Bacterial kidney disease (BKD) in Michigan salmonids

Bacterial Kidney Disease (BKD) caused by a Gram-positive bacterium, Renibacterium salmoninarum (R. salmoninarum) is a systemic disease that threatens the expansion of both cultured and wild salmonines worldwide. Historical records show that BKD affected Michigan's brook trout as early as 1955 (Allison 1958) and continued its spread to most of other salmonid species such as coho salmon (Oncorhynchus kisutch ) spawners in the late sixties (MacLean and Yoder 1970) followed by a potent epizootic among the chinook salmon (Oncorhynchus tshawytscha ) populations in Lake Michigan in the late 1980's (Holey et al. 1998). Despite the magnitude of the setback to fisheries conservation efforts in Michigan, relatively little research has been done on R. salmoninarum , primarily due to its slow-growing nature, which takes up to 12 weeks to obtain growth upon primary isolation. The tissue processing protocol and optimized culture technique developed in this study, has facilitated the isolation of large number of R. salmoninarum and achieved a remarkably shorter incubation time for primary isolation.; A sort of disagreement in results among the three used diagnostic assays (nPCR, Culture, Q-ELISA) was recorded during BKD testing of the feral and captive salmonid stocks for BKD, which may reflect the different phases of R. salmoninarum infection at the time of sampling. Further, the testing results demonstrated the presence of six patterns, with each of the patterns representing a probable stage along the course of R. salmoninarum infection.; Data also demonstrated that male spawner salmon play the same role played by female in transmission of R. salmoninarum by shedding of the bacteria and its soluble antigens in milt. Moreover, results revealed that Hinchenbrook coho strain is more susceptible to R. salmoninarum than the Michigan adapted coho salmon strain. Data also, supported the previous reports, which indicated that brook trout are highly susceptible to BKD. Also, data showed that prevalence of R. salmoninarum in the hatchery-raised brook trout is the same as wild strains residing in the water source and that Iron River brook trout are more vulnerable to R. salmoninarum infection than Assinica strain. Last, external parasites could played a possible role in initiation, speeding up the R. salmoninarum infection and BKD occurrence and mortalities is not related to changes in seasons. Finally, findings indicated that the adult parasitic sea lamprey is a new host range for R. salmoninarum where the bacteria were isolated from the kidneys of a number of sea lampreys from Lake Ontario in 2003 and 2004.