Colorado tick fever

A viral infection (Coltivirus) transmitted from the bite of an infected Rocky Mountain wood tick (Dermacentor andersoni).

It is not the same as bacterial tick-borne infection, Rocky Mountain spotted fever.

The Coltivirus, responsible for Colorado tick fever virus infects haemopoietic cells, particularly erythrocytes.

Signs or symptoms occur about three to six days after the initial tick bite, although it can have incubation periods of up to 20 days.

The disease develops from March to September, with the highest infections occurring in June.

Infections are found almost exclusively in the western United States and Canada, mostly in high mountain areas such as Colorado and Idaho.

It is acquired by tick bite, and no evidence of natural person-to-person transmission has been found.

Rarely, transmitted from blood transfusions, as the virus may stay in the blood for as long as four months after onset of the illness.

There usually is a two-staged fever and illness which can continue for three days, diminish, and then return for another episode of one to three days.

Initial symptoms include fever, chills, headaches, light sensitivity, muscle pain, malaise, abdominal pain, hepatosplenomegaly, nausea and vomiting, and a rash.

The second phase of the illness, a high fever can return with an increase in symptoms.

Infections in children may be severe, requiring hospitalization.

CTF can be very severe in cases involving children and can even require hospitalization.

The virus has the ability to survive in the blood stream for up to 120 days.

Infected donors can transmit the virus through blood transfusion.

Rarely associated with aseptic meningitis, encephalitis, and hemorrhagic fever complications.

It occurs mostly in the Rocky Mountain region, and at altitudes from 4,000 to 10,000 feet.


Occurs mostly among campers and young males.

Colorado tick fever virus is about 80 nm in diameter and is generally not enveloped.

Coltivirus is a double-stranded RNA viral genome is about 20,000 bp long and is divided into 12 segments, which are termed Seg-1 to Seg-12.

Evidence suggests the virus is present in mature erythrocytes is a result of replication of the virus in hematopoitic erythrocyte precursor cells.

The Rocky Mountain wood tick is usually found attached to a host.

The Rocky Mountain wood tick hides in cracks and crevices, as well as soil.

During winter the Rocky Mountain wood tick stay under groundcover until spring, when it can resume its search.

The Rocky Mountain wood tick does not typically seek hosts in the hottest summer months.

Adult Rocky Mountain wood ticks attach to passing hosts by locating at the top of grasses or low shrubs

Adult Rocky Mountain wood ticks secrete a cement-like substance from their mouths, inserting it into the host to establish attachment.

Diagnosis is established by clinical signs, symptoms, and laboratory tests.

Common laboratory findings suggestive of CTF, including leucopenia, thrombocytopenia, and mildly elevated liver enzyme levels.

Laboratory findings include complement fixation to Colorado tick virus, and immunofluorescence for Colorado tick fever, and the detection of viral antibodies on red blood cells.

Prevention includes:

Avoid tick-infested areas

Wearing light-colored clothing to identify ticks.

Wearing long sleeved shirts, and pants,and a hat.

Avoidance of contact with grass and brush.

Surveillance of clothing and the body should be checked every few hours for ticks when spending time outdoors in tick-infested areas.

Ticks are most often found on the thigh, arms, underarms, and legs.

The use of insect repellents containing DEET on skin or permethrin on clothing can be effective.

Ticks should be removed fully and immediately.

Ticks should be removed with tweezers with the application of gentle, steady traction.

The body of the tick should not be crushed when it is removed to avoid leaving tick mouthparts in the skin.

Allowing tick mouthparts to be left in the skin can allow secondary infections.

Hands should be protected during tick removal by gloves or tissues and thoroughly washed with soap and water after the removal process.

No specific treatment is available.

Acetaminophen and analgesics can be used to help relieve the fever and pain.

Using a flame can cause the tick to regurgitate expelling any disease it may be carrying into the bite wound.

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