Close Geographic Association of Human Neoehrlichiosis and Tick Populations Carrying Candidatus Neoehrlichia mikurensis in Eastern Switzerland

Neoehrlichiosis caused by Candidatus Neoehrlichia mikurensis is an emerging zoonotic disease. In total, six patients have been described in Europe, with the first case detected in 2007. In addition, seven patients from China were described in a report published in October 2012. In 2009, we diagnosed the first human case of Ca. Neoehrlichia mikurensis infection in the Zurich area (Switzerland). Here, we report two additional human cases from the same region, which were identified by broad-range 16S rRNA gene PCR. Both patients were immunocompromised and presented with similar clinical syndromes, including fever, malaise, and weight loss. A diagnostic multiplex real-time PCR was developed for specific detection of Ca. Neoehrlichia mikurensis infections. The assay is based on the signature sequence of a 280-bp fragment of the Ca. Neoehrlichia mikurensis 16S rRNA gene and incorporates a Ca. Neoehrlichia mikurensis species, a Ca. Neoehrlichia genus, and an Anaplasmataceae family probe for simultaneous screening. The analytical sensitivity was determined to be below five copies of the Ca. Neoehrlichia mikurensis 16S rRNA gene. Our results show that the assay is suitable for the direct detection of Ca. Neoehrlichia mikurensis DNA in clinical samples from, for example, blood and bone marrow. In addition, it allows for monitoring treatment response during antibiotic therapy. Using the same assay, DNA extracts from 1,916 ticks collected in four forests in close proximity to the patients' residences (<3 km) were screened. At all sampling sites, the minimal prevalence of Ca. Neoehrlichia mikurensis was between 3.5 to 8% in pools of either nymphs, males, or females, showing a strong geographic association between the three patients and the assumed vector.