Bacterial Kidney Disease (BKD) is a chronic, granulomatous infectious disease of cultured and wild salmonids. The etiological agent, Renibacterium salmoninarum, is a small gram positive diplobacillus which causes multisystemic pathology involving considerable immunological alterations and immunopathology. Techniques using artificial routes of exposure and high levels of bacteria, namely parenteral injections of viable bacterial suspensions, have routinely been used to produce BKD in salmonid fish in the laboratory. The effects of these means of exposure upon systemic pathology and immunological responses as compared to those encountered in naturally occurring infections are currently unknown.

This pilot study explored the possibility of utilizing a gastrointestinal route of exposure via the feeding of R. salmoninarum infected viscera as a more "natural" means of reproducing the BKD disease condition in laboratory fish. Sixty brook trout were fed R. salmoninarum infected viscera taken from Chinook salmon fingerlings which had recently died of BKD. Unexposed control fish and exposed fish were sampled, and at various time intervals, fish were examined for immunological and morphological alterations related to BKD development. Renibacterium salmoninarum antigen prevalence was assessed via direct fluorescent antibody test (DFAT) and enzyme-linked immunosorbent assay (ELISA), both of which showed an increased antigen prevalence as early as twenty-one days post-exposure. Histopathological examination showed clear progression from normal morphology to moderate granulomatous lesions and degenerative changes of renal and splenic tissue sections.