Johnston

First Isolation of an Acipenserid Herpesvirus (Family Alloherpesviridae) From Great Lakes Lake Sturgeon (Acipenser fulvescens)

1,2Amber E. Johnston, 1,2Megan A. Shavalier, 2Kim T. Scribner, 3Esteban Soto, 3Susan Yun, 4Edward A. Baker, 2Douglas L. Larson, 5Matti Kiupel, 1,2,5Thomas P. Loch

1Michigan State University - Aquatic Animal Health Lab, Aquatic Animal Disease Ecology Program, 1129 Farm Lane, Rm 340G, East Lansing MI, 48824; 2Department of Fisheries and Wildlife, College of Agriculture and Natural Resources, Michigan State University; 3Department of Epidemiology, School of Veterinary Medicine, University of California-Davis; 4Michigan Department of Natural Resources 5; Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University

ABSTRACT

Despite being the only native Great Lakes (GL) sturgeon species and having suffered dramatic population declines, little is known about infectious diseases of GL lake sturgeon (Acipenser fulvescens, LST). In an ongoing study aiming to fill this knowledge gap, we recently documented the presence of grossly similar cutaneous lesions in adult GL-LST sampled from the St. Clair and Black Rivers (1.3%-5.8% prevalence). Subsequent molecular and phylogenetic analyses of lesion tissues revealed genetic traces of a virus most similar, yet distinct from, two Acipenserid Herpesviruses (Family Alloherpesviridae, AcHVs) that cause significant disease and mortality in other sturgeon species; however, attempts to isolate the virus in vitro were unsuccessful. Given an AcHV had never been detected in the GL basin and facing more questions than answers, we began devising alternative approaches to isolate this GL-AcHV in vitro, a notoriously difficult task given the delicate tegument layer of alloherpesviruses required for infection/replication. Equipped with newly modified tissue preservation methods and returning to Black River in 2020, identical lesions were observed (15.2% prevalence). Preserved lesion tissues were inoculated onto multiple cell lines, whereby the formation of large, multinucleated cells (syncytia) were observed (n=10/12 lesions) on a sturgeon hybrid cell-line. Transmission electron microscopy of infected cells revealed herpesvirus-like enveloped, icosahedral virions, and molecular analyses revealed the recovered virus was nearly identical to the AcHV detected in 2019, marking the first time an AcHV has been isolated from GL-LST. With virus in hand, we began investigating the health effects this AcHV has on juvenile GL-LST via controlled laboratory experiments. Although multiple challenge experiments are ongoing, results to date confirm that this GL-AcHV is capable of inducing skin lesions and subsequent mortality in juvenile GL-LST. The discovery of a potentially lethal AcHV likely has important implications for GL-LST conservation and management efforts that require immediate investigation.

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