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Lyme borreliosis (LB) is a common and increasing tick-borne disease in Europe. The risk of acquiring a Borrelia infection after a tick bite is not fully known. Therefore, we investigated the incidence of Borrelia infection after a bite by a Borrelia-infected tick and if the Borrelia load and/or the duration of tick-feeding influenced the risk of infection. During 2008-2009, ticks and blood samples were collected from 1546 tick-bitten persons from Sweden and the Åland Islands, Finland. Follow-up blood samples were taken 3 months after the tick bite. The duration of tick feeding was microscopically estimated and Borrelia was detected and quantified in ticks by real-time PCR. Anti-Borrelia antibodies were detected in sera using ELISA tests and immunoblot. Five percent (78/1546) of the study participants developed Borrelia infection (LB diagnosis and/or seroconversion) after a tick bite (45% bitten by Borrelia-infected ticks and 55% bitten by uninfected ticks). Of these, 33 developed LB (whereof 9 also seroconverted) while 45 participants seroconverted only. Experience of non-specific symptoms was more frequently reported by Borrelia-infected participants compared to uninfected participants. All who seroconverted removed "their" ticks significantly later than those who did not. The Borrelia load in the ticks did not explain the risk of seroconversion. Regional and sex differences in the Borrelia seroprevalence were found. The risk of developing a Borrelia infection after a bite by a Borrelia-infected tick is small but increases with the duration of tick feeding., (Copyright © 2015 Elsevier GmbH. All rights reserved.)

Tick-borne encephalitis, TBE, has been observed in Aland Islands (population 26,500) for more than 60 years. Because of the small population, the relative incidence is high. Antibodies to TBE virus have been found in ca. 5% of healthy blood donors, indicating that subclinical infection must be common. This study is a review of the symptoms and signs of all the 301 serologically verified cases of TBE seen in Aland during 1959-2005. It also aims at analysing any possible changes in the symptoms and signs of TBE over time. The annual number of patients has been from 1 to 26, and has increased over time. The clinical picture has not undergone any conspicuous changes during these years. A few patients have had permanent neurological damage. There were no certain deaths from TBE. Simple practical measures may be taken to diminish, but not to eliminate, the risk of tick bites. Vaccination of exposed people is recommended, and general vaccination against TBE has commenced in Aland, beginning 2006. This is expected to reduce the incidence of TBE among the population to almost nil, provided that new inhabitants are vaccinated and that booster vaccinations are carried out as required.