Pathogen-specific leptospiral proteins in urine of patients with febrile illness aids in differential diagnosis of leptospirosis from dengue.

Leptospirosis and dengue are two commonly seen infectious diseases of the tropics. Differential diagnosis of leptospirosis from dengue fever is often difficult due to overlapping clinical symptoms and lack of economically viable and easy-to-perform laboratory tests. The gold standard for diagnosis is the microscopic agglutination test (MAT). In this study, the diagnostic potential of screening for pathogen-specific leptospiral antigens in urine samples is presented as a non-invasive method of disease diagnosis. In a study group of 40 patients, the serum was tested for anti-leptospiral antibodies by MAT and enzyme-linked immunosorbent assay (ELISA). Urine of these patients was screened for leptospiral antigens by ELISA using specific antibodies against LipL32, LipL41, Fla1, HbpA and sphingomyelinase. Group I patients (n = 23) were classified as leptospirosis-positive based on MAT and high titres of circulating IgM-specific anti-leptospiral antibodies. All of these patients excreted all five leptospiral antigens in the urine. The 17 MAT-negative cases included six patients with pyrexia of unknown origin (PUO; Group II) and 11 confirmed dengue patients (Group III). The latter tested negative for both serum anti-leptospiral antibodies and urinary leptospiral antigens. A salient outcome of this study was highlighting the usefulness of screening for urinary leptospiral antigens in disease diagnosis, as their presence confirmed leptospiral aetiology in two PUO patients. Immunoblots of urinary antigens identified well-defined bands corresponding to LipL32, HbpA and sphingomyelinase; the significance of the 42- and 58-kDa sphingomyelinase bands is discussed.