IHNV

Infectious hematopoietic necrosis virus (IHNV) is a member of the genus Novirhabdovirus in the family Rhabdoviridae. It is an enveloped, single-stranded negative-sense RNA virus that infects salmonid fishes. IHNV causes infectious hematopoietic necrosis, a systemic disease affecting the kidney and immune tissues, particularly in juvenile salmonids.

Natural and cultured hosts include rainbow trout, chinook salmon, sockeye salmon, steelhead trout, and other salmonids. Clinical signs in fry and fingerlings include lethargy, pale gills, darkening, swelling, and exophthalmia; necropsy shows hemorrhages in the kidney and spleen, anemia, and edema. Mortality can be rapid, especially in hatcheries, leading to significant economic losses.

IHNV is primarily waterborne and transmitted horizontally through infected fish, water, and fomites. Eggs and milt can carry the virus; vertical transmission has been reported in some cases. The virus is distributed in Pacific salmonid populations and has been detected in North America, Europe, and parts of Asia, with outbreaks associated with hatchery operations.

Diagnosis relies on RT-PCR, virus isolation, and antigen detection from kidney and spleen samples. Histopathology reveals necrosis of hematopoietic tissues. Control measures emphasize biosecurity, sanitation of eggs and rearing water, vaccination where available, and surveillance to prevent introduction and spread.

IHNV is a notifiable or regulated disease in several jurisdictions due to its economic impact on aquaculture. Research continues on vaccines and management strategies to reduce outbreaks in hatcheries and farms.