Submitted to: Aquaculture Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/28/2005
Publication Date: 3/27/2006
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 Research. 37:742-750. Interpretive Summary: Therapeutic and preventative vaccination with three Streptococcus iniae vaccines: formalin-killed whole cells (FKC vaccine), concentrated extracellular products (greater than 2 kDa) (ECP vaccine), and a combination of killed cells and extracellular products (FKC+ECP vaccine) were tested in naturally and experimentally infected hybrid striped bass, Morone crysops x Morone saxatilis. Streptococcus iniae ECP and FKC+ECP vaccines confer prophylaxis for sub-clinically infected hybrid striped bass against immersion challenge with virulent S. iniae. Furthermore, ECP and FKC+ECP vaccines enhance survival of fish with preexisting infection and thus have therapeutic merit. 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. This is the first demonstration of a therapeutic effect of ECP and FKC + ECP vaccines against S. iniae and protective effects of these S. iniae vaccines in hybrid striped bass.
Technical Abstract: Therapeutic and prophylactic immunization with three Streptococcus iniae vaccines: formalin-killed whole S. iniae cells (FKC vaccine), concentrated S. iniae extracellular products (greater than 2 kDa) (ECP vaccine), and a combination of killed cells and extracellular products (FKC+ECP vaccine) were tested in hybrid striped bass, Morone chrysops x Morone saxatilis, naturally infected with S. iniae. Fish (mean weight, 10.0 g) were injected intraperitoneally (IP) or intramuscularly (IM) with one of each of the vaccines, tryptic soy broth (TSB-control) or non-injected (non-injected control) to evaluate therapeutic effects (trial 1). Survivors of the natural infection and ECP and FKC+ECP vaccine immunization and another lot of non-injected control fish were immersion challenged with 1.47 × 106 CFU of S. iniae mL '1 at 44 days post immunization to evaluate vaccine efficacy (trial 2). Hybrid striped bass (1.0 g) were also IM injected with S. iniae ECP vaccine at an aquaculture facility and immersion challenged with 1.47 × 106 CFU of S. iniae mL'1 twelve weeks post immunization (Trial 3). The ECP and FKC+ECP vaccines, regardless of injection route, significantly (P < 0.001) increased survival in asymptomatic fish providing a therapeutic effect. Hybrid bass IP or IM immunized with either of these vaccines had mean percent survival values ranging from 78 to 96 at 44 days post immunization. Survival of fish immunized with TSB medium or FKC vaccine 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 vaccine immunized 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 vaccines for 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 trial