Detection of Borrelia burgdorferi (s.l.) in Ixodes ricinus ticks collected in Iceland

Background: Ixodes ricinus is the most common tick species throughout Europe; it can transmit various pathogens that can cause diseases in humans and animals. It is the principal vector of Borrelia burgdorferi sensu lato (s.l.) and tick-borne encephalitis virus (TBEV), and there is increasing concern about I. ricinus's potential to transmit pathogens to humans and animals in Iceland. The aim of this research is to determine whether I. ricinus ticks collected in Iceland carry B. burgdorferi (s.l) and, in a limited number of samples, other pathogens to better understand the potential health risks that I. ricinus bites may pose to both humans and animals in Iceland. Methods: Birds were captured and examined for ticks at the South East Iceland Bird Observatory from 2018 to 2019. All ticks were screened for infection with B. burgdorferi (s.l.). Additionally, 133 ticks collected in Iceland prior to 2018, stored in the collection at the Natural Science Institute of Iceland, were screened for the presence of B. burgdorferi (s.l.), TBEV, Coxiella burnetii, Francisella tularensis and Rickettsia spp. Samples positive for Borrelia were sequenced by Genewiz Azenta, Germany, and BLAST (NCBI) analysis was performed on the obtained sequences. Results: A total of 1209 I. ricinus ticks collected in Iceland were screened for the presence of B. burgdorferi (s.l.); 133 ticks from a museum collection were additionally screened for other pathogens. Borrelia burgdorferi (s.l.) was detected in 9.9% of the tick samples (86/866). DNA sequencing from 28 positive samples revealed three genospecies. The most frequently detected was Borrelia garinii (82.1%), followed by B. valaisiana (14.3%) and B. afzelii (3.6%). TBEV, C. burnetii, F. tularensis and Rickettsia spp. were not detected in ticks from the collection. Conclusions: This research confirms the presence of B. burgdorferi (s.l.) in I. ricinus ticks collected in Iceland. Even though Lyme disease is not endemic and I. ricinus ticks are not considered established, the risk of exposure remains. Further research on B. burgdorferi (s.l.) and other pathogens these ticks may carry is essential along with raising public awareness and fostering collaboration between experts to reduce the risk of tick-borne diseases in Iceland.