Demodex mite
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Demodex brevis |
The demodex mites form a genus of tiny parasitic mites which live in or near hair follicles of mammals. Some species live on humans, for instance Demodex folliculorum which is primarily found in the hair follicles of the eyelashes and eyebrows, and Demodex brevis which lives in sebaceous glands connected to hair follicles.
The adult mites have a semi-transparent elongated body that consists of two segments and is between 0.1 mm and 0.4 mm long. 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 mouth-parts for eating skin-cells, hormones and oils (sebum) which accumulate in the hair follicles. The mite's digestive system is so efficient and results in so little waste that there is no excretory orifice. The mites can leave the hair follicles and slowly walk around on the skin, especially at night.
The total lifespan of a Demodex mite is several weeks. Mating takes place on the skin, and eggs are layed inside the hair follicles or sebaceous glands. The six-legged larvae hatch after 3-4 days, and it takes about seven days for the larvae to develop into adults. The dead mites decompose inside the hair follicles or sebaceous glands.
An estimated 96-98% of all people carry such mites—with up to 25 in each follicle, each person can have a potentially huge population of mites. It is quite easy to look for your own demodex mites, by carefully removing an eyelash or eyebrow hair and placing it under a microscope.
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, characterised by itching, inflammation and other skin disorders.
The mites are transferred between hosts through contact of hair, eyebrows and of the sebaceous glands on the nose. Demodex is typically initially contracted within the first few hours after birth from the birth mother. Different species of animals host different species of demodex; and demodex is not contagious between different species.
There is some evidence linking demodex mites to acne rosacea. Some people believe that there is also a link to acne vulgaris, but there is little research to back this up, and quite reasonable experimental evidence linking acne vulgaris to a sensitivity to Propionibacterium acnes.
The species Demodex canis lives only on the domestic dog. While, like with humans, most dogs live with their mites without harm, a minority do not have immune systems capable of completely controlling the mites, leading to a potentially dangerous infestation called demodectic mange. While direct treatment for severe cases is possible using a drug known as Mitaban which is applied to the skin, improved nutrition and checking for other, immune-system suppressing diseases are also recommended.
[edit] External links and sources
- Demodex, an inhabitant of human hair follicles, and a mite which we live with in harmony, by M. Halit Umar, published in the May 2000 edition of Micscape Magazine, includes several micrographs
- Demodicosis, an article by Manolette R Roque, MD
- Mites might cause mighty problems, USA Today (Magazine), Feb 2004
- Demodex in the Dog, by T. J. Dunn, Jr. DVM
