Demodex brevis
| Demodex brevis | ||||||||||||
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Demodex brevis |
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| Demodex brevis | ||||||||||||
| Akbulatova, 1963 |
Demodex brevis is a species of mite from the hair follicle mite family(Demodicidae). In addition to its sister species Demodex folliculorum , it is one of the two types of mites that colonize human skin, both types arecalled hair follicle mites in German.
Demodex brevis can be found in almost everyone with increasing age and is usually a harmless commensal , but can also cause diseases 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 0.17 millimeters, around two thirds of which are 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, very small thorns on the coxae are cone-like.
The four pairs of legs of the adult animal are located on the ventral 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 have a fine serration on the central edge and do not butt against each other on the midline, the gap between the epimeral plates of the second and third pair of legs is wider than between the others. The penis is 18 microns long.
The genital opening on the back at the level of the second pair of legs is an unlocked, small hole. The bristles on the back of the podosoma are large and round, the back and front pair are equidistant from the center line. The abdomen is furrowed across and pointed at the end. A proctodeum is missing.
Female animals
The females are larger than the males with the same proportions, they reach an average length of 0.21 millimeters, in the extreme case up to 0.44 millimeters. The gnathosoma is the same as that of the males, but on average around 2 micrometers wider and longer. The legs are like those of the males. The epimeral plates meet in the middle, the front edge of those of the fourth pair of legs are angled slightly backwards.
The vulva is a 7 micrometer long, simple longitudinal incision between the fourth pair of epimeral plates. The opisthosoma is furrowed like that of the males, but tapering off more sharply. A proctodeum is missing.
Eggs and larvae
The oval, slightly blunt-tapered eggs are around 60 micrometers long and 34 micrometers wide.
The thread-like, weakly sclerotized larvae are on average 0.11 millimeters long, with a width of up to 33 micrometers on the second pair of legs. The palps consist of two segments, the tarsi section has a four-part claw and a single-pronged claw, which may be a bristle. The front edge of the epistome has a pair of heavily chitinized, backward-facing spines. The horseshoe-shaped pharyngeal bulb is open to the rear, there are no bristles below the gnathosoma.
The very small thorns on the coxes are cone-like. The legs consist of two segments, on the tarsi there is a triple-forked claw both dorsally and ventrally. Solenidia are found immediately behind the dorsal claws of the first two pairs of legs, but they are absent on the third pair. At the level of the second and third pair of legs, there are weakly sclerotized, flat, transversely sickle-shaped pairs of epimeral plates. Between the pairs of legs there are fine furrows along the midline, the body is slightly transversely furrowed behind the last pair of legs.
Protonymph and Nymph
Protonymphs are around 0.15 millimeters in length longer than the larvae, and are at their widest at around 34 micrometers on the second pair of legs. Except for the missing spines of the epistome, they are otherwise the same as the larvae.
The thread-like nymph is on average 165 micrometers long and reaches its greatest width of 41 micrometers between the second and third pair of legs. All legs have three-forked claws, between the second, third and fourth legs there are transversely sickle-shaped epimeral plate pairs. In all other respects the nymph is like the larva.
Way of life
The animals are gender-independent and host-specific, distributed among people of all skin colors and origins, albeit at different frequencies. Hair follicle mites (not differentiated between Demodex folliculorum and Demodex brevis ) were found on Tokelau in 7.6%, while investigations in West New York found them in 55% of those examined. They colonize almost every person in the course of their life, while newborns are still unaffected, they are 100% found in over 70-year-olds
Demodex brevis colonizes the sebum gland primarily on the human face, but is also found (not differentiated between Demodex folliculorum and Demodex brevis ) in breasts, occasionally knees, the tongue and the foreskin. Usually a single animal, occasionally a second, inhabits a sebum gland and feeds on its secretion. The animals also survive the death of their host for some time, reports range from 8 days in already heavily decomposed tissue to 14 days.
Systematics
Demodex brevis was first described in 1963 by L. Akbulatova as a subspecies of Demodex folliculorum . Clifford Desch and William B. Nutting then awarded her Artrang in 1972.
Pathogenicity
The exact medical meaning of Demodex brevis has not yet been clarified; it is considered to be facultative pathogenic (no differentiation between Demodex folliculorum and Demodex brevis ) . As a rule, the infestation has no consequences, but so-called demodicosis can occasionally occur. Factors such as age or a poor general condition favor the increase in the number of animals as well as diseases (e.g. AIDS ). 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 .
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, which is why in some literature, a relationship between Demodex is adopted and the actual rosacea) and
- granulomatous demodicosis, which can result in severe disfigurement.
The therapy is now often successful thanks to the locally applied acaricide ivermectin.
Inflammation of the eyelids ( blepharitis ) is also possible with poor hygiene .
Web links
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 .
- ↑ a b 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 in 2004. Training week for practical dermatology and venereology e. V. c / o Clinic and Polyclinic for Dermatology and Allergology LMU Munich in conjunction with the Professional Association of German Dermatologists e. V. (= 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 .
- ↑ JEADV. PMID 28653460
- ^ Peter Reuter: Springer Lexicon Medicine. DVD-ROM. Springer, Berlin a. a. 2005, ISBN 3-540-21873-4 .