Research has shown that the parasite can pass through the gastrointestinal tract of some birds, such as great blue herons, and remain alive. Certain fish-eating birds have also been shown to disperse the parasite. Park staff have been working with Montana State University’s Department of Ecology to measure how the infection rate might vary in different stream conditions. Yellowstone National Park’s cutthroat trout spawning streams, which vary widely in thermal, hydrological, and geological characteristics, provide an exceptional opportunity to study whirling disease in native trout. The finding of adult fish in the lake with the parasite’s spores that survived their initial infection suggests some resilience of Yellowstone cutthroat trout to whirling disease. Significant declines in Pelican Creek’s spawning population have been attributed to the combination of whirling disease and predation by nonnative lake trout in Yellowstone Lake. Infection has been most severe in Pelican Creek, which once supported nearly 30,000 upstream-migrating cutthroat trout.
The parasite is most prevalent in the two known infected tributaries, Pelican Creek and the Yellowstone River downstream of the lake outlet. In the lake, the infection has spread to about 20% of the cutthroat trout. It has since been found in the Firehole, Madison, Gibbon, Gallatin, and Lamar rivers and throughout the Yellowstone Lake watershed. Whirling disease was first detected in Yellowstone in 1998 in cutthroat trout from Yellowstone Lake. No practical treatment exists for fish infected with this disease or for the waters containing infected fish. Because the fish cannot feed normally and is more vulnerable to predation, whirling disease can be fatal. The parasite feeds on the fish’s cartilage, and the infection can cause skeletal deformities, a blackened tail, and whirling swimming behavior. Cutthroat trout are susceptible, especially during the first months of life. During the parasite’s life cycle, it takes on two different forms as spores and requires two hosts: a common aquatic worm ( Tubifex tubifex) and a susceptible fish.
Whirling disease is caused by a microscopic parasite from Europe ( Myxobolus cerebralis) that can infect some trout and salmon it does not infect humans.
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