The spirochetal etiology of erythema chronicum migrans Afzelius.

We have obtained spirochetes from Ixodes (I.) ricinus ticks collected in different areas in Stockholm where erythema chronicum migrans Afzelius (ECMA) cases are known to occur sporadically. Titers of antibody against spirochetal isolates, cultured in modified Kelly's medium, from Swedish I. ricinus and American I. dammini ticks were determined by indirect immunofluorescence. With the I. ricinus respectively the I. dammini spirochete as antigen the ECMA group had a significantly higher median titer (73 respectively 128) than the control group (28 respectively 31). Spirochetes have also been isolated from the periphery of one ECMA lesion by injecting skin homogenates into rabbit testicles. The findings are in agreement with spirochetal etiology in ECMA.