Volume 12, Number 3—March 2006
Rickettsioses in South Korea, Data Analysis
To the Editor: Choi et al. (1) conducted a study on sequence analysis of a partial rompB gene amplified from sera of humans who were seropositive for spotted fever group (SFG) and typhus group rickettsioses. They write, "These finding suggested that several kinds of rickettsial diseases, including boutonneuse fever, rickettsialpox, R. felis infection, and Japanese spotted fever… are occurring in Korea."
These claims propagate some errors and may lead to an inadequate conclusion. First, rompB is conserved in Rickettsia spp. and consists of 4,968 bp with respect to the published sequence of the R. conorii strain Seven (2,3). Fournier et al. (4) amplified 4,682 bp of rompB and showed a high degree of nucleotide sequence similarity (99.2%) between R. africae and R. sibirica, R. pakeri, and R. slovaca. Choi et al. amplified ≈420 bp of rompB (position 3562–4077) for sequence analysis. This segment is located in a highly conserved region of the gene, which may decrease the ability to differentiate particular species from other SFG rickettsiae. This study cannot prove the existence of specific SFG rickettsioses until the results are confirmed further by, for example, isolating these SFG rickettsiae from humans, animals, or ticks in South Korea. Recently, the authors analyzed nucleotide sequences of 267-bp amplicons of rompB (position 4762–4496) obtained from patient sera and found that R. conorii could not be differentiated from R. sibirica (5). This finding also supports our concerns.
Second, although partial rompB nucleotide sequence analysis of rickettsiae obtained from 1 patient's serum showed 98.87% similarity with R. conorii strain Seven, the finding does not indicate boutonneuse fever is occurring in South Korea because high similarities (98.6%–99.8%) are found among 4 subspecies of R. conorii. Multilocus sequence typing can help differentiate among these subspecies (6).
This study provided a model to amplify SFG rickettsial DNA from sera of patients, and it will be helpful in surveillance of these diseases. However, the results should be interpreted more carefully in the context of clinical and epidemiologic data and combined with different gene sequence analyses to obtain a reliable and specific diagnosis.
- Choi YJ, Jang WJ, Kim JH, Ryu JS, Lee SH, Park KH, Spotted fever group and typhus group rickettsioses in humans, South Korea. Emerg Infect Dis. 2005;11:237–44.
- Roux V, Raoult D. Phylogenetic analysis of members of the genus Rickettsia using the gene encoding the outer-membrane protein rOmpB (ompB). Int J Syst Evol Microbiol. 2000;50:1449–55.
- Ogata H, Audic S, Barbe V, Artiguenave F, Fournier PE, Raoult D, Selfish DNA in protein-coding genes of Rickettsia. Science. 2000;290:347–50.
- Fournier PE, Dumler JS, Greub G, Zhnag J, Wu Y, Raoult D. Gene sequence–based criteria for identification of new Rickettsia isolates and description of Rickettsia heilongjiangensis sp. nov. J Clin Microbiol. 2003;41:5456–65.
- Choi YJ, Lee SH, Park KH, Koh YS, Lee KH, Baik HS, Evaluation of PCR-based assay for diagnosis of spotted fever group rickettsioses in human serum samples. Clin Diagn Lab Immunol. 2005;12:759–63.
- Zhu Y, Fournier PE, Eremeeva M, Raoult D. Proposal to create subspecies of Rickettsia conorii based on multi-locus sequence typing and an emended description of Rickettsia conorii. BMC Microbiol. 2005;5:11.