Erythrocytic Inclusion Body Syndrome (EIBS) Infection of Chinook Salmon in Idaho

Abstract Intracytoplasmic inclusions (0.8–2.0 μm in diameter) were detected in erythrocytes of yearling chinook salmon Oncorhynchus tshawytscha from the Rapid River Hatchery in central Idaho. Virions with a mean diameter of 74 nm were found both free and within membrane-bound vacuoles in the cytoplasm of erythrocytes. Clinical signs of affected fish included anemia, hypoproteinemia, splenomegaly, hemosiderin deposits in the spleen, and concurrent saprolegniosis. Low water temperatures may have been responsible for the reduction in mortality rate and the extended infection period observed during the winter. Attempts at demonstrating horizontal transmission and identifying a source of infection were unsuccessful. This is the first report of erythrocytic inclusion body syndrome (EIBS) among salmonid fish in Idaho.