Leptospirosis is transported by the natural carriers such as feral, semi-domestic, farm and pet animals.^[1] Incubation period for leptospirosis varies between 3-20 days. The disease can cause wide range of symptoms from mild flu-like symptoms to severe disease with multi organ failure causing death. The first phase resolves and the patient is asymptomatic briefly before the second phase begins that is characterized by meningitis, liver damage (causing jaundice), and renal failure.^[2] The disease leptospirosis is poorly known and unaware of its natural history is mainly due to the wide range of non specific symptoms, subclinical nature of the disease in animals and non specific laboratory tests making the disease difficult to diagnose.^[3] Outcome of the patient depends upon the pathogenic serovar and immunological status.

Natural history of leptospirosis varies with each patient. It might be mild or asymptomatic, and go unrecognized or in some patients the illness may progress to kidney or liver failure, aseptic meningitis, life-threatening pulmonary hemorrhage and other syndromes.

• Also known as septicemic phase or leptospiremic phase.
• Begins abruptly
• Bacteria are present in the blood and CSF of the patient
• Characterized by wide spectrum of nonspecific signs and symptoms such as fever, chills, headache and conjunctival suffusion making it very difficult to diagnose.^[4]
• Associate with severe myalgia
• Other less common findings include: Photophobia, lymphadenopathy, abdominal pain, nausea, vomiting, a transient rash, sore throat, coughing or chest pain.
• Characterestic of this phase also includes: Mild form of leptospirosis in ~90% cases which lasts several days to a week, followed by a brief remission, during which the temperature drops and the symptoms disappear

• It is also known as leptospiruric phase.
• Circulating (IgM) antibodies are produced and leptospires are present in the urine.
• Characterestic findings that differentiate from other febrile illnesses are myalgia and conjunctival suffusion.^[5]
• Myalgia often involves in calf muscles, less commonly involves abdominal and para-spinal muscles.

• More common but serious illness is uncommon.
• Most of cases present either subclinical or of very mild severity.
• Few cases present with a febrile illness of sudden onset.
• May progress to aseptic meningitis in ≤25% of patients and more common in younger age group than the patients with icteric leptospirosis.
• Mortality is very less when compared to icteric leptospirosis.

• Rapidly progressive and severe form of leptospirosis(Weil’s disease)
• In the severe form of leptospirosis renal failure, hepatic failure and pulmonary hemorrhage can occur and associate with Icterohaemorrhagiae.^[6]
• Less common form of leptospirosis with incidence of 5%-10%
• Jaundice is not associate with hepatocellular injury, eventually LFT returns to normal after recovery.
• High mortality rate with a range of 5%-15%.

Sever form of leptospirosis with organ failure including liver and kidney involvement is known as Weil’s disease.

• Hepatic: Mild to severe form of jaundice developed within 4-7 days after the initial clinical presentation that can progress to hepatic failure or hepatic encephalopathy.
• Renal: Very common presentation involving kidneys is acute interstitial nephritis, with cola colored urine, oliguria or anuria.
• Pulmonary: Milder form of leptospirosis presents with cough, chest pain and blood tinged sputum, where as in severe form present with cough, hemoptysis, rapidly increasing breathlessness which may lead to respiratory failure and death. Hemorrhagic pneumonitis with interstitial and intra alveolar hemorrhage is the commonest cause of death in leptospirosis with case fatality rate of 0%-15%.
• Cardiovascular: Arrhythmias present with syncope and palpitations.
• Nervous system: Meningitis, encephalitis, focal defecits, spasticity, paralysis, peripheral neuropathies, nerve palsies and radiculopathies.

Complications of leptospirosis are associated with localization of pathogen (leptospires) within the tissues during the immune phase, eventually present during the second week of the illness.

Life threatening complications

• Acute kidney injury
• Disseminated intravascular coagulation
• Gastrointestinal hemorrhage
• Hemorrhagic shock

Common Complications

• Pulmonary: Pulmonary hemorrhage^[7]
• Hematological: Thrombocytopenic purpura, Disseminated intravascular coagulation.
• Neurological: Mild meningitis, encephalitis, radiculopathies, transverse myelitis, cranial nerve palsies and Guillain-Barre syndrome.^[4]
• Cardiac: Myocarditis, pericarditis^[8][9]
  • Conduction abnormalities: First degree atrioventricular block, widespread T-wave inversion^[9][10]
  • Rhythm abnormalities: Atrial fibrillation.
• Renal: Myositis → Rhabdomyolysis → Interstitial nephritis → Renal failure
• Pregnancy: Miscarriages, active leptospirosis in fetus^[11][12]

Less Common Complications

• Cerebrovascular accidents
• Rhabdomyolysis
• Acute acalculous cholecystitis
• Erythema nodosum
• Aortic stenosis
• Kawasaki syndrome
• Reactive arthritis
• Epididymitis
• Nerve palsy
• Male hypogonadism

The prognosis of leptospirosis depends upon several known and unknown factors, among which the type of pathogenic serovar and the host’s immune status are the important factors which determines the outcome.^[1] Most patients recover completely from leptospirosis but the duration of recovery varies from months to years with or without late sequelae. The late sequelae may include neuropsychiatric problems such as paresis, paralysis, mood swings and depression. The major causes of death include renal failure, cardiopulmonary failure and hemorrhage. Patients with risk factors such as old age and multiple underlying co-morbid conditions are often associated with more severe leptospirosis and increased mortality.