Demodex

Demodex is a genus of tiny mites that live in or near hair follicles of mammals. Around 65 species of Demodex are known. Two species live on humans: Demodex folliculorum and Demodex brevis, both frequently referred to as eyelash mites. Different species of animals host different species of Demodex. Demodex canis lives on the domestic dog. Infestation with Demodex is common and usually does not cause any symptoms, although occasionally some skin diseases can be caused by the mites.

Description

Demodex mites are 0.3 to 0.4 mm long. They are fusiform with transverse striations that are covered with scales for anchoring itself in the hair follicle, and the abdomen is short and rounded. The body is covered with semi-transparent scales for anchoring itself in the hair follicle, and the mite has pin-like mouth-parts for eating skin cells, hormones and oils (sebum) which accumulate in the hair follicles. The mites can leave the hair follicles and slowly walk around on the skin, at a speed of about 8–16 cm/hour, especially at night; they try to avoid light.

Life cycle

The entire life cycle of Demodex mites takes place on their host. The mites are transferred between hosts through contact, particularly when the host sleeps. The female mite, having been fertilized, leaves the follicle and lays her eggs in a nearby sebaceous gland. When the eggs hatch, the larvae return to the follicle, where they live and develop into adults. The total lifespan of a Demodex mite is several weeks.

Medical significance

Demodex mites are often found in the human hair follicles. They are usually harmless and cause no symptoms, but in large numbers can cause demodicosis, which is often associated with hair loss, itching and inflammation. Demodex mites can also cause blepharitis, an inflammation of the eyelids.

Treatment

Treatment for demodicosis often involves topical creams or lotions, which kill the mites. In severe cases, oral medications may be necessary. Good hygiene practices can also help control the number of mites on the skin.

See also

• Demodicosis
• Blepharitis
• Mite

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