Whirling Disease - Fact Sheet

What is whirling disease?

Whirling disease is an infectious disease of finfish. It is caused by Myxobolus cerebralis. This is a protozoan in the Class Myxosporea.

What species of finfish can be infected by whirling disease?

Each species of finfish may have several common names, but only one common name is listed.

Species susceptible to whirling disease that occur in the natural environment in Canada:

  • 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)

Is whirling disease a risk to human health?

No. The causal agent of whirling disease is not a risk to human health.

What are the signs of whirling disease?

Whirling disease is a cause of death in the younger life stages of susceptible freshwater finfish. Overall deaths of infected fry and fingerlings can reach 90 percent.

Affected finfish may exhibit any of the following signs:

  • behaviour
    • whirling swimming pattern
  • appearance
    • skeletal deformities of the body or head, for example, shortening of the mandible and indentations on the top of the head
    • tail may appear dark or even black

Is whirling disease found in Canada?

Yes. Whirling disease has been found in Alberta. Information about the locations of confirmed positive samples is available on the CFIA web site.

How is whirling disease spread?

Whirling disease is not spread directly between finfish. The parasite is spread through contact between finfish and a freshwater worm (Tubifex tubifex).

People can spread whirling disease by moving any of the following:

  • infected live or dead finfish,
  • infected worms,
  • contaminated equipment, or
  • contaminated water.

How is whirling disease diagnosed?

Diagnosing whirling disease requires laboratory testing. Not all infected finfish show signs of disease.

How is whirling disease treated?

There are no treatment options currently available for whirling disease.

What measures can be taken to prevent the introduction and spread of whirling disease?

If you frequently handle or work with finfish, be aware of the clinical signs of whirling disease.

Do not import live infected finfish into Canada.

  • An import permit is required from the CFIA for certain species of finfish as of December 2011.
  • People bringing finfish into Canada should check other federal, provincial and/or territorial requirements before entering the country.

Do not introduce live finfish from another country into the natural waters of Canada.

  • People releasing finfish into the natural waters or in rearing facilities within Canada should check if federal or provincial and/or territorial permits are required.

Do not use finfish that were bought in a grocery store as bait for catching finfish or other aquatic animals.

When cleaning and gutting finfish, dispose of all waste in your municipal garbage.

The Canadian Food Inspection Agency (CFIA) recommends that you do not visit Canadian aquaculture sites, zoos or aquariums for 14 days if you have travelled to another country and

  • visited an aquaculture site, or
  • had contact with wild finfish.

Wash and disinfect the footwear you wore to the site or when you had contact with wild finfish. Also wash your clothing thoroughly and dry it at a high temperature.

What is done to protect Canadian aquatic animals from whirling disease?

Whirling disease is a reportable disease in Canada. This means that anyone who owns or works with aquatic animals, who knows of or suspects whirling disease in their fish, is required by law to notify the CFIA.

The CFIA will be working with its federal and provincial partners to the control the spread of whirling disease by implementing disease response activities such as controlling the movements of infected animals that people own or work with.

The control measures chosen will depend on the situation.

What do I do if I think a finfish that I am raising or keeping have whirling disease?

If you suspect a finfish that you are raising or keeping may have whirling disease, you are required under the Health of Animals Act to immediately notify the CFIA of your suspicion.

How do I get more information?

For more information about reportable diseases, visit the Aquatic Animal Health page, contact your local CFIA Animal Health Office, or your CFIA Area office:

  • Atlantic: 506-777-3939
  • Quebec: 514-283-8888
  • Ontario: 226-217-8555
  • West: 587-230-2200
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