In general, it was considered a hatchery problem rather than a disease among wild trout fisheries. Four years of coordinated research, including 31 projects funded by theNational Partnership on the Management of Wild and Native Cold Water Fisheries based at MSU-Bozeman, have yielded some concrete data.
Rainbow trout are the most susceptible.
Whether whitefish and bull trout are vulnerable isn't known yet. The microscopic spores produced in infected fish number up to seven digits. Spores can survive for decades before being ingested by the worm. Inside the worm, the spores are transformed and ejected back into the water, sometimes by multiples of thousands per day per worm. Fry from 0 to 2 months are the most likely to be fatally infected.