Prevalence and seasonality of tick-borne pathogens in questing Ixodes ricinus ticks from Luxembourg

Abstract

In Europe, ixodid ticks are important arthropod vectors of human and animal pathogens, but comprehensive studies of the prevalence of all relevant pathogens in Central Europe are scarce. As a result of ecological changes, the incidences of tick-borne infections are expected to increase. In this study, 1,394 nymphal and adult Ixodes ricinus ticks sampled monthly during the active season from 33 ecologically distinct collection sites throughout Luxembourg were screened for all human tick-borne pathogens relevant in Central Europe. Species were identified by sequence analysis of detection PCR amplicons. Mean infection rates of ticks were 11.3% for Borrelia burgdorferi sensu lato, 5.1% for Rickettsia sp., 2.7% for Babesia sp., and 1.9% for Anaplasma phagocytophilum. No tick was found to be infected with Coxiella sp., Francisella tularensis subsp., or Tick-borne encephalitis virus (TBEV). A total of 3.2% of ticks were infected with more than one pathogen species, including mixed Borrelia infections (1.5%). Seasonal variations of tick infection rates were observed for Borrelia, Babesia, and Anaplasma, possibly reflecting a behavioral adaptation strategy of questing ticks. A positive correlation between the grade of urbanization and Borrelia infection rate of ticks was observed, suggesting an established urban zoonotic cycle. We also found Hepatozoon canis (0.1%) and Bartonella henselae (0.3%), which so far have not been found in questing Ixodes ricinus ticks in Central Europe.

FIG. 1.

Overall seasonal activity of the developmental stages of I. ricinus from 33 collection sites collected from May to October 2007 (A) and Borrelia infection rates of ticks (B). The letters M, J, J, A, S, and O represent the months May, June, July, August, September, and October, respectively. s.l., sensu lato; s.s., sensu stricto.

FIG. 2.

Phylogenetic trees for identification of pathogens to the species level based on 209 nucleotides of the FlaB gene of B. burgdorferi sensu lato (nucleotides 151 to 359 of GQ918147.1), including 157 samples and 71 reference sequences (A), on 462 to 465 nucleotides of the OspA gene of B. burgdorferi sensu lato (nucleotides 9441 to 9905 of CP001433.1), including 133 samples and 59 reference sequences (B), on 190 nucleotides of the 17-kDa antigen gene of Rickettsia species (nucleotides 140 to 329 of GU292313.1), including 72 samples and 14 reference sequences (C), on 343 to 370 nucleotides of the 18 rRNA of Babesia species (nucleotides 481 to 850 of EF413181.1), including 36 samples and 32 reference sequences (D), on 293 nucleotides of the 18 rRNA of Hepatozoon species (nucleotides 171 to 461 of FJ608736.1), including 1 sample and 34 reference sequences (E), on 466 nucleotides of the groEL gene of Anaplasma species (nucleotides 45 to 510 of GQ988761.1), including 26 samples and 55 reference sequences (F), and on 313 nucleotides of the 16S-23S region of Bartonella species (nucleotides 1782 to 2094 of AJ749669.1), including 4 samples and 26 reference sequences (G). Bootstrap values above 60 are shown. Asterisks represent (clusters including) our sequences. s.s., sensu stricto; DC, distinct cluster; ST, serotype.

FIG. 3.

Borrelia species composition by habitat category. s.s., sensu stricto.