|Description:||This 1978 transmission electron microscopic (TEM) image depicted a brain capillary of a mouse that had been experimentally infected intravenously with Orientia tsutsugamushi rickettsial micro-organisms. This TEM revealed that one organism was budding from the luminal surface of a hypertrophic capillary endothelial cell, still covered by a third layer consisting of the host cell's plasma membrane. Others are visible free within the endothelial cell's cytoplasm.|
In humans, O. tsutsugamushi attacks endothelial cells resulting in vasculitis. The clinical manifestations are characterized by papular rash, headache, fever, chills, and an eschar at the site of the chigger bite, i.e. the mode of human inoculation. The disease can be tested serologically by the detection of significant increases of IFA (indirect fluorescent antibody) in paired serum drawn at the onset of disease, and 2 - 3 weeks later. Traditionally, isolation of the rickettsia from the blood by inoculation intraperitoneally into white mice is the definite confirmatory method.