Demodex mite
Encyclopedia
Demodex is a genus
of tiny parasitic mite
s that live in or near hair follicles of mammal
s. About 65 species of Demodex are known; they are among the smallest of arthropod
s. Two species living on human
s have been identified: Demodex folliculorum
and Demodex brevis
, both frequently referred to as eyelash mites. 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.
s connected to hair follicles. Both species are primarily found in the face, near the nose, the eyelash
es and eyebrow
s, but also occur elsewhere on the body.
The adult mites are only 0.3–0.4 mm (0.0118110236220472–0.015748031496063 ) long, with D. brevis slightly shorter than D. folliculorum. They have a semi-transparent 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 mouth-parts for eating skin cells
, hormone
s and oils (sebum) 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 ) per hour—especially at night as they try to avoid light.
Female Demodex folliculorum are somewhat shorter 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 larva
e hatch after 3–4 days, and it takes about seven days for the larvae to develop into adults. The total lifespan of a Demodex mite is several weeks. The dead mites decompose inside the hair follicles or sebaceous glands.
Older people are much more likely to carry the mites; it is estimated that about a third of children and young adults, half of adults, and two-thirds of elderly people carry the mites. The lower rate of children may be because children produce much less sebum. It is quite easy to look for one's own Demodex mites, by carefully removing an eyelash or eyebrow hair and placing it under a microscope
.
The mites are transferred between hosts through contact of hair, eyebrows and of the sebaceous glands on the nose. Different species of animals host different species of Demodex; only one zoonosis
of Demodex is known.
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
or Demodex mite bite
, characterised by itching, inflammation and other skin disorders. Blepharitis
(inflammation of the eyelids) can also be caused by Demodex mites.
There is some evidence linking Demodex mites to some forms of the skin disease rosacea
, possibly due to the bacterium Bacillus oleronius
found in the mites.
The species Demodex canis lives predominantly on the domestic dog
, but can occasionally infect humans. Although the majority of infestations are commensal, and therefore sub-clinical, it can develop into a condition called demodectic mange
.
Due to their habitat being deep in the dermis, transmission is only usually possible via prolonged direct contact, such as bitch-to-pup transmission during suckling. As a result, the most common sites for early appearance of demodicodic lesions are the face, muzzle, forelimbs and periorbital regions.
Demodicosis can manifest as lesions of two types: squamous—which causes dry alopecia and thickening of the skin; and pustular—which is the more severe form, causing secondary infection (usually by Staphylococcus
) resulting in the characteristic red, numerous pustules and wrinkling of the skin.
The escalation of a commensal D. canis infestation into one requiring clinical attention usually involves complex immune factors. Demodicosis can follow immunosuppressive conditions or treatments, or may be related to a genetic immune deficiency. This is complicated by the fact that Demodex itself is thought to suppress the normal T-lymphocyte response. There are also certain breeds, such as the Dalmatian
, which appear to be more susceptible.
While direct treatment for severe cases is possible by applying the antiparasitic drug Amitraz
to the skin, improved nutrition also helps and addressing any possible underlying immune-system suppressing diseases. The secondary bacterial infection associated with pustular demodicosis requires treatment with antibiotics.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of tiny parasitic mite
Mite
Mites, along with ticks, are small arthropods belonging to the subclass Acari and the class Arachnida. The scientific discipline devoted to the study of ticks and mites is called acarology.-Diversity and systematics:...
s that live in or near hair follicles of mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s. About 65 species of Demodex are known; they are among the smallest of arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s. Two species living on human
Human
Humans are the only living species in the Homo genus...
s have been identified: Demodex folliculorum
Demodex folliculorum
Demodex folliculorum is a species of face mite. D. folliculorum is one of the parasitic face mites that occur on people . Demodex derives from the Greek roots, demos- fat, and dex- worm. When large numbers of D...
and Demodex brevis
Demodex brevis
Demodex brevis is one of the two species of face mite that afflict humans . They are very similar to the Demodex folliculorum, with just a few differences. They are usually found in the sebaceous glands of the human body. The same way that D. folliculorum reproduces on the follicles, D. brevis...
, both frequently referred to as eyelash mites. Demodex canis lives on the domestic dog
Dog
The domestic dog is a domesticated form of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in...
. Infestation with Demodex is common and usually does not cause any symptoms, although occasionally some skin diseases can be caused by the mites.
Demodex folliculorum and Demodex brevis
Demodex folliculorum and Demodex brevis are typically found on humans. D. folliculorum was first described in 1842 by Simon; D. brevis was identified as separate in 1963 by Akbulatova. D. folliculorum is found in hair follicles, while D. brevis lives in sebaceous glandSebaceous gland
The sebaceous glands are microscopic glands in the skin that secrete an oily/waxy matter, called sebum, to lubricate and waterproof the skin and hair of mammals...
s connected to hair follicles. Both species are primarily found in the face, near the nose, the eyelash
Eyelash
An eyelash or simply lash is one of the hairs that grow at the edge of the eyelid. Eyelashes protect the eye from debris and perform some of the same function as whiskers do on a cat or a mouse in the sense that they are sensitive to being touched, thus providing a warning that an object is near...
es and eyebrow
Eyebrow
The eyebrow is an area of thick, delicate hairs above the eye that follows the shape of the lower margin of the brow ridges of some mammals. Their main function is to prevent sweat, water, and other debris from falling down into the eye socket, but they are also important to human communication and...
s, but also occur elsewhere on the body.
The adult mites are only 0.3–0.4 mm (0.0118110236220472–0.015748031496063 ) long, with D. brevis slightly shorter than D. folliculorum. They have a semi-transparent 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 mouth-parts for eating skin cells
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
, hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
s and oils (sebum) 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 ) per hour—especially at night as they try to avoid light.
Female Demodex folliculorum are somewhat shorter 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 larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e hatch after 3–4 days, and it takes about seven days for the larvae to develop into adults. The total lifespan of a Demodex mite is several weeks. The dead mites decompose inside the hair follicles or sebaceous glands.
Older people are much more likely to carry the mites; it is estimated that about a third of children and young adults, half of adults, and two-thirds of elderly people carry the mites. The lower rate of children may be because children produce much less sebum. It is quite easy to look for one's own Demodex mites, by carefully removing an eyelash or eyebrow hair and placing it under a microscope
Microscope
A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy...
.
The mites are transferred between hosts through contact of hair, eyebrows and of the sebaceous glands on the nose. Different species of animals host different species of Demodex; only one zoonosis
Zoonosis
A zoonosis or zoonoseis any infectious disease that can be transmitted from non-human animals to humans or from humans to non-human animals . In a study of 1415 pathogens known to affect humans, 61% were zoonotic...
of Demodex is known.
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
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
, caused by stress or illness) mite populations can dramatically increase, resulting in a condition known as demodicosis
Demodicosis
Demodicosis, also called demodectic mange or red mange, is caused by a sensitivity to and overpopulation of Demodex canis as the animal's immune system is unable to keep the mites under control....
or Demodex mite bite
Demodex mite bite
Demodex mite bite is a cutaneous condition caused by infestation by Demodex folliculorum....
, characterised by itching, inflammation and other skin disorders. Blepharitis
Blepharitis
Blepharitis is an ocular condition characterized by chronic inflammation of the eyelid, the severity and time course of which can vary. Onset can be acute, resolving without treatment within 2–4 weeks , but more generally is a long standing inflammation varying in severity...
(inflammation of the eyelids) can also be caused by Demodex mites.
There is some evidence linking Demodex mites to some forms of the skin disease rosacea
Rosacea
Rosacea is a chronic condition characterized by facial erythema . Pimples are sometimes included as part of the definition. Unless it affects the eyes, it is typically a harmless cosmetic condition...
, possibly due to the bacterium Bacillus oleronius
Bacillus oleronius
Bacillus oleronius is a Gram-negative bacterium belonging to the genus Bacillus. It was first described in 1995 and was found in the hindgut of the termite Reticulitermes santonensis...
found in the mites.
Demodex canis
Dog
The domestic dog is a domesticated form of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in...
, but can occasionally infect humans. Although the majority of infestations are commensal, and therefore sub-clinical, it can develop into a condition called demodectic mange
Demodicosis
Demodicosis, also called demodectic mange or red mange, is caused by a sensitivity to and overpopulation of Demodex canis as the animal's immune system is unable to keep the mites under control....
.
Due to their habitat being deep in the dermis, transmission is only usually possible via prolonged direct contact, such as bitch-to-pup transmission during suckling. As a result, the most common sites for early appearance of demodicodic lesions are the face, muzzle, forelimbs and periorbital regions.
Demodicosis can manifest as lesions of two types: squamous—which causes dry alopecia and thickening of the skin; and pustular—which is the more severe form, causing secondary infection (usually by Staphylococcus
Staphylococcus
Staphylococcus is a genus of Gram-positive bacteria. Under the microscope they appear round , and form in grape-like clusters....
) resulting in the characteristic red, numerous pustules and wrinkling of the skin.
The escalation of a commensal D. canis infestation into one requiring clinical attention usually involves complex immune factors. Demodicosis can follow immunosuppressive conditions or treatments, or may be related to a genetic immune deficiency. This is complicated by the fact that Demodex itself is thought to suppress the normal T-lymphocyte response. There are also certain breeds, such as the Dalmatian
Dalmatian (dog)
The Dalmatian is a breed of dog whose roots are often said to trace back to Dalmatia, a region of Croatia where the first illustrations of the dog have been found. The Dalmatian is noted for its unique black- or brown-spotted coat and was mainly used as a carriage dog in its early days...
, which appear to be more susceptible.
While direct treatment for severe cases is possible by applying the antiparasitic drug Amitraz
Amitraz
Amitraz is an antiparasitic drug. Product names include Ridd, Aazdieno, Acarac, Aludex, Amitraze, Avartin, Baam, Edrizan, Maitac, Mitac, Mitaban, Triatox, Triatix, Vapcozin Taktic, Triazid, Topline, Tudy, Ectodex, Garial, Danicut, Ovidrex, Acadrex, Bumetran, and Ovasyn.It is an alpha-adrenergic...
to the skin, improved nutrition also helps and addressing any possible underlying immune-system suppressing diseases. The secondary bacterial infection associated with pustular demodicosis requires treatment with antibiotics.
External links
- 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
- Description and pictures
- Demodicosis, an article by Manolette R Roque, MD
- Mites might cause mighty problems, USA Today (Magazine), February 2004
- Demodex in the Dog, by T. J. Dunn, Jr. DVM
- High resolution images of Demodex folliculorum
- Ted's mange cure.