Stress proteins, phagocytes, and pathology in coho salmon with bacterial kidney disease (Oncorhynchus kisutch, Renibacterium salmoninarum)

Bacterial kidney disease (BKD) is an important disease of wild and cultivated salmonid fish in Canada and around the world. It is known to be caused by a slow growing Gram positive bacterium, Renibacterium salmoninarum, which grows as an intracellular pathogen of phagocytic cells. The disease can not currently be prevented and BKD cannot be cured with antibiotic treatment. Stress is a major factor in the susceptibility of fish to BKD and the disease can itself be considered a chronic stressor.; I am the first to report SP induction in a fish disease and this work is one of only two known examples of SP induction in fish during pathophysiological processes. Using an enzyme linked immunosorbent assay (ELISA) for HSP-70 and immunofluorescent staining of tissue sections, I found that in the tissue of coho salmon (Oncorhynchus kisutch) with active BKD, host HSP-70 was induced in the vicinity of bacterial microcolonies. This localized SP expression may have important implications for the pathology of BKD and possibly for diseases caused by other Gram positive bacteria and intracellular pathogens. The presence of elevated HSP-70 levels in these diseased fish also raises the practical concern that disease in natural populations might interfere with the use of SP levels as an indicator of environmental stress.; I found no compelling evidence to support the hypothesis that this SP induction resulted from the action of phagocytes at the sites of infection. Culture experiments with rainbow trout (Oncorhynchus mykiss) phagocytes, with hepatocytes and with mixtures of those cells support the idea that salmonid phagocytes may have a weak stress response, at least when cultured in vitro. The hepatocyte cultures had a strong SP response to heat shock, but in mixed cultures I saw no evidence for SP induction by phagocyte oxidants or direct induction by R. salmoninarum. (Abstract shortened by UMI.)...