Photographer: Dr. Thomas L. Wellborn, Jr Affiliation:DOI Fish and Wildlife Service Source:www.commons.wikimedia.org Copyright: Public domain
The parasite causing whirling disease (Myxobolus cerebralis) will not be seen free swimming in water although it does have a brief free swimming stage. Instead, whirling disease is evident in the symptoms shown in infected hosts shown through repeated swimming in circles. The final host of M. cerebralis are the common sport fish trout and salmon. The intermediate host will not be noticeably effected by the presence of the parasite.
Symptoms: Hosts that are infected with whirling disease can be easily identified by behavior where they swim in constant circles or whirls. The parasite received its name from the behavior exhibited by the host caused by attachment of the parasite to the host's equilibrium organ. This prevents the fish from foraging for food and evading predators, resulting in death of the host.
Host(s): Trout and salmon
Whirling disease has a devastating effect on many popular sport fish by drastically reducing populations. The parasite is able to survive freezing temperatures and dessication in the spore stage. The spores are also able to survive 20 to 30 years in a stream before finding an intermediate host. The parasite is also readily transferred unknowingly by humans and birds into uncontaminated waters facilitating further infection of sport fish. Anglers are effected the most by the reduction of the sport fish, however overall biodiversity and balance of streams is effected by the loss of trout and salmon.
The parasite M. cerebralis begins in egg form and is taken up by a tubifex worm which serves as the intermediate host. The parasite is shed from the worm and forms a free floating stage where it attaches to a juvenile trout or salmon. Penetration occurs in the head cartilage of the host followed by rapid reproduction of the parasite. As the parasite population increases so does the pressure applied to the equilibrium organ causing the host to swim in characteristic circles leading to death of the host.
Introduction of whirling disease occurred accidentally in the 1950's.
Native Origin: Eurasia
U.S. Habitat: The parasite causing whirling disease can be found in cooler northern water where the preferred hosts trout and salmon are found.
U.S. Present: AL, CA, CO, CT, DE, ID, MI, MT, NH, NJ, NM, NY, NV, OH, OR, PA, UT, VA, WA, WV, WY
Anglers and boaters can help prevent the spread of the parasite causing whirling disease. If you are unaware if the parasite exists in the water you are using, it is safe to assume that it is present and to take the necessary precautions. The following tips can be utilized to help prevent further spread of the parasite to uninfected waters:
Densmore, C. L., V. S. Blazer, T. B. Waldrop, and P. S. Pooler. 2001. Effects of whirling disease on selected hematological patterns in rainbow trout. Journal of Wildlife Diseases 37(2): 375-378.
Huffman, G. L., and R. E. Putz. 1971. Effect of freezing and aging on the spores of Myxobolus cerebralis, the causative agent of salmonid whirling disease. Progressive Fish Cultivating 33(2): 95-98.
Markiw, M.E., and K. Wolf. 1983. Myxosoma cerebralis (Myxozoa: Myxosporea) etiologic agent of salmonid whirling disease requires tubificid worm (Annelida: Oligochaeta) in its life cycle. Journal of Protozology 30(3): 561-564.
Wild Trout Research Laboratory Operated by the Montana Water Center on the campus of Montana State University-Bozeman