BACKGROUND

This study aimed at investigating the diversity of pathogens in human-biting ixodid ticks, in relation to their seasonality and associated clinical symptoms.

METHODS

Hard ticks, collected from humans in the course of 23 years, were identified to the species level on a morphological basis. This was followed by DNA extraction and molecular analyses. The latter served to confirm tick species, and to detect important tick-borne pathogens, in particular rickettsiae, Anaplasmataceae, borreliae, and piroplasms.

RESULTS

Among 502 ticks, six species were identified, with the predominance of Ixodes ricinus. Considering tick-borne pathogens, four Rickettsia spp., Anaplasma phagocytophilum, seven genospecies of Borrelia burgdorferi sensu lato, and three Babesia spp. were detected. Some of these predominated in nymphs or females of I. ricinus. Tick-infested patients presented with six types of clinical signs. Approximately one out of seven ticks from patients presenting with erythema migrans were unengorged. Shorter, spring-associated presence of Babesia microti-, A. phagocytophilum-, and Dermacentor-borne rickettsiae was observed in ticks, while Rickettsia helvetica and borreliae persisted until late autumn.

CONCLUSIONS

The seasonal occurrence of I. ricinus-borne pathogens appeared to be genus-dependent, but did not correlate with known typical reservoirs (rodents, birds, reptiles), nor with tick developmental stage or transstadial versus transovarial transmission. Pathogen detection in ticks that bit humans did not necessarily imply an infection.