The initial attempts to produce vaccines for ERM may be traced back to the work

The initial attempts to produce vaccines for erm may

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The initial attempts to produce vaccines for ERM may be traced back to the work of Ross and Klontz (1965). These workers used a phenol-inactivated vaccine, which was administered orally, via the food. Success was most encouraging, insofar as 90% of the vaccinated fish survived subsequent infection with Y. ruckeri. A comparison of different methods of bacterial inactivation convinced Anderson and Ross (1972) that 3% chloroform was better than sonication, 1% formalin, or 0.5% or 3% phenol. Passive immunisation confirmed that the fish produced humoral antibodies to chloroform-inactivated cells (Busch, 1978). Commercial interest in Y. ruckeri vaccines grew with the involvement of the now defunct Tavolek Company. Amend et al. (1983), examining factors affecting the potency of preparations, reported that potency was not affected by pH values of 6.5 to 7.7, or by cultivation for up to 96 h in TSB at room temperature. This team concluded that inactivation, whether by formalin or chloroform, did not matter. However, there was good evidence that protection was enhanced by culturing the cells for 48 h at pH 7.2, lysing them at pH 9.8 for 1-2 hours and then adding 0.3% (w/v) formalin. A live auxo- trophic aroA mutant was evaluated by i.p. injection in rainbow trout, and an RPS of 90% recorded after challenge (Temprano et al, 2005). Application of these vaccine formulations may be by the oral route, i.e. on food (Klontz, 1963; Ross and Klontz, 1965; Anderson and Nelson, 1974), by injection (Anderson and Nelson, 1974; Cossarini-Dunier, 1986), by immersion, shower or spray (Johnson and Amend, 1983a, b), or by anal intubation (Johnson and Amend, 1983b). Problems have been recorded with the oral method, insofar as protection is short-lived. Thus, in a comparison of injection and oral methods of uptake with a chloroform-inactivated vaccine, Anderson and Nelson (1974) did not find any anti- body in fish fed with a vaccine for 7 days; whereas a low titre of 1:16 and 1:32 resulted in trout which were injected. Moreover, injected fish were protected for 12 weeks compared with only 6 weeks in the group which received the oral prepara- tion. Similarly, a comparison of injection, immersion, shower and spray methods
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368 Bacterial Fish Pathogens showed that injection offered the best protection against artificial challenge with Y. ruckeri (Johnson and Amend, 1983a). In a comparison of the efficacy of injection, oral uptake and anal intubation, Vigneulle (1990) favoured the first-mentioned in terms of protection. Interestingly, antibodies were found in the serum of rainbow trout vaccinated by injection and anal intubation, but not by the oral route. Unfortu- nately, it must be emphasised that injection is only feasible for large and/or valuable fish and not for the millions of fry/fingerlings which abound on the typical fish farm. However, ERM vaccines have been used successfully on fish farms when adminis- tered by bathing (Tebbit et al, 1981). In one investigation, 22,959,239 rainbow trout were vaccinated by a 90 sec dip in a commercial vaccine preparation. The results were very encouraging with significantly reduced losses attributable to ERM. In this
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