What are the symptoms and treatment of scrub typhus?

Scrub Typhus: Clinical Presentation and Management

Primary Symptoms

Scrub typhus presents with sudden onset fever (6-10 days after mite bite), headache, myalgia, and malaise as the most consistent features, with the characteristic eschar at the bite site being pathognomonic when present. 1

Cardinal Clinical Features

• Fever: The most consistent symptom, typically beginning 6-10 days after the chigger bite (incubation range 6-21 days) 1, 2
• Headache: Frequently reported alongside fever 1, 2
• Myalgia: Muscle pain is a prominent early symptom 1, 2
• Malaise: Generalized weakness and discomfort 1, 2

Characteristic Physical Finding

• Eschar: A painless, necrotic lesion with a black crust surrounded by erythema at the site of mite feeding and inoculation 1
  • Appears as a primary papular lesion that later crusts to form a flat black eschar 2
  • Present in approximately 50% of proven cases 3
  • Commonly located in the axilla, groin, inguinal region, or other hidden areas 3, 4
  • Critical pitfall: The eschar may be easily overlooked during initial examination, particularly in concealed locations like the medial malleolus 4

Additional Common Symptoms

• Gastrointestinal symptoms: Nausea, vomiting, abdominal pain, and diarrhea 2, 5
• Respiratory symptoms: Cough and shortness of breath, especially in severe cases 5, 3
• Lymphadenopathy: Regional and generalized lymph node enlargement is common 6

Laboratory Findings

• Thrombocytopenia: Low platelet count 2, 3
• Leukopenia or leukocytosis: Variable white blood cell abnormalities 2, 3
• Elevated liver transaminases: Deranged hepatic function 2, 3
• Renal dysfunction: Elevated creatinine and proteinuria 2

Pathophysiology

The pathogen Orientia tsutsugamushi multiplies in endothelial cells, causing disseminated vasculitis and perivascular inflammation that results in significant vascular leakage and end-organ injury. 1, 2

• Focal or disseminated vasculitis from endothelial cell destruction and perivascular leukocyte infiltration 6
• Vascular leakage leads to complications including interstitial pneumonia, interstitial edema, and hemorrhage 6

Severe Manifestations and Complications

• Respiratory failure: Pneumonia, ARDS, and interstitial lung disease 5, 6, 3
• Circulatory shock: From severe vascular leakage 3
• Central nervous system involvement: Meningoencephalitis occurs in almost all patients to varying degrees 6, 3
• Multi-organ failure: Hepatic, renal, and hematological abnormalities 3
• Mortality: Up to 4% overall; as high as 24% in severe cases with multi-organ failure 1, 3

Treatment

Doxycycline is the drug of choice for scrub typhus in patients of all ages, including children under 8 years, and should be initiated immediately when scrub typhus is suspected—never delay treatment while awaiting laboratory confirmation. 1

Dosing Regimens

• Adults: Doxycycline 100 mg twice daily (oral or IV) for at least 3 days after fever subsides; minimum 5-7 days total 1
• Children <45 kg: Doxycycline 2.2 mg/kg body weight twice daily (oral or IV) 1
• Alternative agents: Azithromycin, chloramphenicol, tetracycline, ciprofloxacin, rifampicin, or roxithromycin 2
• Pregnancy: Azithromycin is preferred and has been used successfully without relapse and with favorable pregnancy outcomes 2

Treatment Response

• Expected response: Patients typically respond within 24-48 hours of appropriate antibiotic therapy 1
• Lack of response: Failure to improve within 24-48 hours should prompt consideration of alternative diagnoses 1

Critical Treatment Principles

• Historical dental staining concerns in children under 8 years should not prevent short-course doxycycline use 1
• Delay in treatment can lead to severe disease, long-term sequelae, or death 1
• Severe or complicated disease may require longer treatment courses beyond the standard 5-7 days 1

Diagnostic Challenges

• Nonspecific presentation: Symptoms resemble malaria, enteric fever, dengue, or leptospirosis 3
• Eschar may be absent or overlooked: Only present in ~50% of cases and easily missed in hidden locations 4, 3
• Serologic confirmation: IFA for IgM antibodies is the reference test; paired samples 2 weeks apart showing ≥4-fold rise confirms diagnosis 3
• Clinical diagnosis: Must be based on exposure history, clinical suspicion, and empiric treatment should not await serologic confirmation 1, 2