First Isolation of a Herpesvirus (Family Alloherpesviridae) from Great Lakes Lake Sturgeon (Acipenser fulvescens)

SIMPLE SUMMARY: Throughout the Great Lakes basin, infectious diseases likewise threaten wild and hatchery reared fishes, and often require management attention. The lake sturgeon (Acipenser fulvescens) is the only sturgeon species native to the Great Lakes, where it is the largest and longest living fish therein. Due to multiple known and unknown factors, current Great Lakes lake sturgeon populations are estimated to be <1% of historical abundances. One potential contributing factor about which little remains known, especially when compared to other Great Lakes fishes, is the impact of infectious diseases. To address this knowledge gap, a two-year disease surveillance study was undertaken, resulting in the detection and isolation of a herpesvirus from lesions observed on wild adult lake sturgeon in two Great Lakes watersheds (Erie and Huron). Genomic analyses revealed the recovered virus was most similar to, yet molecularly distinct from, a herpesvirus recently recovered from lake sturgeon in the Lake Michigan watershed (Wisconsin, USA). This newly described virus, proposed as Lake Sturgeon Herpesvirus 2, proved virulent to juvenile (<1 year old) lake sturgeon, whereby disease and mortality occurred in virus-exposed fish under laboratory conditions. Overall, results from this study highlight the potential threat this newly described virus poses to Great Lakes lake sturgeon conservation efforts. ABSTRACT: The lake sturgeon (Acipenser fulvescens; LST) is the only native sturgeon species in the Great Lakes (GL), but due to multiple factors, their current populations are estimated to be <1% of historical abundances. Little is known about infectious diseases affecting GL-LST in hatchery and wild settings. Therefore, a two-year disease surveillance study was undertaken, resulting in the detection and first in vitro isolation of a herpesvirus from grossly apparent cutaneous lesions in wild adult LST inhabiting two GL watersheds (Erie and Huron). Histological and ultrastructural examination of lesions revealed proliferative epidermitis associated with herpesvirus-like virions. A virus with identical ultrastructural characteristics was recovered from cells inoculated with lesion tissues. Partial DNA polymerase gene sequencing placed the virus within the Family Alloherpesviridae, with high similarity to a lake sturgeon herpesvirus (LSHV) from Wisconsin, USA. Genomic comparisons revealed ~84% Average Nucleotide Identity between the two isolates, leading to the proposed classification of LSHV-1 (Wisconsin) and LSHV-2 (Michigan) for the two viruses. When naïve juvenile LST were immersion-exposed to LSHV-2, severe disease and ~33% mortality occurred, with virus re-isolated from representative skin lesions, fulfilling Rivers’ postulates. Results collectively show LSHV-2 is associated with epithelial changes in wild adult LST, disease and mortality in juvenile LST, and is a potential threat to GL-LST conservation.