Tick-borne relapsing fever
From IDWiki
- Tick-borne relapsing fever (TBRF) is caused by a number of non-Lyme Borrelia species
Background
Microbiology
- Tick-borne relapsing fever is caused by multiple non-Lyme Borrelia species with global distribution, usually carried by Ornithodorus ticks
- Other non-Lyme Borrelia species include B. miyamotoi and B. lonestari, although B. lonestari may also be able to cause TBRF
- Borrelia are spirochetes
- Serotypes are determined by the outer membrane variable major proteins (vmp)
- Grow in modified Kelly medium and stained by Wright stain (in peripheral blood film)
| Species | Vector | Distribution | Reservoir |
|---|---|---|---|
| B. hermsii | O. hermsii | Western US and Canada (most common) | squirrels and chipmucks |
| B. turicatae | O. turicata | Southwestern US | Rodent |
| B. parkeri | O. parkeri | Western US and Baja California | Rodent |
| B. mazzottii | O. talaje | Mexico and Central America | Rodent |
| B. venezuelensis | O. rudis | South America | Rodent |
| B. crocidurae | O. erraticus | Middle East | Rodent |
| B. hispanica | O. marocanus | Iberian peninsula and North Africa |
Epidemiology
- TBRF is transmitted by Ornithodoros ticks, with rodent reservoirs
- Present on every continent except Australia and Antarctica
- In North America, it is mostly in the Rocky Mountain regions above 1500 feet elevation
- Most have exposure to woodpiles or cabins with rodents
- Spirochetes can survive in the tick for years, and can be transmitted vertically within ticks
- Doesn't need its mammalian host to complete its life cycle
- Ticks feed for short periods (20 min) and are painless, so is often not noticed
- Can be transmitted vertically, by transfusion, and from laboratory exposure
Pathophysiology
- During febrile periods, spirochetes divide rapidly and cause a spirochetemia
- This is followed by an immune response to the vmp proteins, which clears the spirochetemia and the patient becomes afebrile
- The vmp proteins undergo rearrangement, evading the immune system and allowing another spirochetemia
- This is the cause of the relapsing fever
Clinical Presentation
- Incubation period of 7 days (range 2 to 18 days)
- Relapsing fever: febrile for 3 days (range 12 hours to 17 days), afebrile for 7 days
- TBRF can relapse up to 30 times, whereas LBRF is usually self-limited after a single relapse
- Febrile periods may be associated with headache, myalgias, chills, arthralgias, dizziness, and vomiting
- Sometimes abdominal pain, confusion, non-productive cough, eye pain, diarrhea, photophobia, and neck pain
- Each relapse is usually less severe
- A minority of patients will have lymphadenopathy, hepatosplenomegaly, a rash, dysuria, jaundice
- Rare complications include lymphocytic meningitis, Bell palsy and other cranial nerve palsies, paralysis, seizure, uveitis, endophthalmitis, ARDS, and myocarditis
- Thrombocytopenia on bloodwork
- May be septic, with multiple organ involvement
- Can cause spontaneous abortion in pregnant women
- May have a Jarisch-Herxheimer reaction following antibiotics
Differential Diagnosis
- Colorado tick fever (Coltivirus)
- Brucellosis
- Tularemia
- Juvenile rheumatoid arthritis
- Leptospirosis
- Occult malignancy
- Lyme disease
Diagnosis
- Often seen on blood film
- Giemsa or Wright stains
- 70% sensitive during febrile period for TBRF, lower for LBRF
- Acute-convalescent serology with IFA/EIA
- May cross-react with Lyme disease
- Can cause a false-positive VDRL
- Can be cultured with modified Kelly medium
Management
- First-line: doxycycline 100 mg po bid for 7 to 10 days
- Alternatives: erythromycin 500 mg qid for 10 days
- If CNS involvement:
- Penicillin G 3 mU IV q4h for 10-14 days, or
- Ceftriaxone 2 g IV q24h for 10-14 days
Prevention
- Can do post-exposure prophylaxis with doxycycline 200 mg po once followed by 100 mg daily for 4 days
