Sleeping disease and pancreas disease: comparative histopathology and acquired cross‐protection

Sleeping disease (SD), a disease of freshwater‐reared rainbow trout, Oncorhynchus mykiss (Walbaum), was histologically compared to pancreas disease (PD), a disease of sea water‐reared Atlantic salmon, Salmo salar L. Some weeks after injection of kidney homogenates from SD‐ or PD‐affected fish in rainbow trout, the fish successively developed pancreatic, heart and muscular lesions in both populations, although the SD‐injected population was the most affected. An acquired protection was observed against PD and SD after an initial injection with PD‐ or SD‐infective material. This acquired cross‐protection and the similar histopathologies in PD and SD suggest the two diseases could be caused by a similar or identical agent.