Health Care Providers: Clinical & Laboratory Evaluation

Colorado tick fever (CTF) is a self-limited infection characterized by sudden onset of fever, chills, headache, myalgia, and malaise. Sore throat, vomiting, abdominal pain, and a maculopapular or petechial rash also have been reported. About half of all patients experience a biphasic illness and adults >30 years of age may have prolonged weakness and fatigue. Rare reports of more severe sequelae include meningitis, encephalitis, hepatitis, epididymo-orchitis, pericarditis, myocarditis, pneumonia, and coma. Death is rare and usually associated with disseminated intravascular coagulation or meningoencephalitis in children.

Laboratory abnormalities observed in patients with CTF can be largely attributed to infection of hemopoietic progenitor cells. Leukopenia is commonly observed. Differential white blood cell counts may show a relative lymphocytosis and the presence of atypical lymphocytes. Moderate thrombocytopenia is also common.