What are the key points to consider for scrub typhus, including symptoms, diagnosis, and treatment?

Key Points of Scrub Typhus

Scrub typhus is a potentially serious rickettsial disease caused by Orientia tsutsugamushi, transmitted by the bite of larval trombiculid mites (chiggers), requiring prompt diagnosis and treatment with doxycycline as the first-line therapy. 1

Etiology and Transmission

• Caused by the bacterium Orientia tsutsugamushi 2
• Transmitted through bites of infected chiggers (larval stage of trombiculid mites) 2, 3
• Endemic in the "tsutsugamushi triangle" of Asia-Pacific region 3
• Previously considered rural, now increasingly reported in urban areas 4

Clinical Presentation

• Incubation period: 6-21 days after mite bite 2
• Initial symptoms:
  • Sudden onset of fever (present in nearly all cases) 1
  • Severe headache
  • General malaise and myalgias
  • Chills
  • Gastrointestinal symptoms (nausea, vomiting, abdominal pain) 1, 2
  • Cough
• Characteristic eschar:
  • Primary papular lesion that crusts to form a flat black eschar 2
  • Present in only about 33% of patients 4
• Rash:
  • Typically appears 2-4 days after fever onset 1
  • Maculopapular rash that may become petechial
  • Classically involves palms and soles
  • Less than 50% of patients present with rash in first 3 days
  • Up to 20% never develop a rash 1

Complications

• Disseminated vasculitis and perivascular inflammation 2
• Significant vascular leakage and end-organ injury if untreated 2
• Neurological manifestations (18% of patients) 4
• Acute respiratory distress syndrome (9% of patients) 4
• Multi-organ dysfunction 4
• In pregnancy: increased fetal loss, preterm delivery, small for gestational age infants 2

Laboratory Findings

• Leukopenia
• Thrombocytopenia
• Elevated liver enzymes (hepatic dysfunction) 1, 4
• Hyponatremia 1, 4
• Proteinuria
• Reticulonodular infiltrates on chest imaging 2

Diagnosis

• Clinical suspicion is crucial in endemic areas
• Diagnostic tests:
  • Serology: Most accessible method 1
    • IgM ELISA (enzyme-linked immunosorbent assay)
    • Indirect immunofluorescence assay (IFA) - reference standard
  • PCR: Specific for detecting rickettsial DNA, especially useful in early disease (<7 days) 1, 3
  • Immunohistochemistry: For detecting rickettsiae in skin biopsies 1
  • Weil-Felix test: No longer recommended due to poor sensitivity and specificity 3
• Differential diagnosis includes other causes of acute febrile illness:
  • Other rickettsial diseases
  • Malaria
  • Dengue
  • Leptospirosis
  • Typhoid fever
  • Viral infections
  • Acute abdomen (can mimic acute acalculous cholecystitis) 5

Treatment

• First-line therapy: Doxycycline 6, 1, 7
  • Adults: 100 mg twice daily (orally or IV)
  • Children <45 kg: 2.2 mg/kg twice daily (maximum 100 mg per dose)
  • Duration: Minimum 5-7 days or until 48-72 hours after fever resolution
• Alternative therapies:
  • Azithromycin (especially for pregnant women and children) 2, 4, 5
  • Chloramphenicol
  • Tetracycline
  • Rifampicin (second-line option after excluding tuberculosis) 7
• Treatment principles:
  • Early empiric treatment is essential
  • Do not delay treatment pending laboratory confirmation 1
  • Treatment should be initiated within the first 5 days of illness to reduce mortality 1

Prevention

• Avoid tick-infested habitats 6, 1
• Use protective clothing (long sleeves, long pants) 6, 1
• Apply DEET-containing repellents 6, 1
• Perform regular tick checks on persons and pets 6
• Remove ticks immediately using tweezers or forceps 6
  • Grasp tick close to skin and pull with steady pressure
  • Do not use gasoline, kerosene, petroleum jelly, or lit matches to remove ticks
  • Clean bite area with soap, alcohol, or iodine scrub after removal 6
• Permethrin-treated clothing can reduce tick bites 6
• Protect pets with regular ectoparasite control products 6

Prognosis

• Good prognosis with early diagnosis and appropriate treatment
• Mortality rate increases with delayed treatment
• Approximately 4% mortality due to multiorgan dysfunction in untreated cases 4

Special Populations

• Pregnant women:
  • Azithromycin is the preferred treatment 2, 4
  • Can be successfully treated without relapse and with favorable pregnancy outcomes 2
• Children:
  • Similar presentation but gastrointestinal symptoms may be more prominent 1
  • Doxycycline is recommended for all ages, including children 1
  • Azithromycin is an effective alternative 5