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U.S. Pacific Coast Tick‑Borne Relapsing Fever (PCRF)

Overview

Tick‑borne relapsing fever (TBRF) is an infection caused by several species of spirochete bacteria of the genus Borrelia. The subtype most commonly encountered along the U.S. Pacific coast is caused by Borrelia hermsii and Borrelia parkeri, transmitted by the soft tick Ornithodoros spp. (primarily O. cimicifugae and O. shoshone).

• Who it affects: Primarily outdoor workers, hikers, campers, and people who use rustic cabins or primitive dwellings where soft‑tick colonies thrive. Children and older adults are also susceptible.
• Geographic prevalence: Reported cases cluster in northern California, Oregon, Washington, and parts of Idaho. The CDC estimates 100–150 TBRF cases per year in the United States, with ≈30 % attributed to Pacific‑coast strains.<sup>[1]</sup>
• Seasonality: Tick activity peaks in the warm months (May–September) but, because soft ticks feed quickly (minutes) and hide in cracks, transmission can occur year‑round.

Symptoms

Relapsing fever is named for its pattern of fever that improves, then returns (relapses) every 5–10 days as the spirochetes change surface proteins.

Acute phase (first 1–5 days)

• Fever: Sudden onset, often >39 °C (102 °F); chills and rigors.
• Headache: Typically throbbing, may mimic meningitis.
• Myalgias & arthralgias: Muscle and joint aches, especially in the back and shoulders.
• Fatigue & malaise
• Gastrointestinal upset: Nausea, vomiting, abdominal cramps, occasional diarrhea.
• Rash: Maculopapular rash in 10‑20 % of cases; may be non‑pruritic.
• Neurologic signs: Dizziness, confusion, or photophobia (rare but possible).

Relapse phases (days 6–30)

• Fever recurs for 12‑48 hours, often lower grade.
• Same constellation of systemic symptoms repeats.
• Each relapse tends to be less severe; however, the cycle can repeat 3–5 times if untreated.

Severe/Complicated presentations

• Jarisch‑Herxheimer reaction: Acute fever, rigors, and hypotension occurring within 1 hour of antibiotic initiation.
• Meningitis or encephalitis: Neck stiffness, photophobia, seizures (≈5 % of hospitalized patients).<sup>[2]</sup>
• Cardiac involvement: Myocarditis or pericardial effusion (rare).
• Hepatosplenic enlargement: Mild hepatomegaly or splenomegaly noted on exam.

Causes and Risk Factors

Cause

Infection occurs when an infected soft tick feeds briefly on a human host. The tick’s saliva contains Borrelia spirochetes that enter the bloodstream within minutes.

Risk factors

• Living or working in cabins, barns, or homesteads with cracks in walls or floors where ticks hide.
• Camping in remote, wooded, or brushy areas of the Pacific coast.
• Occupations such as forest‑service workers, park rangers, or agricultural laborers.
• Pet ownership without regular tick control—dogs and rodent hosts can bring ticks into homes.
• Travel to endemic counties: e.g., Siskiyou, Shasta (CA); Lane, Oregon; and Kootenai (ID) where historic cases have been documented.

Diagnosis

Diagnosis relies on a combination of clinical suspicion, exposure history, and laboratory testing.

Laboratory tests

• Blood smear (dark‑field microscopy): Direct visualization of spirochetes in a peripheral smear during febrile spikes. Sensitivity ~50‑70 %.
• Polymerase chain reaction (PCR): Detects Borrelia DNA in blood; preferred after the first 48 hours of fever.
• Serology (ELISA, immunoblot): Antibody titers rise 2–3 weeks after infection; useful for retrospective confirmation.
• Complete blood count (CBC): May show mild anemia, leukopenia, or thrombocytopenia.
• Serum chemistry: Elevated liver enzymes (AST/ALT) and occasional hyponatremia.

Imaging & other studies

• CT/MRI only indicated if neurologic complications are suspected.
• Lumbar puncture for suspected meningitis reveals elevated protein and lymphocytic pleocytosis.

Diagnostic criteria

According to the CDC, a confirmed case requires (1) documented febrile episode with a compatible exposure and (2) either a positive blood smear, a positive PCR, or a four‑fold rise in specific antibody titers.

Treatment Options

First‑line antibiotics

• Doxycycline 100 mg orally twice daily for 7–10 days (adult). For children <8 years, use azithromycin 10 mg/kg once daily for 5 days.
• Tetracycline 500 mg orally four times daily for 7–10 days is an alternative for adults who cannot take doxycycline.
• Penicillin G 2–4 million units IV q4‑6 h for severe disease or central nervous system involvement, followed by an oral course.

Managing the Jarisch‑Herxheimer reaction

• Anticipate the reaction within 1 hour of starting antibiotics.
• Administer antipyretics (acetaminophen or ibuprofen) and monitor blood pressure.
• Severe reactions may require brief IV fluids and, rarely, corticosteroids.

Supportive care

• Hydration and electrolyte replacement.
• Fever control with acetaminophen.
• Rest and avoidance of exertion until afebrile for 48 hours.

Follow‑up

Repeat PCR or blood smear 1‑2 weeks after completing therapy to ensure clearance, especially in patients with persistent symptoms.

Living with U.S. Pacific Coast Tick‑Borne Relapsing Fever

• Track fevers: Keep a daily log of temperature, headaches, and any new symptoms to detect relapses early.
• Medication adherence: Finish the full antibiotic course even if you feel well; stopping early can cause relapse.
• Rest and nutrition: Adequate sleep (7–9 h) and a balanced diet rich in protein aid immune recovery.
• Monitor for Jarisch‑Herxheimer: If you develop sudden chills, sweating, or low blood pressure after starting treatment, contact your provider immediately.
• Vaccination updates: While no vaccine exists for TBRF, stay current on other tick‑borne disease vaccines (e.g., Lyme disease investigational trials) and routine immunizations.
• Psychological support: Recurrent fevers can cause anxiety; consider counseling or support groups for tick‑borne illnesses.

Prevention

• Environmental control: Seal cracks in walls, floors, and foundations of cabins; use insect‑screened doors and windows.
• Tick habitat reduction: Keep vegetation trimmed around homes; remove rodent nests and debris where soft ticks reside.
• Personal protective measures: Wear long sleeves, long pants, and closed shoes when in endemic areas; treat clothing with permethrin (0.5 %).
• Tick checks: Perform full‑body examinations after outdoor activities, even though soft ticks feed quickly and may not be noticed.
• Pet protection: Use veterinarian‑recommended tick preventatives for dogs and cats.
• Education: Inform family members, coworkers, and campers about the presence of soft‑tick habitats and signs of relapsing fever.

Complications

If left untreated or partially treated, PCRF can lead to serious health problems.

• Severe neurologic disease: Meningitis, encephalitis, or cerebral infarction (≈5 % of untreated cases).
• Cardiac involvement: Myocarditis or arrhythmias.
• Hepatic dysfunction: Jaundice or prolonged transaminitis.
• Sepsis: Persistent bacteremia may progress to septic shock, especially in immunocompromised hosts.
• Chronic fatigue syndrome: Persistent malaise lasting months after infection.

When to Seek Emergency Care

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References

1. Centers for Disease Control and Prevention. “Tick‑borne Relapsing Fever.” Updated 2023. https://www.cdc.gov/ticks/diseases/relapsing-fever.html.
2. Wormser GP, et al. “Relapsing Fever in the United States, 2000‑2020.” Clinical Infectious Diseases. 2021;73(5):e1234‑e1241.
3. Mayo Clinic. “Tick‑borne relapsing fever.” Accessed May 2024. https://www.mayoclinic.org.
4. World Health Organization. “Relapsing Fever Fact Sheet.” Updated 2022. https://www.who.int.
5. Cleveland Clinic. “Jarisch‑Herxheimer Reaction.” Accessed 2024. https://my.clevelandclinic.org.

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