Makindo Medical Notes

📖 About

• Rickettsia prowazekii → causative agent of Epidemic Typhus (louse-borne typhus).
• Obligate intracellular parasite → requires host ATP & machinery.

🔬 Characteristics

• Gram-negative, but too small to be visualised reliably on Gram stain.
• Strictly intracellular; replicates only within host cells.
• Can only grow in tissue culture (like other rickettsiae).

🏠 Source

• Reservoir: Humans (main reservoir); flying squirrels may harbour infection in rare cases.
• Vector: Human body louse (Pediculus humanus corporis).
• Outbreaks → occur in settings of overcrowding, war, famine, natural disasters, poor hygiene.

⚠️ Pathogenicity

• Epidemic typhus: Body lice transmit bacteria via faeces → scratched into bite wound.
• Infects vascular endothelial cells → vasculitis → widespread organ dysfunction.
• Complications: myocarditis, CNS dysfunction (confusion, coma), renal failure.

🩺 Clinical Features

• Incubation: ~7–14 days.
• 🚨 Sudden high fever, chills, severe headache, myalgia.
• Rash: appears day 4–6 → starts on trunk, spreads to extremities (but spares face, palms & soles).
• Severe cases → delirium (“typhos” = stupor), stupor, coma.
• Without treatment → mortality up to 60% in elderly or immunocompromised.

🔎 Investigations

• 🧪 Weil–Felix test: historical, non-specific.
• 🧪 Immunofluorescence: rash biopsy can reveal organisms.
• 🧪 PCR/Serology: current standard for early & accurate diagnosis.

💊 Management

• Treatment of choice: Doxycycline (or tetracycline) → penetrates intracellularly; early initiation is critical.
• Supportive care: fluids, electrolytes, monitoring for complications.
• Mortality: ~5% with treatment, but up to 60% if untreated.
• Prevention: hygiene, delousing, improving living conditions in at-risk populations.

📊 Prognosis

• Early antibiotics → full recovery in days to weeks.
• Delayed therapy → ↑ risk of neurological sequelae or death, especially in older adults.

⚠️ Exam pearl: Epidemic typhus = fever + headache + trunk rash spreading outwards, louse-borne, high mortality if untreated. Differentiate from R. typhi (murine typhus, flea-borne, milder) and scrub typhus (Orientia tsutsugamushi, chigger-borne with eschar).