Detection, isolation and characterization of Orientia tsutsugamushi in Leptotrombidium intermedium

Unfed trombiculid mites were collected from endemic areas for detection and isolation of Orientia tsutsugamushi. The mites were compressed between a pair of slide glasses to make samples of the cuticles and smears of the tissues. Mite species were identified by observation of the cuticles, and infection with O. tsutsugamushi was examined in the tissues by improved immunofluorescent microscopy. The microorganisms were detected not only in Leptotrombidium pallidum but also in 0.17% of L. intermedium collected in Kyoto Prefecture. One strain of O. tsutsugamushi was isolated from 146 L. intermedium collected in Niigata Prefecture. Analyses of virulence to mice, antigenicity and nucleotide sequence of the 56 KDa type-specific antigen gene indicated that the isolate is closely related to a strain isolated from a patient in Niigata.