• Clinical and Experimental Pediatrics
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• v.46 no.7
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• pp.710-713
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• 2003

Purpose : Although chloramphenicol and doxycycline have been used for the treatment of tsutsugamuchi disease, a difficulty exists in determining which drugs to use in treating children because of potential complications such as aplastic anemia or teeth discoloration. We evaluated the effect of roxithromycin, a macrolide antibiotic, on tsutsugamushi disease in children. Methods : A retrospective analysis was conducted on 39 children with tsutsugamuchi disease(scrub typhus) who were treated with doxycycline(DC), chloramphenicol(CM), or roxythromycin(RM) between 1991 and 2000. We divided the patients into a DC-treated group(DC group; 16 children), a CM-treated group(CM group; 14 children), and RM-treated group(RM group; 9 children) and compared these groups. Results : Most cases(97%) developed in October and November. Fever and rash were observed in all 39 cases and an eschar was noted in 36 cases(92%). No statistical differences could be found between the three groups in mean age, duration of fever before admission, white blood cell(WBC) count, and complications including abnormal liver enzymes. In most cases defervescence after treatment was within 24 hours(34 cases, 87%), and during 24-48 hours in two cases in the DC group, one in the CM group, and two in the RM group(no statistical difference). Conclusion : Roxythromycin was as effective as conventional doxycycline or chloramphenicol, in children with scrub typhus and may be safer to use.

• Parasites, Hosts and Diseases
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• v.61 no.3
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• pp.272-281
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• 2023

Chigger mites are the vector of scrub typhus. This study estimates the infestation status and ecological characteristics of chiggers on the chestnut white-bellied rat Niviventer fulvescens in Southwest China between 2001 and 2019. Chiggers were identified under the microscope, and infestation indices were calculated. The Preston's log-normal model was used to fit the curve of species abundance distribution. A total of 6,557 chiggers were collected in 136 of 342 N. fulvescens rats, showing high overall infestation indices (prevalence=39.8%, mean abundance=19.2, mean intensity=48.2) and high species diversity (S=100, H'=3.0). Leptotrombidium cangjiangense, Neotrombicula japonica, and Ascoschoengastia sifanga were the three dominant chigger species (constituent ratio=42.9%; 2,736/6,384) and exhibited an aggregated distribution among different rat individuals. We identified 100 chigger species, with 3 of them (Leptotrombidium scutellare, Leptotrombidium wenense, and Leptotrombidium deliense) as the main vectors of scrub typhus in China and nine species as potential vectors of this disease. Disease vector occurrence on N. fulvescens may increase the risk of spreading scrub typhus from rats to humans. Chigger infestation on N. fulvescens varied significantly in different environments. The species abundance distribution showed a log-normal distribution pattern. The estimated number of chigger species on N. fulvescens was 126 species.

• Korean Journal of Microbiology
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• v.41 no.3
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• pp.232-235
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• 2005

Transcripts levels of superoxide dismutases increase slightly following infection of human dermal microvascular endothelial cells(HMEC-1) by the obligae intracellular bacterium Orientia tsutsugamushi, the causative agent of scrub typhus. In addition, fluorescence-activated cell sorter analysis demonstrates significant intracellular peroxide activity in infected cells within 5 hr after exposure to O. tsutsugamushi. Furthermore, infected cells experienced a significant depletion of glutathiones. These results support hypothesis that cells infected by this intracellular bacterium experience oxidant-mediated injury.

• 대한예방의학회:학술대회논문집
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• 2005.10a
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• pp.481-481
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• 2005

• Journal of Microbiology
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• v.39 no.2
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• pp.142-145
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• 2001

Changes in the Activities of several antioxidant enzymes in transformed human dermal microvascular endothelial Cells (HMEC-1) by infection with the obligate intracellular bacterium Orientia tsutsugamushi, the causative agent of scrub typhus, were investigated. The activities of glucose-6-phosphate dehydrogenase, catalase, and glutathione peroxidase were significantly decreased in HMEC-1 cells infected with Ο. tsutsugamushi. However, the level of superoxide dismutase increased slightly. Furthermore, Increased levels of intracellular peroxide was observed in HMEC-1 during infection. These results support the hypothesis that cells infected by this intracellular bacterium experience oxidant-mediated injury that may eventually contribute to cell death.

• The Journal of the Korean Society for Microbiology
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• v.35 no.2
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• pp.159-169
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• 2000

Scrub typhus is caused by Orientia tsutsugamushi characterized by fever, headache, lymphadenopathy and eschar formation. Infiltration of inflammatory cells around blood vessels and within the affected organs isS known to be pathologic hallmark of the scrub typhus. Recently, expression of adhesion molecules on vascular endothelial cells was implicated as an important pathogenic mechanism in rickettsial disease. This study was performed to examine the expression of adhesion molecules and to investigate its role in the pathogenesis of O. tsutsugamushi infection. The expression of adhesion molecules on human umbilical vein endothelial cells (HUVEC) was measured by flow cytometry and indirect immunofluorescence. Expression of E-selectin, ICAM-1 and VCAM-1 was significantly increased 4 hours after the infection and persisted at least for 24 hours. Expression of those molecules was not induced by killed O. tsutsugamushi. Adhesion of polymorphonuclear cells and mononuclear cells to HUVEC was increased after the infection with O. tsutsugamushi. In conclusion, adhesion molecules are expressed on HUVEC during the infection of live O. tsutsugamushi and those molecules can contribute to the infiltration of inflammatory cells during the infection.

• IMMUNE NETWORK
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• v.23 no.6
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• pp.47.1-47.16
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• 2023

Scrub typhus, a mite-borne infectious disease, is caused by Orientia tsutsugamushi. Despite many attempts to develop a protective strategy, an effective preventive vaccine has not been developed. The identification of appropriate Ags that cover diverse antigenic strains and provide long-lasting immunity is a fundamental challenge in the development of a scrub typhus vaccine. We investigated whether this limitation could be overcome by harnessing the nanoparticle-forming polysorbitol transporter (PST) for an O. tsutsugamushi vaccine strategy. Two target proteins, 56-kDa type-specific Ag (TSA56) and surface cell Ag A (ScaA) were used as vaccine candidates. PST formed stable nano-size complexes with TSA56 (TSA56-PST) and ScaA (ScaA-PST); neither exhibited cytotoxicity. The formation of Ag-specific IgG2a, IgG2b, and IgA in mice was enhanced by intranasal vaccination with TSA56-PST or ScaA-PST. The vaccines containing PST induced Ag-specific proliferation of CD8⁺ and CD4⁺ T cells. Furthermore, the vaccines containing PST improved the mouse survival against O. tsutsugamushi infection. Collectively, the present study indicated that PST could enhance both Ag-specific humoral immunity and T cell response, which are essential to effectively confer protective immunity against O. tsutsugamushi infection. These findings suggest that PST has potential for use in an intranasal vaccination strategy.

• Parasites, Hosts and Diseases
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• v.58 no.2
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• pp.153-159
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• 2020

The chigger mite Leptotrombidium sialkotense is one of the 6 main vectors of scrub typhus in China. Before present study, L. sialkotense was found in some parts of Hunan province, China with a narrow geographical distribution. During field investigation 2016-2017, we found L. sialkotense in Jingha, southern Yunnan, China. Of 15 small mammal host species, L. sialkotense were collected from 6 species of the hosts. Rattus brunneusculus was a dominant host of L. sialkotense, from which 98.3% of the mites were collected. The chigger mite showed a relatively high infestation prevalence (P_M =11.7%) and mean abundance (MA=0.5) in comparison with the rest 5 host species. These results reveal a certain host specificity of L. sialkotense to a rat R. brunneusculus. The mite L. sialkotense showed an aggregated distribution on the host (P<0.05). A positive correlation observed between L. sialkotense and the body length of hosts. There was a positive interspecific association between L. sialkotense and 2 other dominant vectors, L. deliense and L. scutellare.

• Journal of Microbiology
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• v.40 no.2
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• pp.151-155
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• 2002

A Superoxide Dismutase (SOD) gene from the obligate intracellular bacterium Orientia tsutsugamushi has been cloned by using the polymerase chain reaction with degenerate oligonucleotide primers corresponding to conserved regions of known SODs. Nucleotide sequencing revealed that the predicted amino acid sequence was significantly more homologous to known iron-containing SODs (FeSOD) than to manganese-containing SODs (MnSOD). Conserved regions in bacterial FeSOD could also be seen. Isolation of the oriential SOD gene may provide an opportunity to examine its role in the intracellular survival of this bacterium.

• Parasites, Hosts and Diseases
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• v.58 no.4
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• pp.445-450
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• 2020

Trombiculid "chigger" mites (Acari) are ectoparasites that feed blood on rodents and another animals. A crosssectional survey was conducted in 7 ecosystems of southern Vietnam from 2015 to 2016. Chigger mites were identified with morphological characteristics and assayed by polymerase chain reaction for detection of rickettsiaceae. Overall chigger infestation among rodents was 23.38%. The chigger index among infested rodents was 19.37 and a mean abundance of 4.61. A total of 2,770 chigger mites were identified belonging to 6 species, 3 genera, and 1 family, and pooled into 141 pools (10-20 chiggers per pool). Two pools (1.4%) of the chiggers were positive for Orientia tsutsugamushi. Ricketsia spp. was not detected in any pools of chiggers. Further studies are needed including a larger number and diverse hosts, and environmental factors to assess scrub typhus.