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Vector-Borne and Zoonotic Diseases Program

Colorado Tick Fever

What is Tick-borne Colorado Tick Fever (CTF)?

Colorado tick fever (CTF) is a tick-borne viral illness of humans in the United States. This disease is caused by infection with the Colorado tick fever virus, a member of the Coltivirus genera. In the past, it has been named Mountain fever or American mountain fever. CTF virus was first isolated from human blood in 1944.

How do people get CTF?

The organism that causes CTF is transmitted by the bite of an infected tick. The Rocky Mountain wood tick (Dermacentor andersoni) is the principal carrier of CTF in the United States. Some cases have been associated with exposures to the virus in laboratory settings and one case followed transfusion of blood from a person infected with CTF virus within 4 months of donation.

What are the symptoms of CTF?

Patients infected with CTF virus often develop a two-staged fever and illness following an average incubation period of 4 days (range of 1-19 days) after a tick bite. The early signs of CTF are often nonspecific and may resemble many other infectious and non-infectious diseases. Initial symptoms may include sudden onset of fever, chills, headache, pain behind the eyes, light sensitivity, muscle pain, and generalized malaise. Abdominal pain, nausea and vomiting may occur during the course of the illness in addition to a rash. Flat or pimply rashes may occur in 5% to 12% of cases. The acute illness lasts 5 to 10 days, and in half of the cases, a first phase, with fever lasting 2 to 3 days is followed by a period without fever of 24 to 72 hours with anorexia and malaise. A second phase consisting of a return of fever and an increase in symptoms lasts for about 48 hours. Two important symptoms are fever (two-staged in 50% of cases) and a recent tick bite. CTF can be a severe illness, especially in children under 10 and older adults. Hospitalization may occur in 20% of CTF cases.

Where do the most cases of CTF occur in the United States?

CTF is a seasonal disease, and occurs in mountain forest habitats at altitudes from 4,000 to 10,000 feet in the Rocky Mountain region of the United States during the months of February through October. Approximately 90% of cases occur between April and July. Half of all cases are reported from Colorado and Idaho. An assessment of reported cases 1980 and 1988 revealed that of the 1,432 cases reported, the highest number (256) was from Colorado. Although no asymptomatic infections are known to occur, the disease is easily confused with other infections and is extensively underreported. The risk for getting CTF in Arizona is extremely low as the tick vectors are rare. However, CTF infections have been reported in Arizona residents who have traveled in states where CTF is more common (e.g. Colorado and Utah).

How is CTF diagnosed?

A diagnosis of CTF is based on a combination of clinical signs and symptoms and specialized confirmatory laboratory tests, including antibody assays and cell culture. Other common laboratory findings suggestive of CTF fever include leukopenia (reduced white blood cells), thrombocytopenia (reduced platelets) and mildly elevated liver enzyme levels.

What is the treatment for CTF?

There is no specific treatment for CTF. Symptomatic relief includes treatment of fever and pain with acetominophen and analgesics. Salicylates should not be used because of thrombocytopenia and the rare occurrence of bleeding disorders following CTF virus infection.

Can a person get CTF more than once?

Infection with CTF virus is thought to provide long lasting immunity against reinfection. However, prior illness with CTF should not deter persons from practicing good tick-preventive measures or visiting a physician if signs and symptoms consistent with CTF occur, especially following a tick bite.

How can Tick-borne Colorado Tick Fever be prevented?

Limiting exposure to ticks reduces the likelihood of CTF virus infection. In persons exposed to tick-infested habitats, prompt, careful inspection and removal of crawling or attached ticks is an important method of preventing disease. Children should be examined frequently as they are less sensitive to the tick's presence and bite, should it occur. It may take several hours of attachment before organisms are transmitted by an infected tick.

  • Wear light-colored clothing to allow you to see ticks that are crawling on your clothing.
  • Tuck your pants legs into your socks so that ticks cannot crawl up the inside of your pants legs.
  • Apply repellents to discourage tick attachment. Repellents containing permethrin can be sprayed on boots and clothing, and will last for several days. Repellents containing DEET (n, n-diethyl-m-toluamide) can be applied to the skin, but will last only a few hours before reapplication is necessary. Use DEET with caution on children. Application of large amounts of DEET on children has been associated with adverse reactions.
  • Conduct a body check upon return from potentially tick-infested areas by searching your entire body for ticks. Use a hand-held or full-length mirror to view all parts of your body. Remove any tick you find on your body.
  • Parents should check their children for ticks, especially in the hair, when returning from potentially tick-infested areas. Additionally, ticks may be carried into the household on clothing and pets. Both should be examined carefully

What is the best way to remove ticks?

To remove attached ticks, use the following procedure:

  1. Use fine-tipped tweezers or shield your fingers with a tissue, paper towel, or rubber gloves. When possible, persons should avoid removing ticks with bare hands.
  2. Grasp the tick as close to the skin surface as possible and pull upward with steady, even pressure. Do not twist or jerk the tick; this may cause the mouthparts to break off and remain in the skin. (If this happens, remove mouthparts with tweezers. Consult your health care provider if infection occurs.)
  3. Do not squeeze, crush, or puncture the body of the tick because its fluids (saliva, body fluids, gut contents) may contain infectious organisms.
  4. After removing the tick, thoroughly disinfect the bite site and wash your hands with soap and water.
  5. Save the tick for identification in case you become ill. This may help your doctor make an accurate diagnosis. Place the tick in a plastic bag and put it in your freezer. Write the date of the bite on a piece of paper with a pencil and place it in the bag.

Folklore Remedies Don't Work!

Folklore remedies, such as the use of petroleum jelly or hot matches, do little to encourage a tick to detach from skin. In fact, they may make matters worse by irritating the tick and stimulating it to release additional saliva or regurgitate gut contents, increasing the chances of transmitting the pathogen. These methods of tick removal should be avoided. A number of tick removal devices have been marketed, but none are better than a plain set of fine-tipped tweezers.

For more information, please visit the CDC's website: CDC Division of Vector-Borne Infectious Diseases