A nested PCR assay was developed for the detection of spotted fever group (SFG) rickettsiae in serum samples. The assay was based on specific primers derived from the rickettsial outer membrane protein B gene ( rompB ) of Rickettsia conorii . An SFG rickettsia-specific signal is obtained from R. akari , R. japonica , R. sibirica , and R. conorii . Other bacterial species tested did not generate any signal, attesting to the specificity of the assay. As few as seven copies of the rompB gene of R. conorii could be detected in 200 μl of serum sample. The assay was evaluated with a panel of sera obtained from patients with acute-phase febrile disease tested by immunofluorescent antibody assay (IFA). The SFG rickettsia-specific DNA fragment was detected in 71 out of 100 sera, which were proven to have immunoglobulin M antibodies against SFG rickettsial antigen by IFA. The results were further confirmed by restriction fragment length polymorphism and sequencing analysis of the DNA fragments. The results indicated that this PCR assay is suitable for the diagnosis of spotted fever group rickettsiosis in Korea.

This study revealed the presence of various rickettsial agents in mites from wild rodents collected in Southern Jeolla Province, Korea, by nested polymerase chain reaction (PCR) and sequence analysis of a partial citrate synthase and rickettsia outer membrane protein B genes. Rickettsial agents closely related to the Rickettsia species TwKM02, R. australis, and the Rickettsia species Cf15 were successfully identified in this study, for the first time in Korea, and R. japonica, R. akari, R. conorii, R. felis, and R. typhi were also detected, as previously described. The data presented in this paper extend knowledge on the geographic distribution of SFG rickettsiae in eastern Asia and it may necessary to consider the role of mites in rickettsial transmission.

Rickettsia monacensis, a spotted fever group rickettsia, was isolated from Ixodes nipponensis ticks collected from live‐captured small mammals in South Jeolla province, Korea in 2006. Homogenates of tick tissues were inoculated into L929 and Vero cell monolayers using shell vial assays. After several passages, Giemsa staining revealed rickettsia‐like organisms in the inoculated Vero cells, but not the L929 cells. Sequencing analysis revealed that the ompA‐small part (25–614 bp region), ompA‐large part (2849–4455 bp region), nearly full‐length ompB (58–4889 bp region) and gltA (196–1236 bp region) of the isolates had similarities of 100%, 99.8%, 99.3% and 99.5%, respectively, to those of R. monacensis. Furthermore, phylogenetic analysis showed that the isolate was grouped into the cluster in the same way as R. monacensis in the trees of all genes examined. These results strongly suggest that the isolate is closely related to R. monacensis. As far as is known, this is the first report of isolation of R. monacensis from ticks in Korea.