ABSTRACT
Rocky Mountain spotted fever (RMSF) and epidemic typhus are the major rickettsial diseases. Specific rickettsias commonly infect ticks and lice, which are the common vectors of RMSF and typhus; Rickettsia rickettsii and Rickettsia prowazekii belong to the family Rick-ettsiaceae. In RMSF and typhus, the Weil-Felix reaction is positive in many cases, and antibodies to each specific antigen appear and permit confirmation of the specific diagnosis. After rickettsias gain access to man via the skin or mucous membranes, the agents of RMSF and epidemic typhus distribute widely throughout the vascular system. In RMSF and epidemic typhus, small blood vessels characteristically show endothelial cell swelling, cellular proliferation, and degeneration with thrombus formation and partial or full occlusion of the vascular lumen. Louse-borne typhus fever ranks among the top epidemic diseases causing suffering and death. Epidemic typhus is just as severe as RMSF; murine typhus resembles mild epidemic typhus or epidemic typhus modified by prior immunization.
