Grankvist, Anna

Abstract Background Candidatus (Ca.) Neoehrlichia (N.) mikurensis is an emerging tick-borne pathogen of humans that is closely related to Ehrlichia and Anaplasma species. This strict intracellular bacterium escapes detection by routine microbiologic diagnostic methods such as blood culture, leading to considerable under-diagnosis of the infectious disease it causes, neoehrlichiosis. Methods Here, we describe the vascular and thromboembolic events afflicting a series of 40 patients diagnosed with neoehrlichiosis in Sweden during a 10-year period (2009–2019). Results The majority of the patients (60%) developed vascular events ranging from repeated thrombophlebitis, deep vein thrombosis, pulmonary embolism, transitory ischemic attacks, to arteritis. Younger age was a risk factor for vascular complications. In contrast, there was no difference in the incidence of vascular events between immunosuppressed and immunocompetent patients. However, there were qualitative differences, such that deep vein thrombosis exclusively afflicted the immunosuppressed patients, whereas arteritis was restricted to the immunocompetent persons. We also present the case histories of two patients who developed vasculitis mimicking polyarteritis nodosa and giant cell arteritis. Both were cured by doxycycline treatment. Conclusions Ca. N. mikurensis infection should be considered in patients living in tick-endemic areas of Europe and northern Asia who present with atypical vascular and/or thromboembolic events. Early diagnosis and antibiotics targeting this emerging infectious agent can eradicate the infection and prevent the development of new vascular events.

“CandidatusNeoehrlichia mikurensis” is the tick-borne agent of neoehrlichiosis, an infectious disease that primarily affects immunocompromised patients. So far, the genetic variability of “Ca. Neoehrlichia” has been studied only by comparing 16S rRNA genes andgroELoperon sequences. We describe the development and use of a multilocus sequence analysis (MLSA) protocol to characterize the genetic diversity of clinical “Ca. Neoehrlichia” strains in Europe and their relatedness to other species within theAnaplasmataceaefamily. Six genes were selected:ftsZ,clpB,gatB,lipA,groEL, and 16S rRNA. Each MLSA locus was amplified by real-time PCR, and the PCR products were sequenced. Phylogenetic trees of MLSA locus relatedness were constructed from aligned sequences. Blood samples from 12 patients with confirmed “Ca. Neoehrlichia” infection from Sweden (n= 9), the Czech Republic (n= 2), and Germany (n= 1) were analyzed with the MLSA protocol. Three of the Swedish strains exhibited identicallipAsequences, while thelipAsequences of the strains from the other nine patients were identical to each other. One of the Czech strains had one differing nucleotide in theclpBsequence from the sequences of the other 11 strains. All 12 strains had identical sequences for the genes 16S rRNA,ftsZ,gatB, andgroEL. According to the MLSA, among theAnaplasmataceae, “Ca. Neoehrlichia” is most closely related toEhrlichia ruminantium, less so toAnaplasma phagocytophilum, and least toWolbachiaendosymbionts. To conclude, three sequence types of infectious “Ca. Neoehrlichia” were identified: one in the west of Sweden, one in the Czech Republic, and one spread throughout Europe.