ABSTRACT
Rocky Mountain spotted fever (RMSF) was rst identied in Idaho during the 1800s by Edward Maxey, initially referred to as the spotted fever of Idaho. In 1904, Louis Wilson and William Chowning concluded that ticks of the genus Dermacentor were responsible for spreading the infection to humans. By 1910, Howard Ricketts rst identied the pathogen and isolated it in both ticks and mammals. Later this pathogen was named Rickettsia rickettsii in honor of him. Rickettsia are small (0.3-2.0 µm), polymorphic coccobacilli (Figure 15.1), Gram negative, and die quickly outside of a cell. Rickettsia populations can double every 10-13 hours, relatively long for a disease that can spread throughout the body so rapidly. The speed of infection is accelerated because Rickettsia can pass through a cell membrane without killing the cell. This allows the pathogen to spread quickly from one cell to another (Dumler 1994). Other species of Rickettsia that occur in North America include R. montanensis, R. rhipicephali, and R. parkeri, but only the last species causes human illness (Parola et al. 2005).
