Rickettsia and Orientia

Abstract

The family Rickettsiaceae comprises two genera of small, obligately intracellular bacteria that reside free within the host cell's cytosol, namely, Rickettsia and Orientia . Pathogenic Rickettsia spp. reside in an arthropod host for at least a part of their life cycle, during which they are maintained by transovarian transmission and/or cycles involving horizontal transmission to vertebrate hosts. Nucleic acid amplification testing has been applied to the amplification of the DNA of spotted fever group and typhus group rickettsiae, usually from peripheral blood, buffy coat, or plasma and occasionally from fresh, frozen, or paraffin‐embedded tissue and from swabs of the ulcerated bases of eschars. The limited quantities of circulating rickettsial DNA during infection greatly hinder the clinical sensitivity of molecular detection from peripheral blood specimens. Species identification of rickettsial isolates was performed by microimmunofluorescence serotyping. Enzyme immunoassay has become an increasingly used method to detect antibodies reactive against Orientia tsutsugamushi .