Evidence for a risk of tick-borne infection in the city parks of Vilnius, Lithuania

Thirty-six adult ticks collected in the parks of the Lithuanian capital Vilnius in the spring of 2005 were identified as Ixodes ricinus (L.) and studied for the presence of live pathogens by darkfield microscopy, of exoskeleton anomalies by light stereomicroscopy, and of several tickborne pathogens by PCR. One of the ticks was positive for three pathogens simultaneously: Ehrlichia muris (monocitic ehrlichiosis agent), Borrelia afzelii, and Borrelia garinii; one was dually infected by both species of Borrelia. In addition, ticks positive for several species of Borrelia were detected: B. afzelii (n = 5), B. garinii (n = 2), some other species of B. burgdorferi sensu lato (n = 2), Ehrlichia muris (n = 1). The total proportion of infected ticks was 27.8% (10 of 36), of which 20% (2 of 10) were multiply infected; 47.2% of ticks had exoskeleton anomalies, and such specimens had more multiple infections (35.3% versus 21%). One triply infected tick was found only among the anomalous specimens. Live spirochaetes prevailed among the anomalous specimens: 35.3% (6/17) vs. 5.3% (1/19). The difference was statistically significant: chi square was equal 5.166, P < 0.05. In conclusion, even this small sample size reveals several important tick-borne pathogens in the newly detected focus in the centre of Vilnius, transmitted by I. ricinus. It suggests that people visiting these parks are exposed to the risk of tick-borne infection, especially when resting on the grass.