No easy solution is envisaged unless research costs are supported by public

No easy solution is envisaged unless research costs

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attitude undermines the whole basis of prophylaxis. No easy solution is envisaged unless research costs are supported by public monies or even from the aquaculture industry itself, as already happens in Scotland with the salmon growers. Historically, the first serious attempt to develop a bacterial fish vaccine may be traced to the work of Duff (1942), who used chloroform-inactivated cells to protect cutthroat trout (Salmo clarki) against furunculosis. Since then, vaccines have been formulated against approximately half of the total number of bacterial fish patho- gens. From these endeavours, vaccines to protect against edwardsiellosis, ERM, furunculosis, Hitra disease and vibriosis have reached large-scale commercial produc- tion. This is hardly encouraging for a primary prophylactic tool. It is noteworthy that the simplistic approach of using formalin-inactivated whole cells, which works well with edwardsiellosis, ERM, Hitra disease and vibriosis, has met with conflicting results with furunculosis. However, more sophisticated approaches, such as involving genetic engineering techniques, offer hope for the future.
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Control 345 Composition of bacterial fish vaccines The composition of bacterial fish vaccines may be categorised as follows: Chemically or heat-inactivated whole cells. These vaccines may be mono- or polyvalent. Essentially, these are the simplest, crudest and cheapest forms of fish vaccines. Inactivated soluble cell extracts, i.e. toxoids. Cell lysates. Attenuated live vaccines, possibly genetically engineered cells. These would be unacceptable to some regulatory authorities because of the perceived risk that the vaccine strain may revert to a pathogenic mode. Subunit vaccines, e.g. the gene product of the tapA gene for the control of Aer. salmonicida infections (Nilsson et ai, 2006). DNA vaccines (e.g. Pasnik and Smith, 2006). Purified sub-cellular components, e.g. OMP and LPS. These vaccines require a detailed understanding of microbial chemistry, aspects of which are deficient for many of the bacterial fish pathogens. Serum for passive immunisation (e.g. Shelby et ai, 2002). This is largely of academic interest only, insofar as it is difficult to envisage use of the technique in the fish farm environment. A possible exception is for brood stock or pet fish. Mixtures of the components detailed above. It is difficult to identify any particular type of preparation which excels in terms of protection. Generally, the simplest approach of using inactivated whole cells has received greatest attention. This technique has been successful with a wide assortment of pathogens, including Aer. hydrophila, Edw. ictaluri, Fla. columnare, Ph. damselae subsp. piscicida, V. anguillarum, V. ordain, V. salmonicida and Y. ruckeri. Indeed, with these pathogens (except V. anguillarum and V. ordalii) whole-cell vaccines gave superior results to other more complex forms of vaccines (Austin, 1984b). However, even the best vaccines do not completely prevent the occurrence of disease, necessitat- ing the use of costly drugs to combat low levels of infection. Clearly, more research is
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  • Spring '20
  • Bacteria, representative, gram-negative bacteria

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