TWENTY-THIRD ANNUAL EASTERN FISH HEALTH WORKSHOP JOHN CARVER INN, PLYMOUTH, MA 30 MARCH - 2 APRIL, 1998 Evaluation Of A Phylogenetically Related Bacterium For Use As A Bacterial Kidney Disease Vaccine In Farmed Atlantic Salmon (Salmo salar). Kira Salonius1, A. MacKinnon1, and D.Groman2 and S. Griffiths3 1 Aqua Health Ltd. West Royalty Industrial Park, Charlottetown, Prince Edward Island, Canada C1E 1B0 2 Aquatic Diagnostic Services, Atlantic Veterinary College, UPEI, Prince Edward Island, Canada C1A 4P3 3 Research and Productivity of New Brunswick, 921 College Hill Rd., Fredericton, New Brunswick, Canada E3B 6Z9. RSX II, a phylogenetically related species of bacterium sharing common antigenic determinants to Renibacterium salmoninarum is currently being investigated as a Bacterial Kidney Disease vaccine. The lyophilized vaccine is presented as reconstituted live cells in sterile diluent. In this study, two efficacy assessment methods were used at six weeks post-infection and evaluated as alternate methods to testing based on differential mortality, 12 to 15 weeks post-infection. Atlantic salmon (Salmo salar) parr, mean weight 15 g, were vaccinated with an intraperitoneal (i.p.) injection of 0.1 ml of the vaccine 483 degree days prior to direct i.p. injection challenge with 1.4 x 104 colony forming units of virulent R. salmoninarum. Renal and splenic tissues from 20 vaccinated and unvaccinated fish were evaluated without bias for histopathological alterations caused by R. salmoninarum infection. A qualitative assessment criterion was applied using three categories of morphological lesion. A numeric code was assigned to the histopathological alterations and the total score compared using a non-parametric technique (Kruskal-Wallis). Kidney tissue samples were cultured on SKDM-2 from 60 vaccinated and 86 unvaccinated fish. The total scores (combined indices) in the unvaccinated fish were significantly (P< 0.0025) greater than those of the vaccinated fish. The prevalence of R. salmoninarum by culture in the unvaccinated fish was 83%, as compared to those fish in the vaccinated group, where only 37% were culture positive. In this test system, the combined histopathological indices were considered to be valuable in evaluating vaccine efficacy. Culture activity of R. salmoninarum, recorded as positive for fish with heavy culture growth, but also for fish with relatively few colonies cultured, may possibly result in an overestimation of the severity of infection in the vaccinated fish, where it has been observed that fewer colony numbers are cultured. Further evaluation of the vaccine and the test methods will be investigated in Coho (Oncorhynchus kisutch) and Chinook (O.tshawytscha) salmon.   Return to 23rd Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page