Rocky Mountain spotted fever (RMSF) is the most frequently reported tick-borne disease in Georgia; however, Rickettsia rickettsii, its etiologic agent, is rarely found in ticks. In contrast, Rickettsia amblyommatis and R. parkeri are often detected in Georgia. This study examined whether sera from healthy Georgian individuals test positive by diagnostic tests used for RMSF surveillance. Indirect microimmunofluorescence assay (IFA) was utilized to test 113 sera for IgG-type antibodies reacting with R. rickettsii and R. amblyommatis antigens. Seventy-eight sera with IFA titer > 256 were then examined by western blotting (WB). 102 and 103 sera tested IFA-positive with R. rickettsii and R. amblyommatis antigens, respectively. By WB, 18 sera reacted only with Rickettsia surface protein antigens (SPA), 57 reacted with SPA, lipopolysaccharide, and/or other Rickettsia antigens, while 3 had non-specific reactivity. Preliminary WB cross-absorption indicated that R. amblyommatis was the source of exposure. Georgia residents are commonly exposed to tick-borne rickettsiae.
