Infectious Disease Compendium

Colorado Tick Fever

Diagnosis

An acute febrile illness and leukopenia after a tick bite.

Often biphasic.

Fever, chills, headache, pain behind the eyes, light sensitivity, myalgias, malaise, abdominal pain, hepatosplenomegaly, nausea and vomiting, and a rash. The second phase is 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. Let us just say the sweetish haze in the air at U of O was not the burning of grass of a lawn kind.

Cases may be increasing in Eastern Oregon (PubMed).

(Geographic Distribution Map)

Microbiology

Due to the Coltiviruses.

Empiric Therapy

None. Supportive.

Pearls

The tick should be present at the time of illness. Look carefully.

Last Update: 04/02/19.