New paper enzyme-linked immunosorbent technique compared with microimmunofluorescence for detection of human serum antibodies to Rickettsia tsutsugamushi

A new paper enzyme-linked immunosorbent assay was developed for the screening and titration of human serum antibodies against the scrub typhus rickettsia, Rickettsia tsutsugamushi. The objetive was to provide a relatively simple method for antibody screening which required neither sophisticated laboratory equipment nor a high degree of technological skill. The technique develops an enzyme product from filter paper saturated with a 5-aminosalicylic acid substrate and enzymatically reacted with a commerically available anti-human immunoglobulin G peroxidase conjugate. The product of the enzymatic reaction can be interpreted visually. Comparison of 351 human sera tested by the immunofluorescent and paper enzyme-linked immunosorbent assays against a three-antigen pool of the Karp, Kato, and Gilliam strains of R. tsutsugamushi demonstrated an agreement of 96%. The sensitivity of the paper enzyme-linked immunosorbent assay as compared to immunofluorescence was 98.2%, and the specificity was 94.4%.