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''Demodex'' is a genus of tiny parasitic mites that live in or near hair follicles of mammals. Around 65 species of ''Demodex'' are known. Two species living on humans have been identified: ''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. ''Demodex'' is derived from Greek ''dēmos'' fat + ''dēx'', a wood worm.〔(【引用サイトリンク】 Demodex )〕 ==''D. folliculorum'' and ''D. brevis''== ''D. folliculorum'' and ''D. brevis'' are typically found on humans. ''D. folliculorum'' was first described in 1842 by Simon; ''D. brevis'' was identified as separate in 1963 by Akbulatova. ''D. folliculorum'' is found in hair follicles, while ''D. brevis'' lives in sebaceous glands connected to hair follicles. Both species are primarily found in the face, near the nose, the eyelashes, and eyebrows, but also occur elsewhere on the body. The adult mites are only long, with ''D. brevis'' slightly shorter than ''D. folliculorum''. Each has a semitransparent, elongated body that consists of two fused segments. Eight short, segmented legs are attached to the first body segment. The body is covered with scales for anchoring itself in the hair follicle, and the mite has pin-like mouthparts for eating skin cells 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 8–16 cm per hour, especially at night, as they try to avoid light.〔 The mites are transferred between hosts through contact with hair, eyebrows, and the sebaceous glands of the face. Females of ''D. folliculorum'' are larger and rounder than males. Both male and female ''Demodex'' mites have a genital opening, and fertilization is internal. Mating takes place in the follicle opening, and eggs are laid inside the hair follicles or sebaceous glands. The six-legged larvae hatch after three to four days, and the larvae develop into adults in about seven days. The total lifespan of a ''Demodex'' mite is several weeks. Research about human infection by ''Demodex'' mites is ongoing,〔 with several preliminary studies suggesting an association between mite infection and rosacea. Older people are much more likely to carry the mites; about a third of children and young adults, half of adults, and two-thirds of elderly people carried them. The lower rate in children may be because children produce less sebum. Recently, a study of 29 adults (18 and over) in North Carolina, USA, found that 70% of those 18 years of age carried mites, and that all adults over 18 (''n'' = 19) carried them. This study (using a DNA detection method, more sensitive than traditional sampling and observation by microscope), along with several studies of cadavers, suggests that previous work may have underestimated the mites' prevalence. However, the small sample size and small geographical area involved prevent drawing broad conclusions from these data. In the vast majority of cases, the mites go unobserved, without any adverse symptoms, but in certain cases (usually related to a suppressed immune system, caused by stress or illness), mite populations can dramatically increase, resulting in a condition known as demodicosis or ''Demodex'' mite bite, characterised by itching, inflammation, and other skin disorders. Blepharitis (inflammation of the eyelids) can also be caused by ''Demodex'' mites. Evidence of a correlation between ''Demodex'' infection and acne vulgaris exists, suggesting it may play a role in promoting acne. Only one zoonosis of ''Demodex'' is known. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Demodex」の詳細全文を読む スポンサード リンク
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