Published: 2021 – Ongoing
Authors: Universidade do Porto, Portuguese Institute of Rheumatology, Centro de Investigação Interdisciplinar Egas Moniz

Abstract:

“Demodex mite is an obligate human ecto-parasite found in or near the pilo-sebaceous units. Demodex folliculorum and Demodex brevis are two species typically found on humans.

Demodex infestation usually remains asymptomatic and may have a pathogenic role only when present in high densities and also because of immune imbalance…

… a high index of clinical suspicion about the etiological role of Demodex in various dermatoses can help in early diagnosis and appropriate, timely, and cost effective management.”

Introduction:

“Demodex mite infestation usually remains asymptomatic, but may be an important causative agent for many dermatological conditions…

… Infestation with Demodex is common; prevalence in healthy adults varying between 23-100%. Demodex infestation usually remains asymptomatic, although occasionally some skin diseases can be caused by imbalance in the immune mechanism…

… Two species D. folliculorum and Demodex brevis, collectively referred to as Demodex, are typically found on humans, occurring in 10% of skin biopsies and 12% of follicles…

Demodex is an ecto-parasite of pilo-sebaceous follicle and sebaceous gland, typically found on the face including cheeks, nose, chin, forehead, temples, eye lashes, brows, and also on the balding scalp, neck, ears…

D. folliculorum is more commonly localized to the face, while D. brevis is more commonly found on the neck and chest.

Infestation with D. folliculorum is more common than with D. brevis, but the later has wider distribution on the body.

D. folliculorum is usually found in the upper canal of the pilo-sebaceous unit at a density of ≤ 5/sq cm and uses skin cells and sebum for nourishment…

The number of Demodex mites present in the lesion increases with age. The prevalence of infestation with Demodex mites is highest in the 20-30 years age group, when the sebum secretion rate is at its highest.

Older people are also more likely to carry the mites. Demodicosis is exceptionally seen in children aged <5 years. Presumably, Demodex passes to newborns through close physical contact after birth; however, due to low sebum production, infants and children lack significant Demodex colonization.

Infestation of both species is more common in males than in females, with males more heavily colonizing than females (23% vs 13%) and harboring more D. brevis than females (23% vs 9%)…

Most people are only carriers of Demodex mites and do not develop clinical symptoms. Human demodicosis can therefore be considered as a multi-factorial disease, influenced by external and/or internal factors.

One of the factors for the transition from a clinically unapparent colonization of mites to dermatoses can be the development of primary or secondary immunodepression.

Primary immune suppression is most probably based on hereditary defect of T cells, subsequently reinforced by substances that are produced by mites and by bacteria, with intact B cell immunity.

The fact that people and animals with immunodeficiency are prone to infestation with Demodex mites has been shown repeatedly.

Secondary immune suppression predisposing to demodicosis follows corticosteroid, cytostatic therapy, or due to diseases of an immune-compromised nature such as malignant neoplasia, hepatopathies, lymphosarcoma, and HIV infection.

There may, however, be factors other than generalized immunosuppression leading to the development of demodicosis.

It has been suggested that infestation may be related to genetic predisposition and also with special types of HLA, although some HLA types are considered to be resistant to demodicosis…

These findings suggest that colonization of the skin with Demodex could be a reflection of immune response of the host to organism…

Demodex may have a direct role in rosacea or may manifest as rosacea like dermatitis. Numerous studies have reported elevated emodex density in patients with rosacea…

Increased number of Demodex mites has also been observed in peri-oral dermatitis, acarica blepharo-conjuctivitis (blepharitis), grover’s disease, eosinophilic folliculitis, papulovesicular facial, papulopustular scalp eruptions, pityriasis folliculorum, pustular folliculitis, Demodex abscess, and demodicosis gravis (granulomatous rosacea like demodicosis).”

Other points of importance:

As a vector for transmission:

“Demodex may act as a vector of transmission of various infections from one area of body to another or between individuals by its potential to ingest and transport various microorganisms that are found in its niche, as demonstrated by potassium hydroxide mount of skin scraping from a mycotic plaque, which showed numerous Demodex mites containing spores of Microsporum canis inside them.”

Defense against bacteria

“Similar to bacterial flora found on human skin, follicle mites have been shown to contain immune-reactive lipase, which can produce free fatty acids from sebum triglycerides.

Therefore, follicle mites could play a role in the defense of human skin against pathogenic bacteria, particularly against Staphylococcus aureus and Streptococcus pyogenes.”

Prevention/treatment of human demodicosis

“Demodex can only live in the human hair follicle and, when kept under control, causes no problems. However, to reduce the chance of the mites proliferating excessively, following preventive measures are important:

• Cleanse the face twice daily with non-soap cleanser

• Avoid oil-based cleansers and greasy makeup

• Exfoliate periodically to remove dead skin cells

After clinical manifestations, the mites may be temporarily eradicated with topical insecticides, especially crotamiton cream, permethrin cream, and also with topical or systemic metronidazole. In severe cases, such as those with HIV infection, oral ivermectin may be recommended.”

Conclusion:

“Human demodicosis is caused by the clinical manifestation of otherwise asymptomatic infestation of humans by two species of Demodex mite, i.e., D. folliculorum and D. brevis.

The etiological role of this versatile mite should be kept in mind as human demodicosis can present as a variety of clinical manifestations mimicking many other dermatoses.

This can help in early diagnosis and proper treatment, thereby saving time and at the same time being cost effective.”