Rickettsia typhi (Murine/Endemic typhus)
📖 About
- Rickettsia typhi → causes murine (endemic) typhus, a flea-borne zoonotic infection, common in urban & tropical settings.
🔬 Characteristics
- Gram-negative but poorly visualised with Gram stain (tiny, intracellular).
- Obligate intracellular parasite → depends on host cell ATP & machinery.
- Grows only in tissue culture → highlights strict host dependency.
🏠 Source
- Reservoirs: rats 🐀 & small mammals.
- Transmission: flea bites (rat flea Xenopsylla cheopis, cat flea in urban areas).
🌍 Epidemiology
- Endemic in tropical/subtropical climates.
- More common in crowded urban areas with poor sanitation & rodent infestations.
⚠️ Pathogenicity & Clinical Presentation
- Incubation: 6–14 days post exposure.
- Early features: sudden fever 🌡️, chills, headache, myalgia.
- ~50% → maculopapular rash starting on trunk → spreading to extremities.
- Other features: nausea, vomiting, abdominal pain, hepatosplenomegaly (severe).
- Complications if untreated: renal impairment, pneumonia, meningoencephalitis.
🧪 Virulence Factors
- Adheres & invades host endothelial cells.
- Utilises host nutrients, impairing function & facilitating dissemination.
🔎 Investigations
- 🧪 Weil–Felix test: historical, low sensitivity/specificity.
- 🧪 Immunofluorescence: staining of rash biopsy specimens.
- 🧪 Serology: preferred diagnostic method (IgM/IgG antibodies).
- 🧪 PCR: sensitive, detects organism in blood/tissue early.
💊 Management
- First-line: Doxycycline (5–7 days, or until 3 days after fever subsides).
- Alternative (pregnancy): Chloramphenicol (with caution).
- Supportive care: Hydration, antipyretics, monitor for complications.
📊 Prognosis
- With prompt treatment → mortality <5%.
- Without treatment → higher complication risk.
- Some patients may have prolonged fatigue even after cure.
🛡️ Prevention
- Rodent control 🐀 + flea eradication.
- Good sanitation & waste disposal → reduce reservoirs.
- Personal protection: insect repellents, protective clothing in endemic areas.
⚠️ Exam pearl: Rickettsia typhi → flea-borne, endemic typhus, maculopapular trunk rash, treated with doxycycline. Distinguish from epidemic typhus (R. prowazekii, louse-borne).
