Objectives: The risk of developing Lyme borreliosis (LB) from Borrelia burgdorferi sensu lato (Bb)-infected ticks in Sweden is largely unknown. In the current study, we investigated the prevalence of Bb in ticks that had bitten humans and the risk of developing LB from Bb-infected ticks. Methods: Health questionnaires, blood samples, and ticks were collected from 394 tick-bitten study subjects in the County of Ostergotland, Sweden, at the time of the tick bite. Questionnaires and blood samples were also collected 3 months later. Ticks were screened for Bb DNA with PCR, while sera were analyzed for antibodies against Bb using two ELISA assays. Seroconversion, i.e., an at least two-fold increase in anti-Bb antibodies after 3 months, was confirmed using a Strip-Immunoassay. Results: Seventy-five of 397 ticks collected from the study subjects were determined to be Bb-positive. Sixty-four of the tick-bitten subjects had been bitten by Bb-infected ticks. Four of them showed seroconversion and were therefore considered to have an active Bb infection. None of these four subjects had sought health care due to symptoms, but one reported symptoms. Conclusions: Our data suggest that the risk of developing LB after being bitten by a Bb-infected tick is low, and asymptomatic Bb infections appear to be more frequent than symptomatic infections.

Background: Despite the good prognosis of erythema migrans (EM), some patients have persisting symptoms of various character and duration post-treatment. Several factors may affect the clinical outcome of EM, e. g. the early interaction between Borrelia (B.) burgdorferi and the host immune response, the B. burgdorferi genotype, antibiotic treatment as well as other clinical circumstances. Our study was designed to determine whether early cytokine expression in the skin and in peripheral blood in patients with EM is associated with the clinical outcome. Methods: A prospective follow-up study of 109 patients with EM was conducted at the A land Islands, Finland. Symptoms were evaluated at 3, 6, 12 and 24 months post-treatment. Skin biopsies from the EM and healthy skin were immunohistochemically analysed for expression of interleukin (IL)-4, IL-10, IL-12p70 and interferon (IFN)-gamma, as well as for B. burgdorferi DNA. Blood samples were analysed for B. burgdorferi antibodies, allergic predisposition and levels of systemic cytokines. Findings: None of the patients developed late manifestations of Lyme borreliosis. However, at the 6-month follow-up, 7 of 88 patients reported persisting symptoms of diverse character. Compared to asymptomatic patients, these 7 patients showed decreased expression of the Th1-associated cytokine IFN-gamma in the EM biopsies (p = 0.003). B. afzelii DNA was found in 48%, B. garinii in 15% and B. burgdorferi sensu stricto in 1% of the EM biopsies, and species distribution was the same in patients with and without post-treatment symptoms. The two groups did not differ regarding baseline patient characteristics, B. burgdorferi antibodies, allergic predisposition or systemic cytokine levels. Conclusion: Patients with persisting symptoms following an EM show a decreased Th1-type inflammatory response in infected skin early during the infection, which might reflect a dysregulation of the early immune response. This finding supports the importance of an early, local Th1-type response for optimal resolution of LB.

Resolution of Lyme borreliosis has previously been shown to be associated with a strong initial Th1 response, followed by a subsequent Th2 response,  shutting off inflammation. We mapped markers for Th1, Th2, Th17, cytotoxic and T regulatory subsets in a murine model, where the outcome of Borrelia (B.) burgdorferi sensu stricto (s.s.) infection was altered by immune-deviation towards Th2 by exposure to a subtoxic dose of mercury. Twenty-one B. burgdorferi s.s.-infected (Bb), 21 immune-deviated B. burgdorferi s.s.-infected (BbId), and seven control C3H/HeN mice were sacrificed on days 15, 28 and 43 post-infection (p.i.) with B. burgdorferi s.s. BbId mice had increased joint swelling compared with Bb at the height of the disease (28 p.i.), and also showed a trend for increased spirochaetal load that became significant on day 43 p.i. BbId had an increased histopathology score on day 28 p.i. compared with both earlier and later time points. mRNA expression of IL-4 (p=0.018), IL-10 (p=0.018) and EBI-3 (p=0.009) decreased in Bb mice, but not in BbId, over the course of infection. A trend for higher expression of IL-12p40 mRNA in Bb mice compared with BbId was seen late in the disease course, while BbId showed trends for higher levels of Foxp3 and GM-CSF. At the protein level, BbId showed decreased levels of CXCL9 compared to the Bb group on day 15 p.i (p=0.007). Bb mice showed increases of CXCL9 and CXCL10 at all time points compared with day 0 p.i. (p≤0.014), whereas BbId mice showed an initial decrease in both chemokines at day 15 p.i. compared with day 0 (p≤0.008). In conclusion, both the clinical signs of infection and the trends for increased expression of pro-inflammatory GM-CSF and T-regulatory marker Foxp3 in BbId mice suggested ongoing inflammation. Although our findings support the need for a strong Th1 response followed by anti-inflammatory response for optimal resolution, the anti-inflammatory response seems to be more complex than only dampening the inflammation by a Th1-antagonistic Th2 response.

The clinical outcome following infection with Borrelia (B.) burgdorferi sensu lato (s.l.) differs between individuals, ranging from asymptomatic infection to Lyme borreliosis (LB) with persistent symptoms post-treatment. Previous studies in mice and humans have generated the hypothesis that a successful outcome of B. burgdorferi s.l. infection is associated with an early strong pro-inflammatory T helper (Th)1-like immune response. The aim of this study was to assess the early course of events in B. burgdorferi s.l.-associated inflammation by screening for possible early immune biomarkers in peripheral blood from newly tick-bitten persons. The study subjects bitten by B. burgdorferi s.l.-infected ticks were divided into (1) those later developing clinical LB, (2) those who developed anti-B. burgdorferi s.l. antibodies but not clinical LB, (3) those who neither developed antibodies nor clinical LB. A fourth group consisted of bitten study subjects without development of antibodies or clinical LB. Two sets of samples, both comprising all four groups, were collected in order to repeat the analyses and confirm the data. Sera or plasma collected a few days after the tick bite were analysed for 18 biomarkers (IL-1β, IL-6, CXCL8/IL-8, IL-12p70, IL-17A, IL-27, TNF, CCL18, CCL20, CCL22, CXCL1, CXCL9, CXCL10, CXCL11, calprotectin, MMP-3, MMP-8, MMP-9) by multiplex bead assay and ELISA. In the first set of samples, the neutrophil activation marker calprotectin was increased in subjects who developed clinical LB compared with subjects who developed antibodies against B. burgdorferi s.l. but did not develop LB. However, the finding could not be confirmed in the second set of samples, thus the study failed to identify an early prognostic marker for development of clinical LB. Interestingly, both sets of samples showed increases in two different Th1-associated markers, CXCL10 and IL-12p70, respectively, in subjects who following a bite by a B. burgdorferi s.l.-infected tick developed antibodies against B. burgdorferi s.l. but did not develop LB compared with subjects who developed clinical LB, thus supporting the hypothesis of an early strong Th1-response being important for optimal resolution of B. burgdorferi s.l. infection.