Hemostatic changes in Rocky Mountain spotted fever and Mediterranean spotted fever.

Rocky Mountain spotted fever and Mediterranean spotted fever are rickettsial infections primarily of endothelial cells that normally have a potent anticoagulant function. As a result of endothelial cell infection and injury, the hemostatic system is perturbed and shows changes that vary widely from a minor reduction in the platelet count (frequently) to severe coagulopathies, such as deep venous thrombosis and disseminated intravascular coagulation (rarely). Changes favoring a hypercoagulable state include endothelial injury and release of procoagulant components, activation of the coagulation cascade with thrombin generation, platelet activation, increased antifibrinolytic factors, consumption of natural anticoagulants, and possibly high levels of coagulation-promoting cytokines. Yet, most studies have been performed on endothelial cell cultures that provide nonphysiologic, reductionistic, experimental conditions. The lack of flow, platelets, and WBCs makes these experiments far from simulating the response of endothelial cells in the human body. Coagulopathies and thrombotic events should be considered as potential complications of severe Rocky Mountain spotted fever and Mediterranean spotted fever.