Serological study with rickettsial antigens in erythema chronicum migrans

21 sera of 13 patients with erythema chronicum migrans (ECM) and related diseases were examined for the presence of antibodies against 14 rickettsial antigens by using 3 serological techniques in 2 laboratories. Most tests were negative. This indicates that ECM and related diseases are not due to an hitherto known rickettsia. 5 out of 158 tests showed, however, positive reactions in low titers against Rickettsia akari and Coxiella burnetii. Thus, an antigenic relationship may exist between one or more rickettsia(e) and the etiologic agent of ECM.