Ultrastructural visualization of Orientia tsutsugamushi in biopsied eschars and monocytes from scrub typhus patients in South Korea

Abstract

Scrub typhus, which is caused by Orientia tsutsugamushi, is a public health problem in the Asian-Pacific region and is the third most frequently reported infectious disease in South Korea. While ultrastructural studies have been performed on O. tsutsugamushi in murine fibroblasts, its variable locations in patients have hampered similar studies in humans. Two patients with scrub typhus agreed to provide an eschar biopsy and peripheral blood, respectively. Transmission electron microscopy was performed separately on the necrotic crust and perifocal skin of the eschar, the peripheral blood, and the infected murine L cells. O. tsutsugamushi was located within or adjacent to the outermost layer of the perifocal inflamed skin of the eschar but not in the necrotic centre. O. tsutsugamushi in peripheral blood monocytes exhibited the characteristic features of O. tsutsugamushi in L cells, namely, nearly round shaped bacteria with a size of 1–2 µm and a double membrane bearing a clear halo-like outer layer. The findings confirmed that the bacterium was predominantly located in the inflamed skin around the eschar and that the bacterium had the same ultrastructural features in human monocytes as in L cells. These findings suggest that the perifocal area, not the necrotic centre, should be sampled for diagnosis.

The Obligate Intracellular Bacterium Orientia tsutsugamushi Targets NLRC5 To Modulate the Major Histocompatibility Complex Class I Pathway

“…tsutsugamushi reduces NLRC5 and MHC-I levels in THP-1 monocytic cells during early infection, but these phenomena reverse thereafter. Monocytes are infected by O. tsutsugamushi in vivo and are hypothesized to contribute to disseminating the bacterium (13)(14)(15)18). Therefore, it was next examined if O. tsutsugamushi reduces NLRC5 levels and MHC-I expression in THP-1 monocytic cells.…”

“…The median mortality rate is 7% to 15% but can be as high as 70% (9,12). At the chigger inoculation site, O. tsutsugamushi infects dendritic and mononuclear cells (13,14). Peripheral blood mononuclear cells obtained from scrub typhus patients and experimentally infected monkeys and dogs harbor O. tsutsugamushi (14)(15)(16).…”

“…At the chigger inoculation site, O. tsutsugamushi infects dendritic and mononuclear cells (13,14). Peripheral blood mononuclear cells obtained from scrub typhus patients and experimentally infected monkeys and dogs harbor O. tsutsugamushi (14)(15)(16). The bacterium replicates in monocytes and monocyte-derived dendritic cells in vitro (16,17), yet O. tsutsugamushi replication in monocytes is less efficient than that in other cell types, as it lags at between 24 h and 72 h and resumes thereafter (16).…”

Three‐year surveillance (2016–2018) of chigger mites vector for tsutsugamushi disease in the Hwaseong‐Si area of Gyeonggi‐Do, Republic of Korea

“…; Ro et al . ); it is caused by infection with the intracellular parasite, Orientia tsutsugamushi , a Gram‐negative α‐proteobacterium of the Rickettsiaceae family, first isolated and identified in 1930 in Japan, which is transmitted to humans through the bite of chigger mites. These arthropods serve as vectors of the disease and their endemicity is closely associated with their habitation (Cho et al .…”

“…Tsutsugamushi disease (scrub typhus) was the third most frequently reported infectious disease in the Republic of Korea (Korea) in 2012 (Park et al 2015;Ro et al 2018); it is caused by infection with the intracellular parasite, Orientia tsutsugamushi, a Gram-negative α-proteobacterium of the Rickettsiaceae family, first isolated and identified in 1930 in Japan, which is transmitted to humans through the bite of chigger mites. These arthropods serve as vectors of the disease and their endemicity is closely associated with their habitation (Cho et al 2007;Jensenius et al 2004;Seong et al 2001).…”