Tick Fever

Tick Fever: Excerpt from The 5-Minute Pediatric Consult

Brian Fisher, MDJames M. Callahan, MD (4th Edition)

Tick Fever - BASICS

Tick Fever - description

• Relapsing fever in its endemic form is a vector-borne infection with characteristic recurrent fevers caused by several species of spirochetes of the genus Borrelia. In the US, the vector for endemic relapsing fever is ticks of the genus Ornithodoros. Epidemic relapsing fever is transmitted by the body louse and is no longer found in the US.
• Colorado tick fever (CTF) is a febrile, usually benign, systemic illness caused by a double-stranded RNA coltivirus in the family Reoviridae transmitted by the Dermacentor andersoni wood tick. The virus is referred to as Colorado tick fever virus.

Tick Fever - general prevention

• Both of these diseases can be prevented by avoidance or protection from the vector.
• Avoid rodent-infested homes in endemic areas. If necessary, rodent-nesting materials should be removed with protective gloves.
• Light-colored, long-sleeved shirts and pants should be worn when infested areas cannot be avoided.
• Permethrin should be applied to clothing and diethyltoluamide (DEET) applied to exposed skin to help repel ticks.
• Persons who enter endemic areas should inspect themselves and each other frequently for adherent ticks.
• Confirmed cases should be reported to health authorities so control measures can be instituted.

Tick Fever - epidemiology

• Endemic relapsing fever:
  • Occurs in the US among people who are exposed to the habitat of the ticks that serve as vectors.
  • Almost all western states have reported cases, with California, Colorado, and Washington reporting the most cases.
  • A majority of cases present during June through September. ~450 cases were reported in the US between 1977 and 2000.
  • Infection commonly occurs after exposure to rural cabins infested with rodents. In Texas, a majority of cases are contracted during limestone cave exploration.
• CTF: Annual incidence in the US has declined to 200–300 reported cases:
  • Human infections typically occur in areas where D. andersoni is found: Western US and southwestern Canada at elevations of 4,000–10,000 feet
  • Cases usually occur between April and July when adult ticks are most active.
  • Infection is more common in males and in persons between 20–30 years old.
  • Infection commonly occurs between April and June when the adult tick is most active.
  • Transfusion-related and laboratory-associated infection are rare but have been reported.

Tick Fever - pathophysiology

• Endemic relapsing fever:
  • When an Ornithodoros tick feeds on a natural host (e.g., squirrels, chipmunks, and rodents), Borreliae subsequently invade all tissues of the tick including the female genital tract. Once infected, ticks remain capable of transmitting disease for many years. Transovarial infection of tick offspring is possible but is thought to be rare.
  • Borreliae are transmitted to humans when the tick takes a blood meal and then detaches itself. Bites are usually painless, and the tick may remain attached for 15–90 minutes. Transmission is possible after only 30 seconds of feeding.
  • All stages of the tick (larvae, nymphs, and adults) are capable of transmitting the spirochete.
  • Ornithodoros ticks typically feed at night on unsuspecting humans asleep in mountain cabins.
  • After transmission, spirochetemia develops resulting in systemic symptoms. Antibody production ultimately leads to agglutination and phagocytosis of the spirochetes with symptom resolution.
  • The spirochete undergoes spontaneous antigenic variation by plasmid-mediated recombination. This causes recurrent spirochetemia with associated febrile episodes. Tick-borne disease may relapse 10–15 times before final resolution.
  • Between episodes of spirochetemia organisms likely persists in the CNS, bone marrow, liver, and spleen.
  • Pathologic findings in humans include petechial hemorrhages on visceral surfaces, hepatosplenomegaly, and a histiocytic myocarditis.
• CTF:
  • Ticks are infected during their larval stage when they feed on viremic, intermediate hosts such as chipmunks, ground squirrels, and porcupines.
  • Human infection takes place when the adult D. andersoni wood tick attaches and ingests a blood meal from an incidental human host.
  • Colorado tick fever virus is thought to infect hematopoietic cells causing leukopenia and prolonged viremia for up to 3–4 months.

Tick Fever - etiology

• Relapsing fever is caused by several species of spirochetes in the genus Borrelia. B. hermsii, B. parkerii, and B. turicatae are the species found in the US. Epidemic relapsing fever is caused by B. recurrentis which is transmitted by Pediculus humanus (human body louse).
• CTF is caused by Colorado tick fever virus, a double-stranded RNA coltivirus in the family Reoviridae.

Tick Fever - DIAGNOSIS

Tick Fever - signs & symptoms

Tick Fever - history

• Both endemic relapsing fever and CTF most commonly present with symptoms including high fever, headache, myalgias, and chills. A thorough history documenting recent travel and a description of the fever curve are necessary to help direct the clinician to either diagnosis.
• Endemic relapsing fever:
  • Fevers present after a mean incubation period of 5–7 days (range 4–18 days). Symptoms resolve after 3–6 days but then recur within 7 days. Relapses may be less severe then the initial episode with prolonged asymptomatic intervals.
  • Patients commonly complain of nausea, vomiting, arthralgias, and abdominal pain. Less commonly, patients are symptomatic with dry cough, confusion, photophobia, rash, or dysuria.
  • Patients rarely are aware of a recent tick bite.
• CTF:
  • CTF has a usual incubation period of 3–4 days (range 1–14 days):
    • In ~50% of patients, fever will present in a “saddleback” pattern. The fever persists for 2–3 days with resolution for 2–3 days. Fever then recurs and lasts for another 2–3 days. Some patients will have a 3rd febrile period.
    • Patients may complain of lethargy, photophobia, retro-orbital pain, and conjunctival injection.
    • Less commonly, patients will have gastrointestinal symptoms, pharyngitis, nuchal rigidity, and a rash.
    • Unlike endemic relapsing fever, 90% of patients presenting with CTF will have a previous history of tick exposure.

Tick Fever - physical exam

High fevers (39–41°C) are common to both endemic relapsing fever and CTF.

• Endemic relapsing fever:
  • Beyond the typical fever curve and symptoms described above, the clinical presentation is varied and the physician’s exam should evaluate for but not be limited to the following:
    • Elevated pulse and BP are common.
    • Tender hepatosplenomegaly with jaundice
    • Nuchal rigidity suggesting meningitis
    • Gallop on cardiac auscultation suggesting underlying myocarditis
    • A macular rash starting on the trunk that becomes generalized and or petechial in nature
    • Neurological deficits are less common but can include delirium, cranial nerve deficits (7th or 8th nerve palsy), and visual impairment from iridocyclitis.
• CTF:
  • Similar to that of endemic relapsing fever, the clinical presentation for CTF is varied but may include the following:
    • A small, red painless papule may be seen.
    • A maculopapular rash with petechial lesions has been reported in ~10% of cases.
    • Pharyngitis is reported in 20% of cases.
    • Hepatosplenomegaly has been found in some patients.
    • Nuchal rigidity and delirium are rare but, if present, suggest meningitis or encephalitis.

Tick Fever - tests

• Endemic relapsing fever:
  • The diagnosis can be readily made by identification of loosely coiled spirochetes on thin and thick smears of the peripheral blood. Blood samples taken at the time of fever have the highest yield.
  • Increased sensitivity can be obtained by examining Acridine orange–stained preparations of dehemoglobinized thick smears or buffy coat preparations.
  • Intraperitoneal inoculation of immature laboratory mice with an infected patient’s blood leads to spirochetemia in the mice and is a sensitive and specific diagnostic tool.
  • The organism can only be cultured on special culture medium.
  • Multiple serologic antibody studies exist including direct and indirect immunofluorescence, ELISA, and immunoblot analysis.
    • A 4-fold rise in titers between acute and convalescent studies is considered confirmatory.
    • These studies may have false-positive reactions in patients with prior spirochete infections such as Lyme disease.
  • Polymerase chain reaction (PCR) analysis is available in some research laboratories but is not routinely performed.
  • Other nonspecific laboratory findings may include leukocytosis, anemia, thrombocytopenia, unconjugated hyperbilirubinemia, elevated hepatic transaminases, and proteinuria.
  • If myocarditis is present, an electrocardiogram can reveal abnormalities such as a prolonged corrected Q-T interval.
  • In cases complicated by meningitis, the CSF will typically have moderately elevated protein and a mononuclear pleocytosis.
• CTF:
  • PCR testing and viral culture are available in certain laboratories and are likely the most sensitive for diagnosing acute infection.
    • Direct immunofluorescent examination of blood for viral antigen is an alternative for diagnosis of acute infection.
    • Serologic testing for antibody presence is not diagnostic in the acute phase as antibodies are slow to rise. Presence of a 4-fold rise in neutralizing antibody titers at >2 weeks after onset can be confirmatory.
    • Associated laboratory findings include leukopenia and thrombocytopenia.
    • In patients with meningitis or encephalitis, CSF studies may also reveal elevated protein and a mononuclear pleocytosis.

Tick Fever - differencial diagnosis

• Endemic relapsing fever and CTF resemble each other clinically. Presence of biphasic or relapsing fever along with a history of travel to an area where appropriate vectors are found are helpful clues in diagnosing either disease. Leukopenia and a history of a tick bite may differentiate CTF from endemic relapsing fever.
• Relapsing fever and CTF may be misdiagnosed as influenza or enteroviral infections, especially with the 1st febrile episode.
• Other infectious illnesses that may present with recurrent fevers include yellow fever, dengue fever, lymphocytic choriomeningitis, brucellosis, malaria, leptospirosis, rat bite fever, and chronic meningococcemia. The patient travel history and animal exposure should help differentiate among some of these diagnoses.

Tick Fever - TREATMENT

Tick Fever - medication

• Endemic relapsing fever:
  • The treatment of choice is oral tetracycline for 7–10 days. Children <8 years of age and pregnant women should receive erythromycin or penicillin.
  • The newer macrolides, clarithromycin or azithromycin, may be effective but are not routinely recommended.
  • In >50% of cases, treatment results in a Jarisch–Herxheimer reaction (severe fevers, rigors, diaphoresis, and hypotension) related to rapid clearing of the spirochetemia. Close observation, intravenous fluids, and good supportive care are important in treating possible reactions.
  • Some experts support the use of an initial single dose of oral penicillin (7.5 mg/kg) or IV penicillin G (10,000 U/kg given over 30 minutes) in patients presenting with systemic symptoms. It is thought that this initial dose of penicillin leads to gradual clearance of spirochetes decreasing the risk of the Jarisch–Herxheimer reaction. These patients should then receive a 10-day course of tetracycline or erythromycin as penicillin has been associated with an increased rate of relapse.
  • Single-dose tetracycline or erythromycin has been successful for the treatment of louse-borne epidemic relapsing fever in Ethiopia.
• CTF:
  • There is no specific therapy for patients with CTF. Treatment is primarily supportive.
  • Thrombocytopenia should be monitored closely as generalized bleeding rarely results in death of children.
  • Ribavirin may be helpful in certain severe situations.

Tick Fever - FOLLOW UP

Tick Fever - prognosis

• Endemic relapsing fever:
  • Generally responds rapidly to appropriate antibiotic therapy and leaves no significant sequelae.
  • Mortality in patients treated appropriately is thought to be <1%.
  • Untreated louse-borne relapsing fever is associated with a much higher rate of fatality.
• CTF:
  • Usually a self limiting illness without sequelae
  • Death is rare but has been reported in children with generalized bleeding likely secondary to thrombocytopenia.
  • Prolonged weakness may persist for ≥3 weeks and is more likely in those patients >30 years old.

Tick Fever - complications

• Endemic relapsing fever:
  • May be associated with splenic rupture, diffuse histiocytic interstitial myocarditis, hepatitis, pneumonia, and iridocyclitis.
  • CNS complications include meningitis, meningoencephalitis, and cranial nerve palsy.
  • In utero infection may result in fetal loss or severe neonatal infection.
• CTF:
  • Complications are rare but most commonly occur in children.
  • May lead to aseptic meningitis, encephalitis, myocarditis, pneumonia, hepatitis, hemorrhage, and epididymo-orchitis.

Tick Fever - bibliography

Boyer KM. Borrelia (relapsing fever). In: Feigin RD, Cherry JD, Demmler GJ, et al. eds. Textbook of Pediatric Infectious Disease. 5th ed. Philadelphia, PA: WB Saunders; 2004:1695–1700.
1. Dworkin MS, Schwan TG, Anderson Jr DE. Tick-borne relapsing fever in North America. Med Clin North Am. 2002;86:417–433.
2. Klasko R. Colorado tick fever. Med Clin North Am. 2002;86:435–440.
3. Roscoe C, Epperly T. Tick-borne relapsing fever. Am Fam Physician. 2005;72:2039–2044.
Tsai TF. Orbiviruses and coltiviruses. In: Feigin RD, Cherry JD, Demmler GJ, et al. eds. Textbook of Pediatric Infectious Disease. 5th ed. Philadelphia, PA: WB Saunders; 2004:2106–2108.

Tick Fever - CODES

Tick Fever - icd9

• 066.1 Tick-borne fever
• 087 Relapsing fever

Book Source Details

• Book Title: The 5-Minute Pediatric Consult
• Author(s): M. William Schwartz MD; et al.
• Year of Publication: 2008
• Copyright Details: The 5-Minute Pediatric Consult, Copyright © 2008 Lippincott Williams & Wilkins.

More About Colorado tick fever

• Back to disease: Colorado tick fever: Introduction
• Next Book Extract About Colorado tick fever: STARI
• More Book Extracts: All Online Books for Colorado tick fever

More Medical Textbooks Online about Colorado tick fever

Review other book chapters online related to Colorado tick fever:

Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.

More About This Book: Title: The 5-Minute Pediatric Consult Authors: M. William Schwartz MD; et al. Publisher: Lippincott Williams & Wilkins Copyright: 2008 ISBN: 0-7817-7577-9

 » Next page: STARI

Rate This Website

What do you think about the features of this website? Take our user survey and have your say:

Website User Survey

Medical Tools & Articles:

Tools & Services:

• Bookmark this page
• Symptom Search
• Symptom Checker
• Medical Dictionary
• Give your feedback

Medical Articles:

• Disease & Treatments Search
• Misdiagnosis Center
• Full list of interesting articles

Forums & Message Boards

• Ask or answer a question at the Boards:
• I cannot get a diagnosis. Please help.
• Tell us your medical story.
• Share your misdiagnosis story.
• What is the best treatment for my condition?
• See all the Boards.

Enter your search terms Submit search form
Search The Web Search wrongdiagnosis.com

Common Health Mistakes

Symptom
Checker

Search Specialists by State and City