Colorado Tick Fever Clinical Presentation

Updated: Mar 20, 2017
  • Author: Cassis Thomassin, MD; Chief Editor: Jeter (Jay) Pritchard Taylor, III, MD  more...
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Colorado tick fever presents as a nonspecific febrile illness with few historical clues (other than the epidemiology) to suggest the disease. [7] Consider the diagnosis in any patient with a febrile illness who lives in or who recently visited an endemic area. Most patients are males aged 15-45 years who present between April and August. Findings may include a history of tick bite, fever, and flulike symptoms.

Most patients have a history of exposure to ticks, but only about half recall tick attachment. Therefore, although a history of a tick bite is an important clue, its absence does not exclude the diagnosis. The patient may also have a history of participation in activities that put him or her at risk for a tick bite.

Fever is present in nearly all cases. A characteristic fever pattern noted in about one half of cases of Colorado tick fever is so-called “saddleback fever”, which strongly suggests the diagnosis. Patients with this pattern have a fever for 2-3 days, followed by an afebrile period of similar duration and then by another 2-3 days of fever.

Common flulike symptoms include the following:

  • Headache

  • Myalgias

  • Arthralgias

  • Fatigue

In addition, a nonspecific evanescent rash may be present (5-15% of cases), sometimes with a palatal enanthema. Stiff neck, retroorbital pain, photophobia [1] , nausea and vomiting, abdominal pain, diarrhea, and sore throat all have been reported in a minority of patients. In one series, patients with suspected Colorado tick fever and symptoms of abdominal pain, rash, or sore throat were less likely to have Colorado tick fever on the basis of serologic diagnoses.


Physical Examination

Physical examination is not particularly helpful for diagnosing Colorado tick fever. Findings may include rash and nuchal rigidity.

In 5-15% of patients, a macular, maculopapular, and petechial rash is present. Occasionally, a small, red, painless papule (presumably at the bite site) is present. The distribution is often truncal, in contrast to the more acral rash in Rocky Mountain spotted fever. The rash tends to be short lived, which is another difference compared with Rocky Mountain spotted fever. Petechiae occur in rare cases and may be complicated by thrombocytopenia. A palatal enanthema is sometimes present.

Nuchal rigidity is found in 15-20% of cases. Splenomegaly may occur. Some patients have altered sensorium or even coma.

Complications of Colorado tick fever are unusual and rare. Cases with neurologic disease, including meningitis and meningoencephalitis, are reported, especially in children. [6]