ABSTRACT
Members of the family Rickettsiaceae are fastidious bacteria and obligate intracellular parasites. Rickettsial species are arthropod-associated bacteria which are capable of infecting vertebrates, including human beings. The order Rickettsiales has been divided historically into three families: Rickettsiaceae, Bartonellaceae, and Anaplasmataceae. The family Rickettsiaceae was divided into three tribes: Rickettsieae, Ehrlichieae, and Wolbachieae, and the tribe Rickettsieae has long been composed of the genera Coxiella, Rickettsia, and Rochalimaea. Phylogeny and taxonomy of rickettsiae have been studied in recent years by the introduction of new phylogenetic tools. DNA sequence analysis of 16S rRNA, citrate synthase, rOmpA, and rOmpB genes have delineated the phylogeny among rickettsial species (1-8) (Figure 1). Coxiella burnetii, the agent of Q fever, has been removed from the order Rickettsiales and replaced in the y subgroup ofProteobacteria, whereas Rickettsia belongs to the al subgroup (9). Moreover, the genus Rochalimea has been unified to the genus Bartonella, removed from the order Rickettsiales, and replaced with Brucella spp. in the a2 subgroup of Proteobacteria (10). The Rickettsieae tribe now comprises only the genus Rickettsia which was subdivided into three subgroups: the typhus group (TG), the spotted fever group (SFG), and the scrub typhus group (STG) (Table 1). Rickettsia tsutsugamushi, the only member of the STG, has been recently reclassified in a new genus and is now named Orientia tsutsugamushi (11). The TG includes R. prowazekii, the agent of epidemic typhus, and R. typhi, the agent of murine typhus. Among the SFG, the six previously described SFG rickettsioses are Rocky Mountain Spotted Fever (RMSF) caused by R. ricketts ii, Mediterranean Spotted Fever (MSF) caused by R. conorii, Siberian tick typhus caused by R. sibirica, Israeli spotted fever caused by R. conorii serotype israeli, Queensland tick typhus caused by R. australis, and rickettsialpox caused by R. akari. Since1984, six new SFG rickettsioses were described: Japanese spotted fever caused by R. japonica described in 1984 (12), Flinders Island spotted fever caused by R. honei described in 1991 (13), Astrakhan fever caused by R. conorii serotype astrakhan reported in 1991 (14), African tick-bite fever caused by R. africae described in 1992 (15), a new spotted fever due to "Rickettsia mongolotimonae" reported in 1996 (16,17) in France, and very recently R. slovaca isolated in our laboratory in a tick from a patient (18).
