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Colorado tick fever



Colorado tick fever is an acute viral infection spread by the bite of the Dermacentor andersoni (wood) tick.

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.

Risk factors are recent outdoor activity and recent tick bite.

Colorado tick fever is seen most often in Colorado. Up to 15% of campers have been exposed to the virus that causes the disease. The disease is much less common in the rest of the United States.


Symptoms of Colorado tick fever start 3 to 6 days after getting 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:

  • Excessive sweating
  • Generalized weakness
  • Headache
  • Joint stiffness
  • Nausea and vomiting
  • Occasional rash (may be light-colored)
  • Sensitivity to light ( photophobia)
  • Severe muscle aches
Signs and tests

Tests are done to confirm the infection. These may include:

  • Complement fixation to Colorado tick virus
  • Immunofluorescence for Colorado tick fever -- will be positive if the person has the disease

Other blood tests may include:

Support Groups

Expectations (prognosis)

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

Calling your health care provider

Call your health care provider if you are unable to fully remove a tick embedded in the skin, if you or your child develop symptoms of this disease, if symptoms worsen or do not improve with treatment, or if new symptoms develop.


There is a risk for aseptic meningitis, encephalitis, and hemorrhagic fever, but these complications are extremely rare.


Make sure the tick is fully removed from the skin. Take a pain reliever if necessary (do not give aspirin to children -- it is associated with Reye syndrome in some viral illnesses). If complications develop, treatment will be aimed at controlling the symptoms.


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 a tweezers, pulling carefully and steadily. Insect repellent may be helpful.


Naides SJ. Arthropod-borne viruses causing fever and rash syndromes. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 405.

Tsai TF. Coltiviruses and seadornaviruses (Colorado tick fever). In: Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice of Infectious Diseases. 6th ed. Philadelphia, Pa: Churchill Livingstone Elsevier; 2005: chap 145.

Review Date: 9/28/2008
Reviewed By: Linda Vorvick, MD, Seattle Site Coordinator, Lecturer, Pathophysiology, MEDEX Northwest Division of Physician Assistant Studies, University of Washington School of Medicine; Jatin M. Vyas, MD, PhD, Instructor in Medicine, Harvard Medical School, Assistant in Medicine, Division of Infectious Disease, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
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