Leptospira Species - Leptospirosis

Diagnosis

Indications for Testing

• Fever >3 days with severe myalgia in patients with
  • Contact with infected animals or
  • Contact with water or soil contaminated with urine of infected animal

Laboratory Testing

• Darkfield microscopic exam of peripheral blood smear during first few days may demonstrate leptospires
  • Low sensitivity and specificity
  • May also use urine or cerebrospinal fluid (CSF) specimens
  • 1x10⁴ leptospires/mL necessary to observe 1 cell/field
• Antibody testing
  • IgM testing in acute phase
    • Low sensitivity in first week of illness
    • Methods include microscopic agglutination (MAT), enzyme-linked immunosorbent assay (ELISA), indirect hemagglutination antibody (IHA) – MAT has highest specificity
    • Titer >1:200 and compatible symptoms are suggestive of human infection
  • IgG testing in convalescent phase
    • ≥2 weeks after initial testing
    • 4-fold increase in titer confirms human infection
• Molecular testing – polymerase chain reaction (PCR)
  • Sensitive and rapid but not widely available
  • First 7 days of illness only
• Culture – gold standard, but not often used in diagnosis
  • 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
  • Urine preferable after 10 days

Differential Diagnosis

• Dengue fever virus
• Infectious diarrhea
• Salmonella typhi
• Hantavirus
• Plasmodium species
• Rickettsial disease (eg, scrub typhus)
• Ehrlichiosis
• Influenza

Background

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) – primary natural reservoir
    • Domestic animals (dogs, cattle, swine, horses) – major source 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 infected animals
    • 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

• Occupational exposure – farmers, ranchers, trappers, lab workers
• Recreational exposure – canoeing, kayaking, rafting, swimming, wading
• Household exposure – livestock, pets, rodents
• Other – flooding, walking barefoot through surface water

Clinical Presentation

• Variable clinical course
  • Subclinical – only detectable by serologic means (~90% of infections)
  • Self-limiting influenza-like illness
    • Fever, chills, rigor, myalgia, abdominal pain, vomiting, and diarrhea
    • Coincides with leptospiremia following a 2-day to 4-week (CDC, 2017) incubation period
  • Severe, life-threatening multiorgan failure – often follows influenza-like stage and transient reduction in severity of symptoms (immune phase)
• Leptospiral meningitis – accounts for 5-13% of sporadic lymphocytic meningitis cases
• Renal involvement common
  • 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 case