Rickettsia prowazekii (Epidemi/Louse-borne Typhus)
📖 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).
