Marine anemia in farmed chinook salmon (Oncorhynchus tshawytscha): Development of a working case definition

Marine anemia (plasmacytoid leukemia) is a histologically defined syndrome affecting farmed chinook salmon (Oncorhynchus tshawytscha) in British Columbia, Canada. Although the disease has received recent attention and has been diagnosed in many fish farms, past criteria for diagnosis have limited the depth and breadth of epidemiological investigations. By identifying a repeatably diagnosable subset of signs and symptoms of affected fish, a new working case definition of marine anemia was developed. This definition relied exclusively on histological features to achieve the diagnosis. The intra-observer repeatability of diagnoses using the new definition was high ( κ = 0.84). An algorithm employing gross pathological signs was created for field investigation of the disease. The algorithm was capable of predicting histological diagnosis with a reasonable level of accuracy, and was judged to be a valuable tool for diagnostic decisions. We concluded that by using the case definition created in this study together with the algorithm, the comparability and accuracy of clinical and epidemiological research of marine anemia could be improved.