Infectious Hematopoietic Necrosis

IHNV on epithelioma papulosum cyprini (EPC) cells at 14 days post-exposure. (USFWS)

Infectious hematopoietic necrosis (IHN) is a viral disease of samonids (salmon and trout). The disease occurs on the west coast of North America from California to Alaska and inland as far as Idaho. IHN has also been reported in the Far East and throughout Europe. Atlantic salmon, rainbow trout, chinook and sockeye salmon are susceptible to IHN.

Affected fish usually become lethargic, dark in color with swollen stomachs and “pop eyes”. Internally, the virus attacks the organs and can cause extensive tissue damage. Deaths are highest among fry and fingerlings, and outbreaks can quickly kill large numbers of fish.

The IHN virus can be transmitted directly from fish to fish and from parents to offspring. The parasites Salmincola and some leeches have been shown to carry the virus and transmit it to fish.