Rocky Mountain Spotted Fever. Ultrastructural findings.

A case of Rocky Mountain Spotted Fever in a human is presented with special emphasis on ultrastructural aspects of the disease. Electron microscopic examination of the tick bite site demonstrated the presence of rickettsial organisms both within the cytoplasm and nucleus of endothelial cells, as well as within the periendothelial cell environment. Several ultrastructural reports of rickettsia localization and morphology within experimental animal and tissue culture models have been reviewed. This report, to our knowledge, represents the first documented demonstration of rickettsial organisms in an acute human disease case. The size, location and morphologic features of the organisms in our case compare closely with the previously reported experimental results.