Investigation of Orientia tsutsugamushi Strains in Tak Province of Thailand

Orientia tsutsugamushi which is the causative agent of scrub typhus, commonly found in the border areas of Thailand. The purpose of this study is to identify pathogenic strains of O. tsutsugamushi circulated in T ak province of Thailand during 2008 to 2010. Eighty-two blood specimens of patients diagnosed with pyrexia of unknown origin were collected from Mae Sot Hospital, T ak province. Fragments of O. tsutsugamushi 56-kDa gene were obtained from Nested PCR of specimens and subsequently restricted with Pst I enzyme by RFLP analysis. The Pst I restriction pattern of samples was compared with those of reference strains, Karp, Kato and Gilliam. We found that fragments of 56 kDa O. tsutsugamushi gene specific were amplified from 27 of total 82 patients (32.9%). RFLP analysis revealed that the majority (10/27) of these patients was infected with the Gilliam strain, three each with the Karp and Kato strains and eleven with other unknown strains. The highest infection rate (63%) was found at Mae Sot district. Other unknown strains of O. tsutsugamushi are currently spread in T ak province due to genetic variation of bacterial cell membrane. Thus, surveillance of pathogenic O. tsutsugamushi strains excluding Karp, Kato and Gilliam strains is encouraging by DNA Sequence-based analysis.