Infectious Hematopoietic Necrosis (IHN) - FHP

Science Center Objects

Fish Diseases

Infectious Hematopoietic Necrosis (IHN)

Photo of Rainbow trout with IHN

Rainbow trout fry experimentally exposed to infectious hematopoietic necrosis virus. Typical signs include darkening and exopthalmia (popeye) as shown by the fish in the lower portion of the photo. Other external signs may include fluid accumulation in the abdomen (ascites), trailing fecal casts, and small hemorrhages in the fins and body musculature. Credit: USGS, Western Fisheries Research Center (Public domain.)

Infectious haematopoietic necrosis (IHN) is an infectious viral disease of salmon and trout. It was first recognized in the 1950s in sockeye and Chinook salmon. The disease has the most economic significance for freshwater farms, however Pacific and Atlantic salmon (Salmo salar L.) in both fresh and sea water have been severely affected.

Fry and small fingerlings become infected very readily, becoming more resistant as they mature. The infection is often lethal and the mortality rate can be 100% in fry. Some fish that survive an outbreak of IHN may become carriers of the virus, providing a reservoir of infection. In addition, infected juveniles shed IHN virus particles in the faeces, urine and external mucus.

Researchers at the WFRC are creating a set of molecular tools by cloning each of the viral genes and sequencing the entire genome. This information is stored in an IHN database. When an IHN virus epidemic occurs, our researchers use molecular genetic methods to characterize the specific virus type, and compare it with other known IHNV types in our database. Similar methods are used for other fish viruses and for epidemics of flu, SARS, and anthrax. Over 600 IHN virus samples from throughout the Pacific Northwest have been characterized to date.

Molecular Epidemiology of Aquatic pathogens – IHNV Fish Virus Database 

This website provides the ability to look at geographic distribution of genetic diversity in the IHN virus on maps. It also allows comparison by number of base pairs difference between isolates. Click here to launch the MEAP-IHNV database interface.


Kurath, G. 2012. An online database for IHN virus in Pacific Salmonid fish—MEAP-IHNV. U.S. Geological Survey Fact Sheet 2012–3027, 4 p.