Erythrocytic inclusion body syndrome: First report of natural infection in juvenile coho salmon [Oncorhynchus kisutch] reared in freshwater in Japan

Since 1986 mass mortalities attributable to erythrocytic inclusion body syndrome (EIBS) have occurred in juvenile coho salmon (Oncorhynchus kisutch) reared in freshwater in Japan during May to July every year. The manifest sign of the diseased fish was severe anemia. Fish affected with fungi and/or with damage in snout increased in number as mortality rose. Erythrocytic inclusion bodies contained enveloped viral particles 70-80 nm in diameter and similar in morphology to the EIBS virus were found in the erythrocytes of the diseased fish and the syndrome was induced by artificial infection with the blood homogenates from the diseased fish, and hence the disease was diagnosed as EIBS. Survivors of the disease were resistant to artificial infection with EIBS. This is a first report of the occurrence of a natural infection of EIBS in juvenile coho salmon in freshwater in Japan.