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Abstract Background Borrelia infection is caused by Borrelia burgdorferi sensu lato and transmitted by Ixodes ricinus ticks, a common tick-borne infection in Northern Europe. The establishment of Borrelia infection depends on transmission of the spirochetes, as well as the immune response generated in the skin after a bite. Here we aim to investigate the local immune response in the skin after a tick bite and assess the possible direct effects of Borrelia, by applying gene expression analysis of the immune response in skin exposed to Borrelia-infected and non-infected ticks, respectively. Methods Skin biopsies from the study participants were taken 7–10 days after the tick-bite. The ticks and skin biopsies were analysed by real-time PCR for Borrelia spp. and other tick-borne pathogens. Dermal transcriptome profiles derived from RNA sequencing with focus on immune system regulation were created. In addition, we performed enrichment analysis of dermal transcriptome profiles with focus on immune system regulation. Results Skin biopsies exposed to a Borrelia-positive tick induced an overall higher expression of immune-related genes. Cytokines involved in the regulation of T-cell and macrophage activation, pro-inflammatory regulators and Toll-like receptor 2, 3 and 7 involved in pathogen recognition were upregulated in skin exposed to Borrelia, although Borrelia DNA was not detected in the biopsies. Conclusion The evidence of upregulation of genes in Borrelia exposed skin suggests an influence on the immune system of ticks and spirochetes. Characterization of Borrelia-associated gene expression signatures in the skin could contribute to future diagnostics and increase our understanding of the development of various manifestations of Borrelia infection.

A milder climate has during the last decade contributed to an increased density and spreading of ixodid ticks, thus enhancing their role as emerging vectors for pathogenic microorganisms in northern Europe. It remains unclear if they contribute to the occurrence of infections caused by the bacteria Bartonella spp., Francisella tularensis subspecies holarctica and the parasite Toxoplasma gondii in Sweden and on the Åland islands, Finland. In this study, we want to improve understanding of the tick-borne transmission of these pathogens. Volunteers were recruited at primary healthcare centers. Ticks and blood samples were acquired from participants recruited in 2008 and 2009. Health questionnaires were completed, and medical records were acquired where applicable. Feeding time was estimated and screening of pathogens in the ticks was performed through real-time PCR. Ticks (n = 1849) were of mixed developmental stages: 76 larvae, 1295 nymphs, 426 adults and 52 undetermined. All analyzed ticks were considered negative for these pathogens since the CT-values were all below the detection limit for Bartonella spp. (1663 ticks), Francisella spp. (1849 ticks) and Toxoplasma gondii (1813 ticks). We assume that infections with these pathogens are caused by other transmission pathways within these regions of Sweden and the Åland islands, Finland.