Real-Time RT-PCR Detection of Scrub Typhus Total Nucleic Acid Assay with High Sensitivity and Specificity

Scrub typhus is a bacterial disease caused by Orientia tsutsugamushi (O. tsutsugamushi or Ots) that is spread to people through bites of infected chiggers (larval mites). The most common symptoms can include fever, headache, body aches, and sometimes rash. Severe illness can lead to organ failure and bleeding which can be fatal if left untreated. Most cases of scrub typhus occur in Asia Pacific countries, however, recent reports document establishment in the Arabian Peninsula, Chile, and possibly Kenya. Anyone living in or traveling to areas where scrub typhus is found could get infected if they come in contact with infected mites. Currently available DNA molecular tests lack sensitivity to reproducibly detect the low level of scrub typhus bacteria circulating in blood.

CDC scientists developed a real-time reverse transcriptase PCR (real-time RT PCR) assay targeting both ribosomal RNA (rRNA) and ribosomal DNA (rDNA) in total nucleic acid (TNA) to detect Ots. Analytical specificity was tested with 17 Ots strains for inclusivity, and exclusivity with 7 near neighbors and 9 background clinical and environmental Ots DNAs. Initial tests on patient samples show high specificity and sensitivity. CDC’s assay improves diagnostic accuracy by increasing Ots detection sensitivity 10 to 100 times over current molecular DNA tests. CDC technology uses uncomplicated steps so that early acute stage diagnosis of scrub typhus now becomes feasible.