Viral hemorrhagic septicemia

Viral hemorrhagic septicemia (VHS) is a deadly infectious fish disease caused by Piscine novirhabdovirus (originally called 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. Viral hemorrhagic septicemia (VHS) is a deadly infectious fish disease caused by Piscine novirhabdovirus (originally called 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. 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. 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). 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. This system allows the investigators to explore the functional properties of individual viral genes of VHSV in detail. This system was immediately utilized to characterize the non-virion (NV) gene of novirhabdoviruses. Even though it has been demonstrated that the NV gene is not necessary for viral replication, it is highly essential for viral pathogenesis. A new role of NV protein has been discovered and demonstrated that it inhibits apoptosis at the early stage of viral infection. This discovery unlocked the mystery of presence of NV proteins in novirhabdoviruses. Different isolates (unique strains) of VHSV are typically grouped by genotyping. It is found that genotype groups are divided more geographically than by host species. Earlier studies used different numbering systems, but the following system has come into common usage based on genotype similarity based on sequencing of the N- and G-genes. Types I-III are enzootic to Europe, and Type IV to North America, and Type I and type IV isolates are further subdivided, as follows: Type I-a was the only strain known from VHSV's discovery in 1963 until the late 1988, isolated to fish farms in continental Europe, affecting primarily rainbow trout and occasionally brown trout or pike. In 1988, the first marine strain of VHSV, now designated type IV, was found in normal-appearing salmon returning from the Pacific to rivers of Washington State. This strain and other marine strains were not lethal to rainbow trout. The discovery prompted further studies, and by the mid-1990s, marine VHSV was found in eight species along the northern North America's Pacific coast, and 14 species in and around the Atlantic's North Sea. 1996 saw the first VHSV in Japan, among Japanese flounder farmed in the Seto Inland Sea, and different genotypes have appeared in different areas since then. Type IV was later found off North America's northern Atlantic coast, in Atlantic herring (Clupea harengus) mummichog (Fundulus heteroclitus), stickleback (Gasterosteus aculeatus aculeatus), brown trout (Salmo trutta), and striped bass (Morone saxatilis), as well as dozens of freshwater species in the Great Lakes.