Borrelia burgdorferi sensu lato infection rate of ticks collected from Harghita county, Romania

Lyme disease is one of the most prevalent vector-borne diseases in Europe. The disease is primarily transmitted by Ixodes ricinus ticks infected with members of the Borrelia burgdorferi sensu lato (s.l.) group of spirochetes. Local tick infection rates exceeding 20% may warrant antibiotic prophylaxis following tick bites. The aim of this study was to assess the infection rate of ticks collected along frequently used tourist routes and to compare tick collection methods. Questing ticks were collected using the dragging method along six tourist routes in Harghita County in 2022, while ticks from a seventh location were collected from a white dog. The locations of tick findings were recorded using GPS coordinates. Samples were stored in 70% ethyl alcohol until identification by light microscopy. Genomic DNA was extracted using the Quick-DNA Tissue/Insect Kit (Zymo Research) and subsequently screened for Borrelia burgdorferi s.l. by PCR. Amplicons were visualized using a standard gel electrophoresis protocol. Positive pools were subsequently re-examined individually. The 51 ticks collected along the tourist routes were predominantly nymphs (41/51) and all tested negative for Borrelia burgdorferi s.l. Samples collected from the dog were predominantly adult male ticks (46/54), with 12 positive samples detected overall. Among the positive samples, one was a larva, two were adult females, and nine were adult males. Consequently, the local infection rate reached 22.2%, while the overall Borrelia prevalence was 11.4%. Of the 105 ticks collected, 104 were Ixodes ricinus, whereas only one specimen was identified as Dermacentor reticulatus. This study confirmed the presence of Borrelia burgdorferi s.l. infection in tick populations occurring along hiking trails in Harghita County. Further nationwide surveillance studies are warranted to accurately assess B. burgdorferi s.l. infection rates in Ixodes ricinus ticks. Companion animals, particularly dogs, may be at a substantially higher risk of exposure to B. burgdorferi s.l. than humans; therefore, we recommend thorough post-exposure examinations of both animals and humans for attached ticks following outdoor activities.