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Colorado tick fever virus
Virus classification
Group: Group III (dsRNA)
Family: Reoviridae
Genus: Coltivirus
Species: Colorado tick fever virus
Colorado tick fever
Classification and external resources
ICD-10 A93.2
ICD-9 066.1
DiseasesDB 31134
MedlinePlus 000675
eMedicine emerg/586
MeSH D003121

Colorado Tick Fever (CTF) (also called Mountain tick fever, Mountain fever, and American mountain fever) is an acute viral infection transmitted from the bite of an infected wood tick (Dermacentor andersoni). It should not be confused with the bacterial tick-borne infection, Rocky Mountain Spotted Fever.

The type species of the genus Coltivirus, Colorado tick fever virus (CTFV) infects haemopoietic cells, particularly erythrocytes, which explains how the virus is transmitted by bloodsucking ticks and also accounts for the incidence of transmission via blood transfusion.



The disease develops from March to September, with the highest infections occurring in May and June.[1] The disease is found almost exclusively in the western United States and Canada, mostly in high mountain areas such as Colorado and Idaho. The CTFV was first isolated from human blood in 1944.[2]


The virus particle, like other Coltiviruses, is ~80 nm in diameter and is generally non-enveloped. The double stranded RNA viral genome is ~20,000bp long and is divided into 12 segments, which are termed Seg-1 to Seg-12. Viral replication in infected cells is associated with characteristic cytoplasmic granular matrices. Evidence suggests that viral presence in mature erythrocytes is a result of replication of the virus in hematopoitic erythrocyte precursor cells and simultaneous maturation of the infected immature cells rather than off direct entry and replication of CTFV in mature erythrocytes.[3]

One component is VP9.[4]


The wood tick is usually found attached to a host, but when it is without a host it hides in cracks and crevices as well as soil. If for some reason the tick is not able to find a host before the winter months, it will stay under groundcover until spring when it can resume its search. The wood tick typically does not seek out available hosts in the hottest summer months as well. Adult ticks, for the most part, tend to climb to the top of grass and low shrubs to attach themselves to a host that is wandering by. These ticks are able to attach to their hosts by secreting a cement-like substance from their mouths and inserting it into the host.[5]

Transmission and symptoms

Colorado Tick Fever is acquired by tick bite. There is no evidence of natural person-to-person transmission. However, rare cases of transmission from blood transfusions have been reported. The virus which causes Colorado Tick Fever may stay in the blood for as long as four months after onset of the illness.

First signs of symptoms can occur about 3–6 days after the initial tick bite, although it can have incubation periods of up to 20 days. Patients usually experience a two-staged fever and illness which can continue for three days, diminish, and then return for another episode of 1–3 days. The virus has the ability to live in the blood stream for up to 120 days; therefore coming in contact without proper precautions and the donation of blood are prohibited.

Initial symptoms include: fever, chills, headaches, pain behind the eyes, light sensitivity, muscle pain, generalized malaise abdominal pain, nausea, vomiting as well as a flat or pimply rash.[2] During the second phase of the virus a high fever can return with an increase in symptoms. CTF can be very severe in cases involving children and have even required hospitalization. Complications with this disease have included aseptic meningitis, encephalitis, and hemorrhagic fever, but these are rare.

CTF is seasonal, mostly occurring in the Rocky Mountain region of the United States and usually in altitudes from 4,000 to 10,000 feet.[2] Patients with CTF are mostly campers and young males, who most likely have been bitten because of their occupational activities.


A combination of clinical signs, symptoms and laboratory tests can confirm the likelihood of having CTF. Some tests include complement fixation to Colorado tick virus, Immunofluoresence for Colorado tick fever, and some other common laboratory findings suggestive of CTF including leucopenia, thrombocytopenia, and mildly elevated liver enzyme levels.

Detection of antibodies is possible.[6]


At this time there is no specific treatment for CTF. The first thing to do is make sure the tick is fully removed from the skin, then Acetaminophen and analgesics can be used to help relieve the fever and pain. Aspirin is not recommended for children it has been linked to Reye’s syndrome in some viral illnesses. Salicylates should not be used because of thrombocytopenia, and the rare occurrence of bleeding disorders. Someone who suspects that they have been bitten by a tick or is starting to show signs of CTF should contact their physician immediately.[1]

Proper Tick Removal

Ticks should be removed promptly and carefully with tweezers and by applying gentle steady traction. The tick's body should not be crushed when it is removed and the tweezers should be placed as close to the skin as possible to avoid leaving tick mouth parts in the skin. Ticks should not be removed with bare hands. Hands should be protected by gloves and/or tissues and thoroughly washed with soap and water after the removal process. This should be performed with great care. Putting vaseline over the tick will prevent air from reaching it, causing the tick to retract itself from the skin. Be ready to grab it off when it does. Make sure after you pull it out that the nose is not left in your skin. This can cause painful infection to occur.

A match or flame should NOT be used to remove a tick. This method, once thought safe, can cause the tick to regurgitate expelling any disease it may be carrying into the bite wound.[7]


To avoid tick bites and infection, experts advise:

  • Avoid tick infested areas, especially during the warmer months.
  • Wear light colored clothing so ticks can be easily seen. Wear a long sleeved shirt, hat, long pants, and tuck pant legs into socks.
  • Walk in the center of trails to avoid overhanging grass and brush.
  • Check your body every few hours for ticks when you spend a lot of time outdoors in tick infested areas. Ticks are most often found on the thigh, arms, underarms and legs. Ticks can be very small (no bigger than a pinhead). Look carefully for new "freckles".
  • Use insect repellents containing DEET on your skin or permethrin on clothing. Be sure to follow the directions on the container and wash off repellents when going indoors.
  • Remove attached ticks immediately.

Contracting the CTF virus is thought to provide long lasting immunity against reinfection. However it is always wise to be on the safe side and try to prevent tick bites.[2]


  1. ^ a b "Medical Encyclopedia: Colorado tick fever (Print Version)". Retrieved 2009-01-20. 
  2. ^ a b c d "Colorado Tick Fever". Retrieved 2009-01-20. 
  3. ^ Philipp CS, Callaway C, Chu MC, et al. (1 April 1993). "Replication of Colorado tick fever virus within human hematopoietic progenitor cells". J. Virol. 67 (4): 2389–95. PMID 8445735. PMC 240408. 
  4. ^ Mohd Jaafar F, Attoui H, De Micco P, De Lamballerie X (August 2004). "Termination and read-through proteins encoded by genome segment 9 of Colorado tick fever virus". J. Gen. Virol. 85 (Pt 8): 2237–44. doi:10.1099/vir.0.80019-0. PMID 15269364. 
  5. ^ "Rocky Mountain wood tick: Information from". Retrieved 2009-01-20. 
  6. ^ Mohd Jaafar F, Attoui H, Gallian P, et al. (May 2003). "Recombinant VP7-based enzyme-linked immunosorbent assay for detection of immunoglobulin G antibodies to Colorado tick fever virus". J. Clin. Microbiol. 41 (5): 2102–5. doi:10.1128/JCM.41.5.2102-2105.2003. PMID 12734255. PMC 154693. 
  7. ^ "The Claim: Remove a Tick From Your Skin by Burning It - New York Times". Retrieved 2009-01-20. 


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