POTENCY TESTING OF A LIVE, GENETICALLY ATTENUATED VACCINE FOR SALMONIDS

Studies have been performed on the use of a live vaccine for immunizat ion of salmonids against the bacterial disease furunculosis. The prote ction elicited by a kanamycin-resistant aroA mutant of A. salmonicida (Brivax I) and an unmarked arA deletion mutant (Brivax II) has been ex amined, and data compared with protection seen using a freeze-dried Br ivax II preparation and a commercial, oil-adjuvanted killed vaccine fo r furunculosis. Whilst high relative percent survival (RPS) values wer e seen in fish (70-100%), much lower RPS values (30-40%) were seen wit h Brivax II vaccinated fish after an experimental challenge. Neverthel ess, the freeze-dried Brivax II formulation performed as well as the b roth-grown Brivax II formulation and a commercial vaccine in these stu dies. In addition, the environmental impact in terms of bacterial shed ding into the tank water has been estimated, and shown to similar to 0 .03% of the total inoculum used. Lastly, the freeze-dried formulation has been tested for its ability to infect fish and prime for lymphocyt e proliferation and antibody production, relative to broth-grown prepa rations, In all three experiments no significant differences were seen between fish given the broth-grown and freeze-dried formulations. Suc h data, together with observations that the freeze-dried live preparat ion had an extended shelf life with the same potency as freshly grown bacteria, show that the potential exists for a commercially viable liv e vaccine to be produced for use in aquaculture. (C) 1998 Elsevier Sci ence Ltd. All rights reserved.