Candidatus Neoehrlichia mikurensis in Ixodes ricinus ticks collected near the Arctic Circle in Norway

Background: Candidatus Neoehrlichia mikurensis is a gram-negative bacterium belonging to the family Anaplasmataceae that, in Europe, is transmitted by Ixodes ricinus ticks. Candidatus N. mikurensis can cause a severe systemic inflammatory syndrome, neoehrlichiosis, mostly in persons with other underlying diseases. To date, Ca. N. mikurensis has been found in ticks in different countries in Asia and Europe, but never as far north as at the Arctic Circle. Methods: A total of 1104 I. ricinus ticks collected from vegetation and from animals in northern Norway (64-68 degrees N) were analysed for the prevalence of Ca. N. mikurensis. Of them, 495 ticks were collected from vegetation by flagging and 609 ticks were collected from dogs and cats. Total nucleic acid extracted from the ticks were converted to cDNA and analyzed with real-time PCR targeting the 16S rRNA gene of Ca. N. mikurensis. Positive samples were further analysed by nested PCR and sequencing. Results: Candidatus N. mikurensis was detected in 11.2% of all collected I. ricinus ticks in northern Norway. The prevalence differed between ticks collected from vegetation (18.2%; 90/495) compared to ticks collected from dogs and cats (5.6%; 34/609). The ticks from dogs and cats were collected in Bronnoy area and seven additional districts further north. The prevalence of Ca. N. mikurensis in these ticks differed between geographical localities, with the highest prevalence in the Bronnoy area. Conclusions: The detection of Ca. N. mikurensis in I. ricinus ticks from the Arctic Circle in northern Norway indicates potential risk for tick-bitten humans at this latitude to be infected with Ca. N. mikurensis.