A method for specific diagnosis of rocky mountain spotted fever on fixed, paraffin-embedded tissue by immunofluorescence

For specific demonstration of Rickeltsia rickettsii in fixed, paraffin-embedded tissues, the technique of trypsin digestion of deparaffinized, rehydrated sections was investigated. It was determined that 3.5 hr of digestion was optimal for achieving discrete, bright, green immunofluorescence of rickettsiae. At autopsy kidneys from seven of 10 cases of probable Rocky Mountain spotted fever contained structures that were specifically stained and that had the size and shape of rickettsiae. These structures were strictly limited to the endothelium and vascular walls of renal capillaries, veins, and arteries. Results from controls indicated the specificity of the immunofluorescence. R. rickettsii may be demonstrated by this method with greater sensitivity and specificity than by current histological methods. The technique allows retrospective analysis of certain organs for pathogenesis of involvement in Rocky Mountain spotted fever and offers a specific diagnostic test.