Prevalence of Borrelia miyamotoi and Neoehrlichia mikurensis in a cohort of tick-exposed individuals and population controls in Denmark 2002-2021.

Borrelia miyamotoi and Neoehrlichia mikurensis are recently discovered tick-borne pathogens. The aim of this study was to ascertain the extent of transmission among high-risk groups and healthy controls. The study design is retrospective cohort study. Blood from a total of 1180 individuals, collected between 2002-2021: (i) 180 tick-exposed individuals, (ii) 400 immunocompromised individuals and (iii) 600 blood donors was included. Infection was examined by a protein array (B. miyamotoi) and PCR. Neoehrlichia mikurensis DNA was detected in only one individual with Lyme neuroborreliosis (LNB) with symptoms compatible with both infections. Borrelia miyamotoi seroprevalence (being either IgM or IgG positive) among tick-exposed individuals (8.3 %, 95%CI 5.1-13.3) was significantly higher compared to healthy blood donors (1.5 %, 95 % CI 0.8-2.8) and immunocompromised individuals (3.3 %, 95 %CI 1.9-5.5), p < 0.0001. Altogether, 37 of 1180 individuals (3.1 %, 95 %CI 2.2-4.3) were found to be B. miyamotoi seropositive. Neoehrlichiosis and Borrelia miyamotoi disease should be considered in patients with febrile illness and relevant exposure and in non-characteristic presentations of Lyme borreliosis in Denmark.