The presence of neutralizing antibodies against viral hemorrhagic septicemia virus (VHSV-IVb) was investigated in sera of 13 fish species collected from Lake St. Clair, Michigan, USA, a VHSV-endemic water body. We tested 297 sera collected May 2004–June of 2010, using a complement-dependent 50% plaque neutralization test (50% PNT). Neutralizing antibodies were detected in 23% (67/297) of the samples. The highest overall antibody prevalence (85%, 34/40) and mean positive antibody titer (12,113±11,699 SD) were detected in muskellunge (Esox masquinongy). Antibodies were also detected in 50% (15/30) of sampled northern pike (E. lucius), 25% (15/61) of freshwater drum (Aplodinotus grunniens), and 7% (3/41) of smallmouth bass (Micropterus dolomieu). All sera from channel catfish (Ictalurus punctatus), lake sturgeon (Acipenser fulvescens), quillback (Carpiodes cyprinus), rock bass (Ambloplites rupestris), shorthead redhorse (Moxostoma macrolepidotum), silver redhorse (M. anisurum), walleye (Sander vitreus), white perch (Morone americana), and yellow perch (Perca flavescens) were negative. Antibodies in one or more fish species were detected in all sampling years (2004, 2006, 2007, 2009, and 2010), whereas in parallel sampling periods, VHS virus was detected only in 2006 and 2009. Our results suggest the continued presence of VHSV-IVb in the Lake St. Clair ecosystem, and underscore the importance of assessing immune responses of fish populations to determine prior virus exposure.

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