GENETIC-VARIATION IN AUSTRALIAN SPOTTED-FEVER GROUP RICKETTSIAE

Rickettsiae were isolated by cell culture of buffy coat blood from six patients with spotted fever from southeastern Australia and Flinders Island in Bass Strait. The isolates were genetically compared with two previous Rickettsia australis patient isolates. The genus-specific 17 -kDa genes from the isolates were compared after DNA amplification and restriction fragment analysis of the amplified DNA. This comparison r evealed that mainland rickettsial isolates from southeastern Australia were identical to two previous isolates of R. australis from northeas tern Australia. Rickettsial isolates from Flinders Island were distinc t from the mainland isolates. The 16S rRNA gene sequences from the iso lates were determined and compared. The Flinders Island rickettsial ag ent was most closely related (0.3% structural divergence) to Rickettsi a rickettsii, Rickettsia conorii, and Rickettsia slovaca. The Flinders Island rickettsial agent was 1.3 and 2.1% structurally divergent from R. australis and Rickettsia akari, respectively. The 16S rRNA gene se quence from the Flinders Island agent shows that this rickettsia is mo re closely related to the rickettsial spotted fever group than is R. a ustralis. We conclude that there are two populations of spotted fever group rickettsiae in Australia and propose that the genetically distin ct causative organism of Flinders Island spotted fever be designated R ickettsia honei. The extent of distribution and animal host reservoirs remain to be elucidated.