Makindo Medical Notes

📖 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).