Leptospira

Leptospira are Gram-negative spirochetes that cause zoonotic disease worldwide with at least 20 different species in the genus. Leptospira interrogans is most commonly associated with human leptospirosis. 

Leptospirosis is endemic in Southeast Asia, Central America, and the Caribbean. In the United States, leptospirosis is most commonly diagnosed among travelers who have returned from these tropical or semitropical regions. Leptospirosis also affects residents of Hawaii. Multiple reported outbreaks have been associated with adventure races and ecotourism. Cities with large populations of rat-infested homes are also at increased risk of leptospirosis infection. 

Rodents and small mammals are the most important reservoirs of leptospirosis. The primary route of transmission is contact with water that has been contaminated with the urine of infected animals. Leptospira enters the body through direct cutaneous or mucosal contact or by aerosolization. Water exposure is a key risk, both domestically and abroad.

Symptoms develop after an incubation period of 5 to 14 days. Leptospirosis causes a broad range of symptoms from mild self-limited disease to Weil’s syndrome, which is characterized by renal failure, jaundice, and hemorrhage. Weil’s syndrome has a 5 to 15% mortality rate. Common symptoms are conjunctival suffusion, muscle tenderness, and aseptic meningitis. Cardinal features of severe leptospirosis include nonoliguric renal failure and significant hyperbilirubinemia. Bilirubin level may be 30 to 40 mg per deciliter. Serious infections may be complicated by diffuse alveolar hemorrhage and acute respiratory distress syndrome. 

Confirmation of the diagnosis can be difficult. Leptospira is a fastidious organism that requires specialized culture media and requires a prolonged incubation time up to 6 weeks. Polymerase-chain-reaction–based nucleic acid amplification testing of blood, urine, or cerebrospinal fluid is much more sensitive than culturing and can be performed early in the course of the disease, but is not widely available. Given these limitations, serologic testing for Leptospira IgM antibodies remains the best test for rapid diagnosis. IgM antibodies become detectable by the sixth day of symptom onset and remain detectable up to 3 months. 

The Leptospirosis IgM antibody test is an enzyme-linked immunoassay. The reference value for Leptospira IgM is negative. Specimen requirement is a red top tube of blood. 

Reference

Mixter, S and Others. Spiraling out of control: what are risk factors for leptospirosis and how is it transmitted? N Engl J Med 2017;376:2183-2188.