Lauri Tolkki, Kati Hokynar, Seppo Meri, Jaana Panelius, Mirja Puolakkainen, Annamari Ranki
DOI: 10.2340/00015555-2831

A retrospective study of 109 skin biopsies with granuloma annulare (GA) or morphea histology from patients with suspected tick bite was performed. Biopsies were tested for cutaneous Borrelia burgdorferi DNA using PCR. The same biopsies were analysed for tick-borne novel agents, Chlamydia-related bacteria (members of the Chlamydiales order), using a PCR-based method. Borrelia DNA was detected in 7/73 (9.6%) biopsies with GA and in 1/36 (2.8 %) biopsies with morphea, while Chlamydiales DNA was found in 53/73 (72.6%) biopsies with GA and 25/34 (73.4%) biopsies with morphea. All Borrelia DNA-positive GA samples were also positive for Chlamydiales DNA. The Chlamydiales sequences detected in GA were heterogeneous and contained Waddliaceae and Rhabdochlamydiaceae bacteria, which are also present in Ixodes ricinus ticks, while the Chlamydiales sequences detected in morphea closely resembled those found in healthy skin. In conclusion, tick-mediated infections can trigger GA in some cases, while correlation of either Borrelia or Chlamydiales with morphea is unlikely.