Widespread Seropositivity to Viral Hemorrhagic Septicemia Virus (VHSV) in Four Species of Inland Sport Fishes in Wisconsin

Serological assays were conducted for anti-viral hemorrhagic septicemia virus (VHSV) antibodies in four species of fish in Wisconsin (Bluegill Lepomis macrochirus, Brown Trout Salmo trutta, Northern Pike Esox lucius, and Walleye Sander vitreus) to examine spatial and temporal distributions of exposure. Sera were tested for non-neutralizing anti-nucleocapsid antibodies to VHSV by blocking enzyme-linked immunosorbent assay (ELISA). Results (percent inhibition [%I]) were analyzed for differences among species, across geographic distance, and among water management units. Positive fish occurred in 37 of 46 inland water bodies tested, including in water bodies far from reported outbreak events. Using highly conservative species-specific thresholds (mean %I of presumptive uninfected fish + 2 SDs), 4.3% of Bluegill, 13.4% of Brown Trout, 19.3% of Northern Pike, and 18.3% of Walleye tested positive for VHSV antibodies by ELISA. Spatial patterns of seropositivity and changes in %I between sampling years were also analyzed. These analyses explore how serology might be used to understand VHSV distribution and dynamics and ultimately to inform fisheries management.