Molecular characterization of Orientia tsutsugamushi serotypes causing scrub typhus outbreak in southern region of Andhra Pradesh, India.

Background & objectives: Scrub typhus is a vector-borne zoonotic infection caused by Orientia tsutsugamushi. Local epidemiology of the circulating serotypes of scrub typhus is not available from most parts of India. We conducted this study for the diagnosis of scrub typhus using IgM ELISA and to detect O. tsutsugamushi serotypes circulating in southern AndhraPradesh, India. Methods: Samples were collected from patients clinically suspected to have scrub typhus and were subjected to IgM ELISA to measure IgM antibodies against O. tsutsugamushi. Nested polymerase chain reaction (PCR) was performed targeting strain-specific regions in ELISA-positive samples. Results: Of a total of 663 samples, 258 (38.91%) were found to be positive by IgM ELISA. Serotypes could be detected in 230 (34.69%) samples only. Only two serotypes, Karp and Kawasaki, were found in the serum samples, with the former being predominant. The dual infection of Karp and Kawasaki serotypes was found in seven patients. Other serotypes such as Gilliam, Kuroki and Kato were not detected in the samples. Interpretation & conclusion: The nested PCR products proved useful in presumptively identifying the endemic O. tsutsugamushi serotypes. The present study could be significant in understanding scrub typhus epidemiology in this region.