Erythrocytic inclusion body syndrome: a light and electron microscopic study of infected erythrocytes of Chinook Oncorhynchus ishawyiscna and coho O. kisutch salmon

Investigat~on of natural infections of viral erythrocytic inclusion body syndrome (EIBS) were conducted at Washington Department of Fisheries (MIDF) salmon hatcheries.Comparisons were made of morphological changes seen in stained blood cells by light microscopy with those seen by electron microscopy, and it was determined whether erythrocytic inclusions were of viral ongin.Blood was collected from 10 to 12 fish for each of 8 stocks of salmon.Blood smears and whole blood were processed for microscopic evaluation.By light microscopy infected erythrocytes typically had single, pale blue (Leishman-Giemsa stain) inclusions.Erythrocytes in many stages of development were common, and In some stocks immature erythrocytes dccounted for 50 to 75 "/o of cells present.Electron micrographs showed infected cells with 1 to 3 viral inclusions.Intact inclusions contained densely packed icosahedral virions.Dense-staining inclusions, by light microscopy, were seen infrequently and by electron microscopy appeared to be accumulations of membrane-bound material and not viral inclusions.