Detection of three species of Borrelia burgdorferi in I. ricinus in northern Italy by polymerase chain reaction

Rationale. The prevalence of Borrelia burgdorferi in Ixodes ricinus ticks is one indicator for identifying the risk of infection in a given territory. Methods. Two PCR procedures were developed to detect B. burgdorferi infection in Ixodes ricinus nymphs. For the first method we used primers to amplify a fragment of the flagellin gene (fla) specific for B. burgdorferi sensu lato. In the second, we employed species-specific oligonucleotides directed against 16S rRNA which were able to specifically identify the genospecies of B. burgdorferi sensu stricto, B. garinii and B. afzelii, and another set for B. burgdoroferi sensu lato. Results. No amplification product was detected in uninfected control ticks whereas both techniques gave positive amplification for B. burgdorferi sensu lato in 73.8-79.0% of the field-collected ticks. The two PCR procedures were in agreement in identifying B. burgdorferi sensu lato infection. The use of flagellin primers seemed more sensitive than the oligonucleotide-based approach but it was also more complex for processing a large number of tick samples. The most prevalent species were B. burgdorferi sensu stricto and B. garinii and co-infected the same tick in 25% of PCR-positive samples. Only a few ticks proved to be infected by B. afzelii. We believe that use of PCR is accurate for prevalence studies. Moreover, it provides information about the geno-species of B. burgdorferi circulating in the tick vectors.