RAPID DIAGNOSIS OF SCRUB TYPHUS BY A PASSIVE HEMAGGLUTINATION ASSAY USING RECOMBINANT 56-KILODALTON POLYPEPTIDES

The genes encoding the 56-kDa polypeptides were amplified by polymeras e chain reaction from the genomic DNAs of three serotypes of Rickettsi a tsutsugamushi, Gilliam, Karp, and Boryong. The amplified products we re cloned into expression vector pIH821, and the recombinant antigens were expressed in Escherichia coli as fusion proteins with maltose-bin ding protein. The recombinant 56-kDa polypeptides were purified by aff inity chromatography for the sensitization of sheep erythrocytes. The recombinant 56-kDa polypeptides were evaluated with 89 serum specimens from healthy blood donors, 94 serum specimens from scrub typhus patie nts, and 31 serum specimens from patients with other febrile diseases by a passive hemagglutination assay (PHA). Among the scrub typhus pati ents diagnosed by indirect immunofluorescent-antibody testing, the ant ibodies to R. tsutsugamushi were detected in 93 patients (99%). One se rum specimen from a healthy person showed a false-positive reaction by this method. The recombinant PHA showed no cross-reactions with sera obtained from other febrile patients with diseases such as murine typh us, hemorrhagic fever with renal syndrome, and leptospirosis. In concl usion, this recombinant PHA could be substituted for the conventional indirect immunofluorescent-antibody test and the immunoperoxidase test .