Novel Demodex detection method involving non-invasive sebum collection and next-generation sequencing

Introduction
Demodex mites are common human ectoparasites found across a broad geographical range. They reside in pilosebaceous units of the skin and feed on sebum, epithelial and glandular cells. D. folliculorum is the more common mite, inhabiting the upper end of the pilosebaceous unit while D. brevis resides deeper in the skin and meibomian glands. Until now, Demodex mites have been obtained by various techniques such as skin scraping, cellophane tape, plucking eyelashes, and also by invasive biopsies.

Aim
To assess whether non-invasively collected sebum samples of patients suspected of rosacea or demodicosis are suitable for NGS DNA Demodex analysis.

Material and methods
Suspicion of seborrheic dermatitis or rosacea was the inclusion criterion. The study group consisted of 20 males, 1 female, age: 33–83, median: 58. Nasal dorsum was moisturized and an adhesive strip was applied. DNA was isolated from the sebum and sequenced with the use of MiSeq® Reagent Kit v2 and MiSeq® System.

Results
Out of 7 patients who were positive by microscopy, 6 were found positive by NGS. Additional 4 patients were found positive only by NGS, adding to a total of ten. The NGS approach showed superior sensitivity compared to light microscopy (63% and 44%, respectively). In 3 patients, both Demodex species were identified by NGS.

Conclusions
We believe to have proven that it is possible to study Demodex mites by NGS with sebum as the input sample. Furthermore, it is possible to identify and distinguish Demodex folliculorum from D. brevis in individual patients.