Development of a chimeric 56-21 kDa antigen-based ELISA for serodiagnosis of Orientia tsutsugamushi infection

At present, indirect fluorescent antibody testing (IFA) for the traditional diagnosis of scrub typhus (ST) requires high biosafety facilities to prepare whole bacterial antigens that can cross-react with similar diseases. IFA is also not suitable for large-scale epidemiological investigation. Therefore, a simple, fast, and safe serological diagnostic method with high sensitivity and specificity is needed. In this study, a chimeric protein was expressed that binds to 56-kDa proteins from Karp and Kawasaki serotypes and 21-kDa from Gilliam. The chimeric protein was used to establish an Enzyme-Linked Immunosorbent Assay (ELISA) to detect antibodies against Orientia tsutsugamushi in serum. ELISA had no cross-reaction with spot fever, murine typhus, and Q fever. Compared with IFA, the sensitivity and specificity of ELISA were 94.9 % and 97.2 %, respectively, and it detected the serotypes prevalent in China, including Karp, Gilliam, Kato, and Boryong in the initial application. The results showed that ELISA could be used for serological diagnosis of ST and large-scale serological investigation. Large-scale surveys in endemic areas can be conducted for further evaluation.