Demodex folliculorum
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Demodex folliculorum , stages (from left to right): |
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| ( Simon , 1842) Owen |
Demodex folliculorum is a species of mite from the family of hair follicle mites (Demodicidae). In addition to its sister species Demodex brevis , it is one of the two mite species that colonize human skin, both species arecalled hair follicle mites in German.
Demodex folliculorum occurs in almost everyone with increasing age and is usually a harmless commensal , but can also cause disease if the infestation is increased.
description
The body of the animals is almost transparent. In addition to eggs and larvae , further stages before the adult stage are protonymph and nymph .
Male animals
Males reach an average length of 280 micrometers , 70 percent of which is in the abdomen. The mouth area ( Gnathosoma ) is trapezoidal and wider than long at the base. The horseshoe-shaped pharyngeal bulb is open to the rear and there are very small bristles to the side in front of it below the gnathosoma. The backward-pointing thorns on the coxae are cone-like.
The four pairs of legs of the adult animal are located on the stomach side of the front part of the body, the podosoma , they are arranged at regular intervals. At each tarsus there are two claws that are divided into two at the outer end and that have a large spur pointing backwards. The pedipalps have five tiny, recurved claws. Solenidia are found on the first two pairs of legs, but are absent on the third and fourth. The epimeral plates butt against each other at the midline. The penis is 24 microns long.
The genital opening on the back at the level of the second pair of legs is a narrow incision in a small, triangular bulge. The bristles on the back of the podosoma are round, the rear pair is at the level of the genital opening and closer to each other than the front pair. The part of the body behind the legs, the opisthosoma , is furrowed across and rounded at the end. An anus is missing; the feces remain in the abdomen during the lifetime.
Female animals
The females are larger than the males with the same proportions, they reach an average length of 290 micrometers, in the extreme case up to 440 micrometers. The gnathosoma is the same as that of the males, but on average around 2 micrometers wider and longer. The legs and epimeral plates are like those of the males. The bristles on the back of the podosoma are teardrop-shaped, the rear pair being further apart than the front pair.
The vulva is a 8.5 micrometer long, simple longitudinal incision between the fourth pair of epimeral plates and is covered by this in the rear. The opisthosoma is like that of the males. The finger-shaped, 13 micrometer long rectum ends in the final quarter of the opisthosoma.
Eggs and larvae
The arrowhead-shaped eggs are around 100 micrometers long and 42 micrometers wide at the central bulge.
The slender, worm-shaped larvae are on average 280 micrometers long, with up to 33 micrometers at their widest between the second and third pair of legs. The palps consist of two segments, the tarsi section has five bent claws with one prong each. The horseshoe-shaped pharyngeal bulb is open to the rear, there are no bristles below the gnathosoma.
The thorns clearly protruding on the coxes and pointing to the side are cone-like. The legs consist of two segments, on the tarsi there is a triple forked claw and a spur protrudes to the front. At the level of the second and third pair of legs there are pairs of epimeral plates. Behind the last pair of legs, the body has slight transverse furrows.
Protonymph and Nymph
At around 360 micrometers in length, protonymphs are significantly longer than the larvae; at their widest, up to 36 micrometers, they are between the second and third pair of legs. The Gnathosoma resembles that of the larva, as do the legs, which end in a pair of tripartite claws. There are pairs of epimeral plates between each pair of legs. The body is furrowed slightly transversely behind the third, last pair of legs.
At around 390 micrometers in length, the slender, worm-shaped nymph is the longest of all stages. At 41 micrometers, it reaches its greatest width on the third pair of legs. The Gnathosoma resembles that of the larva, but is wider and longer. Between each of the now four pairs of legs there are pairs of epimeral plates, behind the fourth pair of legs the body is slightly grooved across.
Way of life
The animals are gender-independent and host-specific, distributed among people of all skin colors and origins, albeit at different frequencies. For example, hair follicle mites (not differentiated between Demodex folliculorum and Demodex brevis ) were found on Tokelau in 7.6 percent, in studies in West New York, however, in 55 percent of those examined. They colonize almost every person in the course of their life; while newborns are still unaffected, 100 percent of them are found in those over 70 years of age.
Demodex folliculorum colonizes the hair follicles above the sebum gland, preferably on the human face, but is also found in breasts, occasionally knees, the tongue and the foreskin. The animals also survive the death of their host for some time, corresponding reports range from 8 days in already strongly decomposed tissue up to 14 days.
The animals feed on sebum, the secretion of the gland. Usually three or more animals inhabit one follicle. The gnathosoma is always turned downwards, the legs to the epithelium of the follicle, the long end of the body in adult animals occasionally looks clearly out of the follicle opening.
Systematics
Demodex folliculorum was first described in 1842 by the dermatopathologist Gustav Simon as Acarus folliculorum . Richard Owen then placed them in a separate genus in 1843, the name Demodex , which comes from the Greek, means something like "larder worm" and refers to the first finds in the human ear canal . In 1963 L. Akbulatova separated the species into two subspecies, Demodex folliculorum longus and Demodex folliculorum brevis , which Clifford Desch and William B. Nutting then each assigned species rank in 1972.
Pathogenicity
The exact medical meaning of Demodex folliculorum has not yet been clarified, they are considered to be facultative pathogenic , so a disease caused by them is possible, but not mandatory. Factors such as age or a poor general condition favor the increase in the number of animals as well as existing diseases in the patient (e.g. AIDS ). As a rule, the infestation has no consequences, but so-called demodicosis can occasionally occur. When a particularly high density of mites is reached, skin diseases similar to acne or rosacea can occur, possibly triggered by the excrement or the eggs . Last but not least, the animals also have a certain potential as disease carriers, especially bacteria that they introduce into the sebum glands through their surface. Inflammation of the eyelids ( blepharitis ) is also possible with poor hygiene .
There are three variants of demodicosis, namely
- Pityriasis folliculorum , a reddening of the skin with keratoses of the follicles and follicular flaking, which makes the skin feel like sandpaper.
- the rosacea -like Demodikose (the difficult to distinguish from the real rosacea, in some literature as a link between is Demodex and the actual rosacea accepted)
- as well as granulomatous demodicosis, which can result in severe disfigurement.
Therapy is not easy - especially in patients with granulomatous demodicosis - topical applications are usually unsuccessful.
Individual evidence
- ↑ a b c d e f g h i j k Clifford Desch, William B. Nutting: Demodex folliculorum (Simon) and D. brevis Akbulatova of Man: Redescription and Reevaluation. In: The Journal of Parasitology. Vol. 58, No. 1, 1972, pp. 169-177, doi : 10.2307 / 3278267 .
- ↑ discovermagazine.com: Everything you never wanted to know about the mites that eat, crawl, and have sex on your face
- ↑ a b c Martin Schaller: Demodex folliculitis. In: Gerd Plewig , Peter Kaudewitz, Christian A. Sander (eds.): Advances in practical dermatology and venereology 2004. Lectures and slide clinic of the 19th training week 2004. Training week for practical dermatology and venereology eV c / o clinic and polyclinic for Dermatology and Allergology LMU Munich in conjunction with the Professional Association of German Dermatologists eV (= progress in practical dermatology and venereology. 19). Springer Berlin, Berlin 2005, ISBN 3-540-21055-5 , pp. 273-276.
- ↑ a b c Clifford E. Desch: Human hair follicle mites and forensic acarology. In: Experimental and Applied Acarology. Vol. 49, No. 1/2, 2009, pp. 143-146, doi : 10.1007 / s10493-009-9272-0 .
- ↑ Gustav Simon: About a mite living in the sick and normal hair sacs of humans. In: Archives for Anatomy, Physiology and Scientific Medicine. 1842, ZDB -ID 505386-9 , pp. 218-237, digitized .
- ^ Frank P. English, Takeo Iwamoto, Richard W. Darrell, Arthur Gerard DeVoe: The Vector Potential of Demodex folliculorum. In: Archives of Ophthalmology. Vol. 84, No. 1, 1970, pp. 83-85, doi : 10.1001 / archopht . 1970.00990040085020 .
- ^ Peter Reuter: Springer Lexicon Medicine. DVD-ROM. Springer, Berlin et al. 2005, ISBN 3-540-21873-4 .
- ↑ José L. Diaz-Perez: Demodex mites in rosacea. In: Journal of the American Academy of Dermatology . Vol. 30, No. 5, Part 1, 1994, pp. 812-813, doi : 10.1016 / S0190-9622 (08) 81529-0 .
- ^ Elizabeth Bonnar, Peter Eustace, Frank C. Powell: The Demodex mite population in rosacea. In: Journal of the American Academy of Dermatology. Vol. 28, No. 3, 1993, pp. 443-448, doi : 10.1016 / 0190-9622 (93) 70065-2 .
