Viruses of Freshwater Mussels during Mass Mortality Events in Oregon and Washington, USA

Freshwater mussels (Unionida) are globally imperiled, in part due to largely unexplained mass mortality events (MMEs). While recent studies have begun investigate the possibility that mussel MMEs Eastern USA may be caused by infectious diseases, Western received relatively little attention this regard. We conducted a two-year epidemiologic investigation of role viruses ongoing pearlshell (Margaritifera falcata) and ridged (Gonidea angulata) Chehalis River Columbia watersheds USA. characterized viromes hemolymph from 5 locations 2018 2020 using metagenomic methods identified 557 based on assembled contiguous sequences, most which novel. also distribution diversity previously Gammarhabdovirus related pathogenic finfish viruses. Overall, we found few consistent associations between health status. Variation was strongly driven location, with influence date, species, or status, though these variables together only explained ~1/3 variation virome composition. Our results demonstrate freshwater host remarkably diverse viromes, but no single virus combination appears associated morbidity during MMEs. findings implications for conservation imperiled mussels, including efforts enhance natural populations through captive propagation.