In 2003, viral hemorrhagic septicemia virus (VHSV) emerged in the Laurentian Great Lakes causing serious losses in a number of ecologically and recreationally important fish species. Within six years, despite concerted managerial preventive measures, the virus spread into the five Great Lakes and to a number of inland waterbodies. In response to this emerging threat, cooperative efforts between the Michigan Department of Natural Resources (MI DNR), the Michigan State University Aquatic Animal Health Laboratory (MSU-AAHL), and the United States Department of Agriculture-Animal and Plant Health Inspection Services (USDA-APHIS) were focused on performing a series of general and VHSV-targeted surveillances to determine the extent of virus trafficking in the State of Michigan. Herein we describe six years (2005–2010) of testing, covering hundreds of sites throughout Michigan’s Upper and Lower Peninsulas. A total of 96,228 fish representing 73 species were checked for lesions suggestive of VHSV and their internal organs tested for the presence of VHSV using susceptible cell lines. Of the 1,823 cases tested, 30 cases from 19 fish species tested positive for VHSV by tissue culture and were confirmed by reverse transcriptase polymerase chain reaction (RT-PCR). Gene sequence analyses of all VHSV isolates retrieved in Michigan demonstrated that they belong to the emerging sublineage “b” of the North American VHSV genotype IV. These findings underscore the complexity of VHSV ecology in the Great Lakes basin and the critical need for rigorous legislation and regulatory guidelines in order to reduce the virus spread within and outside of the Laurentian Great Lakes watershed.

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Bacterial kidney disease (BKD), caused by Renibacterium salmoninarum, is a slowly progressing disease that threatens salmon conservation and restoration programs in North America. The purpose of this study was to track naturally occurring R. salmoninarum infection in representative, Michigan, USA, salmonid stocks using nested polymerase chain reaction (nPCR), quantitative enzyme-linked immunosorbent assay (Q-ELISA), and culture. The Q-ELISA test detected 67.6% infection prevalence, which is lower than culture (77.2%) or nPCR (94.2%), yet it provided semiquantitative data on infection intensity. The disagreement in results among the three assays may reflect the different phases of R. salmoninarum infection at the time of sampling. The testing results demonstrated the presence of six patterns, with each of the patterns representing a probable stage along the course of natural R. salmoninarum infection. Findings also suggest that fish stocks tested in this study were not uniform in the distribution of the diagnostic patterns and that, from studying such patterns, one can determine the course of BKD infection in a particular population.

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