Rocky Mountain spotted fever, infectious disease caused by a rickettsia. The germ is harbored by wild rodents and other animals and is carried by infected ticks that attach themselves to humans. Despite its name, Rocky Mountain spotted fever is most prevalent in the S United States from Virgina, the Carolinas, and Georgia W to Oklahoma; it may be encountered in other tick-infested regions. Symptoms include chills and high fever; a rose-colored skin rash that appears first on the wrists and ankles and spreads to the trunk, the spots turning deep red and running together; headache; and pains in the back, muscles, and joints. In severe cases there may be delirium or coma. Spotted fever is a serious disease; however, it is not usually fatal if prompt antibiotic treatment is administered. Immunization with vaccine is effective.