American mountain fever

American mountain fever


Colorado tick fever is an acute viral infection transmitted by the bite of the Dermacentor andersoni tick.

Alternative Names

Mountain tick fever; Mountain fever; American mountain fever


This disease most commonly develops from March to September, with the highest numbers of infections occurring in May and June.

Risk factors are recent outdoor activity and recent tick bite. The rate of Colorado tick fever is high in Colorado, where blood tests have shown that up to 15% of campers have previously been exposed to virus that causes the disease.

The disease is much less common in the rest of the United States.


Symptoms start about 3 to 6 days after the tick bite. Symptoms of fever continue for 3 days, stop, then come back 1 to 3 days later for another few days.

  • Sudden fever
  • Excessive sweating
  • Severe muscle aches
  • Joint stiffness
  • Headache
  • Photophobia (sensitivity to light)
  • Nausea and vomiting
  • Generalized weakness
  • Occasional rash (may be light-colored)

Exams and Tests

Tests will be done to confirm 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:

  • Liver function tests
  • Creatine phosphokinase
  • Complete blood count (CBC) -- will show a lower-than-normal number of white blood cells.


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's syndrome in some viral illnesses). If complications develop, treatment will be aimed at controlling the symptoms.

Outlook (Prognosis)

The disease is usually self-limiting and not dangerous.

Possible Complications

There is a risk for aseptic meningitis, encephalitis

When to Contact a Medical Professional

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 suggestive 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, tuck long pants into socks to protect the legs, and wear shoes and long-sleeved shirts. Ticks will show up on white or light colors better than dark colors, making them easier to remove from your clothing.

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.

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