Distribution and prevalence of spotted fever group rickettsiae in ticks from South Carolina, with an epidemiological survey of persons bitten by infected ticks.

Live ticks removed from human hosts were tested for the presence of spotted fever group rickettsiae from 1974 through 1976. Spotted fever group rickettsiae were detected in Dermacentor variabilis, Amblyomma americanum, Amblyomma maculatum, and Ixodes scapularis. Persons from whom positive ticks were removed in 1974 and 1975 were questioned about ensuing illness. Eleven of 51 persons from whom rickettsia-positive D. variabilis were removed reported some unexplained combination of symptoms compatible with Rocky Mountain spotted fever. Persons with positive ticks other than D. variabilis reported no illness in the 2 weeks following exposure. D. variabilis from the Coastal Plain of South Carolina have a higher percentage of infection than those from the Piedmont region. Conversely, most reported human cases of spotted fever are from the Piedmont.