Infectious diseases in Southeast Asia and the tropics I: leptospirosis, malaria utility and limitation of antigen-antibody detection system

Abstract

A rapid and reliable diagnostic test is of greater requirement for early detection and management of patient. Conventional tests are less sensitive to detect infecting leptospires and a low antibody level during acute phase, lead to un-recognition and disease severity. Previous whole clinical isolate, Leptospira-based IgM ELISA was suggestive for leptospirosis diagnosis with higher sensitivity (62%) accessed during the first week of illness compared to other whole-Leptospira based assays (35–49%) and increased to 91.7% sensitivity during the second week of illness. However, a half of patients remain reactive up to 5 years after illness and may reduce discriminating capacity between acute and convalescent leptospirosis. For possible improvement, our established IgM-based immunochromatography (LEPkit) assay has utilized lipopolysaccharide (LPS) as test antigen and estimated 2.9–3.5 times sensitive to MAT (≥1:400) and culture results. Significantly, LEPkit assessed with 98.6% sensitivity and 93.8% specificity. On further analysis of point-of-care implementation, 135 achieved sera of leptospirosis patients having mean 3 days fever onset and at recovery (≥3–180 days after illness) showed 99.3% positivity and critically enhanced detection for 65% of undetermined samples (MAT≤1:400). This supports future use of the LEPkit targeting anti-LPS IgM antibody combined with clinical examination for diagnosis of acute leptospirosis.