Nevertheless several types of preparations including heat killed and formalised

Nevertheless several types of preparations including

This preview shows page 394 - 396 out of 594 pages.

Nevertheless, several types of preparations, including heat-killed and formalised vaccines, have been evaluated by injection. In addition, passive immunisation (by injection) has demonstrated the transfer of immunity between fish. In one compar- ison, it was clearly demonstrated that heat-killed preparations were more successful than products treated with formalin, when administered by injection. Reference is made to the work of Antipa (1976), who injected chinook salmon with vaccines and, following challenge with the pathogen, reported cumulative mortalities of: Unvaccinated controls 85.4% Formalised vaccine 37.8% Heat-killed vaccine 22.3% Sonicated heat-killed vaccines, administered in adjuvant, also stimulate elevated levels of antibody in the skin and mucus (Harrell et al., 1976; Evelyn, 1984). At least these studies indicate the presence of heat-stable antigen, which features significantly in the establishment of protective immunity. Anal intubation, but not i.p. injection, of African catfish (Clarias gariepinus) with a whole-cell vaccine of V. anguillarum 02 led to increased antibody levels after 14 days in the bile and skin mucus as detected by ELISA (Vervarcke et al, 2005).
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376 Bacterial Fish Pathogens Antibodies in a group vaccinated by oral intubation were lower, but still higher than the i.p.-vaccinated group (Vervarcke et ai, 2005). Immersion techniques are most suited for the vaccination of animals in the fish farm environment. Formerly, considerable attention was focused on hyperosmotic infiltration, involving use of a strong salt solution prior to immersion in a vaccine suspension (Croy and Amend, 1977; Aoki and Kitao, 1978; Nakajima and Chikahata, 1979; Antipa et ai, 1980; Giorgetti et ai, 1981). However, it is now appreciated that the technique is extremely stressful to fish (Busch et ai, 1978), and the level of protection achieved is only comparable with the much simpler direct immersion method (Antipa et al, 1980), which is consequently favoured. Indeed, many articles have been published about the benefit of immersion vaccination (Hastein et ai, 1980; Song et ai, 1982; Amend and Johnson, 1981; Giorgetti et aL, 1981; Home et aL, 1982; Johnson et aL, 1982a, b; Kawai and Kusuda, 1995) and the longer, i.e. 2h, "bath" technique (Egidius and Andersen, 1979). A further refinement involves use of low-pressure sprays, which are easy to use, and apparently economic in the quantity of vaccine administered (Gould et al, 1978). The success was illustrated by 0% mortalities in a group of fish spray-vaccinated compared with 80% mortalities among unvaccinated controls after challenge (Gould et al, 1978). All of the aforementioned methods enable fish to develop an immune response to the pathogen. This aspect has been discussed comprehensively, as regards chinook salmon, by Fryer et al. (1972). It is thought that the maximum agglutination titre is in the region of 1:8,192, depending on the fish species used (Groberg, 1982). The development of immunity is clearly a function of water temperature, and generally humoral antibodies are formed more rapidly at high rather than low temperatures.
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