Whirling Disease

Whirling disease is a disease affecting juvenile salmonid fish including trout and whitefish. It is caused by a microscopic parasite, Myxobolus cerebralis, which infects fish through their skin. Although there is no risk to human health, the parasite can be lethal in rainbow (including steelhead) and cutthroat trout under four months of age.

The spread of whirling disease can be prevented by following the Clean Drain Dry steps for all boats, equipment and material.

On this page

• Background
• Lifecycle
• Monitoring for whirling disease
• Preventing the spread of whirling disease
• Contact information
• For more information

Background

Whirling disease was first confirmed in Canada in 2016 after it was detected in Alberta. It has since been confirmed in four major watersheds across central and southern Alberta. B.C. monitors for whirling disease in priority water bodies in the east Kootenay region near the Alberta border due to its proximity to infected areas in Alberta. Whirling disease is a federally reportable disease through the Canadian Food Inspection Agency (CFIA).

In infected waters, whirling disease may cause high mortality in fish populations depending on the age and size of the salmonid host (trout, salmon, whitefish); juvenile fish are most susceptible to infection. The severity of an outbreak is difficult to predict due to various interacting factors between habitat, and environmental conditions.  However, in extreme circumstances, localized population collapses of more than 90% have been observed in some streams in the Western United States.

There are no health concerns for people or other mammals swimming in or drinking water that contains whirling disease. Eating an infected fish is not known to cause harmful effects.

There is no treatment currently available for whirling disease therefore containment and prevention are the best response.

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juvenile trout displaying tail deformities associated with whirling disease

Lifecycle

Whirling disease is caused by Myxobolus cerebralis, a microscopic parasite with a complex lifecycle that involves both juvenile fish and bottom dwelling aquatic worms as hosts. The parasite invades the head and spinal cartilage, and nervous tissue of fish. Damage to the brain stem and spinal cord results in the characteristic erratic "whirling" swimming pattern of infected subjects. When infected fish die, spores are released into the water and substrate to seek out aquatic worm hosts to repeat the cycle.

Outward signs of infection include a blackened and/or deformed tail and skull deformities. These deformities are not exclusive to whirling disease and are not considered proof of infection. Parasites may also be present even where these external signs are not present.

Wild fish species susceptible to whirling disease include:

• Oncorhynchus clarkii (cutthroat trout)
• Oncorhynchus kisutch (coho salmon)
• Oncorhynchus mykiss (rainbow trout)
• Oncorhynchus nerka (sockeye salmon)
• Oncorhynchus tshawytscha (chinook salmon)
• Prosopium williamsoni (mountain whitefish)
• Salmo salar (Atlantic salmon)
• Salmo trutta (brown trout)
• Salvelinus confluentus (bull trout)
• Salvelinus fontinalis (brook trout)

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Monitoring whirling disease

Due to the small size of the parasite and its complex life cycle, it is difficult to contain or eradicate from waterbodies once established. Monitoring of waterbodies and prevention of spread by boats, fishing gear and transported fish are the most effective ways to reduce the spread of this parasite.

The province has established a monitoring program for waterbodies in southern B.C., primarily along the border with Alberta. Continued prevention of spread will only occur with the active participation of boaters, anglers and others who enjoy B.C.’s streams and lakes.

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Preventing the spread of whirling disease

The movement of fish, mud, and water can spread whirling disease. It can be transmitted through spores that attach to equipment (used for swimming, paddling, boating, water pumping, fishing), pets, or through infected fish (alive or dead) and fish parts.

Best Practices for preventing the spread of whirling disease:

• Never move fish or fish parts from one waterbody to another.
• Use fish cleaning stations where available or put fish parts in the local solid waste system. Do not dispose of fish or any fish parts in a kitchen garburator.
• Clean, Drain and Dry boats or any equipment (waders, life jackets, kayaks, etc.) before moving between waterbodies.

Clean

• Clean and inspect watercraft, trailers, and all equipment that has been in contact with water or fish. This includes boats, motors, bait buckets, and swim floats.
• Remove all mud, sand and plant material before leaving the shore.
• Rinse, scrub, or pressure wash your boat away from storm drains, ditches or waterways.
• Bathe pets before allowing them to enter another water body.

Drain

• Before leaving the shoreline, drain water from watercraft and equipment onto dry land.

Dry

• Dry the watercraft and/or equipment completely between trips and allow the wet areas to air dry. Allow a minimum of 24 hours of drying time before entering new waters.
• Leave compartments open on boats and equipment and sponge out standing water.

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