Molecular Diagnostics for Rickettsial diseases: Insights into Scrub typhus laboratory diagnostics in IMR

Molecular Diagnostics for Rickettsial diseases: Insights into Scrub typhus laboratory diagnostics in IMR Shirley Hii Yi Fen1, Nadia Abd Manan1, Wan Norazanin Kassim1, Rohaidah Hashim1, Siti Roszilawati Ramli1 1Bacteriology unit, Infectious Diseases Research Centre, Institute for Medical Research, National Institutes of Health, Ministry of Health Malaysia Abstract Introduction Institute for Medical Research (IMR) has played a key role and pioneering in research on rickettsial diseases especially scrub typhus since a century ago initiated by Fletcher and team. Scrub typhus caused by gram-negative bacteria, Orientia tsutsugamushi (OT), is one of the major causes of acute febrile illness in Malaysia. Here, we present the current approach on OT molecular diagnostics in IMR to detect acute scrub typhus and surveillance on the circulating OT genotypes in Malaysia. Methods Bacteriology unit of IMR is the national reference laboratory for rickettsial diseases in Malaysia. We have started molecular diagnostics service to all Malaysian hospitals since the end of year 2022 until now. The types of specimens received include whole blood, eschar tissue, swab, cerebrospinal fluid and urine. Real-time PCR and nested PCR are utilised to detect the presence of OT heat shock protein (htrA) and 56 kDa type specific antigen (tsa56), respectively. Simultaneously, genotype analysis was performed based on tsa56. Results A total of 1,232 samples were received from October 2022 to December 2024. An increasing trend was observed in the number of samples received yearly. This could be due to the increase in awareness on the service. There is approximately 16 % of positive cases reported within the 27 months. Out of 106 samples analysed, there are 4 OT genotypes circulating in Malaysia: Gilliam (29%) and Karp (29%) are the predominant OT genotypes followed by TA763 (21%) and Kato (21%). Conclusions Molecular detection of scrub typhus is important in clinical diagnostics setting to improve diagnosis of acute scrub typhus in Malaysia. In addition, genotypic analysis aids in the surveillance on circulating OT genotypes in Malaysia. Keywords: Malaysia, Acute Scrub typhus, Orientia tsutsugamushi, Molecular diagnostics, PCR, Genotypes