Rocky Mountain spotted fever

R ocky Mountain spotted fever (RMSF), a classic metazoonosis that involves both vertebrate and nonvertebrate reservoir hosts, is a seasonal disease of dogs and humans in the Americas. The clinical illness was first described among Native Americans, soldiers, and settlers in the Bitterroot River and Snake River valleys of Montana and Idaho during the late 1890s, but remained unrecognized in dogs until the late 1970s. The causative organism, Rickettsia rickettsii, was first described by Howard T. Ricketts in 1909 and is maintained in nature by ixodid (hard-bodied) ticks via transmission to-andfrom various rodent reservoirs. As primary reservoir hosts, the ticks vector R rickettsii to larger mammals; however, dogs and humans are the only ones that display clinically recognizable illnesses. Rickettsia rickettsii are not naturally transmitted dog-to-dog, dog-tohuman, or human-to-human. Public health surveillance, since the 1930s, has revealed RMSF to be the most frequently reported and most severe human rickettsial illness in the United States and, probably, in the Western Hemisphere. Reducing exposure to ticks, prompt removal of ticks, and early diagnosis with appropriate antibiotic treatment are the most important factors in reducing morbidity and mortality from RMSF.