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

Nithiyanandan Saravanan1, Prashanth Rajendiran1, Sathish Sankar1, Mageshbabu Ramamurthy1, Archana Sasimohan2, Vishnu Vineeta2, George Varghese2, Mercy John Idikula2, Mary V Jesudason3, Raja Rajeswari Mangalakumar4, Aravindan Nair5, Ranganathan Babujanarthanam6, Balaji Nandagopal1, Gopalan Sridharan1
1Sri Narayani Hospital and Research Centre, Sri Sakthi Amma Institute of Biomedical Research, Vellore, Tamil Nadu, India.
2Department of Microbiology, Pushpagiri Institute of Medical Sciences, Thiruvalla, Kerala, India.
3Department of Microbiology, Sri Narayani Hospital and Research Centre, Vellore, Tamil Nadu, India.
4Department of Diagnostics, King Institute of Preventive Medicine and Research, Chennai, Tamil Nadu, India.
5Department of General Surgery, Sri Narayani Hospital and Research Centre, Vellore, Tamil Nadu, India.
6Department of Biotechnology, Nano and Energy Biosciences Laboratory, Thiruvalluvar University, Vellore, Tamil Nadu, India.
DOI: 10.4103/jnsbm.JNSBM_156_19


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.

Keywords: Acute febrile illness, Orientia tsutsugamushi, real-time polymerase chain reaction, scrub typhus.

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