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Colorado tick fever


Colorado tick fever is a viral infection spread by the bite of the Rocky Mountain wood tick (Dermacentor andersoni).

Alternative Names

Mountain tick fever; Mountain fever; American mountain fever


This disease is usually seen between March and September. Most cases occur in April, May, and June.

Colorado tick fever is seen most often in Colorado, especially in campers. The disease is much less common in the rest of the United States.


Symptoms of Colorado tick fever most often start 3 to 6 days after the tick bite. A sudden fever continues for 3 days, goes away, then comes back 1 to 3 days later for another few days. Other symptoms include:

  • Feeling weak all over and muscle aches
  • Headache behind the eyes
  • Nausea and vomiting
  • Rash (may be light-colored)
  • Sensitivity to light (photophobia)
  • Skin pain
  • Sweating

Exams and Tests

The health care provider will examine you and ask about your signs and symptoms. If the provider suspects you have the disease, you will also be asked about your outdoor activity.

Blood tests will usually be ordered. Antibody tests can be done to confirm the infection. Other blood tests may include:


There are no specific treatments for this viral infection.

The provider will make sure the tick is fully removed from the skin.

You may be told to take a pain reliever if you need it. DO NOT give aspirin to a child who has the disease. Aspirin has been linked with Reye syndrome in children. It may also cause other problems in Colorado tick fever.

If complications develop, treatment will be aimed at controlling the symptoms.

Outlook (Prognosis)

Colorado tick fever usually goes away by itself and is not dangerous.

Possible Complications

Complications may include:

Call your provider if you or your child develop symptoms of this disease, if symptoms worsen or do not improve with treatment, or if new symptoms develop.


When walking or hiking in tick-infested areas, wear closed shoes, long sleeves, and tuck long pants into socks to protect the legs. Wear light-colored clothing, which shows ticks more easily than darker colors, making them easier to remove.

Check yourself and your pets frequently. If you find ticks, remove them immediately by using tweezers, pulling carefully and steadily. Insect repellent may be helpful.


Meagher KE, Decker CF. Other tick-borne illnesses: tularemia, Colorado tick fever, tick paralysis. Dis Mon. 2012;58:370-376. PMID 22608124. Available at:

Traub SJ, Cummins GA. Tick-borne diseases. In: Auerbach PS. Wilderness Medicine. 6th ed. Philadelphia, PA: Elsevier Mosby; 2012:chap 51.

Review Date: 12/7/2014
Reviewed By: Jatin M. Vyas, MD, PhD, Assistant Professor in Medicine, Harvard Medical School; Assistant in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital, Boston, MA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.
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