Testing for Demodex

Testing for Demodex is not commonly performed in human medicine, though we hope that will change so that more targeted treatment can be given. Where confirmation is required due to uncertainty over clinical signs, the following tests can be done quickly with minimal resources:

1. In eyelashes: Lateral eyelash tension. Requires an optometrists’ slit lamp and tweezers – See Müntz Video 1, Müntz Video 2. ¹ Remember that Demodex can be found in clean lashes too.
   This technique avoids epilation of eyelashes.

• In the skin: Standardised skin surface biopsy (SSSB). Requires ‘Superglue’ and a standard light microscope – See Forton Video ²

• Skin scrapes are done on inflamed skin putting mineral oil on the affected area then scraping with a scalpel blade to collect samples for microscopy. Some authors advocate squeezing the area to the extent that some bleeding may occur. ³ Use of dark field microscopy helps visualisation as Demodex are bioluminescent.⁴

PCR: Digital polymerase chain reaction based on the 18S ribosomal RNA (18SrRNA) gene may also be used to detect Demodex in Demodex blepharitis⁵ and presumably from many other tissue or fluid samples. However, be aware that some of the other ectoparasites which may affect humans could be missed if the corresponding primer for that species is not used.

1. Zhang, AC, Müntz, A, Wang, MTM, Craig, JP, & Downie, LE. Ocular Demodex: a systematic review of the clinical literature. Ophthalmic Physiol Opt 2020; 40: 389– 432. Doi: 10.1111/opo.12691
   doi.org/10.1111/opo.12691 ↩︎
2. Forton FMN & De Maertelaer V. Two consecutive standardized skin surface biopsies: An improved sampling method to evaluate demodex density as a diagnostic tool for rosacea and demodicosis. Acta Dermato-Venereologica.2017; 97(2): 242–248. doi.org/10.2340/00015555-2528 ↩︎
3. Foley R, Kelly P, Gatault S, Powell F. Demodex: a skin resident in man and his best friend. J Eur Acad Dermatol Venereol. 2021;35(1):62-72 doi.org/10.1111/jdv.16461 ↩︎
4. Aytekin S, Yaşar S, Göktay F, Güneş P. Spontaneous fluorescence of Demodex in the dark. (letter) JEADV 2016, 30, 320–38.  doi:10.1111/jdv.12776
   https://www.infona.pl/resource ↩︎
5. Kasetsuwan N, Kositphipat K, Busayarat M, Threekhan P,Preativatanyou K, Phumee A, Siriyasatien P. Prevalence of ocular demodicosis among patients at Tertiary Care Center, Bangkok, Thailand. Int J Ophthalmol. 2017;10(1):122-127. Published 2017 Jan 18. doi:10.18240/ijo.2017.01.20 https://www.ncbi.nlm.nih.gov ↩︎