B-Cell-Specific Peptides of Leptospira interrogans LigA for Diagnosis of Patients with Acute Leptospirosis

Leptospirosis is a reemerging infectious disease that is underdiagnosed and under-recognized due to low-sensitivity and cumbersome serological tests. Rapid reliable alternative tests are needed for early diagnosis of the disease. Considering the importance of the pathogenesis-associated leptospiral LigA protein expressed in vivo, we have evaluated its application in the diagnosis of the acute form of leptospirosis. The C-terminal coding sequence of ligA (ligA-C) was cloned into pET15b and expressed in Escherichia coli. Furthermore, the B-cell-specific epitopes were predicted and were synthesized as peptides for evaluation along with recombinant LigA-C. Epitope 1 (VVIENTPGK), with a VaxiJen score of 1.3782, and epitope 2 (TALSVGSSK), with a score of 1.2767, were utilized. A total of 140 serum samples collected from leptospirosis cases during the acute stage of the disease and 138 serum samples collected from normal healthy controls were utilized for evaluation. The sensitivity, specificity, positive predictive value, and negative predictive value were calculated for the recombinant LigA-C-specific IgM enzyme-linked immunosorbent assay (ELISA) and were found to be 92.1%, 97.7%, 92.8%, and 97.5%, respectively. Epitopes 1 and 2 used in the study showed 5.1 to 5.8% increased sensitivity over recombinant LigA-C in single and combination assays for IgM antibody detection. These findings suggest that these peptides may be potential candidates for the early diagnosis of leptospirosis.