Detection of scrub typhus by real-time polymerase chain reaction and immunoglobulin M ELISA among patients with acute febrile illness

Background: Scrub typhus caused by Orientia tsutsugamushi is a vector-borne zoonotic infection endemic in several parts of the globe. The infection generally presents with fever and nonspecific clinical features but may lead to severe complications with a high mortality rate if untreated. Early diagnosis and timely management are therefore important. Serological diagnosis such as Weil–Felix test, indirect immunofluorescence assay, immunoglobulin (Ig) M/IgG ELISA, and rapid antibody detection assays are either less sensitive or laborious. Molecular detection by polymerase chain reaction (PCR) targeting specific gene targets of O. tsutsugamushi is warranted. Materials and Methods: We developed a real-time PCR assay targeting 47-KDa htrA gene for the specific diagnosis of the pathogen. The assay was evaluated in a buffy coat from whole blood or serum samples collected from patients presenting with acute febrile illness. Randomly selected samples were also tested for IgM by commercial IgM ELISA assay. Results: The real-time PCR assay was able to detect <1 genome copy per the PCR input and specific to O. tsutsugamushi on heterologous pathogens testing. The samples were negative by real-time PCR and 13 samples were positive by IgM ELISA. This study found a relatively low prevalence of scrub typhus in the population. Conclusion: The assay developed in this study could be a useful diagnostic tool for the detection of O. tsutsugamushi in clinical samples. The study also indicated the need for a wide epidemiological survey that could help determine appropriate health measures including treatment and prevention.