Infection dynamics of the tick-borne pathogen 'Candidatus Neoehrlichia mikurensis' and co-infections with Borrelia afzelii in bank voles in Southern Sweden.

The tick-borne bacterium 'Candidatus Neoehrlichia mikurensis' has recently been recognized as a human pathogen. Together with Borrelia afzelii, it is one of the most common pathogens found in the tick Ixodes ricinus. Here, we compared the epidemiology of 'Candidatus N. mikurensis' and B. afzelii by longitudinal sampling from May to September in one of their most abundant vertebrate hosts, the bank vole (Myodes glareolus), using real-time PCR for detection and quantification. The prevalence of 'Candidatus N. mikurensis' and B. afzelii was 19% (50/261) and 22% (56/261), respectively. The prevalence of 'Candidatus N. mikurensis' increased significantly during the sampling season. The clearance rate of 'Candidatus N. mikurensis' was significantly higher than that of B. afzelii. We found a high frequency of double infections; 46% of all samples infected with 'Candidatus N. mikurensis' also had a co-infection with B. afzelii. The frequency of co-infections was significantly higher than expected from the prevalence of each pathogen. The high level of co-infections can be caused by interactions between the pathogens or might reflect variation in general susceptibility among voles.