Molecular Assay Diagnoses Neoehrlichiosis

A diagnostic multiplex real-time polymerase chain reaction (PCR) was developed specifically for the detection of Candidatus N. mikurensis infections, which is a rare organism in humans, but is classified as an emerging disease.

Scientists at the University of Zurich, (Switzerland) developed assay based on the signature sequence of a 282-bp fragment of the Candidatus N. mikurensis 16S ribosomal ribonucleic acid (rRNA) gene and incorporates a Candidatus N. mikurensis species, a Neoehrlichia genus and an Anaplasmataceae family probe for simultaneous screening. The analytical sensitivity of was determined to be below five copies of the Candidatus N. mikurensis 16S rRNA gene.

The assay was found to be suitable for the direct detection of Candidatus N. mikurensis DNA in clinical samples like blood and bone marrow. In addition, it allows for monitoring treatment response during antibiotic therapy. DNA extracts from 1,916 ticks collected in four forests within less than 3 km proximity to the patients' residences were screened using the same assay. At all sampling sites, the minimal prevalence of Candidatus N. mikurensis was 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.

Guido V. Bloemberg, PhD, the senior author of the study said, “Because the bacteria that cause neoehrlichiosis could not be bred in the laboratory until now and thus no rapid tests were available, many infections might have remained undetected. How well the bacterium is transmitted to humans via a bite from an infected tick, however, still needs to be researched.” The study was published on October 31, 2012, in the Journal of Clinical Microbiology.

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