A national crowdsourcing-based tick collection campaign was organized in 2015 with the objective of producing novel data on tick distribution and tick-borne pathogens in Finland. Nearly 20 000 Ixodes ticks were collected. The collected material revealed the nationwide distribution of I. persulcatus for the first time and a shift northwards in the distribution of I. ricinus in Finland. A subset of 2038 tick samples containing both species was screened for Borrelia burgdorferi sensu lato (the prevalence was 14.2% for I. ricinus and 19.8% for I. persulcatus), B. miyamotoi (0.2% and 0.4%, respectively) and tick-borne encephalitis virus (TBEV; 0.2% and 3.0%, respectively). We also report new risk areas for TBEV in Finland and, for the first time, the presence of B. miyamotoi in ticks from mainland Finland. Most importantly, our study demonstrates the overwhelming power of citizen science in accomplishing a collection effort that would have been impossible with the scientific community alone.

We investigated the epidemiology of Lyme borreliosis (LB) in Finland for the period 1995–2014 by using data from 3 different healthcare registers. We reviewed data on disseminated LB cases from the National Infectious Diseases Register (21,051 cases) and the National Hospital Discharge Register (10,402 cases) and data on primary LB (erythema migrans) cases from the Register for Primary Health Care Visits (11,793 cases). Incidence of microbiologically confirmed disseminated LB cases increased from 7/100,000 population in 1995 to 31/100,000 in 2014. Incidence of primary LB cases increased from 44/100,000 in 2011 to 61/100,000 in 2014. Overall, cases occurred predominantly in women, and we observed a bimodal age distribution in all 3 registers. Our results clearly demonstrate that the geographic distribution of LB has expanded in Finland and underscore the importance of LB as an increasing public health concern in Finland and in northern Europe in general.

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Risk factors for the widely endemic and much-debated tick-borne infection, Lyme borreliosis (LB), are unknown. The mannose-binding lectin (MBL) pathway of the complement cascade has an essential role in the eradication of Borrelia burgdorferi. A sufficient concentration of biologically active MBL in body fluids is an indicator of proper function of the MBL pathway. In this study, we investigated whether impaired MBL pathway function, represented by reduced serum MBL concentration, predisposes individuals to LB. First, we determined a serum MBL concentration cut-off level associated with diminished MBL pathway function in a group of 201 individuals. Then, we identified 350 borrelia Ab+ LB patient serum samples and 350 Ab− control samples from the archives of our laboratory and measured serum MBL concentrations in both sample groups. The concentration data were analyzed statistically using logistic regression, controlling for MBL cut-off, age, gender, and age and gender interaction. Serum MBL concentrations < 787 and < 445 ng/ml were associated with diminished and deficient MBL pathway function, respectively. Using these cut-offs, diminished (41.4 versus 27.4%, p = 0.0027) and deficient (26.3 versus 17.1%, p = 0.0361) MBL pathway functions were observed statistically more frequently in the LB patient samples than in the control samples. Also, the age-adjusted median serum MBL concentrations were significantly lower in the LB patient samples than in the non-LB controls. Our findings indicate that a deficiency in the MBL pathway of the complement cascade is a risk factor for developing disseminated Ab+ LB.

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