Rickettsioses of the Spotted Fever Group around the World

Spotted fever group rickettsioses comprise Rocky Mountain spotted fever (Rickettsia rickettsii), boutonneuse fever (R. conorii), North Asian tick typhus (R. sibirica), Queensland tick typhus (R. australis), rickettsialpox (R. akari), and Oriental spotted fever (R. japonica). Ticks or mites serve as the vector and reservoir hosts of the rickettsiae. These obligate intracellular bacteria invade vascular endothelial cells, which are damaged directly, causing increased vascular permeability. The rash usually appears in Rocky Mountain spotted fever on the third day of illness and later evolves to become petechial maculopapules in 50% of cases with involvement of the palms and soles in a similar proportion of patients. Eschar occurs in some SFG rickettsioses at the site of tick bite, but rarely in Rocky Mountain spotted fever. Diagnosis often proves difficult, and laboratory assays for antibodies to SFG rickettsiae are generally useful only in convalescence. Rickettsiae are demonstrable by diagnostic immunohistology in biopsies of rash or eschar. Empiric treatment with doxycycline, tetracycline, or chloramphenicol should be given early in the course on the basis of clinical suspicion of the diagnosis of a SFG rickettsiosis.