP or IM immunized with either of these vaccine preparations had mean percent survival values ranging from 78 to 96 at 44 days post immunization. Survival of fish immunized with TSB media or FKC was significantly decreased and ranged from 12-13 % by IP injection and 40-50 by IM injection. The relative percent survival (RPS) for challenged ECP vaccinated survivors was 76 and 48 by IM and IP routes, respectively. However, the FKC+ECP vaccine increased the RPS values for IM and IP routes to 87 and 95, respectively. The RPS values for ECP or FKC+ECP by IM injection were 66 and 63, respectively over the duration of trials 1 and 2. Percent survival of hybrid striped bass IM immunized with S. iniae ECP vaccine in field trials was 91 and the RPS was 83. Streptococcus iniae ECP and FKC+ECP vaccine preparations can enhance survival of fish with preexisting infection and confer therapeutic benefits. Vaccine performance is not significantly impaired by use in sub-clinically infected hybrid striped bass. Furthermore, these preparations confer prophylaxis for natural infected hybrid striped bass against immersion challenge with virulent S. iniae. Therapeutic vaccination is an immunization program that needs further exploration as it may prove to be adapted to specific species of fish, pathogens and conditions of production facilities.