Some science behind the scenes

Skin mites

The following was extracted from a marvellous site describing all sorts of parasites and mites.  I have given the website reference below.  No changes have been made to the text

 

Mites On Your Face (Class Arachnida: Order Acarina)

 

 

Hair Follicle Mite Family (Demodicidae): Ubiquitous Obligatory Ectoparasites

 

Of all the many thousands of plant and animal images I have taken and uploaded to Wayne's Word, this is truly one of the most amazing. It even surpasses the dust mites I found in my pillow. I didn't have to travel that far or spend a lot of money on gasoline or airline tickets. I didn't even have to look any further than my nose to find such a remarkable animal. In fact, I actually found this microscopic relative of spiders deep in a sebaceous gland of my nose. Most of the images were taken with a compound microscope and a Sony W-300 digital camera. Although the backlit, high magnification images appear two-dimensional with limited depth of field, you can clearly see the slender, fusiform body and eight stubby legs, each tipped with a pair of pincerlike claws. Illustration (left) modified from T. Ross and photos of the dorsal side of Demodex brevis by W.P. Armstrong.

 

Note: These minute mites are invisible to the naked eye: See Cell Size Comparison Table On Wayne's Word: Demodex.

Hair follicle mites of the genus Demodex are among the smallest multicellular animals. They were first described in humans in 1841 by Frederick Henle who reported this minute parasite from "miliary glands" of the ear canal. He was uncertain about the parasite's taxonomic position in the animal kingdom. [Henle is also known for the Henle's loop in the vertebrate nephron.] Another scientist from this time period by the name of Berger (1845) thought it was a member of the phylum Tardigrada. Tardigrades are minute animals often found on lichens and mosses. According to Desch and Nutting (1972), there are two species of follicle mites on humans. Demodex folliculorum measures 0.3 to 0.4 mm in length and typically occupies hair follicles. It is also called an "eyelash mite" because it commonly occurs in follicles at the base of eyelashes. Demodex brevis is about half that size (0.15 to 0.2 mm) and typically lives in sebaceous glands adjacent to hair follicles. The latter mite is only about the size of a unicellular Paramecium and appears to be the species I found in my nose.

 

These microscopic spider relatives (arachnids) live in the hair follicles and adjacent sebaceous glands of human eyelashes, noses, cheeks and foreheads. In heavily infested cases, the posterior ends of D. folliculorum can be seen around the bases of eyelashes. Their mouthparts resemble those of spiders, scorpions and other arachnids, but are much smaller. They are designed to feed on skin cells (cytoplasm) and the oily sebum produced by sebaceous glands. Males come out at night and move around on the skin surface to look for potential females to mate with. Unsubstantiated reports state that these mites can move on your skin at a rate of 8 to 16 mm per hour. Their digestive system is reportedly so efficient that they have very little excretory waste and no excretory orifice. This is reassuring news to those of us who worry about them defecating on our faces and in our eyes.

Most people have these minute parasites living relatively harmlessly in their skin pores and hair follicles, although people with oily skin, or those who use cosmetics heavily and don't wash thoroughly, reportedly have the heaviest infestations. They are transferred by facial contact and are apparently more common in adults than in children. In some people, high mite populations can cause demodicosis and blepharitis, possibly due to a suppressed immune system. Theses conditions are characterized by itching and inflammation of the skin and eyelids. High densities of Demodex have also been found in people with the skin disorder rosacea. A cell-mediated immune response involving cytotoxic "killer" T-cells may be involved in the inflammation associated with acne rosacea. There are numerous species of Demodex that live on many different mammals, including rodents, monkeys, cattle and bison. In fact, they have been found in 11 of the 18 orders of eutherian (placental) mammals, with most species harboring two or more species of Demodex (Desch, 2009). One species Demodex canis lives on domestic dogs and causes a condition called "demodectic mange." There is a plethora of information about these amazing animals on the Internet. You might start with an excellent summary of Demodex on Wikipedia.

All species of Demodex are obligate ectoparasites that cannot live independently of their host. In parasitism, the parasite benefits by obtaining nutrients from the host's body, which is often harmed by the relationship. In most humans, these ubiquitous parasites may not cause any harm to their host. In fact, some author's refer to the relationship as commensalism rather than parasitism. In commensalism, one organism benefits from the relationship while the other neither benefits nor is harmed. The dorsal fin of the remora is modified into a sucker which forms a temporary attachment to the shark. The shark does not seem to be inconvenienced by this and makes no attempt to remove the remora. When the shark feeds, the remora is in a good position to pick up scraps of food left by the shark. Marine mammals, including whales and manatees, often carry harmless hitchhikers called barnacles on their backs. The barnacles benefit from the ride through nutrient-rich waters. In my opinion, the term parasite is more appropriate because these mites are definitely feeding on human cells and glandular secretions (sebum). A few mites feeding on dead skin cells and sebum deep within hair follicles are probably harmless unless their populations get out of control. Recent peer-reviewed articles accessible through Google Scholar indicate there is considerable dermatological research on human follicle mites and different opinions regarding their detrimental effects.

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Images From Prepared Microscope Slides

 

 

Prepared microscope slide from the dermis layer of human skin showing a hair follicle and sebaceous gland. Deeply embedded within the hair follicle is a slender, elongate follicle mite (Demodex folliculorum). Magnification 400x. Inset: Close-up view of hair follicle containing a mite. Several legs are visible at anterior end of mite (yellow arrow). Part of the mite has been sectioned during the preparation of slide. Magnification 1000x.

 

Fresh Mites From Mr. Wolffia's Nose

 

The following images of a folicle mite came from my own nose. Based on its size and presence in sebum, it appears to be Demodex brevis. I squeezed a skin pore and collected the whitish sebum from sebaceous glands. With a toothpick I carefully transferred the sebum to a drop of olive oil on a clean microscope slide. [Other salad oils, such as soybean oil, will work just as well.] I added a cover slip and examined the slide under low magnification (40x) with a compound microscope using substage illumination (not a dissecting microscope). When I spotted a small fusiform body with eight stubbly legs, I switched to higher magnifications of 100x, 400x and 1000x. This may seem a little gross to some readers, but it is not nearly as shocking as the bot fly larva that emerged from a colleague's arm after returning from Central America.

 

 

 

Ventral view of follicle mite (Demodex brevis) removed from Mr. Wolffia's nose. Several squamous epithelial cells are also included in the image. The epithelial cells have an average diameter of about 60 micrometers (0.06 mm). Magnification 300x.

 

 

Dorsal view of follicle mite (Demodex brevis) removed from Mr. Wolffia's nose. Magnification 400x.

 

 

 

A follicle mite (Demodex brevis) compared in size with an average grain of table salt (NaCl). The mite is about 1/2 the length of one side of the grain. Magnification 400x.

 

 

 

Demodex brevis compared in size with the freshwater protozoan Paramecium bursaria. Magnification 400x.

 

 

Dorsal view of follicle mite (Demodex brevis) from Mr. Wolffia's nose under high magnification (1000x). The bifid, pincerlike claws and mouth are clearly visible.

References

Obtained from the following website - Wayne's world