ABSTRACT

Some members of the family Anaplasmataceae are tickborne or ecologically associated with ticks. The term "tickborne rickettsiae" could refer to a variety of related and unrelated organisms if it is not further qualified. The spotted fever group rickettsiae were antigenically defined by Lackman and Pickens on the basis of a common soluble antigen that fixed complement in the presence of convalescent Rocky Mountain spotted fever guinea pig serum. The official classification of tickborne rickettsiae includes: Rickettsia conorii, R. Sibirica, R. rickettsii, R. parkeri, R. Canada, R. australis and R. akari. The identity of the tick typhus strains in Southeast Asia and their relationship to R. conorii has not been established. Distribution of R. conorii beyond the Ethiopean Region via domestic animal ticks is an attractive hypothesis and undoubtedly has occurred to some extent. The natural acarine hosts of R. rickettsii in North America are several species of Dermacentor and possibly Haemaphysalis leporispalustris.