Colorado Tick Fever

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Colorado tick fever (CTF) virus is spread to people through bites of infected ticks. People who live in or visit areas in the western United States or western Canada that are 4,000‒10,000 feet above sea level may be at risk of becoming infected. Most cases of CTF occur during spring and summer months when ticks are most active. The most common symptoms of CTF are fever, chills, headache, body aches, and feeling tired. There are no medications to treat or vaccines to prevent CTF.

The following ticks are known to transmit Ehrlichiosis in humans:

  • Rocky Mountain Wood Tick  (Dermacentor andersoni)


Signs + Symptoms

The incubation period (time from tick bite to onset of illness) ranges from about 1 to 14 days with the most common symptoms being fever, chills, headache, body aches, and feeling tired. Some patients may also have a sore throat, vomiting, abdominal pain, or a skin rash. About half of patients have a “biphasic” fever, which means they have several days of fever, feel better for several days, and then have a second short period of fever and illness.

Most people who become ill have mild symptoms and recover completely – however, weakness and fatigue may last several weeks. In rare cases, some patients may develop more severe illness that affects the central nervous system with symptoms that include stiff neck and confusion. Life-threatening illnesses or deaths due to CTF virus are extremely rare.



There are no medications to treat CTF virus infection. If you think you or a family member may have CTF, see your healthcare provider immediately. Persons with severe CTF illnesses may need to be hospitalized. Treatment may include intravenous fluids and medications to reduce pain and fever. People who have CTF should not donate blood or bone marrow for 6 months after their illness. The virus may stay in red blood cells for several months and can be passed to others by blood transfusion or bone marrow transplant.