Scrub Typhus: Symptoms, Transmission, Diagnosis, and Prevention in Endemic Regions

Overview

Scrub typhus is a potentially life-threatening rickettsial infection caused by Orientia tsutsugamushi, transmitted by the bite of infected larval trombiculid mites (chiggers). Endemic in the "tsutsugamushi triangle": Southeast Asia, Japan, northern Australia, India, Pakistan, China, Russia, Korea.

Transmission Cycle

• Natural reservoir: Wild rodents (rats, mice).
• Vector: Leptotrombidium mite larvae (chiggers) — only larval stage feeds on vertebrates.
• Human infection: Accidental; chiggers bite in scrub vegetation, forest edges, rice paddies, gardens.
• No person-to-person transmission.

Clinical Presentation (Incubation 6–21 days, mean 10–12)

• Eschar: Painless, necrotic ulcer with black crust at bite site (pathognomonic but absent in 20–50%).
• Fever: High, often >39°C (102°F).
• Headache, myalgia, malaise.
• Rash: Maculopapular, starts trunk → extremities (40–50%); may be absent.
• Lymphadenopathy: Regional or generalized.
• GI: Nausea, vomiting, abdominal pain, diarrhea.
• Respiratory: Cough, pneumonitis.
• Neurologic: Meningoencephalitis (confusion, seizures, cranial nerve palsies).

Severe Complications (if untreated)

• Interstitial pneumonia, ARDS.
• Acute kidney injury, hepatic dysfunction.
• Myocarditis, circulatory collapse.
• Cerebral edema, coma.
• Mortality: <1% with treatment; up to 30–70% untreated.

Diagnosis

• Clinical + epidemiologic suspicion.
• Serology: Indirect immunofluorescence assay (IFA) – gold standard; ≥4-fold rise in paired titers (acute/convalescent 2 wks apart). Single titer ≥1:128 suggestive.
• PCR: Blood, eschar swab, CSF — rapid, sensitive early.
• Immunohistochemistry: Eschar biopsy.

Treatment

• Doxycycline 100 mg PO/IV BID × 7–14 days — first-line for all ages (including children; short course safe).
• Azithromycin 500 mg daily × 3–5 days — alternative (pregnancy, doxycycline intolerance).
• Chloramphenicol — historical alternative.
• Defervescence typically within 48 hrs; treat full course to prevent relapse.

Prevention

• Personal protection: Permethrin-treated clothing (0.5%), DEET (≥20%), picaridin, IR3535 on exposed skin.
• Avoidance: Stay on cleared paths; avoid sitting on grass/logs; don't pitch tents in scrub.
• Post-exposure: Shower, scrub skin; inspect for attached chiggers (remove with tweezers).
• Rodent control: Around dwellings in endemic areas.
• No vaccine available.

Scrub typhus is eminently treatable if recognized. Consider it in any febrile traveler or resident from endemic areas with eschar, rash, or multi-system involvement. Early doxycycline saves lives.