What are Demodex Mites?
Demodex mites are microscopic parasites which feed off the oils, hormones, and fluids present around human hair follicles.
Microscopic Demodex mites are a natural part of the human microbiome — the ecological community of microorganisms that live within and on the body. Two species of Demodex are found in humans. Demodex folliculorum live in hair follicles, primarily on the face, as well as in the meibomian glands of the eyelids; Demodex brevis live in the sebaceous glands of the skin.
General considerations of Demodex
Demodex mite is an obligatory human ectoparasite, and it is resident in or near the pilosebaceous units.
About 65 species of Demodex are known. Two species D. folliculorum and Demodex brevis collectively referred to as Demodex, are typically found on humans, occurring in 10% of skin biopsies and 12% of follicles. Identification of these mites dates back to 1841-42 for D. folliculorum by Simon and 1963 for D. brevis by Akbulatova.
Demodex is a saprophytic mite that belongs to family Demodicidae, class Arachnida, and order Acarina.
Adult D. folliculorum mites are 0.3-0.4 mm in length and D. brevis are slightly shorter of 0.15-0.2 mm in length, with females somewhat shorter and rounder than males. According to this fact, they are invisible to the naked eye, but, under the microscope, their structure is clearly visible. It has a semi-transparent, elongated body that consists of two fused segments. Eight short, segmented legs are attached to the first body segment. The eight legs of this mite move at a rate of 8-16 mm/h and this is mainly done during the night as bright light causes the mite to recede into its follicle. The body is covered with scales for anchoring itself in the hair follicle and the mite has pin-like mouthparts for eating skin cells, hormones, and oils (sebum) accumulating in the hair follicles.
The prevalence of infestation with Demodex mites is highest in the 20-30 years age group when the sebum secretion rate is at its highest. Older people are also more likely to carry the mites.
The prevalence of infestation with Demodex mites is highest in the 20-30 years age group, when the sebum secretion rate is at its highest. Older people are also more likely to carry the mites.
Mode of transmission
The mites are transferred between hosts through contact of hair, eyebrows, and sebaceous glands on the nose.
Methods of detection on body
Demodex is not easily detected in histological preparations; therefore, skin surface biopsy (SSB) technique with cyanoacrylic adhesion is a commonly used method to measure the density of Demodex.
The resulting number of mites measured varies greatly depending on the method used.
With modern, and more sensitive, assays, the prevalence of Demodex in skin samples approaches 100%; therefore, mere presence of Demodex does not indicate pathogenesis. Rather, more important in diagnosing Demodex pathology is the density of mites or their extra-follicular location.