| Since 2005, fish health in the Laurentian Great Lakes region of North America has been affected by a new strain of viral hemorrhagic septicemia virus (VHSV IVb). Uncertainty about persistence of VHSV IVb in infected systems arose when it caused a large fish die-off in Budd Lake, Michigan, in 2007 without subsequent mortality events or isolations several years after. One purpose of this thesis was to determine if VHSV IVb still existed in Budd Lake (i.e. active infections, production of antibodies, or reservoir sources). Additionally, the consequences of stocking naive fish into systems that have experienced VHSV IVb outbreaks were explored by performing a mock stocking event with age-0 sentinel Largemouth Bass. Despite four years of negative surveillance results, the virus was isolated from resident Muskellunge and Largemouth Bass and stocked sentinel fish in Budd Lake in spring 2011, and Muskellunge, Largemouth Bass, Bluegills, and Pumpkinseeds tested positive for antibody production using the 50% plaque neutralization test, the competitive enzyme-linked immunosorbent assay, or both. The virus was not detected in leech, mussel, water, or sediment samples; however, the virus was detected in amphipods in both 2011 and 2012. Based on the study results, it is concluded that VHSV IVb has likely persisted in Budd Lake since the initial outbreak without causing additional mortality events, and that amphipods may be an incidental reservoir for the virus. In systems where VHSV IVb outbreaks have occurred, managers should be aware that the virus may be circulating in populations even though surveillance efforts may fail to find evidence of active infections. |
