Changing Ecology of Rocky Mountain Spotted Fever

Abstract Rocky Mountain spotted fever (RMSF) is caused by Rickettsia rickettsii, a prototype species of the spotted fever group (SFG) rickettsiae. The disease was not recognized as a clinical entity until 1899 when pioneers began clearing the Bitterroot Valley of northwestern Montana for farms and settlements (Burgdorfer, 1975). Between 1873 and 1910 there were 295 cases of RMSF in Bitterroot Valley of western Montana, 190 of these were fatal (Burgdorfer, 1989). Most RMSF cases occurred in males, as they ventured into the field to hunt, fish, and trap. The development of this RMSF focus and the circumstances surrounding it, i.e., rickettsiae, harbored by ticks, being actively passed to humans establishing their residences in the previously uninhabited lands, have since been repeated in numerous areas. The discovery of the etiologic agent, the tick vector (Dermacentor andersoni), and vertebrate reservoirs (rodents) of RMSF in the northwestern Rocky Mountains was a significant scientific achievement in the area of disease ecology.