ABSTRACT
All the organisms which are maintained naturally by ticks are included in the term tickborne rickettsiae. The most common synonyms for this group are tick typhus rickettsiae or spotted fever rickettsiae. Rickettsia tsutsugamushi is immunologically distinct from all other rickettsiae but shows considerable antigenic variation within the species. The rickettsiae maintained by trombiculid mites, the numerous serotypes of R. tsutsugamushi, are classified as trombiculidborne rickettsiae. The infection they cause is termed chiggerborne rickettsiosis in recognition that only the larvae of the trombiculid mites are parasitic on vertebrates, and only they can transmit the rickettsiae. Based on immunological criteria the rickettsia stem, divorced of Coxiella burnetii and Rochalimaea quintana, is composed of a rather homogeneous group of organisms. Gildemeister and Haagen added tool to the serologists' armamentarium by showing that murine typhus rickettsiae produce a toxic factor with immunologic properties, and Hamilton demonstrated that toxins produced by R. typhi and R. prowazekii are immunologically distinct.
