Traditionally oral vaccines were considered to be the least successful insofar

Traditionally oral vaccines were considered to be the

This preview shows page 383 - 385 out of 594 pages.

Traditionally, oral vaccines were considered to be the least successful insofar as it was reasoned that the antigens became degraded during passage through the stomach and possibly there were issues regarding access to the antibody-producing sites. Liposome-entrapped antigens of atypical Aer. salmonicida were fed to carp with the result that there was a stimulation of the immune response, specifically the presence of antibodies in bile, intestinal mucus and serum, and greater protection (fewer mortalities) and a reduction in ulceration compared with the controls (Irie et al, 2005). Gradually, however, oral vaccines have attained favour, and commercial products are now available. Some of the difficulties with ascertaining the efficacy of vaccines have been ascribed to methods of experimental challenge. Indeed, it is not unusual for vaccines to appear to work in laboratory conditions but to fail dismally in field trials. Under such circumstances, it is questionable whether or not meaningful challenge techniques have been used. For example, the precise dosage of cells to be employed remains undetermined. Apparently, there is substantial variation in virulence among strains. In addition, the most effective means of administering the challenges remains to be elucidated. In this respect, Michel (1980) and Cipriano (1982b) suggested standard- ised methods of challenge. However, the effectiveness of these techniques awaits clarification. It is readily admitted that much effort has been expended on the development of furunculosis vaccines. Yet, after 40 years the quest continues. Most studies, to date, have measured effectiveness in terms of the humoral antibody response (e.g. Michel et al, 1990). Unfortunately, there is now some doubt as to whether the presence of humoral agglutinins actually correlates with protection. Maybe, it would be prefer- able to emphasise other aspects of fish immunology, such as cell-mediated immunity, a notion which has been suggested by McCarthy and Roberts (1980). Ford et al. (1998) treated sea run salmon brood stock with oxolinic acid and vaccinated with a formalised whole-cell vaccine in an attempt to reduce the impact of furunculosis. Encouraging results were obtained insofar as of 2,552 fish captured from the rivers Connecticut and Merrimack and treated in 1986-1992 only 362 died, of which 65 (18%) were diagnosed with furunculosis. In comparison, 206 fish served as untreated controls, with just over half, i.e. 109, dying, of which 63 (=58%) had furunculosis. There is ongoing concern about the value of those furunculosis vaccines devel- oped for use in salmonids containing antigens o^ Aer. salmonicida subsp. salmonicida, for application in other groups of fish, which may be affected by atypical isolates of the pathogen. For example, a commercial polyvalent product for salmon failed to protect turbot from experimental challenge with Aer. salmonicida subsp. achromo-
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Control 365 genes (Bjornsdottir et ai, 2005). However, Santos et al. (2005) appear to have experienced better success with turbot, although the specific pathogen was not equated with subsp. achromogenes.
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