Introduction
Background
Observation of the arachnid, Demodex folliculorum, has been reported since 1840. This hair follicle mite is the only metazoan organism commonly found in the pilosebaceous components of the eyelid of humans. Coston "opened the eyes" of ophthalmologists when he described 22 patients with demodectic eyelid signs and symptoms.1
Pathophysiology
D folliculorum (all stages) is found in small hair follicles and eyelash hair follicles. In all forms, immature and adult, it consumes epithelial cells, produces follicular distention and hyperplasia, and increases keratinization leading (in eyelashes) to cuffing, which consists of keratin and lipid moieties. Demodex brevis (all stages) is present in the eyelash sebaceous glands, small hair sebaceous glands, and lobules of the meibomian glands. Adults and immature forms consume the gland cells in all of these loci and, when infestations are heavy, can affect the formation of the superficial lipid layer of the tear film coacervate. Demodectic mites produce histologically observable tissue and inflammatory changes, epithelial hyperplasia, and follicular plugging.
Infestation of the eyelash hair follicle results in easier epilation and more brittle cilia. These mites also serve as vectors of infective elements and interrupt tissue integrity. They have been implicated in meibomian granulomas and are associated with certain dermatologic changes. All reported histologic sections of lid follicles infested with D folliculorum show distention and thickening. Coston claims that less than one half of the specimens he observed showed perifollicular lymphocytic infiltration.1
Follicular inflammation produces edema and results in easier epilation of the eyelashes. It also affects cilia construction, and lashes are observed to be more brittle in the presence of demodicosis. Madarosis (loss of lashes) is associated with abundant mites, the loss of eyelashes as a result of intercellular edema in the hair shaft, and loss of hair resiliency. Although epithelial hyperplasia associated with follicular plugging is often encountered, dermal changes seldom extend beyond the perifollicular epidermal area. Once believed to be mite excreta, this plugging is now known to be epithelial hyperplasia with interspersed layers of lipid. The formation of a collar of tissue around the base of the lashes is observed clinically. This occurs significantly more often in follicles infected with D folliculorum. The epithelial hyperplasia is hypothesized to be most likely a product of the abrasive action of the mite's claws.
Accumulation of waste material of the follicle mite may occur in affected follicles or sebaceous glands. Electron micrographs of the mite surface and feces show bacterial, viral, and rickettsial elements. Specific reports have revealed that both species pierce epithelial cells and consume cytoplasm. Only D brevis has been observed with channels burrowed to the germinal epithelium in the sebaceous glands.
Demodex species-induced pathologic changes have been implicated in dry eye conditions. When follicular plugging involves the meibomian gland (D brevis) or the gland of Zeis (D folliculorum or D brevis), reduction of the superficial lipid layer of the tear film occurs. The effect of D brevis on the meibomian structure has been implicated in chalazion formation. Chalazia are granulomatous inflammation of the meibomian glands, made of an organized core of epithelioid cells and histocytes surrounded by fibroblasts, lymphocytes, and plasma cells. These defense cells encircle particles too large for normal macrophages to engulf. D brevis has been observed in the center of these meibomian granulomas. Lid infestation by the Demodex species may or may not accompany dermatologic changes of the nose, the cheek, or the forehead.
D folliculorum has been suggested as a factor in pityriasis folliculorum. This dermal inflammation manifests itself as a diffuse erythema of the affected areas; scaly, dry skin; and, in certain cases, rosacealike lesions. The dry skin cycle described by Ayres is initiated when the demodectic mite plugs the follicle and reduces the sebaceous outflow, which leads to scaling as well as rough and dry skin texture.2 Sebaceous outflow is further reduced when patients inadvertently decide to apply facial cream. The mite flourishes in this environment of oily additives, leading to an increase in the population of the mites and a continuation of the dry skin cycle.
Frequency
International
Several individuals have attempted to estimate the prevalence of D folliculorum in the eyelash follicles. The initial report in 1961 suggested a prevalence of 95%.3
Mortality/Morbidity
Madarosis (loss of lashes) may result from untreated demodicosis.
Race
No racial predilection has been observed.
Sex
Infestation by these parasites is equal in males and females. Infestation is correlated to the number of sebaceous glands but not to the density of the hair follicles.
Age
Post reported that D folliculorum was observed in 84% of the sample population with a mean age of 61 years and in 100% of those older than 70 years.4
Clinical
History
- Symptoms
- Ocular irritation
- Itching
- Scaling of lids
- Past ocular history - Recurrent failed treatment of blepharitis
Physical
- Gross observation
- Lid thickening
- Scaling of lids
- Madarosis (loss of lashes)
- Conjunctival inflammation
- Meibomian gland dysfunction
- Rosacea
- Decreased vision
- Slit lamp findings
- Collar of tissue around the base of the eyelashes
- Follicular distention
- Dry eye
- Cornea
- Superficial corneal vascularization
- Marginal corneal infiltration
- Phlyctenule-like lesion
- Superficial corneal opacity
- Nodular corneal scar
Causes
- Demodex species specific to humans occupy 2 periocular sites hidden from external observation. They are small in size and possess the ability to move across the skin surface.
- D folliculorum is found in hair and eyelash follicles associated with pilosebaceous glands in the eye or elsewhere on the face and the body. A single follicle may contain as many as 25 D folliculorum organisms.
- D brevis leads a much more solitary lifestyle in sebaceous glands of the body and in the meibomian gland and the gland of Zeis.
- D folliculorum measures 0.3-0.4 mm in length, whereas D brevis is one half the size of D folliculorum (0.15-0.2 mm) with similar structure of the head and the thorax but a shorter abdomen.
- The 8 legs of this arachnid are segmented and provide locomotion at a rate of 8-16 mm/h.
- D folliculorum and D brevis, also known as follicle mites, are believed to be more active in the dark, although capture in daylight is possible.
- The bright light of the day and especially the biomicroscope cause the mite to recede back into the follicle. Therefore, the mite can be observed only when an epilated lash is observed under a low-power microscope.
- The life stages of D folliculorum begin with copulation at the mouth of the follicle. Reproduction is believed to occur in darkness; a fact that is significant in symptomatology and treatment.
- Following copulation, the female burrows back into the follicle near the opening of the pilosebaceous gland and lays her eggs.
- Spickett reported the life cycle of D folliculorum and estimated that only 14.5 days elapse from ovum to adult stage, including 120 hours as an adult. Females may live an additional 5 days after oviposition.3
- Sexes are separate; sexual maturity is reached in the larval form (neoteny).
- Females are territorial; they remain in their respective follicles and wait for the nomadic philandering males that travel over the surface of the skin from one follicle to another in seek of females.
- Adults reside in the follicle parallel to the hair shaft, head inward, often with the tail end (opisthosoma) protruding onto the surface of the skin at the base of the eyelash.
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References
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Further Reading
Keywords
Demodex folliculorum, Demodex folliculorum longus, Demodex folliculorum brevis, Demodex folliculorum hominis, Demodex mites, follicle mites, blepharitis, common ectoparasites of the ocular adnexa, hair follicle mites
