Further evidence for a viral etiology in plasmacytoid leukemia of Chinook salmon Oncorhynchus tshawytscha

Abstract

Plasmacytoid leukemia (PL) is an important disease of seawater pen-reared chinook salmon Oncorhynchus tshawytscha in British Columbia, Canada. The disease is caused by an infectious agent, and the microsporidium Enterocytozoon salmonis, Renibacterium salmoninarum (the cause of bacterial kidney disease, BKD), and a retrovirus have been suggested as possible causes. Experimental transmission studies were conducted to elucidate the etiology of PL and they strongly indicate that a virus is the cause of the disease. The disease was transmitted using an inoculum prepared from affected kidney and spleen that had been passed through a 0.22 gm filter. Oral treatment with Fumagillin DCH, an antiprotozoan compound used in other studies to treat E. salmonis infection, had no effect on the disease. Injection of R. salmoninarum that was isolated from a fish with PL caused BKD and no signs of PL.