Short report: variation in the 56-kD type-specific antigen gene of Orientia tsutsugamushi isolated from patients in Thailand.

The sequences of a 300-base pair region of the 56-kD type-specific antigen gene from 12 Orientia tsutsugamushi isolates from Thailand were compared with isolates from other regions in Asia. A high degree of heterogeneity was found among the 12 Thai isolates, with the C3 strain most commonly found. The abundance of the C3 strain of O. tsutsugamushi is of particular concern because doxycycline and chloramphenicol resistance have previously been reported in this strain.