Leptospira interrogans !
- Bacterium
- Does not Gram-stain
- Exam priority: high
A spirochete from the urine of rats and other animals; caught from water or mud, especially after floods, it can harm kidneys and liver.
Updated 2026-11-01
At a glance
- Gram
- Does not Gram-stain
- Shape
- Thin spirochete with hooked ends
- Oxygen
- Aerobe
- Family
- Leptospiraceae
- Stain
- Stains poorly with Gram; dark-field or silver stain
Morphology
- Tightly coiled spiral with one or both ends shaped like a question mark
- Highly motile thanks to endoflagella
- Grows slowly in special media (EMJH)
Transmission
- Contact of broken skin or mucosa with water, mud or soil contaminated by animal urine
- Direct contact with urine or tissues of infected animals (farm, veterinary, sewer work)
- Outbreaks after heavy rain and floods; almost never person-to-person
Reservoir: Rats and other rodents; Dogs, pigs, cattle and wild animals
Isolation precautions
What the care team adds to standard precautions.
- Standard
Virulence factors
- Penetrates the skin and spreads rapidly through the blood (leptospiraemia)
- Capillary endothelial damage: bleeding, vasculitis and kidney and liver injury
- Colonises renal tubules and is shed in urine
Diseases it causes
- Leptospirosis: from mild febrile illness to severe forms Leptospirosis →
- Acute kidney injury in Weil syndrome Acute kidney injury →
- Pulmonary haemorrhage syndrome and aseptic meningitis
Clinical picture
- Early phase: sudden fever, headache, severe calf myalgia and conjunctival suffusion
- Immune phase: fever may return with meningitis or uveitis
- Weil syndrome: jaundice, kidney failure and bleeding
- Mimics dengue, malaria and hepatitis in the tropics
Diagnosis
- Microscopic agglutination test (MAT): serological reference, with paired samples
- IgM ELISA from the first week
- PCR on blood in the first days; on urine later
- Lab clues: raised CK, low platelets, high creatinine and bilirubin
Treatment
Early antibiotics: doxycycline or amoxicillin for mild disease; intravenous penicillin or ceftriaxone for severe disease, with renal and respiratory support. A Jarisch-Herxheimer reaction may occur.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
Prevention
- Rodent control and waste management
- Waterproof boots, gloves and clothing when working in water or mud; cover wounds
- Doxycycline chemoprophylaxis for high-risk exposures, per health authorities
- Vaccination of dogs and livestock
Vaccine: There is no human vaccine in the PAI schedule; veterinary vaccines exist.
Test yourself
Think of the answer, then tap the question to see it.
What is the classic urban reservoir of Leptospira?
Rats, which shed the bacterium in urine for a long time.
Which triad defines Weil syndrome?
Jaundice, acute kidney injury and bleeding.
Which eye sign suggests leptospirosis in a febrile patient?
Conjunctival suffusion: red eyes without purulent discharge.
What is the reference serological test for leptospirosis?
The microscopic agglutination test (MAT), ideally with paired samples.
Related
Related conditions
← Back to the group: Spirochetes
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: About Leptospirosis | Leptospirosis | CDC (Centers for Disease Control and Prevention (CDC), 2024); Leptospirosis - PAHO/WHO | Pan American Health Organization (Pan American Health Organization (PAHO), 2024).
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Representative model, for educational purposes only.