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|Rocky Mountain Spotted Fever
🧾 About
- Rocky Mountain Spotted Fever (RMSF) is a potentially fatal rickettsial infection affecting both children and adults.
- Originally described in the Rocky Mountains, RMSF is now reported across the USA (East, South, and Southwest) and in parts of Central & South America.
- ⚠️ Mortality may reach 10%, especially if treatment is delayed.
- Risk ↑ with recent outdoor activity (e.g. camping, hiking) in endemic areas.
- Males appear to be slightly more frequently affected than females.
🦠 Aetiology
- Caused by Rickettsia rickettsii.
- Spread via tick bites.
- USA: Dermacentor variabilis (dog tick), Dermacentor andersoni (wood tick).
- Brazil: Amblyomma cajennense.
- ❗ Not confined to the Rocky Mountain region → must be considered in wider geography.
🩺 Clinical Features (Incubation ~7 days)
- Prodrome: Malaise, anorexia, fever, chills.
- Systemic: Severe headache, rigors, myalgia.
- Rash:
- Starts as blanching macules (measles-like) → wrists, ankles, forearms.
- Becomes petechial/hemorrhagic (usually delayed 2–5 days).
- Spreads centrally → trunk, palms, soles (teaching pearl!).
- Other: Respiratory problems (e.g. cough, pulmonary edema in severe disease).
🧪 Investigations
- FBC: Thrombocytopenia, anaemia.
- Inflammatory markers: ↑ CRP, markedly ↑ LDH.
- Serology: Useful but delayed → treatment must not wait.
- CXR: May show diffuse alveolar infiltrates (severe cases).
💊 Management
- Supportive: ABC approach, O₂, fluids, monitor for organ dysfunction.
- Empirical antibiotics (do not delay):
- First-line: Doxycycline (safe in children if life-threatening infection).
- If contraindicated: Chloramphenicol.
- Therapy is guided by clinical suspicion — waiting for serology can be fatal.
💡 Teaching Pearls
- Rash starting on wrists/ankles → spreads centripetally → classic OSCE/MCQ clue.
- Delay in rash onset (2–5 days) can mislead diagnosis — maintain suspicion if fever + headache + outdoor history.
- Unlike meningococcal sepsis, patients usually remain alert until late stages.
- Treatment should never be delayed for test confirmation.
📚 References
