Colorado tick fever

Colorado tick fever (CTF) is a rare disease that is caused by the CTF virus. CTF virus is spread to people through bites of infected ticks. The most common symptoms of CTF are fever, chills, headache, body aches, and feeling tired.

Negative contrast electron micrograph of CTF virus

Transmission

• CTF virus is transmitted by the bite of an infected Rocky Mountain wood tick (Dermacentor andersoni).
• The virus is not spread from person to person, except in rare instances by blood transfusion.

Epidemiology

• CTF occurs in people who live in or visit areas of the western United States and western Canada that are 4,000–10,000 feet above sea level.
• Most cases of CTF occur during spring or summer months when ticks are most active.

Risk factors

• Anyone bitten by a tick in an area where the virus is circulating can get infected with CTF virus.
• People who work outdoors or participate in outdoor activities are most likely to be exposed to ticks.

Transmission

Colorado tick fever (CTF) virus is an RNA virus that belongs to the genus Coltivirus.

• People become infected with CTF virus from the bite of an infected Rocky Mountain wood tick (Dermacentor andersoni).
• Rocky mountain wood ticks are found in the western United States and western Canada at 4,000–10,000 feet above sea level.
• Ticks become infected with CTF virus when they feed on the blood of a reservoir animal (an animal that has the virus circulating in its bloodstream).
• The most important reservoirs for CTF virus are small rodents such as squirrels, chipmunks, and mice.
• After the tick becomes infected, it passes the virus to other hosts (animal or human) while it feeds.
• The virus is not transmitted from person to person, except in rare instances by blood transfusion.
• Since CTF virus can remain in red blood cells for several months, blood and bone marrow should not be donated for 6 months following infection.

Onset

The incubation period (time from tick bite to onset of illness) ranges from 1 to 14 days.

Symptoms

• The incubation period (time from tick bite to onset of illness) ranges from about 1 to 14 days.
• The most common symptoms of Colorado tick fever (CTF) are fever, chills, headache, body aches, and feeling tired.
• Some patients have sore throat, vomiting, abdominal pain, or skin rash.
• About half of patients have a “biphasic” fever.
• This 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 disease 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 rare.

Diagnosis

• Diagnosis of Colorado tick fever (CTF) is through clinical history, physical examination and labs.
• It is characterized by sudden onset of fever, chills, headache, myalgia, and malaise.
• Sore throat, vomiting, abdominal pain, and a maculopapular or petechial rash also have been reported.
• About half of all patients experience a biphasic illness and adults >30 years of age may have prolonged weakness and fatigue.
• Laboratory abnormalities observed in patients with CTF can be largely attributed to infection of hemopoietic progenitor cells.
• Leukopenia is commonly observed.
• Differential white blood cell counts may show a relative lymphocytosis and the presence of atypical lymphocytes.
• Moderate thrombocytopenia is also common.

Treatment

• There are no medications to treat CTF virus infection.
• If you think you or a family member may have CTF, see your healthcare provider.
• 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.

Diagnosis

• Preliminary diagnosis is based on a patient’s symptoms and history of probable exposure to a tick in an area where CTF occurs.
• Laboratory tests typically detect CTF virus genetic material (RNA) or antibodies against the virus in blood.

Complications and sequelae

• Rare reports of more severe sequelae include meningitis, encephalitis, hepatitis, epididymo-orchitis, pericarditis, myocarditis, pneumonia, and coma.
• Death is rare and usually associated with disseminated intravascular coagulation or meningoencephalitis in children.

Treatment

There are no medications to treat Colorado tick fever (CTF) virus infections; clinical management is supportive. Patients with severe symptoms may need to be hospitalized for intravenous fluids and medications to reduce pain and fever.

Prevention

There is no vaccine to prevent CTF. The best way to prevent CTF is to reduce your risk of tick bites.

• Use insect repellent
• Wear long sleeves and pants
• Avoid wooded and bushy areas with high grass
• Perform thorough tick checks after spending time outdoors

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