Whirling disease parasite found in Washington; precautions will prevent its spread

ASOTIN -- The parasite that causes whirling disease has been found in wild Washington trout for the first time, the Washington Department of Fish and Wildlife announced today.

The parasites were found in rainbow trout in the Grande Ronde River and a tributary, Cottonwood Creek. The parasites may have entered Washington waters from the Oregon portion of the Grande Ronde.

The department is asking fishers, boaters and others to clean their boats and equipment to prevent the spread of the parasite which disables young rainbows and makes them vulnerable to predators. The department exercises great care to ensure the parasite does not enter its hatcheries.

"This discovery of the whirling disease parasite in some wild trout in Washington waters is unfortunate but not surprising," said Bern Shanks, director of the Department of Fish and Wildlife. "We don't think it will become a major problem if everyone who uses our lakes and rivers exercises good judgment to prevent the spread of the parasite."

The parasite, named Myxobolus cerebralis, invades the cartilage of young wild trout and salmon and may cause skeletal deformities and nerve damage. The nerve damage causes fish to appear to chase their tails in a whirling fashion. Diseased young fish afflicted with the parasite are very vulnerable to predators. The parasite does not afflict older fish because their cartilage skeletons have turned to bone.

The parasite is transmitted to fish from small worms that live in the sediments of streams and ponds, according to Kevin Amos, manager of the Department of Fish and Wildlife's fish health division.

Because the infection is transmitted from small, mud-dwelling worms, the department is asking fishers and other recreationists to:

• Remove all mud from boats, vehicles, anchors, trailers, waders and boots after leaving a body of water

• Transport only dead fish

• Refrain from disposing of fish entrails, bones or other parts in state waters

• Refrain from transporting aquatic plants

The Washington Department of Fish and Wildlife takes many precautions to keep the parasite from spreading in Washington. Those steps include:

• Banning the importation of fish unless they are from pathogen-free water

• Inspecting imported fish to ensure they do not carry the parasite

• Routine health monitoring of fish in hatcheries

• Restricting the intrastate transfer of fish

Whirling disease is most notable for reducing the number of rainbow trout in portions of Montana's Madison River. Other trout species in the Madison have not been harmed by the disease. The parasite also has been found to be widely distributed in California, Idaho, Colorado and in parts of Oregon. Grande Ronde fish bearing the parasite may have migrated into Washington from waters outside the state.

There is no indication the parasite has caused the deaths of large numbers of fish in any neighboring states, said Amos.

Fish bearing the parasite apparently were imported into the United States from Europe more than 50 years ago. The parasite can survive in the digestive tracts of birds and other animals so it spreads easily. The parasite does not harm humans.