Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content + Download Section PDF Listen ++ For further information, see CMDT Part 32-05: Other Systemic Viral Diseases + Key Features Download Section PDF Listen +++ +++ Essentials of Diagnosis ++ Onset 1–19 days (average, 4 days) following tick bite Fever, chills, myalgia, headache, prostration Leukopenia, thrombocytopenia Second attack of fever after remission lasting 2–3 days +++ General Considerations ++ Transmitted by Dermacentorandersoni tick bite Disease is limited to the western United States and Canada and is most prevalent during the tick season (March to November) Virus infects the marrow erythrocyte precursors, leading to viremia lasting the life span of the infected red cells Blood transfusions can be a vehicle of transmission + Clinical Findings Download Section PDF Listen +++ +++ Symptoms and Signs ++ Incubation period is 3–6 days, rarely as long as 19 days Onset is usually abrupt with high fever, sometimes with chills Severe myalgia, headache, photophobia, anorexia, nausea and vomiting, and generalized weakness are prominent Faint rash (occasionally) Acute symptoms resolve within a week Remission is followed in 50% of cases by recurrent fever and a full recrudescence lasting 2–4 days +++ Differential Diagnosis ++ Influenza Rocky Mountain spotted fever Numerous other viral infections Relapsing fevers + Diagnosis Download Section PDF Listen +++ +++ Laboratory Findings ++ Leukopenia with a shift to the left and atypical lymphocytes occurs, reaching a nadir 5–6 days after the onset of illness Thrombocytopenia may occur An RT-PCR assay may be used to detect early viremia Detection of IgM by capture ELISA or plaque reduction neutralization is possible after 2 weeks from symptom onset + Treatment Download Section PDF Listen +++ ++ No specific treatment is available Ribavirin has shown efficacy in an animal model Antipyretics are used Salicylates should be avoided due to potential bleeding + Outcome Download Section PDF Listen +++ +++ Prevention ++ Tick avoidance Tick control, particularly from March to November +++ Complications ++ Aseptic meningitis (particularly in children), encephalitis, and hemorrhagic fever occur rarely Malaise may last weeks to months Spontaneous abortion and multiple congenital anomalies associated with Colorado tick fever infection during pregnancy (rarely) +++ Prognosis ++ Disease is usually self-limited and benign + References Download Section PDF Listen +++ + +Kadkhoda K et al. Case report: a case of Colorado tick fever acquired in southwestern Saskatchewan. Am J Trop Med Hyg. 2018 Mar;98(3):891–3. [PubMed: 29363458] + +McDonald E et al. Notes from the field: investigation of Colorado tick fever virus disease cases—Oregon, 2018. MMWR Morb Mortal Wkly Rep. 2019 Mar 29;68(12):289–90. [PubMed: 30921304]