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Rickettsia africae (African Tick Bite Fever): An Overview
📖 About
- Organism: Rickettsia africae, a spotted fever group rickettsia.
- Disease: Causes African Tick Bite Fever, an emerging zoonosis and common cause of fever in travellers returning from rural sub-Saharan Africa.
🧬 Characteristics
- Gram Reaction: Gram-negative, but tiny and not easily visible on standard Gram stain.
- Obligate intracellular parasite: Relies on host ATP (“energy parasite”).
- Culture: Requires tissue culture systems; not grown on routine agar.
🦟 Source & Transmission
- Vector: Hard ticks (Amblyomma species) act as both reservoir and vector.
- Transmission: Acquired via tick bites during rural/agricultural exposure.
- Epidemiology: Endemic in sub-Saharan Africa & Caribbean islands; important in safari travellers.
🩺 Clinical Presentation
- Incubation: ~5–7 days after tick bite.
- Symptoms: Fever, headache, myalgia, multiple inoculation eschars (necrotic black lesions at bite sites).
- Lymphadenopathy: Tender regional nodes.
- Rash: Often mild or absent (unlike R. conorii in Mediterranean spotted fever).
- Severity: Usually mild; complications rare compared with other rickettsioses.
🧾 Differential Diagnosis
- ⚠️ Malaria (must always exclude first in returning traveller).
- Meningococcal disease (acute febrile illness with rash).
- Other rickettsioses (Mediterranean spotted fever, scrub typhus).
- Viral haemorrhagic fevers (if epidemiologically relevant).
🔍 Investigations
- Bloods: Neutrophilia, thrombocytopenia, mild transaminitis.
- Serology: IFA/ELISA detecting anti-rickettsial antibodies (may lag behind clinical illness).
- PCR: If available, confirms diagnosis from eschar/whole blood.
💊 Management
- First-line: Doxycycline (100 mg PO BD, 5–7 days) → rapid defervescence.
- Alternatives: Ciprofloxacin or chloramphenicol if doxycycline contraindicated.
- Supportive care: Antipyretics, analgesics.
💡 Clinical Pearls
✅ Multiple eschars + safari traveller = African Tick Bite Fever.
✅ Rash is less common than in Mediterranean spotted fever.
✅ Always rule out malaria first in a febrile returning traveller.
