The microscopic mite that lives on the skin of human beings is called Demodex folliculorum.
Demodex is a genus of tiny mites that live in or near hair follicles of mammals. รอบๆ 65 species of Demodex are known.Two species live on humans: Demodex folliculorum และ 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.
What is Demodex Folliculorum
Demodex folliculorum is a microscopic mite that can only survive on the skin of humans.Most people have D.folliculorum on their skin. โดยปกติ, the mites do not cause any harm, and are therefore considered an example of commensalism rather than parasitism.If D.folliculorum does cause disease, this is known as demodicosis.
Demodex. folliculorum and Demodex. brevis
NS. folliculorum และ NS. brevis are typically found on humans. NS. folliculorum was first described in 1842 by Simon; NS. brevis was identified as separate in 1963 by Akbulatova. NS. folliculorum is found in hair follicles, ในขณะที่ NS. 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 0.3–0.4 mm (0.012–0.016 in) long, กับ NS. brevis slightly shorter than NS. 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, 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 (3.1–6.3 in) ต่อชั่วโมง, 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 NS. 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 3–4 days, and the larvae develop into adults in about 7 วัน. The total lifespan of a Demodex mite is several weeks.
Role Of Demodex To Human Skin
Demodex folliculorum or Demodex brevis inhabit the eyelash,hair follicles, and sebaceous glands.
Other mite species, specific to each mammal, are similarly harbored by their host species. Mites are not found on the skin of newborns. Hair follicles are thought to become colonized by mites during childhood and early life by transmission from adults, similar to the process of acquiring other microbes (microbes include bacteria, protozoa, เชื้อรา, สาหร่าย, อะมีบา, and slime molds). Microbe acquisition is a lifelong activity that begins the moment we are born.
Though babies develop in a sterile environment, a newborn emerges as a bacterial sponge picking up microbes that contribute to its health.
Microbes can be found in their greatest concentrations in the ears, จมูก, ปาก, vagina, digestive tract, anus, และผิวหนัง. Like microbes, demodex mites are a natural part of the human microbiome and may serve a useful function.
It is important to consider humans are not biologically self-sufficient—they must host microbes to avoid disease. ตัวอย่างเช่น, genes carried by bacteria in the gastro-intestinal tract allow humans to digest foods and absorb nutrients that otherwise would be unavailable.
These fundamental microbes produce beneficial compounds, like certain vitamins and protective anti-inflammatories that humans cannot produce by themselves. ตัวอย่างเช่น, members of the gut microbiota can produce anti-inflammatory factors by enhancing cellular immune responses as well as generate Vitamins K and B.
NS. folliculorum is adapted to live inside hair follicles, and therefore is thin and worm-like, with short legs. As an adult, NS. folliculorum measures 0.3 ถึง 0.4 มม (0.012 ถึง 0.016 ใน) long.Adults have four pairs of legs, larvae and nymphs have only three pairs.NS. folliculorum has a rudimentary gut, and no anus.
Reproduction and life cycle
The entire life cycle of NS. folliculorum takes 14–16 days.Adult mites copulate at the top of the hair follicle, near the skin surface.Eggs are deposited in the sebaceous gland inside the hair follicle.The heart-shaped egg is 0.1 มม (0.0039 ใน) long, and hatches into a six-legged larva.It takes seven days for the larva to develop into a mature adult,with two intervening nymph stages.The adult lives for 4–6 days.
Demodex folliculorum prefers areas where sebum production is high,and is typically found in hair follicles on the human face,generally in greater numbers around the cheeks, จมูก, and forehead, but also elsewhere on the face, eyelids and ears.The mites may also be found on other parts of the body, such as the chest and buttocks.
Within the hair follicle, NS. folliculorum is found above the sebaceous gland,positioned head downwards, with the end of abdomen often protruding from the hair follicle.Infested follicles usually contain 2–6 mites, but greater numbers can occur.
In one hour, NS. folliculorum can travel 8 ถึง 16 มม (0.31 ถึง 0.63 ใน);the mites usually travel at night.
The mites are obligate commensals of humans,and can only live on the skin; they soon dry out and die if they leave the host.Higher numbers of NS. folliculorum are found in the spring and summer than at other times of the year.
The first report of Demodex folliculorum was made by German scientist Jakob Henle in 1841, but his presentation to the Natural Sciences Society of Zurich, reported in a local newspaper, attracted little attention at the time.In 1842, German dermatologist Gustav Simon gave a full report of the appearance of Demodex folliculorum, naming it Acarus folliculorum.The following year, 1843, the genus was named Demodex by English scientist Richard Owen.From Simon’s initial description of NS. folliculorum onwards, two forms were recognized, a long form and a short form.In 1963, it was suggested that these long and short forms were two subspecies of NS. folliculorum, and that the smaller mite be named Demodex brevis, with the larger mite retaining the name NS. folliculorum.มันไม่ได้จนกว่า 1972 that the existence of two separate species was confirmed.
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