Colorado Tick Fever


Colorado tick fever virus

Colorado Tick Virus bloodsmear

Where Found

The geographic range of Colorado tick fever virus includes the Western United States, primarily Colorado, Utah, Montana, and Wyoming. Although rare, the virus can also be transmitted from person-to-person via blood transfusion.

Incubation Period

1–14 days

Signs and Symptoms

  • Fever, chills, headache, myalgias, and lethargy
  • ~50% of patients have a biphasic illness with symptoms remitting after 2 to 4 days, but then recurring 1 to 3 days later.
  • Conjunctival injection, pharyngeal erythema and lymphadenopathy may be present.
  • Maculopapular or petechial rash in <20% of patients
  • Prolonged convalescence characterized by weakness and fatigue is common in adults.
  • Life-threatening complications and death are rare and usually associated with disseminated intravascular coagulation or meningoencephalitis in children.

General Laboratory Findings

  • Leukopenia
  • Moderate thrombocytopenia

Laboratory Diagnosis

  • Culture and RT-PCR during first 2 weeks of illness
  • Serologic assays (e.g., IgM-capture EIA, indirect fluorescent antibody, and plaque-reduction neutralization) on convalescent samples. IgM antibodies usually do not appear until 14–21 days after illness onset.


No specific antiviral treatment is available. Patients with suspected CTF should receive supportive care as appropriate. Patients with confirmed CTF should defer blood and bone marrow donation for at least 6 months after recovery.


Brackney MM, Marfin AA, Staples JE, et al. Epidemiology of Colorado tick fever in Montana, Utah, and Wyoming, 1995–2003. Vector Borne Zoonotic Dis 2010;10:381–385.

Centers for Disease Control and Prevention. West Nile virus and other nationally notifiable arboviral diseases—United States, 2016. MMWR 2018; 67(1);13-17.

Staples JE, Fischer M. Coltiviruses (Colorado Tick Fever). In: Principles and Practice of Pediatric Infectious Diseases, 5th edition. Eds: Long SS, Prober CG, Fischer M. Elsevier 2018:1119–1121.

Goodpasture HC, Poland JD, Francy DB, et al. Colorado tick fever: clinical, epidemiologic, and laboratory aspects of 228 cases in Colorado in 1973–1974. Ann Intern Med 1978;88:303–310.

Lambert AJ, Kosoy O, Velez JO, et al. Detection of Colorado Tick Fever viral RNA in acute human serum samples by a quantitative real-time RT-PCR assay. J Virol Methods 2007;140:43–48.

Romero JR, Simonsen KA. Powassan encephalitis and Colorado tick fever. Infect Dis Clin North Am 2008;22:545–559.

Yendell SJ, Fischer M, Staples JE. Colorado tick fever in the United States, 2002-2012. Vector Borne Zoonotic Dis 2015;15:311–316.