[Tick-borne encephalitis and Lyme borreliosis. Spread of pathogens and risk of illness in a tick-borne encephalitis region].

A knowledge of the distribution of tick-borne agents and the related risks of contracting diseases are essential to ensure an appropriate response between hysteria and disregard, and to decide the appropriateness of vaccination. Illustrated by the German town of Lohr a. M. (Bavaria), the prevalence of TBE-virus and Borrelia burgdorferi in ticks was investigated and compared, and the respective risk of contracting disease from a bite assessed. Using the polymerase chain reaction (PCR), a total of 1657 ticks obtained from five different biotopes around Lohr were examined for the TBE-virus, and 408 ticks for Borrelia burgdorferi. The results were compared with earlier findings in other regions of Germany. The risk of contracting illness was estimated on the basis of transmission and manifestation rates, together with epidemiological data from the region. The prevalence of TBE-virus was 0.12% (95% CI: 0.05-0.44%) in the ticks investigated. This is comparable with that in 4 other regions rated as TBE-risk regions, but significantly lower than that in rated high-risk regions. Borrelia burgdorferi was detected in 14.9% (11.8-19.0%) of adult ticks, roughly twice the prevalence found in nymphs (7.2%, range 4.6-11.7%). On the basis of these prevalences, the risk of contracting meningitis/encephalitis from a tick bite is about 1:10,000, and the risk for Lyme Borreliosis is about 1:100, the latter requiring that the tick remains attached for at least 2-3 days.