Studies of the Coagulation and Complement Systems during Experimental Rocky Mountain Spotted Fever in Rhesus Monkeys.

Alterations in the coagulation and complement systems during Rocky Mountain spotted fever RMSF were studied in Macaca mulatta experimentally infected with Rickettsia rickettsii. Ninety-one percent of monkeys infected iv with a high dose and 56 of monkeys infected with low doses of rickettsiae died after two to four days of illness. With the onset of fever and rickettsemia, animals developed hyperfibrinogenemia, mild thrombocytopenia, prolonged prothrombin and activated partial thromboplastin times, and increased serum fibrinfibrinogen degradation products FDP. Rickettsemia, thromobocytopenia, and FDP were greater in fatally ill monkeys than in survivors. Hemolytic titres of C2 and C3 were not depressed except in a single surviving monkey that developed peripheral gangrenous ecchymoses at a time when both rickettsemia and agglutinating antibody were present.