Hematopoietic intranuclear microsporidian infections with features of leukemia in chinook salmon Oncorhynchus tshawytscha

Abstract

Intranuclear infections of hematopoietic cells with characteristics of lymphoblasts were detected in juvenile chinook salmon Oncorhynchus tshawytscha with a leukemic condition. The microsporidian infection was associated with an anemia secondary to the proliferation of hematopoietic cells in the kidney and spleen. Many of the nuclei of these lymphoid cells contained plasmodia and sporogonic stages of the microsporidian. The characteristic sporogony and spore morphology of the salmonid microsporidian is found only in the genus Enterocytozoon . The microsporidian stimulates an abnormal proliferation of host lymphoblasts and the subsequent migration and invasion of these infected host cells into various tissues resulted in a leukemic condition. A similar disease has recently been described among adult chinook salmon reared in seawater net-pens in British Columbia, Canada. The microsporidian was transmitted to previously uninfected kokanee salmon O. nerka by intraperitoneal injections of cells obtained from kidney homogenates of naturally-infected chinook salmon.