Tick- and louse-borne relapsing fever (Borrelia spp.)

Microbiology

Tick-borne relapsing fever (TBRF) is caused by multiple non-Lyme Borrelia species with global distribution
Louse-borne relapsing fever (LBRF) is caused by B. recurrentis
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
TBRF
B. hermsii	Ornithodoros hermsii	Western US and Canada (most common)	Rodent
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
LBRF
B. recurrentis	Pediculus humanus	Ethiopia/Eastern Africa (previously worldwide)
Other
B. miyamotoi	Ixodes dammini and I. scapularis	US, Russia, and Japan	Deer
B. lonestari	Amblyomma americanum	Southern US	Deer & lizards

TBRF is transmitted by Ornithodoros species 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
LBRF was present nearly worldwide prior to World War II, but is now present in Ethiopia
- Associated with homelessness and refugee camps

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

Incubation period of 7 days (range 2 to 18 days)
Relapsing fevers: febrile for 3 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, myalgia, arthralgia, dizziness, and vomiting
- Each relapse is usually less severe
Some patients will have lymphadenopathy, hepatosplenomegaly, and a rash
Rare complications include lymphocytic meningitis, Bell palsy and other cranial nerve palsies, paralysis, seizure, uveitis, endophthalmitis, ARDS, and myocarditis
Can cause spontaneous abortion in pregnant women
May be septic, with multiple organ involvement
May have a Jarisch-Herxheimer reaction following empiric antibiotics

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

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

Can do post-exposure prophylaxis with doxycycline 200 mg po once followed by 100 mg daily for 4 days