Viral hemorrhagic septicemia (VHS) is a deadly infectious fish disease caused by Viral hemorrhagic septicemia virus. It afflicts over 50 species of freshwater and marine fish in several parts of the Northern Hemisphere. Different strains of the virus occur in different regions, and affect different species. There are no signs that the disease affects human health. VHS is also known as Egtved disease, and the virus as Egtved virus. Historically, VHS was associated mostly with freshwater salmonids in western Europe, documented as a pathogenic disease among cultured salmonids since the 1950s. Today it is still a major concern for many fish farms in Europe and is therefore being watched closely by the European Community Reference Laboratory for Fish Diseases. It was first discovered in the US in 1988 among salmon returning from the Pacific in Washington state. This North American genotype was identified as a distinct, more marine-stable strain than the European genotype. VHS has since been found afflicting marine fish in the northeastern Pacific Ocean, the North Sea, and the Baltic Sea. Since 2005, massive die-offs have occurred among a wide variety of freshwater species in the Great Lakes region of North America. Virus taxonomy VHSV is a negative-sense single-stranded RNA virus of the order Mononegavirales, family Rhabdoviridae, and genus Novirhabdovirus. Another related fish rhabdovirus in the genus Novirhabdovirus is Salmonid novirhabdovirus (formerly Infectious hematopoietic necrosis virus (IHNV)), which causes infectious hematopoietic necrosis (IHN) disease in salmonidae. The viral cause of the disease was discovered in 1963 by M. H. Jenson. The virus is an enveloped, bullet-shaped particle, about 180 nm long by 60 nm in diameter, covered with 5 to 15 nm long peplomers. Molecular virology The genome of VHSV is composed of approximately 11-kb of single stranded RNA, which contains six genes that are located along the genome in the 3′-5′ order: 3′-N-P-M-G-NV-L-5′, nucleocapsid protein (N), polymerase-associated phosphoprotein (P), matrix protein (M), surface glycoprotein (G), a unique non-virion protein (NV), and virus polymerase (L). VHSV enters the host cell through either fusion or endocytosis. It binds to a glycoprotein, called fibronectin, in the extracellular matrix. VHSV does its binding through integrin receptors. Reverse genetics is a powerful tool to study and characterize the previously unknown viral genes. Reverse genetics system is currently available for VHSV. A vaccinia virus free reverse genetic system for Great Lakes VHSV (Genotype IVb) was developed by a research group from the USA.