The persistence of Renibacterium salmoninarum (Rs) in rainbow trout (Oncorhynchus mykiss) experimentally infected with either a virulent or non-virulent strain of Rs was examined in this study. Mortalities from bacterial kidney disease (BKD) peaked at 48 % 6 weeks post-challenge with the virulent strain, but no mortality from BKD occurred in fish infected with the avirulent strain. Culture on Selective Kidney Disease Medium (SKDM), a polymerase chain reaction (PCR) and an enzyme linked immunosorbent assay (ELISA) were used to monitor the duration of the infection. The presence of bacteria in challenged fish could be detected by PCR at 12 and 20 weeks post-challenge with non-virulent and virulent strains, respectively. On the other hand, it was only possible to detect Rs NCIMB 1113 by ELISA and by culture on SKDM up to 10 weeks and 12 weeks, respectively. Furthermore, the avirulent isolate was not detected in fish injected with this strain on SKDM or by ELISA. Using the methods of detection described, it would appear that the fish were able to clear the virulent Rs by week 22 post-challenge
