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Colorado Tick Fever Workup

  • Author: Cassis Thomassin, MD; Chief Editor: Jeter (Jay) Pritchard Taylor, III, MD  more...
 
Updated: Jan 21, 2016
 

Laboratory Studies

Laboratory studies are nonspecific and generally not helpful. The white blood cell (WBC) count is mildly depressed (mean, approximately 3900/µL) in about 66% of patients. Leukopenia may suggest the diagnosis. Rarely, thrombocytopenia occurs. Peripheral smear may show atypical lymphocytes.[1] Occasionally, patients with Colorado tick fever have elevated hepatic transaminase levels (in the mid-hundreds).

Analysis of cerebrospinal fluid (CSF) analysis may demonstrate mild-to-moderate lymphocytic pleocytosis (up to 300 cells/µL) and mildly elevated protein levels.

Because the clinical features of Colorado tick fever are nonspecific, the diagnosis must be established in the proper epidemiologic context. Confirmation is based on serologic test results or virus inoculation in mice. In addition, reverse transcriptase polymerase chain reaction (PCR) techniques are available that may help diagnose the disease in the first 5 days of illness.

Neutralizing antibodies appear in about one third of cases by day 10 and in nearly all patients by 1 month after infection. A 4-fold increase in titers between specimens drawn during the acute phase and those drawn during convalescence is observed in nearly all patients. The assay, performed with complement fixation or immunofluorescent techniques, must be done in a laboratory that has experience with this test.

Antibodies to the Colorado tick virus frequently are found in perennial campers who frequent endemic areas; thus, a single elevated titer of immunoglobulin G (IgG) does not necessarily indicate acute infection. This finding also suggests asymptomatic seroconversion.

Although viral testing is not routinely available, the virus can be detected in the blood for 2-4 weeks after infection. Laboratory techniques also allow isolation of RNA and DNA from the tick itself to detect bacterial and viral pathogens; coinfection is a possibility.[8]

 
 
Contributor Information and Disclosures
Author

Cassis Thomassin, MD Clinical Assistant Instructor, Resident Physician, Department of Emergency Medicine, SUNY Downstate Medical Center

Cassis Thomassin, MD is a member of the following medical societies: American College of Emergency Physicians, Emergency Medicine Residents' Association

Disclosure: Nothing to disclose.

Coauthor(s)

Ninfa Mehta, MD, MPH Clinical Assistant Professor, Ultrasound Fellowship Director, Department of Emergency Medicine, Kings County Hospital, State University of New York Downstate Medical Center

Ninfa Mehta, MD, MPH is a member of the following medical societies: American College of Emergency Physicians, American Medical Association, American Medical Student Association/Foundation, Society for Academic Emergency Medicine, American Association of Physicians of Indian Origin

Disclosure: Nothing to disclose.

Chief Editor

Jeter (Jay) Pritchard Taylor, III, MD Assistant Professor, Department of Surgery, University of South Carolina School of Medicine; Attending Physician, Clinical Instructor, Compliance Officer, Department of Emergency Medicine, Palmetto Richland Hospital

Jeter (Jay) Pritchard Taylor, III, MD is a member of the following medical societies: American Academy of Emergency Medicine, South Carolina Medical Association, Columbia Medical Society, South Carolina College of Emergency Physicians, American College of Emergency Physicians, American Medical Association, Society for Academic Emergency Medicine

Disclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for: Chief Editor for Medscape.

Additional Contributors

Massoud G Kazzi, MD Fellow, Department of Critical Care Medicine, Montefiore Medical Center

Disclosure: Nothing to disclose.

Acknowledgements

Dan Danzl, MD Chair, Department of Emergency Medicine, Professor, University of Louisville Hospital

Dan Danzl, MD is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, American Medical Association, Kentucky Medical Association, Society for Academic Emergency Medicine, and Wilderness Medical Society

Disclosure: Nothing to disclose.

Jonathan A Edlow, MD Associate Professor of Medicine, Department of Emergency Medicine, Harvard Medical School; Vice Chairman, Department of Emergency Medicine, Beth Israel Deaconess Medical Center

Jonathan A Edlow, MD is a member of the following medical societies: American College of Emergency Physicians and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Jon Mark Hirshon, MD, MPH Associate Professor, Department of Emergency Medicine, University of Maryland School of Medicine

Jon Mark Hirshon, MD, MPH is a member of the following medical societies: Alpha Omega Alpha, American Academy of Emergency Medicine, American College of Emergency Physicians, American Public Health Association, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Reference Salary Employment

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Two ticks next to common match. On right is Ixodes scapularis, vector for Lyme disease. On left is Dermacentor tick (the larger one and the vector for Colorado tick fever).
 
 
 
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