Infectious Disease Compendium

Colorado Tick Fever


An acute febrile illness and leukopenia after tick bite.

Often biphasic.

fever, chills, headache, pain behind the eyes, light sensitivity, myalsgias, malaise, abdominal pain, hepatosplenomegaly, nausea and vomiting, and a rash. Second phase worse.

Leukopenia with a relative lymphocytosis and atypical lymphocytes with thrombocytopenia.

Serology or PCR to diagnose.

Epidemiologic Risks

Bit by a wood tick in the western United States and Canada. Dermacentor andersoni is the vector and found at 4000 to 10,000-foot elevations; it is my understanding that Colorado is particularly high, but in a different way than, say, Eugene, Oregon. Lets just say the sweetish haze in the air at U of O was not the burning of grass of a lawn kind.

(Geographic Distribution Map)


Due to the Coltiviruses.

Empiric Therapy

None. Supportive.


The tick should be present.

Last Update: 06/11/18.