A cohabitation challenge to compare the efficacies of vaccines for bacterial kidney disease (BKD) in chinook salmon Oncorhynchus tshawytscha.

The relative efficacies of 1 commercial and 5 experimental vaccines for bacterial kidney disease (BKD) were compared through a cohabitation waterborne challenge. Groups of juvenile chi- nook salmon Oncorhynchus tshawytscha were vaccinated with one of the following: (1) killed Reni- bacterium salmoninarum ATCC 33209 (Rs 33209) cells; (2) killed Rs 33209 cells which had been heated to 37°C for 48 h, a process that destroys the p57 protein; (3) killed R. salmoninarum MT239 (Rs MT239) cells; (4) heated Rs MT239 cells; (5) a recombinant version of the p57 protein (r-p57) emulsi- fied in Freund's incomplete adjuvant (FIA); (6) the commercial BKD vaccine Renogen; (7) phosphate- buffered saline (PBS) emulsified with an equal volume of FIA; or (8) PBS alone. Following injection, each fish was marked with a subcutaneous fluorescent latex tag denoting its treatment group and the vaccinated fish were combined into sham and disease challenge tanks. Two weeks after these fish were vaccinated, separate groups of fish were injected with either PBS or live R. salmoninarum GL64 and were placed inside coated-wire mesh cylinders (liveboxes) in the sham and disease challenge tanks, respectively. Mortalities in both tanks were recorded for 285 d. Any mortalities among the live- box fish were replaced with an appropriate cohort (infected with R. salmoninarum or healthy) fish. None of the bacterins evaluated in this study induced protective immunity against the R. salmoni- narum shed from the infected livebox fish. The percentage survival within the test groups in the R. salmoninarum challenge tank ranged from 59% (heated Rs MT239 bacterin) to 81% (PBS emulsified with FIA). There were no differences in the percentage survival among the PBS-, PBS/FIA-, r-p57- and Renogen-injected groups. There also were no differences in survival among the bacterin groups, regardless of whether the bacterial cells had been heated or left untreated prior to injection.