Early Diagnosis of Leptospirosis by IgM Immunoblot Testing

Department of Pathobiology, Faculty of Science, Bangkok 10400, Thailand; Department of Microbiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand; Department of Disease Control, Ministry of Public Health, Thailand; Veterans Affairs Greater Los Angeles Healthcare System, Los Angeles, CA 90073; Department of Medicine, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095

^* To whom correspondence should be addressed. Email: scgdu{at}mahidol.ac.th.

	Abstract

There is an urgent need for development of serodiagnostic approaches with improved sensitivity in patients with acute leptospirosis. Immunoblots were performed on 188 sera collected from 74 laboratory-confirmed cases of early leptospiral infection to detect IgM antibodies to antigens pooled from ten leptospiral strains prevalent in Thailand. Sera from patients with other febrile diseases served as controls. IgM reactivity was observed to seven distinct antigens with apparent molecular weights of 14-18, 19-23, 24-30, 32, 35/36, 38, and 41/42 kDa. The low molecular weight 14-18 kDa band was the most frequently detected antigen, being recognized in sera from 82.4% of patients during the first 3 days after onset of symptoms. We evaluated the accuracy of the IgM immunoblot (IgM-IB) test using reactivity to the 14-18 kDa band and/or at least two bands among the 19-23, 24-30, 32, 35/36, 38 and 41/42 kDa antigens as diagnostic criteria. The sensitivities of the IgM-IB and MAT tests were 88.2% and 2.0%, respectively, in sera from patients 1-3 days after onset of symptoms. In contrast, the IgM-IB test was positive in only 2/48 (4.2%) sera from patients with other febrile illnesses. The high sensitivity and specificity of the IgM-IB test in acute leptospirosis would provide greatly improved diagnostic accuracy for identification of patients who would benefit from early antibiotic intervention. In addition, the antigens identified by the IgM-IB test may serve as components of a rapid and accurate, point-of-care diagnostic test for early leptospirosis.