Emergence and Spread of Viral Hemorrhagic Septicemia in the Laurentian Great Lakes: Status of Knowledge and Lessons Learned

The Viral Hemorrhagic Septicemia virus (VHSV) has invaded the Laurentian Great Lakes Basin leaving behind trails of ecologic and economic devastation.  This OIE-notifiable disease has been associated with serious infection of 29 freshwater fish species and its range has extended to include the watersheds of the five Great Lakes. The original isolation of VHSV in the Great Lakes was from adult muskellunge Esox masquinongy and sequence analysis of the isolated virus proved that it forms a novel sublineage within VHSV genotype IV, designated IVb.  Experimental infection studies using multiple species demonstrated that mortalities can be induced in more than 10 species, however, the most susceptible species were the bluegill (Lepomis macrochirus), lake herring (Coregonus artedi) muskellunge, and the largemouth bass (Micropterus salmoides). The least susceptible were several salmonid species. On the contrary, the lake sturgeon (Acipenser fulvescens) was resistant to VHSV-IVb. Depending on the dose of exposure, VHSV infection can run a peracute, acute, subacute, or subclinical course of infection. Survivors can harbor the virus for up to nine months with or without shedding into the surrounding water. Moreover, VHSV IVb could be isolated from leeches and amphipods in infected lakes. Since VHSV-strains from other areas of the world have not been associated with large-scale outbreaks in native freshwater fish, there are mounting concerns that VHSV Genotype IVb may continue its devastation outside the Great Lakes Basin. As a result, there is an urgent need to better understand the biological characteristics of this emerging VHSV strain, the host-virus interactions in particular.