particular trial the vaccine effected an 84 reduction in mortalities due to ERM

Particular trial the vaccine effected an 84 reduction

This preview shows page 387 - 389 out of 594 pages.

particular trial, the vaccine effected an 84% reduction in mortalities due to ERM (Tebbit et al., 1981). Of additional benefit, there was a concomitant decrease in the use of medication by 77%, and an increase in food conversion of 13.7%. Analogous findings have been reported by Amend and Eschenour (1980) and Newman and Majnarich (1982). Addressing the question of the interval necessary for the onset and duration of immunity to develop, Johnson et al. (1982a) reported that a 5 sec immersion in a vaccine suspension was sufficient to induce protection within 5 days at 18°C, or 10 days at 10°C. The minimum size of salmonids necessary for maximal protection was estimated to be in the range of 1.0-2.5 g. In fact, these authors concluded that protection was correlated with size of the fish, and not their age. Thus, with 1.0, 2.0 and 4.0 g fish, immunity lasted for approximately 4, 6 and 12 months, respectively (Johnson and Amend, 1983b). There was some variation in results between species, with coho salmon and sockeye salmon retaining immunity for longer than pink salmon. Lamers and Muiswinkel (1984) concluded that a secondary immune response occurred as long as 7 months after primary contact with the antigen, indicating the presence of a fairly long-lived memory. Cossarini-Dunier (1986) found protection lasted for 445 days after intraperitoneal injection of a formalised culture which was suspended in saline or oily adjuvant. Thus, after challenge, 88.5% of the controls died, but only a few vaccinates. The commercial immersion vaccines were less successful at controlling the new biogroup (RPS = 47% compared with 95% for the Hagerman strain). This prompted an approach to supplement a current commercial vaccine with formalised whole cells of the new biogroup (RPS = 56% compared with 97% for the Hagerman strain) or by using an autologous vaccine comprised exclusively of formahn-inactivated cells of the new biogroup (RPS = 76% compared with 58% for the Hagerman strain) (Austin et al, 2005). So, there is the potential to increase protection against the new biogroup but at the expense of the more traditional Hagerman strain. Flavobacteriaceae representatives Vaccines have been developed only for Fla. columnare, although a commercial product is not available. Fujihara and Nakatani (1971) experimented with heat-killed cells, which were administered via food to juvenile coho salmon. The fish responded
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Control 369 with the production of antibody (titre= 1:5,120). Schachte and Mora (1973) con- curred with the general view by demonstrating agglutinating antibody in channel catfish. Survivors of infection experiments resisted re-infection, suggesting the presence of a protective immune response (Fujihara et al, 1971). Formalised cells of Fla. columnare were administered to eel by immersion and injection, resulting in an immune response (in the skin) two weeks later, and survival of 60% and 20%, respectively (Mano et ai, 1996). Interestingly, 14 days following vaccination by immersion and injection of eel with formahn-killed cells of Fla. columnare, agglutinat- ing antibody could not be detected in the serum or mucus. Instead, there was
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