Relapsing Fever (Borrelia)

Relapsing fever is caused by various Borrelia species, characterized by recurrent febrile episodes due to antigenic variation of variable major proteins (VMPs) on the spirochete surface allowing immune evasion. Two main forms: tick-borne relapsing fever (TBRF) caused by various species including B. hermsii (Western US), B. turicatae (Texas, Mexico), B. duttonii (East Africa), B. crocidurae (West Africa), B. miyamotoi (emerging hard tick-borne in temperate regions), B. persica (Mediterranean, Middle East), transmitted by soft (Ornithodoros) ticks; louse-borne relapsing fever (LBRF) caused by B. recurrentis transmitted by body louse Pediculus humanus humanus, classically epidemic in war, famine, refugee crises (Sudan, Ethiopia, recent European refugee outbreaks).

Pathophysiology: spirochete enters via tick saliva or contaminated louse hemolymph crushed on broken skin, invades bloodstream causing first febrile episode, immune system mounts antibody response clearing dominant antigenic variant, but subpopulations with novel surface proteins escape causing relapse, repeated until 3-5 cycles in TBRF or 1-2 in LBRF (more lethal). Clinical features: incubation 4-18 days, sudden onset high fever (39-41°C) with chills, headache, myalgia, arthralgia, fatigue, anorexia, nausea, vomiting, abdominal pain, splenomegaly, hepatomegaly, jaundice, conjunctival suffusion, photophobia, neurological symptoms (meningitis, focal neurological deficits, cranial nerve palsies particularly facial), rash, hemorrhagic manifestations, end of episode with crisis (tachycardia, hypotension, sweating), relapse 5-10 days later.

Diagnosis is by direct visualization of spirochetes in peripheral blood smear (Giemsa, Wright, or dark-field microscopy during febrile period — gold standard but spirochetes detectable only during fever), PCR (more sensitive especially during afebrile periods, useful for B. miyamotoi which is harder to see microscopically), serology (limited utility, ELISA, immunoblot — cross-reacts with Lyme), CSF examination if neurological symptoms (lymphocytic pleocytosis, elevated protein), exclusion of other tropical fevers (malaria, typhoid, leptospirosis, dengue). Treatment: doxycycline 100 mg twice daily for 10 days (preferred for adults and children >8 years), tetracycline 500 mg four times daily, penicillin V 500 mg four times daily, erythromycin 500 mg four times daily for pregnant women and children <8 years, ceftriaxone for CNS involvement; LBRF responds to single dose oral or IV penicillin (very effective). Jarisch-Herxheimer reaction (severe febrile response with hypotension, tachycardia within 2 hours of antibiotic) more common in LBRF (80%) than TBRF (40%) — supportive care with fluids, antipyretics, monitoring critical care setting if severe. Prevention via tick avoidance (especially in cabins, rodent burrows), permethrin-treated clothing, prompt tick removal, body louse control (delousing, hygiene improvements in refugee/disaster settings).