Infection is via ingestion of food contaminated by urine from infected vectors or through skin lesions or mucous membranes exposed to contaminated water or soil. The degree of illness in leptospirosis varies from asymptomatic to a severe or fatal illness.
Anicteric leptospirosis is the more common and milder form, and often is biphasic.
If the second phase occurs, symptoms tend to both milder and more varied than in the first phase - except that aseptic meningitis may occur. Early recognition of decreased renal function is critical to patient survival. Decreased hepatic function and jaundice are common, but hepatic failure is seldom a cause of death - though the degree of jaundice correlates with risk of death. Aseptic meningitis, myocarditis, pulmonary complications, and renal failure with hepatic involvement occur primarily in severe and untreated disease. Pulmonary complications tends to occur earlier in the illness than other complications.