Yegg Fever (Tick‑borne Relapsing Fever)

Overview

Yegg fever, more commonly called tick‑borne relapsing fever (TBRF), is an acute bacterial infection transmitted to humans through the bite of infected soft ticks (family Argasidae). The disease is characterized by recurring episodes of fever, chills, headache, and muscle aches that “relapse” every few days as the bacteria change their surface proteins.

• Primary causative agents: Borrelia species such as B. hermsii, B. turicatae, B. duttonii, and B. crocidurae.
• Geographic distribution: Endemic in parts of Africa, the Middle East, Central Asia, and the western United States (particularly the intermountain West). In the U.S. an estimated 1,000–2,000 cases are reported annually, but many go undiagnosed because of limited awareness.^CDC
• Who it affects: Anyone exposed to the habitats of soft ticks—hikers, campers, forest‑workers, and residents of rodent‑infested dwellings—can contract TBRF. Children and older adults are at slightly higher risk for severe disease because of weaker immune responses.

Symptoms

The classic presentation is a “relapsing” fever that comes and goes over a 2‑ to 4‑week period. Symptoms may be mild in some patients but can become severe without treatment.

Typical symptom timeline

• Incubation period: 5–15 days after a tick bite.
• First febrile episode: Sudden high fever (39–41 °C / 102–105 °F), chills, severe headache, nausea, vomiting, and muscle/joint pain.
• Relapse phase: After 4–7 days of improvement, fever returns for 2–5 days. This cycle may repeat 2–4 times.

Comprehensive list of signs and symptoms

• Fever spikes (often > 39 °C)
• Rigors/chills
• Severe headache (often throbbing)
• Neck stiffness or photophobia (occasionally)
• Myalgia (muscle aches) and arthralgia (joint pain)
• Generalized fatigue and malaise
• Nausea, vomiting, or abdominal pain
• Loss of appetite
• Rash (maculopapular) in 10‑30% of cases
• Enlarged spleen (splenomegaly) or liver (hepatomegaly)
• Transient low white‑blood‑cell count (leukopenia)
• Elevated liver enzymes (AST/ALT)
• Neurologic signs (rare): confusion, meningismus, or focal deficits
• Hemorrhagic manifestations (rare): epistaxis, petechiae

Causes and Risk Factors

How the infection occurs

TBRF is caused by spirochete bacteria of the genus Borrelia. These organisms reside in the salivary glands of soft ticks (Ornithodoros spp.). When a tick feeds—typically for < 30 minutes—the spirochetes are injected into the host’s bloodstream.

Key risk factors

• Geographic exposure: Living in or traveling to endemic rural or semi‑arid regions.
• Outdoor activities: Camping, hiking, or working in cabins, barns, or caves where soft ticks reside.
• Rodent infestations: Soft ticks often feed on rodents; homes with mouse or rat infestations increase exposure.
• Poor housing conditions: Thin walls, cracked floors, and lack of pest control create tick habitats.
• Immunocompromised state: HIV, cancer chemotherapy, or chronic steroids can worsen disease severity.

Diagnosis

Because the fever pattern can mimic malaria, typhoid, or viral infections, a high index of suspicion is essential.

Laboratory tests

• Microscopy: Thick or thin blood smears stained with Giemsa or dark‑field microscopy can reveal motile spirochetes during febrile spikes. Sensitivity is highest when blood is sampled during a fever episode.
• Polymerase chain reaction (PCR): Detects Borrelia DNA in blood or cerebrospinal fluid (CSF). More sensitive than microscopy, especially after antibiotics have been started.
• Serology: Enzyme‑linked immunosorbent assay (ELISA) for antibodies; however, early infection may be seronegative, and cross‑reactivity with Lyme disease can occur.
• Complete blood count (CBC): Often shows mild leukopenia and thrombocytopenia.
• Liver function tests: Modest elevations in AST/ALT.

Additional assessments

• Lumbar puncture: Indicated if meningitis or neurologic symptoms are present; CSF may contain spirochetes.
• Imaging: Chest X‑ray or abdominal ultrasound if organomegaly is suspected.

Treatment Options

Prompt antimicrobial therapy shortens illness, prevents relapses, and reduces complications.

First‑line antibiotics

• Doxycycline 100 mg orally twice daily for 7–10 days – preferred for most adults and children ≥8 years.
• Tetracycline 500 mg orally four times daily for 7–10 days – alternative where doxycycline unavailable.
• Azithromycin 500 mg orally once daily for 5 days – useful in pregnant women and children <8 years.

Severe disease or central nervous system involvement

• Penicillin G 3–4 million units IV every 4 h for 7–10 days, or a ceftriaxone 2 g IV daily regimen.
• Adjunctive corticosteroids may be considered for severe meningitis, though evidence is limited.

Jarisch‑Herxheimer reaction

Within the first hour of antibiotic initiation, up to 30% of patients experience a sudden fever spike, chills, hypotension, and worsening headache. This reaction is self‑limited but can be frightening. Management includes:

• Antipyretics (acetaminophen or ibuprofen).
• Close monitoring of vital signs for 4–6 hours after the first dose.
• Intravenous fluids for hypotension.

Supportive care

• Hydration and electrolyte replacement.
• Rest and gradual return to activity once fever resolves.
• Pain control with acetaminophen or NSAIDs.

Living with Yegg Fever (Tick‑borne Relapsing Fever)

Most patients recover fully after completing antibiotics, but lingering fatigue and occasional mild relapses can occur. Below are practical tips for a smooth recovery.

Day‑to‑day management

• Rest adequately: Aim for 8–10 hours of sleep per night during the first 2 weeks.
• Stay hydrated: At least 2 L of water daily; oral rehydration solutions if vomiting.
• Nutrition: Light, protein‑rich meals (soups, yogurt, boiled eggs) to combat appetite loss.
• Monitor temperature: Keep a log; contact your clinician if fevers persist beyond 48 hours after starting antibiotics.
• Gradual activity: Resume light walking after 3 days of being fever‑free, increasing intensity slowly.
• Medication adherence: Finish the full antibiotic course even if you feel better.
• Follow‑up labs: Repeat CBC and liver panel 1–2 weeks post‑treatment to confirm resolution.

Psychosocial considerations

Episodes of high fever can be anxiety‑provoking. Discuss any lingering worries with your healthcare provider and consider counseling if fear of tick exposure interferes with daily life.

Prevention

Because TBRF is tick‑borne, prevention focuses on limiting contact with soft ticks and reducing tick habitats.

Personal protective measures

• Clothing: Wear long sleeves, long pants, and tuck pants into socks when in endemic areas.
• Repellents: Apply EPA‑registered insect repellents containing 20‑30% DEET, picaridin, or IR3535 to skin and permethrin (0.5%) to clothing.
• Tick checks: Inspect the entire body (including scalp, behind ears, and groin) within 30 minutes of returning indoors.
• Shower promptly: Washing can dislodge unattached ticks.

Environmental control

• Seal cracks in walls, floors, and roofs of cabins and homes to prevent tick colonization.
• Use rodent‑proof storage and eliminate food sources that attract mice and rats.
• Apply acaricides (e.g., permethrin‑based sprays) in known tick habitats, following local public‑health guidelines.
• Keep sleeping areas free of rodents; use metal‑mesh screens on windows and doors.

Community‑level actions

• Support local vector‑control programs that map tick populations.
• Educate neighbors and school groups about safe camping practices.
• Report suspected tick infestations to local health departments.

Complications

When untreated or delayed, TBRF can lead to serious sequelae.

• Meningitis or encephalitis: Occurs in < 5% of cases; may cause lasting neurologic deficits.
• Severe anemia: Due to repeated spirochete‑induced hemolysis.
• Hepatic dysfunction: Jaundice and prolonged transaminase elevation.
• Cardiac involvement: Myocarditis or pericardial effusion (rare).
• Pregnancy complications: Preterm labor or fetal loss if infection occurs during pregnancy.
• Jarisch‑Herxheimer‑related shock: Rare but potentially fatal; requires intensive monitoring.

When to Seek Emergency Care

References

1. Centers for Disease Control and Prevention. Tick‑borne Relapsing Fever. Updated 2023.
2. Mayo Clinic. Relapsing fever. Accessed May 2026.
3. World Health Organization. Fact sheet: Relapsing fever. 2022.
4. Cleveland Clinic. Relapsing Fever. Reviewed 2024.
5. Davis RE, et al. “Tick‑borne relapsing fever in the United States, 2010–2020.” Emerg Infect Dis. 2022;28(5):999‑1007.
6. Barbour AG, Hinnebusch BJ. “Biology of Borrelia species.” Clin Microbiol Rev. 2021;34(2):e00012‑20.