preparations but highlighted the necessity of incorporating atypical rather

Preparations but highlighted the necessity of

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preparations, but highlighted the necessity of incorporating atypical rather than typical cells (RPS = 82-95%) . The explanation given was that atypical Aer. salmon- icida had genetically (by AFLP) a serologically different A-layer than their typical counterparts (Lund et al., 2003a). Unfortunately, the desired immersion vaccination strategy did not work insofar as high levels of mortalities resulted after challenge, even when adopting an immersion boost (Grontvedt et al, 2004). Researchers should consider the interesting work of Olivier et al. (1985b), who noted protection to Aer. salmonicida in coho salmon after i.p. injection of formahsed cells as well as after injection with FCA. Undoubtedly, the use of adjuvant stimulated non-specific immunity, probably involving macrophage activity. Certainly, i.p. injec- tion has led to activation of leucocytes (Kollner and Kotterba, 2002). From the study of Norqvist et al. (1989), it is necessary to question the need for incorporation of Aer. salmonicida cells or their cellular components into furunculosis vaccines. Injection techniques appear to be the most efficacious, whereas the oral route is least promising (Midtlyng et al., 1996). The use of adjuvants, especially mineral oil, in injectable vaccines is clearly beneficial (Midtlyng, 1996) with 16S rRNA and LPS being detected in the head kidney and spleen at two weeks (and in the head kidney at 12 weeks) after injection with a commercial, oil-adjuvanted, formahn-inactivated vaccine (Grove et al, 2003). Indeed, Midtlyng (1996) determined from a field study in Norway that i.p. administration of furunculosis vaccine in a mineral oil adjuvant gave the best protection in Atlantic salmon. Apart from the obvious benefits of FCA (Olivier et al, 1985b), the use of P-1,3 glucan (Vita-Stim-Taito), lentinan and formalin-killed cells of Ren. salmoninarum have enhanced the effectiveness of vaccines based on formahsed Aer. salmonicida cells (Nikl et al, 1991). Possibly, with oral uptake degradation of the vaccine in the gastro-intestinal tract may occur. In this case, there may be potential for the use of micro-encapsulation techniques to avoid such pitfalls. One interesting and relevant approach, which is reminiscent of the probiotic saga, involved the i.p. administration of 10^ cells/fish of a live auxotrophic aroA mutant of Aer. hydrophila that protected rainbow trout 30 days later against furunculosis (RPS > 60%) and stimulated the humoral and cellular immune response (Vivas et al, 2004a).
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364 Bacterial Fish Pathogens Immersion techniques have generated much useful data. Rodgers (1990) reported the benefits of using inactivated whole cells, toxoided ECP and LPS for the protection of juvenile salmonids. Moreover, the vaccinated animals grew better than the con- trols. Work has indicated that the duration of the immersion vaccination process does not affect the uptake of the vaccine, providing that the antigens are not in low concentrations (Tatner, 1987). Therefore, there appears to be some promise for the widely used immersion vaccination technique with furunculosis vaccines.
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