Makindo Medical Notes

📖 About

• Scrub Typhus → infectious disease caused by Orientia tsutsugamushi, transmitted to humans by larval mites (chiggers).
• Belongs to the Rickettsiaceae family (related to rickettsiae but distinct).

🔬 Characteristics

• Gram-negative, though poorly visualised on Gram stain due to tiny size & intracellular nature.
• Obligate intracellular parasite → requires host cell ATP & nutrients.
• Grows only in tissue culture → reflects strict intracellular dependence.

🏠 Source

• Reservoir: Wild rodents (e.g. rats) & small mammals 🐀.
• Transmission: Bite of larval mites (chiggers) found in scrubland, forests & grassy areas of rural Asia-Pacific.

🌍 Epidemiology

• Endemic in the “tsutsugamushi triangle”: SE Asia, China, Japan, Northern Australia.
• Peak during wet seasons when mite populations rise.

⚠️ Pathogenicity & Clinical Presentation

• Incubation: 6–21 days post-bite.
• 🧑‍⚕️ Symptoms: fever, chills, headache, myalgia.
• 🕳️ Eschar: necrotic scab at bite site, surrounded by erythema → classic diagnostic clue.
• Other: lymphadenopathy, GI upset, cough.
• Severe: pneumonitis, myocarditis, meningoencephalitis, multi-organ failure (if untreated).

🧪 Virulence Factors

• Invades vascular endothelial cells → widespread vasculitis.
• Triggers cytokine release → immune-mediated tissue damage.

🔎 Investigations

• 🧪 Weil–Felix test: historic, poor sensitivity/specificity.
• 🧪 Immunofluorescence: rash/biopsy specimens.
• 🧪 Serology: IgM/IgG against Orientia tsutsugamushi (mainstay).
• 🧪 PCR: sensitive, detects early infection in blood/tissue.

💊 Management

• First-line: Doxycycline → shortens illness dramatically (continue for 5–7 days or until 3 days post-fever).
• Alternative: Azithromycin (safe in pregnancy/children).
• Supportive: fluids, oxygen, monitor for complications (respiratory/cardiac/CNS).
• Mortality: <5% with treatment; up to 30% if untreated.

📊 Prognosis

• Excellent recovery with early antibiotics (symptoms often resolve within 48 h).
• Severe/untreated → multi-organ failure & death.

🛡️ Prevention

• Avoid mite-infested scrubland/grassland in endemic areas.
• Use insect repellent (DEET) + protective clothing.
• Community: rodent & mite control; improved sanitation.

⚠️ Exam pearl: Scrub typhus = fever + eschar + lymphadenopathy in Asia-Pacific traveller → treat with doxycycline. Differentiate from murine typhus (R. typhi, flea-borne) & epidemic typhus (R. prowazekii, louse-borne).