We examined by dark field microscopy 195 of 209 Ixodes ricinus ticks that were removed from humans in the Czech Republic (mainly in southern Moravia) during 1997–2001. The majority of the ticks were nymphs (62%), 31% were females and 7% larvae; 10.7% of the nymphs, 20.3% of the females but no larvae were found to be infected with B. burgdorferi s.l., the agent of Lyme borreliosis (LB). This observation supports for Central Europe the conclusions drawn from North America about nymphal ixodid ticks as the most important vector stage in transmission of LB. In the course of the year, we found the highest proportion of infected nymphal and female ticks taken off humans in June. The detection of borreliae in a human-biting tick is an important step that enables the general practitioner to prescribe prophylactic antimicrobial treatment and to reduce significantly the risk of Lyme disease in the patient.

        Key words: ticks – Ixodes ricinus – Lyme disease – Borrelia burgdorferi s.l. – diagnostics – prophylaxis.