Common laboratory tests can be of use in diagnosis. An elevated C-reactive protein level and a slight to moderate increase in hepatic transaminases should be expected. Thrombocytopenia, leukopenia, and elevation of the lactate dehydrogenase level less frequently are present.5,9
Our case de1monstrated a typical presentation. The patient developed a febrile syndrome with a generalized rash and a tache noire–type eschar associated with muscle pain, headache, cough, night sweats, and odynophagia. Because of epidemiologic changes in the area, the familiar clinical findings, and laboratory confirmation, histologic studies were unnecessary. In cases in which the diagnosis is not evident, skin biopsy could be useful, as in the first case reported in Chile.2
In that first case, the patient initially was hospitalized because of a febrile syndrome; eventually, a necrotic eschar was noticed on his leg. He had been staying on Chiloé Island and reported being bitten by leeches on multiple occasions. Laboratory findings revealed only slightly raised levels of hepatic transaminases and alkaline phosphatase. After a more precise dermatologic evaluation, the eschar of a tache noire, combined with other clinical and laboratory findings, raised suspicion of ST. Because this entity had never been described in Chile, biopsy of the eschar was taken to consider other entities in the differential diagnosis. Biopsy showed necrotizing leukocytoclastic vasculitis in the dermis and subcutaneous tissue, perivascular inflammatory infiltrates comprising lymphocytes and macrophages, and rickettsial microorganisms inside endothelial cells under electron microscopic examination. The specimen was tested for the 16S ribosomal RNA Orientia gene; its presence confirmed the diagnosis.2
Classically, histology from the eschar shows signs of vasculitis and rickettsial microorganisms inside endothelial cells on electron microscopy.2,10 More recent publications describe important necrotic changes within keratinocytes as well as an inflammatory infiltrate comprising antigen-presenting cells, monocytes, macrophages, and dendritic cells. Using high-resolution thin sections with confocal laser scanning microscopy and staining of specific monoclonal antibodies against 56 kDa type-specific surface antigens, the bacteria were found inside antigen-presenting cells, many of them located perivascularly or passing through the endothelium.11
The causal agent in Asia is O tsutsugamushi, an obligate intracellular bacterium (genus Rickettsia). Orientia species are transmitted by larvae of trombiculid mites, commonly called chiggers. The reservoir is believed to be the same as with chiggers, in which some vertebrates become infected and trombiculid mites feed on them.12 Recent studies of Chilean cases have revealed the presence of a novel Orientia species, Candidatus Orientia chiloensis and its vector, trombiculid mites from the Herpetacarus species, Quadraseta species, and Paratrombicula species genera.13,14
A high seroprevalence of Orientia species in dogs was reported in the main cities of Chiloé Island. Rates were higher in rural settings and older dogs. Of 202 specimens, 21.3% were positive for IgG against Orientia species.15
In Chile, most cases of ST came from Chiloé Island; some reports of cases from continental Chilean regions have been published.6 Most cases have occurred in the context of activities that brought the patients in contact with plants and firewood in rural areas during the summer.3-6