Colorado Tick Fever

National Organization for Rare Disorders, Inc.

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It is possible that the main title of the report Colorado Tick Fever is not the name you expected. Please check the synonyms listing to find the alternate name(s) and disorder subdivision(s) covered by this report.


  • CTF
  • Mountain Fever
  • Mountain Tick Fever

Disorder Subdivisions

  • None

General Discussion

Colorado Tick Fever is a rare viral disease transmitted by ticks that commonly inhabit the western United States. Major symptoms may include fever, headaches, muscle aches, and/or generalized discomfort (myalgia). The symptoms usually last for about a week and resolve on their own.


Colorado Tick Fever typically has a sudden onset about five days after a tick bite. It usually occurs at moderate altitudes during spring or early summer. The symptoms are flu-like and may include chills, headache, increased sensitivity to light (photophobia), fatigue, nausea, vomiting, and a lack of appetite. Muscle pain occurs, especially in the legs and back. There may be a slight, reddish rash, and the spleen can become enlarged (splenomegaly). Fever may rise sharply for two or three days and then subside only to return after a day or two (biphasic fever). The second fever typically subsides after 2 to 4 days.

In very rare childhood cases, severe illness involving the central nervous system may occur. Symptoms may include acute inflammation of the membranes around the brain (aseptic meningitis) and/or spinal cord (encephalitis).


Colorado Tick Fever is a rare viral disease caused by a virus belonging to the Coltivirus family. It is transmitted to humans through the bite of the wood tick (Dermacentor andersoni).

Affected Populations

Colorado Tick Fever is a rare viral disease that affects males and females in equal numbers. Most reported cases have occurred in the Rocky Mountain area of the United States and the western provinces of Canada. Several hundred cases of this disease are reported each year in these areas where the wood tick lives (endemic). However, it is possible that many additional cases are misdiagnosed or undiagnosed.

Standard Therapies

The diagnosis of Colorado Tick Fever is confirmed by isolation of the virus from the blood. Treatment for Colorado Tick Fever is symptomatic and may include acetaminophen to relieve headaches and muscle pain.

The most effective means of preventing Colorado Tick Fever is the use of protective clothing or chemical tick repellents when visiting endemic areas during the spring and summer. Individuals should inspect themselves frequently for ticks and quickly remove them when found.

Investigational Therapies

Information on current clinical trials is posted on the Internet at All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.

For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222

TTY: (866) 411-1010


For information about clinical trials sponsored by private sources, contact:



Bennett JC, Plum F., eds. Cecil Textbook of Medicine. 20th ed. Philadelphia, PA: W.B. Saunders Co; 1996:1805-07.

Fields BN, et al., Fields Virology, 2nd ed. New York, NY: Raven Press; 1990:1421-27.


Friedman AD., Hematologic manifestations of viral infections. Pediatr Ann. 1996;25:555-60.

Myers SA, et al., Dermatologic manifestations of arthropod-borne diseases. Infect Dis Clin North Am. 1994;8:689-712.


Attoui H, et al., Serologic and molecular diagnosis of Colorado tick fever viral infections. Am J Trop Med Hyg. 1998;59:763-68.

Attoui H, et al., Complete nucleotide sequence of Colorado tick fever virus segments M6, S1 and S2. J Gen Virol. 1997;78:2895-99.


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