Thoracic radiographic findings in dogs infected with Rickettsia rickettsii.

Sixteen beagle dogs were injected intradermally with Rickettsia rickettsii. The dogs were divided into four groups (n = 4): 1) infected, non-treated control; 2) infected, treated with doxycycline; 3) infected, treated with doxycycline and an anti-inflammatory dose of corticosteroid; and 4) infected, treated with doxycycline and an immunosuppressive dose of corticosteroid. Thoracic radiographs were made and ocular fluorescein angiography was performed on days 6, 10, 17 post-inoculation. A mild interstitial lung opacity was noted in 4/16 dogs on day 6, 5/16 on day 10 and 3/16 on day 17 post-inoculation. Increased retinal vascular permeability was noted in 8/16 dogs on day 6, 3/16 on day 10 and 1/16 on day 17 post-inoculation. Correlation between the presence of radiographic and retinal lesions was not significant (p = 0.08). Eleven, naturally infected, dogs with thoracic radiographs and a final diagnosis of RMSF were also evaluated. Four of the 11 dogs had an unstructured interstitial pattern. Dogs with acute, experimentally-infected or naturally-occurring RMSF may have subtle pulmonary changes characterized by an unstructured interstitial pattern.

The chest radiograph in Rocky Mountain spotted fever.

Chest radiographs of 43 patients with Rocky Mountain spotted fever were reviewed to elucidate the frequency and types of involvement of the lower respiratory tract. The abnormal radiographic patterns included localized and diffuse infiltrates of both interstitial and alveolar type. Autopsies were performed in five cases, and findings in several of these are described to help provide radiologic-pathologic correlation. An association of lung involvement (as evidenced by diffuse infiltrates on chest radiographs) and increased mortality was demonstrated.

Roentgenographic abnormalities in Rocky Mountain Spotted Fever.

Rock Mountain spotted fever (RMSF) is a tick-borne rickettsial disease which produces a widespread vasculitis. A mortality of 7% to 13% has been reported in the United States which is due at least in part to delay in diagnosis and appropriate treatment. The classic features of this disease include a history of tick bite with the clinical presentation of skin rash and fever in association with thrombocytopenia. Few reports have emphasized the radiologic chest abnormalities in this disease or their relationship to thrombocytopenia. We review 70 cases of RMSF with abnormal roentgenographic features and their pathologic correlation.