Serologic study of the prevalence of rickettsiosis in Yucatan: evidence for a prevalent spotted fever group rickettsiosis

Because of the discovery of a spotted fever group rickettsiosis with signs and symptoms similar to dengue fever in Yucatan, Mexico, immunofluorescence assay (IFA) serology was performed on sera from 390 persons selected from a representative geographic distribution of rural Yucatan to detect antibod ies reactive with Rickettsia rickettsii, R. akari, a Thai strain (TT-118) t hat is most closely related to a rickettsia identified in Amblyomma cajenne nse ticks in southern Texas, and R. typhi. The LFA antibodies at titers gre ater than or equal to 1:64 against R. akari were detected in 22 (5.6%) of t he samples with the expected cross-reactivity against the other antigens of the spotted fever group. Immunoblotting with antigens of R. akari identifi ed antibodies against antigens of spotted fever group lipopolysaccharides a nd not against rickettsial outer membrane proteins A and B, which contain t he species-specific epitopes. A rickettsiosis most likely caused by a relat ive of R. akari appears to be both prevalent and widely distributed geograp hically in Yucatan.