Experimental interspecies transmission of plasmacytoid leukemia in salmonid fishes

Abstract

Plasmacytoid leukemia (PL), also known as marine anemia, has caused high mortalities in chinook salmon Oncorhynchus tshawytscha reared in netpens in the Sechelt area of British Columbia, Canada, since 1988. The cause of the disease is apparently an infectious agent, but the etiology has yet to be determined. Coho salmon O. kisutch, Atlantic salmon Salmo salar, rainbow trout O. mykiss, and sockeye salmon O. nerka are also raised in netpens, and are important to the sport and commercial fisheries. Their susceptibility to PL was therefore investigated. These species, as well as chinook salmon, were exposed to PL by intraperitoneal injection of a kidney homogenate from affected chinook salmon. At 6 to 16 wk post injection (PI), the chinook and sockeye salmon exhibited gross and histological changes consistent with PL. Two of 22 Atlantic salmon also developed histological signs consistent with the disease. The coho and rainbow trout exhibited renal interstitial hyperplasia and foci of cells suggestive of the leukemic plasmablasts in the mesenteries. However, the lesions were mild and the coho and rainbow trout never developed clinical or gross pathological signs of PL. Transmission of PL between different genera and species further supports the hypothesis that the disease is caused by an infectious agent, and not by the transplantation of neoplastic cells. A solid tumor composed of plasmablasts was observed in the swimbladder of one exposed sockeye. This is additional evidence that the disease is a neoplastic condition rather than a reactive plasmacytosis.