[Serodiagnosis of scrub typhus by dot-blot method]

Microimmunofluorescence (IF) and immunoperoxidase tests are generally used for the serodiagnosis of scrub typhus. While these tests give satisfactory results in the hands of experienced personnel, they can be troublesome for inexperienced technicians. To develop a simpler diagnostic method, dot-blot assay was examined in this study. Six antigenically distinctive strains of Gilliam, Karp, Kato, Shimokoshi, Kawasaki and Kuroki of Rickettsia tsutsugamushi and a strain of Rickettsia sibirica were dotted on a nitrocellulose sheet by a dot-blot instrument. The sheets were treated with patient sera, followed by peroxidase-conjugated anti-human immunoglobulin-antibody and then with the substrate of the enzyme, and the color development on the dots was compared by naked eye observation. By this procedure, anti-rickettsial antibody-positive patient sera showed clear color development on at least one, usually several dots, while the very faint color was observed by the treatment with antibody-negative sera. On the other hand, it was ascertained that the antigens on nitrocellulose sheets were stable for at least 4 months at room temperature. Therefore the diagnostic kits were prepared, and the practical application of this procedure for diagnosis of scrub typhus were tested in Shizuoka and Miyazaki Prefectural Pabulic Health Laboratories. The results indicated a very good comparability between the dot-blot assay and IF-tests, and this dot-blot method was ascertained as a simple and useful method for the scrub typhus serodiagnosis.