Leptospirosis

acute zoonotic bacterial infection caused by pathogenic spirochetes of the genus Leptospira.

Aetiology

Causative Agent

  • Genus: Leptospira
  • Species: Leptospira interrogans (most common pathogenic species)
  • Morphology:
    • Thin, tightly coiled spirochete
    • Aerobic
    • Motile (hooked ends)
      • notion image

Reservoir Hosts

  • Rodents (especially rats) – most important
  • Dogs
  • Cattle
  • Pigs
  • Wild mammals
Animals often carry leptospires in renal tubules and shed them in urine chronically.

Mode of Transmission

Entry through:
  • Abraded skin
  • Mucous membranes (eyes, nose, mouth)
Exposure to contaminated:
  • Water
  • Soil
  • Food
No human-to-human transmission in most cases.

Pathophysiology

  1. Entry through skin/mucosa
  1. Hematogenous dissemination (leptospiremia)
  1. Endothelial damage → vasculitis
  1. Multiorgan involvement:
      • Liver
      • Kidneys
      • Lungs
      • CNS
Immune-mediated injury contributes in later phases.

Clinical presentation

Leptospirosis classically has a biphasic course:
Septicemic (Acute) Phase (First 5–7 days)
  • Sudden onset of:
    • High fever
    • Chills
    • Severe headache
    • Myalgia (especially gastrocnemius and lumbar muscles)
  • Conjunctival suffusion (characteristic)
  • Nausea, vomiting
Immune Phase
  • Occurs after brief improvement
  • Antibody formation
  • Organ involvement becomes evident

Clinical Forms

Anicteric Leptospirosis (Mild Form)
  • Most common
  • Flu-like illness
  • Self-limited
Icteric Leptospirosis (Weil’s Disease)
Severe form, characterized by:
  • Jaundice
  • Acute kidney injury
  • Hemorrhage
  • Hypotension
  • High mortality
Severe Complications
  • Acute renal failure
  • Hepatic dysfunction
  • Pulmonary hemorrhage syndrome
  • Aseptic meningitis
  • Myocarditis

Investigations

Laboratory Findings

  • Leukocytosis
  • Thrombocytopenia
  • Elevated liver enzymes (bilirubin disproportionately high)
  • Elevated creatinine and urea
  • Elevated CK

Specific Diagnostic Tests

Serology
  • Microscopic Agglutination Test (MAT) – gold standard
  • ELISA (IgM)
Molecular Tests
  • PCR (early phase)
Culture
  • Blood & CSF (early phase, within 10 days)
  • Urine (late phase, after 7 days of onset)
  • Slow-growing and rarely used clinically

Management

Mild Disease

  • Doxycycline 100mg BID PO for 7 days → not safe for pregnancy or children
  • Alternatives:
    • Amoxicillin 500mg QID PO for 7 days
    • Azithromycin 500mg QID PO for 7 days

Severe Disease

  • IV Penicillin G 1.5 MU every 6 hours for 7 days
  • Ceftriaxone 1g/24hr or cefotaxime 1g/6hr for 7 days (alternatives)
  • Supportive care:
    • Fluid and electrolyte management
    • Dialysis for renal failure
    • Ventilatory support if pulmonary hemorrhage