What is the difference between leptospirosis and scrub typhus?

Differences Between Leptospirosis and Scrub Typhus

Leptospirosis and scrub typhus are distinct zoonotic diseases with different causative organisms, transmission methods, clinical presentations, and diagnostic approaches, though both respond to doxycycline as first-line treatment.

Causative Organisms and Transmission

Leptospirosis

• Causative agent: Bacteria of genus Leptospira 1
• Transmission: Contact with urine of infected animals or contaminated water/soil 1
• Vector: No arthropod vector; direct contact with contaminated sources
• Geographic distribution: Worldwide, higher incidence in tropical and subtropical regions 1

Scrub Typhus

• Causative agent: Orientia tsutsugamushi (previously classified as Rickettsia) 2
• Transmission: Bites of infected larval mites (chiggers) 2
• Vector: Trombiculid mite larvae
• Geographic distribution: Rural South Asia (especially Laos), Southeast Asia, Western Pacific 2

Clinical Manifestations

Leptospirosis

• Incubation period: 5-14 days
• Key symptoms:
  • Fever, headache, chills, myalgia 2
  • Conjunctival suffusion (distinctive feature) 1
  • Biphasic illness pattern common 2
  • Hepatic involvement with jaundice and hepatomegaly/splenomegaly 1
  • Severe form (Weil's syndrome): jaundice, renal failure, hemorrhage 1
• Mortality rate: 5-15% in severe cases 1

Scrub Typhus

• Incubation period: 5-7 days (up to 10 days) 2
• Key symptoms:
  • Fever, headache, myalgia 2
  • Characteristic eschar at bite site (pathognomonic but present in <50% of cases) 2
  • Rash and regional lymphadenitis 2
  • Less commonly: pneumonitis, meningoencephalitis, acute respiratory distress
• Mortality rate: Up to 4% if untreated 2

Diagnostic Approaches

Leptospirosis

• Laboratory confirmation:
  • Isolation of Leptospira from clinical specimen (blood, CSF) 2
  • Fourfold or greater increase in agglutination titer between acute and convalescent sera 2
  • Demonstration of Leptospira by immunofluorescence 2
  • PCR of blood (early disease) 1
• Case definition:
  • Probable: Clinically compatible with supportive serology (titer ≥200) 2
  • Confirmed: Clinically compatible and laboratory confirmed 2

Scrub Typhus

• Laboratory confirmation:
  • Serological tests (IgM ELISA, immunochromatography) 3
  • PCR from blood or eschar sample 1
  • Immunofluorescence assays 1
  • 4-fold rise in titer between acute and convalescent sera 1
• Diagnostic challenges:
  • Traditional Weil-Felix test has poor sensitivity and specificity 3
  • Diagnosis often delayed due to non-specific symptoms 3

Treatment

Both Diseases

• First-line treatment: Doxycycline 100 mg orally twice daily 1
  • For leptospirosis: 7-day course
  • For scrub typhus: Minimum 5-day course
• Alternative treatment:
  • Azithromycin (better tolerated but more expensive) 4
  • For leptospirosis: Penicillin G, ceftriaxone, or ampicillin as alternatives 1
• Special populations:
  • Pregnant patients should avoid doxycycline; use penicillin G or erythromycin 1

Clinical Pearls and Pitfalls

• Coinfection: Leptospirosis and scrub typhus coinfection can occur, especially in endemic areas, complicating diagnosis and potentially worsening outcomes 5, 6
• Diagnostic pitfalls:
  • Relying solely on Weil-Felix test for scrub typhus diagnosis (poor sensitivity/specificity) 3
  • Failure to consider these diseases in patients with undifferentiated fever from endemic regions 2
• Treatment timing: Treatment should be initiated as soon as either disease is suspected, as delayed treatment increases complication risk 1
• Rare complications: Both can cause acute acalculous cholecystitis and pancreatitis in severe cases 7

Prevention

• Leptospirosis prevention:

  • Avoid swimming in potentially contaminated waters
  • Control rodent populations
  • Improve sanitation
  • Use personal protective equipment in high-risk occupations 1

• Scrub typhus prevention:

  • Limit exposure to mites in endemic areas
  • Use insect repellent
  • Thorough inspection of body and clothing after being in endemic areas 1