Leptospira Species

Diagnosis

Indications for Testing

• Fever >3 days with severe myalgia, usually after contact with animals or contaminated water/soil, or in person with recent travel history

Laboratory Testing

• Darkfield microscopic exam of peripheral blood smear during first few days may demonstrate leptospires but with low sensitivity (~40%) and specificity (~60%)
  • May also use urine or CSF specimens
  • 1x10⁴ leptospires/mL necessary to observe 1 cell/field
• Antibody testing
  • Leptospira antibody testing for IgM in acute phase
    • Low sensitivity in first week of illness
    • Methods include microscopic agglutination (MAT), ELISA, IHA
      • MAT has highest specificity
    • Titer >1:200 and compatible symptoms are suggestive of human infection
  • Convalescent IgG – ≥2 weeks after IgM
    • Fourfold increase in titer when run in parallel with acute sample confirms human case
• Molecular testing – PCR
  • Sensitive and rapid but not widely available
  • Useful only in first 7 days of illness
• Culture – organism is fastidious and slow growing, occasionally requiring weeks to grow
  • May be isolated from blood, CSF and peritoneal dialysate within first 10 days of illness; thereafter, urine preferable
  • Gold standard, but not often used in diagnosis

Differential Diagnosis

• Dengue fever virus
• Infectious diarrhea (bacterial, viral, parasitic)
• Hantavirus
• Plasmodium species
• Rickettsial disease

Clinical Background

Human leptospirosis, an acute febrile illness that presents with many manifestations, is found worldwide.

Epidemiology

• Incidence – ~100-200 cases annually in U.S. (approximately half in Hawaii)
• Transmission
  • Zoonotic disease caused by the spirochete Leptospira interrogans
    • Wild mammals (eg, rodents) serve as a primary natural reservoir, but domestic animals (dogs, cattle, swine, horses) serve as major sources of human infection
  • ~50% of infections occur from July to October
  • Transmission to humans – most often indirect by human contact with soil, food or water contaminated by urine from an infected animal
    • Common sources include contaminated well water, spring water, and food preparation surfaces
    • Transmission also occurs by swimming, rafting, or kayaking in water sources where livestock have been pastured
    • Certain occupational groups (agriculture, sewer, construction, veterinarians, and livestock/farm workers) are at higher risk for leptospirosis

Organism

• Spirochete
  • Member of the family Spirochaetaceae – also includes Treponema and Borrelia

Risk Factors

• Contact with contaminated water (kayaking and rafting)
• Poor sanitation
• Livestock/farm work
• Meat processing work

Clinical Presentation

• Infection has variable clinical course; usually presents as one of the following
  • Subclinical – only detectable by serologic means (~90% of infections)
  • Influenza-like febrile illness with fever, chills, rigor, myalgia, abdominal pain, vomiting and diarrhea; coincides with leptospiremia following an 8-12 day incubation period (septicemic phase)
  • Severe, life-threatening multi-organ failure; often follows influenza-like stage and transient reduction in severity of symptoms (immune phase)
• Jaundice occurs infrequently in the U.S.
• Leptospiral meningitis – occurs more frequently, accounting for 5-13% of sporadic lymphocytic meningitis cases
• Kidneys are invariably involved – urine analysis demonstrates mild proteinuria, leukocytes, casts and variable hematuria
  • Jaundice with nephritis – Weil disease
    • May also have pulmonary dysfunction, hemorrhagic disease
    • Mortality 5-40% in severe cases

Treatment

• Treat with antimicrobials
• Jarisch-Herxheimer reaction (fever, myalgias, headache, tachycardia, hypotension) may occur with initiation of treatment for all spirochetal diseases

Indications for Laboratory Testing

• Tests generally appear in the order most useful for common clinical situations
• Click on number for test-specific information in the ARUP Laboratory Test Directory