Potential Reservoirs and Risk Factors for VHSV IVb in an Enzootic System: Budd Lake, Michigan

Abstract

Viral hemorrhagic septicemia virus genotype IVb (VHSV IVb) has caused major, sporadic fish die-offs in the Laurentian Great Lakes region of North America since 2005. Presently, factors affecting VHSV IVb persistence in enzootic systems are not well understood. Even with annual surveillance, the virus can go undetected for several years after an outbreak before again re-emerging, which suggests that the virus is maintained in the system either below detectable levels or in untested reservoirs. The aim of this study was to identify potential reservoirs of VHSV IVb in Budd Lake, Michigan; VHSV IVb was first detected in Budd Lake in 2007 but remained undetected until 2011. Additionally, we explored the susceptibility of naive fish introduced into a water body enzootic for VHSV IVb by stocking age-0 Largemouth Bass Micropterus salmoides at varying densities into enclosures in the lake. The virus was not detected among samples of the fishes Notropis spp. and Lepomis spp., cylindrical papershell mussels Anodontoides ferussacianus, leeches (subclass Hirudinea), sediment, or water. However, the virus was successfully isolated from amphipods (family Hyalellidae) and Largemouth Bass held in the enclosures. Our finding of VHSV IVb in Hyalellidae amphipods in combination with other research that has detected the virus in Diporeia spp., a large benthic amphipod important as a food resource to Great Lake fishes, suggests that benthic macroinvertebrates are a reservoir for VHSV IVb in infected systems. If there are environmental reservoirs for VHSV IVb in infected systems, they are likely unevenly distributed. Findings of this study add to our understanding of the seemingly complex ecology of this deadly and economically detrimental virus.

Received February 22, 2016; accepted October 16, 2016 Published online February 6, 2017

ACKNOWLEDGMENTS

Funding for this research was provided by the U.S. Fish and Wildlife Service Great Lakes Fish and Wildlife Restoration Program, Agreement Number 30191-A-G198. The authors thank Chris Schelb, Donald Barnard, Vince Balcer, and Jay Wesley from the Michigan Department of Natural Resources for their field assistance and guidance regarding this project. Gerald Smith from the University of Michigan was of great assistance in identifying Notropis spp. in this study. Tiong Gim Aw from Michigan State University provided guidance in the tangential-flow filtration methods. We also thank Heidi Jerrils, Chad Burton, Adam Becker, Carson Prichard, Kyle Molton, Christine Rabaut, Kelly Donohue, Darren Thornbrugh, Maggie Fish, Jared Ross, and Laura Kniffen for assistance in the field and laboratory. Last, Lakeside Motel and Cottages in Harrison, Michigan, generously offered their beach for accessibility for the enclosure study.