Detection and Molecular Characterization of Orientia tsutsugamushi from Suspected Scrub Typhus Patients in Mizoram, India

Serologic and molecular tests were performed for the diagnosis and to detect O. tsutsugamushi genotypes that are circulating in the state of Mizoram, India. Blood samples from scrub typhus-suspected patients were collected from Synod Hospital, Durtlang, Mizoram. Weil-Felix and immunochromatographic test (ICT) were performed from the serum samples. Nested PCR (nPCR) amplification of 47kDa outer membrane protein antigen gene and 56kDa type-specific antigen gene were done from the whole blood. 141/177 (79.66%) and 134/177 (75.7%) cases showed the presence of antibody against scrub typhus by Weil-Felix and ICT assays respectively. 76/177 (42.93%) patients showed the presence of 47kDa OMP antigen gene by nPCR while 55/177 (31.07%) showed the presence of 56kDa TSA gene by nPCR. Phylogenetic analysis of 56kDa TSA gene sequence revealed that Karp-related genotype was the most common genotype in the study area followed by Kato-related genotype. In this study, a high degree of diversity of O. tsutsugamushi was observed similar to the observations reported from other parts of India. Nested PCR of 47kDa OMP antigen gene showed higher sensitivity as compared to nPCR amplification of 56kDa TSA gene suggesting it as the assay of choice for diagnosis of scrub typhus disease.