needed particularly in determining the precise nature of the protective

Needed particularly in determining the precise nature

This preview shows page 364 - 366 out of 594 pages.

needed, particularly in determining the precise nature of the protective antibody and of the important antigens. With this information, it may be possible to synthesise the antigens or use genetic-engineering techniques to create vaccine strains suitable for inactivation in straightforward ways. Methods of vaccine inactivation Attention has focused on seven methods for inactivating bacterial cells for incorpora- tion into fish vaccines (Austin, 1984b). These are the use of chemicals, namely 3% (v/v) chloroform, 0.3-0.5% (v/v) formahn and 0.5-3.0% (v/v) phenol, heat (e.g. 56°C or 100°C for 30 or 60min), sonication, and lysis with sodium hydroxide at pH 9.5 or with SDS. Commercially, most interest has centred on the use of formahn, which has given encouraging results with Aer. hydrophila, Edw. ictaluri, Ph. damselae subsp.
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346 Bacterial Fish Pathogens piscicida, Ps. anguilliseptica, V. anguillarum, V. ordain and V. salmonicida. However, it is unfortunate that only a few studies have been carried out to compare different inactivated preparations. Methods of administering vaccines to fish A number of methods of administering vaccines to fish have been tried with varying degrees of success (see Austin, 1984b), and include: Injection, with or without the presence of adjuvant, such as FCA/FIA. This technique is slow, and will inevitably require prior anaesthesia of the animals. Injection is only feasible for valuable fish, brood stock or pet fish. Fortunately, mass injection techniques are available. Oral uptake, via food. This should be the method of choice insofar as fish could be fed and vaccinated simultaneously. However, there may be problems with the degradation of the vaccine in the gastro-intestinal tract, although this is being overcome by new oraHsing compounds. Immersion in a solution/suspension of the vaccine. This is quick (i.e. taking 30-120 sec to perform) and easy, permitting large numbers offish to be readily vaccinated. However, there could be problems regarding disposal of the spent vaccine. Thus, it is debatable whether or not disposal should take place in the fish farm effluent. Bathing in a very dilute preparation of the vaccine for prolonged periods, i.e. several hours. This is obviously very economic in the use of vaccine. It is feasible that the technique could be carried out during routine periods of confinement, such as during transportation of the stock between sites. However, with immer- sion, careful thought needs to be given to the question of disposal. Spraying or showering the vaccine onto fish. This can be automated, such that fish are vaccinated on conveyor belts during routine grading. Hyperosmotic infiltration. This involves a brief immersion (30-60 sec) in a strong salt solution, i.e. 3-8% (w/v) sodium chloride, followed by dipping for 30-60 sec into the vaccine. This method is very stressful to fish, and its use has been consequently reduced.
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  • Spring '20
  • Bacteria, representative, gram-negative bacteria

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