FUNCTIONAL AND MORPHOLOGIC CHANGES DURING EXPERIMENTAL ROCKY-MOUNTAIN SPOTTED-FEVER IN GUINEA-PIGS

Abstract

Experimental Rocky Mountain spotted fever was studied in guinea pigs following i.p. inoculation of 107 Rickettsia rickettsii. After a 2-day incubation period animals developed fever, progressive emaciation and scrotal swelling with necrosis. Vasculitis, with increased small vessel permeability for colloidal C, was evident in cremaster muscles as early as 1 day after inoculation. Inflammatory changes in vessels became progressively more severe as numbers of circulating rickettsiae increased. Thrombosis and vascular occlusion were first evident on day 4. Mild thrombocytopenia developed, coinciding with the development of vasculitis and preceding the appearance of either fibrin-split products in blood or thrombi in vessels. Rickettsiae were first detected in blood on day 2; peak rickettsemia occurred on days 5-8. Rickettsiae were demonstrated in inflamed vessels on day 5 and later, but no at earlier stages. Serum lysozyme concentration was moderately evaluated, and hemolytic complement was moderately depressed throughout the illness. Agglutinating antibody was present in low titers on days 3-10. Antibody titers increased on days 12-16 after the rickettsiae were cleared from blood. Vasculitis seen early in the course of Rocky Mountain spotted fever is the result of rickettsial infection, but is apparently not dependent on the presence of rickettsiae in endothelial cells or other blood vessel components.