Infectious Hematopoietic Necrosis Virus (IHNV) is an RNA virus of the Novirhabdovirus genus which causes Infectious Hematopoietic Necrosis (IHN), a chronic disease of Salmonoid fish. Thelinear,single-stranded,negative-sense RNA genome of this virus 11,131 nucleotides long and encodes six genes. Fives of these code for structural proteins while the other codes a non-virion protein of unknown function. Transmission of this virus usually occurs via contact with infected bodily secretions and excretions with the virus being able to survive in water for at least a month, particularly if the water contains organic material. The use of contaminated feed is also involved in spread of the virus and vertical transmission is also possible. The virus is known to enter the host via the digestive tract as well as the gills and possibly the base of the fins as well. Once within the host, the virus targets the organs, especially the spleen and kidneys causing a chronic necrosis disease. Infection with IHNV results in clinical symptoms including pale gills, dark skin pigmentation, abdominal distension and lethargy with bouts of hyperexcitability. Currently there is no treatment or cure for the disease. Outbreaks in non-endemic areas are controlled by culling while in endemic regions preventative action is used involving sanitation of farms and disinfectant treatment of eggs. The spread of disease can potentially be limited by raising the water temperature. IHNV is primarily found in the Pacific coast of the USA, Canada and Japan with different clinical isolates being responsible for disease in each area. The M geno group has the greatest genetic diversity and includes isolates found in Idaho, the Columbia River basin, the Washington coast and Europe.The U geno group contains isolates causing disease in Alaska, British Columbia,coastal Washington watersheds and the Columbia River basin but have also been found in Oregon, California and Japan. The L geno group contains isolates predominately found in California and Oregon.