Colorado tick fever overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Ilan Dock, B.S.
Overview
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). A species of the genus Coltivirus, Colorado tick fever virus (CTFV) infects haemopoietic cells, particularly erythrocytes, which explains the viral pathway of transmission within bloodsucking ticks and also accounts for the incidence of transmission via blood transfusion. 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-envolped. 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]
Historical Perspective
Colorado tick fever remains a rare disease without a well established historical perspective.
Classification
There is currently no classification system established for Colorado tick fever.
Pathophysiology
Colorado tick fever is an Orbivirus or Coltivirus that chronically infects Rocky Mountain wood ticks. The virus typically infects cells in bone marrow causing issues with the development of certain blood cells. Infection is transmitted by the bite of an infected Rocky Mountain wood tick.
Differentiating Colorado tick fever from other diseases
Colorado tick fever (CTF) must be differentiated from other diseases that cause fever,chills, headaches, body ache, and rash. When trying to differentiate CTF from other infections, it is important to recognize that the clinical manifestations of CTF greatly resemble those of other tick-borne illnesses, especially those caused by the Rickettsiae family. Examples of misdiagnoses, with the umbrella of tick-borne diseases include typhus-spotted fevers and Ehrlichiosis.
Epidemiology and Demographics
Colorado tick fever remains a rare disease with only 83 cases reported between the years of 2002 and 2012. Incidence of the disease remain primarily confined to the Rocky Mountain States, with a few outliers throughout the United States. Incidence of Colorado tick fever appears to be independent of both demographic and age. [1]
Risk Factors
The primary risk factors associated with Colorado tick fever are exposure to endemic environment and the time of that exposure. Rocky Mountain wood ticks have been identified as the primary vector of Colorado tick fever infections, thus being bitten in an endemic area may result in the contraction of the disease.
Natural History, Complications and Prognosis
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. [4] During the second phase of the virus a high fever can return with an increase in symptoms. Colorado tick fever 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.
History and Symptoms
Colorado tick fever will display itself with a multitude of clinical manifestations. The most common clinical manifestations associated with Colorado tick fever are fever, chills, headache, body aches, and lethargy.
Physical Examination
Early onset signs include fever, lethargy, and overall weakness. As the infection progresses, further clinical manifestations will present themselves in the form of tachycardia, changes in blood pressure, sensitivity of the eye and skin, and the appearance of a rash. Signs may appear to be similar to other diseases within the umbrella of tick-borne fevers however a biphasic fever is a characteristic sign of a Colorado tick fever infection.
Laboratory Findings
A combination of laboratory tests can confirm the likely hood of a Colorado tick fever infection. An Immunofluoresence assay remains the gold standard in testing for infection. Other tests include complement fixation to the viral components that cause Colorado tick fever or acute and convalescent serology. [2]
Medical Therapy
There is currently no specific treatment for Colorado tick fever. Supportive treatment is currently the primary method in care. Certain cases, depending on severity, will require hospitalization.
Prevention
Colorado tick fever prevention strategies are based on avoiding potential, infected, tick bites. Avoiding tick bites may be accomplished through limited exposure to endemic areas. However if it is impossible or impractical to avoid these areas, several preventative strategies may be implemented. These strategies are indicated under the Prevention title below. Other prevention strategies include a proper removal of the tick. This process is also outlined below under the title, the best way to remove a tick.
References
- ↑ Centers for Disease Control and Prevention Colorado tick fever, Statistics. http://www.cdc.gov/coloradotickfever/statistics.html Accessed January 19, 2016
- ↑ Quest Diagnostics. Colorado tick fever diagnostics. http://www.questdiagnostics.com/testcenter/testguide.action?dc=CF_Tick-borneDis. Accessed January 27, 2016.