Molecular epidemiology and genetic diversity of Orientia tsutsugamushi from patients with scrub typhus in 3 regions of India.

Scrub typhus, an acute febrile illness that is widespread in the Asia-Pacific region, is caused by the bacterium Orientia tsutsugamushi, which displays high levels of antigenic variation. We conducted an investigation to identify the circulating genotypes of O. tsutsugamushi in 3 scrub typhus-endemic geographic regions of India: South India, Northern India, and Northeast India. Eschar samples collected during September 2010-August 2012 from patients with scrub typhus were subjected to 56-kDa type-specific PCR and sequencing to identify their genotypes. Kato-like strains predominated (61.5%), especially in the South and Northeast, followed by Karp-like strains (27.7%) and Gilliam and Ikeda strains (2.3% each). Neimeng-65 genotype strains were also observed in the Northeast. Clarifying the genotypic diversity of O. tsutsugamushi in India enhances knowledge of the regional diversity among circulating strains and provides potential resources for future region-specific diagnostic studies and vaccine development.