Edwardsiella tarda Prophylaxis by vaccination has shown some signs of success

Edwardsiella tarda prophylaxis by vaccination has

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Edwardsiella tarda Prophylaxis by vaccination has shown some signs of success (e.g. Guttierez and Miyazaki, 1994; Kwon et al, 2006), with oral administration immunostimulants, namely P-glucan, levamisole and vitamins C and E heightening protection further, especially if harmful (aflatoxin Bl was identified) conditions prevailed (Sahoo and Mukherjee, 2002). Eels responded to the administration of heat- or formalin-killed cells (preferably by injection) by producing humoral antibodies with titres of up to 1:4,096 (Song and Kou, 1981). Song et al. (1982) vaccinated eels by immersion for periods of 20 sec to 3min in suspensions containing 10^ to 10^ bacterial cells/ml. Following the i.m. injection of lOmg amounts of formahsed cells/100 g of Japanese eels and a booster after 7 days, an oral challenge resulted in 60-87.5% mortahties in the vaccinates, compared with 80-100% deaths among controls (Gutierrez and Miyazaki, 1994). Rather better protection resulted from use of 1 mg of LPS/lOOg body weight of Japanese eels. With this vaccine, 40-57% mortahties were recorded compared with 80-90% of the controls (Gutierrez and Miyazaki, 1994). Unfortu- nately, Mekuchi et al. (1995b) did not find any clear sign of protection in Japanese flounder that had been vaccinated with formahsed cells via the i.m., oral or immer- sion routes. Other work has doubted the importance of cell-mediated immunity in the protection of fish against disease (Miyazaki and Egusa, 1976). This is perhaps surprising in view of the current opinions concerning fish immunology. Intramuscular injection of eels and red sea bream with LPS resulted in protection from challenge with a virulent culture o^ Edw. tarda (Salati et al., 1987a, b). More- over, there was a demonstrable humoral immune response (titre = 1:2,048) and phagocytosis by T-lymphocytes. Phagocytic activity in the eels peaked three weeks after vaccination (Kusuda and Taira, 1990). Indeed, the evidence showed that LPS was much more successful as an immunogen than vaccination with a formalised culture (Salati et al, 1987a, b). Igarashi and lida (2002) used live-attenuated and formalin-inactivated cells of a mutant, SPM31, constructed with transposon Tn5 with reduced siderophore produc- ing capabihty. Tilapia were vaccinated intraperitoneally (0.1 mg of vaccine/100 g of fish) whereupon antibodies were produced and protection recorded after challenge for the live (0% mortality), but not the formahn-inactivated (mortality = 80-100%),
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Control 367 preparation (Igarashi and lida, 2002). Also, Kwon et al. (2006) used ghost cells, which were generated by gene ^'-mediated lysis, in tilapia, and demonstrated high protection. Serratia liquefaciens Whole-cell formahsed vaccines and toxoid preparations were effective for prophyl- axis in laboratory-based experiments with Atlantic salmon (Mcintosh and Austin, 1990b). Yersinia vuckevi The development of vaccines is a story of success until the advent of the new biogroup (Austin et al., 2005a), with commercially available products being marketed for use in aquaculture. Ironically, it is still unknown how these vaccines are taken up by the fish, or for that matter the exact mechanism of their action.
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