Tickborne Neoehrlichia mikurensis in the Blood of Blood Donors, Norway, 2023.

The tickborne bacterial pathogen Neoehrlichia mikurensis has been detected in <1% of blood donors in Sweden. N. mikurensis can give rise to asymptomatic persistent infections. Up to 25% of Ixodes ricinus ticks in southern Norway are infected with N. mikurensis. We investigated the incidence of N. mikurensis infection among blood donors in this region. We detected N. mikurensis in the blood of 45/499 (9%) blood donors by independent PCR methods; 69% of those were repeatedly positive 1-7 months after the first detection and tested negative after doxycycline treatment. We tested 8/19 adult recipients of potentially infected blood; none tested positive for N. mikurensis at the time of testing (191-301 days after transfusion). Our study identified a very high rate of infection with N. mikurensis in blood donors in Norway; whether infection can be transmitted by transfusion of blood products, however, remains unclear.