Detection of Candidatus Neoehrlichia mikurensis and Ehrlichia muris in Estonian ticks

Abstract

So far neglected bacteria like Candidatud Neoehrlichia mikurensis and Ehrlichia muris-like agents get increased attention in the recent past. Ixodid ticks were demonstrated to harbor both of these pathogens. Estonia is populated by two medically important tick species, I. ricinus and I. persulcatus. In this study the presence of E. muris and Candidatus N. mikurensis in these two tick species was investigated. Tick DNA was analyzed by nested PCR and subsequent sequencing for the presence of 16S rRNA of E. muris and Candidatus N. mikurensis. Positive samples were further confirmed by amplification and sequencing of the partial groESL-operon. The obtained partial groESL sequences were used for construction of a maximum likelihood tree. In total, 776 ticks from 36 collection sites situated in 7 counties on the mainland of Estonia and 2 sites situated in one county on the island Saaremaa were collected. 548 were I. ricinus and 228 were I. persulcatus. Only in 5 counties (11 sites) samples positive for the Anaplasmataceae 16S rRNA gene were found. The percentage of Candidatus N. mikurensis positive ticks varied from 1% to 9.1% at different sites. In Eastern and South-Eastern Estonia, the area where I. ricinus and I. persulcatus are sympatric, no Candidatus N. mikurensis was found. Ticks carrying E. muris were found in three counties, the site-specific percentage of positive ticks varied from 1.2% to 25.6%. This is the first study revealing the presence of Candidatus N. mikurensis and E. muris in Estonian ticks. Candidatus N. mikurensis was found only in the western part of the country exclusively in I. ricinus and the phylogenetic analysis revealed close relatedness of the Estonian sequences to other European Candidatus N. mikurensis strains. E. muris was detected mostly in I. persulcatus and only in one I. ricinus in the sympatric area of both tick species. This is in correspondence with the observation that this pathogen is more often found in I. persulcatus than in I. ricinus. This study demonstrates the presence of Candidatus N. mikurensis and E. muris in Estonian ticks and highlights the necessity to raise awareness of symptoms by healthcare professionals.

Keywords: Candidatus Neoehrlichia mikurensis; Ehrlichia muris; Ixodes persuclatus; Ixodes ricinus; Tick-borne pathogens.