• Clinical science

Leptospirosis (Mud fever…)


Leptospirosis is a zoonotic disease caused by gram-negative Leptospira bacteria. Direct transmission to humans occurs when broken skin and mucous membranes come into contact with the urine of infected animals such as rodents. The early phase of the disease is mild and characterized by non-specific symptoms (e.g., fever, headache, and myalgia). In most cases, symptoms resolve spontaneously after a week. However, in 10% of cases, the disease progresses rapidly to a severe form (icterohemorrhagic leptospirosis, or Weil disease), which typically presents with a triad of jaundice, bleeding manifestations, and acute kidney injury. Diagnosis is based on patient history, clinical findings, and laboratory tests. Treatment consists of antibiotics and supportive care.


  • Leptospirosis is the most common zoonotic disease worldwide and is most common in the tropics
  • Low incidence in the US (100–200 cases per year): Half of these are cases reported in Hawaii.

Epidemiological data refers to the US, unless otherwise specified.


  • Pathogen: Leptospira; (especially L. interrogans; ) is a genus of gram-negative spirochete bacteria.
  • Route of infection
    • Contact with soil, food, and/or water contaminated with the urine of infected animals; entry of Leptospira through skin/mucous membrane lesions
    • Occupational groups at risk: farmers, sewer workers; water sports enthusiasts may also be affected.

Clinical features

The incubation time is 2–30 days. The disease has a mild form, which is characterized by non-specific symptoms that generally resolve spontaneously after a week. In 10% of cases, the disease progresses rapidly to a severe form (icterohemorrhagic leptospirosis, or Weil disease).

Mild (anicteric) leptospirosis

Most cases of mild leptospirosis resolve spontaneously. Only 10% of patients with mild leptospirosis progress to the severe form (Weil's disease). [1]

Severe leptospirosis (Weil disease, icterohemorrhagic leptospirosis)

Severe leptospirosis is associated with a high mortality rate!



  • Dark-field microscopy of urine or blood samples
  • Serological tests
  • PCR: detect leptospiral DNA in bodily fluids
  • Culture



If leptospirosis is suspected based on a patient's clinical features and history, empiric therapy should be started right away! [4]