Rickettsia helvetica; Detection in arthropods and human tissues and its relation to clinical disease
Sammanfattning: A relation between R. helvetica and perimyocarditis was, in two young men who died of sudden cardiac death during exercise in 1997, suggested by a seminested PCR, for three different genes, sequencing of the amplified products, documentation of a seroresponse and histopathologic changes in accordance with rickettsioses. One of the young men also had a sarcoidosis. When investigating him and another autopsy case with sarcoidosis further, genetic material from R.helvetica was detected by PCR and histologicaland immunohistochemical (IHC) examination with three antibodies of the PCR positive tissues showed presence of rickettsia-like organisms (r.l.o.), which were predominantly located in the endothelium and the macrophages. TEM clearly identified and demonstrated r.l.o. within the granuloma with findings suggestive of ongoing infection. Immuno-gold labeling of the Proteus OX-19 antiserum showed that the gold markers were localized to the r.l.o. These findings, together with histologic and IHC examination of paraffin-embedded biopsy specimens from 30 patients with confirmed sarcoidosis, where 26 specimens were judged to be positive for r.l.o., support the hypothesis that R. helvetica may cause a chronic vasculitis, as in sarcoidosis. An evaluation of three patients with febrile illness, myalgia and eschar, their significant seroconversion together with substantial data including those from IHC and TEM examination, indicate current rickettsial disease. In a prospective study, 35 Swedish recruits, deployed to Gotland, were examined for seroconversion. Of the 35, eight showed a four-fold increase in IgG titer, reflecting a high rate of exposure. The findings supports the hypothesis that Rickettsia helvetica is a human pathogen that has to be taken into consideration in the diagnosis of tick-transmitted infections in Europe.Two collections of Ixodes ricinus ticks were subjected to DNA isolation. By sequencing of the 16SrDNA- and citrate synthase genes it was shown that the detected rickettsia had amplified sequences showing 100% homology with the deposited sequences of Rickettsia helvetica. In the first collection with PCR of the citrate synthase gene the prevalence of rickettsial DNA was 1.7%; in the second collection with a seminested PCR of the 16SrDNA gene the prevalence of rickettsial DNA was found to be in the range from 16% to 36.8%.
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