Demodex // is a genus of tiny mites that live in or near hair follicles of mammals. Around 65 species of Demodex are known. Two species live on humans: Demodex folliculorum and Demodex brevis, both frequently referred to as eyelash mites, alternatively face mites or skin mites. Different species of animals host different species of Demodex. Demodex canis lives on the domestic dog. The presence of Demodex species on mammals is common and usually does not cause any symptoms, although occasionally some skin diseases can be caused by the mites. Demodex is derived from Greek δημός dēmos "fat" and δήξ dēx, "woodworm".
D. folliculorum and D. brevis
D. folliculorum and D. 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 glands connected to hair follicles. Both species are primarily found in the face — near the nose, the eyelashes, and eyebrows — but also occur elsewhere on the body. D. folliculorum is occasionally found as a cause of folliculitis, although most people with D. folliculorum mites have no obvious ill effects.
The adult mites are 0.3–0.4 mm (3⁄256–1⁄64 in) long, with D. brevis slightly shorter than D. folliculorum. Each has a semitransparent, 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 mouthparts for eating skin cells and oils that accumulate in the hair follicles. The mites can leave the follicles and slowly walk around on the skin, at a speed of 8–16 mm (3⁄8–5⁄8 in) per hour, especially at night, as they try to avoid light.: 2 The mites are transferred between hosts through contact with hair, eyebrows, and the sebaceous glands of the face.
Females of D. folliculorum are larger 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 larvae hatch after 3–4 days, and the larvae develop into adults in about 7 days. The total lifespan of a Demodex mite is several weeks.
Older people are much more likely to carry face mites; about a third of children and young adults, half of adults, and two-thirds of elderly people carry them. The lower rate in children may be because children produce less sebum, or simply have had less time to acquire the mite. A 2014 study of 29 people in North Carolina, USA, found that all of the adults (19) carried mites, and that 70% of those under 18 years of age carried mites. This study (using a DNA-detection method, more sensitive than traditional sampling and observation by microscope), along with several studies of cadavers, suggests that previous work might have underestimated the mites' prevalence. The small sample size and small geographical area involved prevent drawing broad conclusions from these data.
- Evidence of a correlation between Demodex infestation and acne vulgaris exists, suggesting it may play a role in promoting acne, including in immunocompetent infants displaying pityriasis and erythema toxicum neonatorum, or simply that Demodex mites thrive in the same oily conditions where acne bacteria thrive.
- Several preliminary studies suggest an association between mite infestation and rosacea.
- Demodex mites can cause blepharitis, which can be greatly reduced with solutions of tea tree oil containing 50% concentrations or greater.
- Demodex mite eradication responds to topical treatments better than oral and intravenous treatments alone. More than one treatment may be required for individuals with prolonged Demodex mite infestation.
- Demodex mites causing a reaction in healthy individuals depends on genealogy. Mites may evolve differently with different bloodlines.
- New studies suggest demodex mites involved in psoriasis and asthma in immunosuppressed individuals.
The natural host of D. canis is the domestic dog. D. canis mites can survive on immunosuppressed human skin and human mites can infect immunosuppressed dogs, although reported cases are rare. Ivermectin is used for demodex mites requiring up to four treatments to eradicate in humans; although only one treatment is usually given to dogs to reduce mite count. Naturally, the D. canis mite has a commensal relationship with the dog, and under normal conditions does not produce any clinical signs or disease. The escalation of a commensal D. canis infestation into one requiring clinical attention usually involves complex immune factors. Under normal health conditions, the mite can live within the dermis of the dog without causing any harm to the animal. However, whenever an immunosuppressive condition is present and the dog's immune system (which normally ensures that the mite population cannot escalate to an infestation that can damage the dermis of the host) is compromised, it allows the mites to proliferate. As they continue to infest the host, clinical signs begin to become apparent and demodicosis/demodectic mange/red mange is diagnosed.
Since "D. canis" is a part of the natural fauna on a canine's skin, the mite is not considered to be contagious. Many dogs receive an initial exposure from their mothers while nursing, during the first few days of life. The immune system of the healthy animal keeps the population of the mite in check, so subsequent exposure to dogs possessing clinical demodectic mange does not increase an animal's chance of developing demodicosis. Subsequent infestations after treatment can occur.
- Owen, [Richard] (1843). "Lecture XIX. Arachnida". Lectures on Comparative Anatomy. London: Longman, Brown, Green, and Longmans. p. 252.
- Yong, Ed (August 31, 2012). "Everything you never wanted to know about the mites that eat, crawl, and have sex on your face". Not Exactly Rocket Science. Discover. Retrieved April 24, 2013.
- Cassidy, Josh (21 May 2019). "Meet the Mites That Live on Your Face". NPR.
- δημός. Liddell, Henry George; Scott, Robert; An Intermediate Greek–English Lexicon at the Perseus Project.
- δήξ. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project.
- "Demodex". Medical Dictionary (medicine.academic.ru).
- Rufli, T.; Mumcuoglu, Y. (1981). "The hair follicle mites Demodex folliculorum and Demodex brevis: biology and medical importance. A review". Dermatologica. 162 (1): 1–11. doi:10.1159/000250228. PMID 6453029.
- Rush, Aisha (2000). "ADW: Demodex folliculorum". Animal Diversity Web. University of Michigan. Archived from the original on 2021-01-25. Retrieved 2022-02-10.
- Sengbusch, H. G.; Hauswirth, J. W. (1986). "Prevalence of hair follicle mites, Demodex folliculorum and D. brevis (Acari: Demodicidae), in a selected human population in western New York, USA". Journal of Medical Entomology. 23 (4): 384–388. doi:10.1093/jmedent/23.4.384. PMID 3735343.
- Thoemmes, Megan S.; Fergus, Daniel J.; Urban, Julie; Trautwein, Michelle; Dunn, Robert R.; Kolokotronis, Sergios-Orestis (27 August 2014). "Ubiquity and Diversity of Human-Associated Demodex Mites". PLoS ONE. 9 (8): e106265. Bibcode:2014PLoSO...9j6265T. doi:10.1371/journal.pone.0106265. PMC 4146604. PMID 25162399.
- Liu, Jingbo; Sheha, Hosam; Tseng, Scheffer C. G. (October 2010). "Pathogenic role of Demodex mites in blepharitis". Current Opinion in Allergy and Clinical Immunology. 10 (5): 505–510. doi:10.1097/ACI.0b013e32833df9f4. PMC 2946818. PMID 20689407.
- Zhao, Ya-e; Peng, Yan; Wang, Xiang-lan; Wu, Li-ping; Wang, Mei; Yan, Hu-ling; Xiao, Sheng-xiang (December 2011). "Facial dermatosis associated with Demodex: a case-control study". Journal of Zhejiang University Science B. 12 (8): 1008–1015. doi:10.1631/jzus.B1100179. PMC 3232434. PMID 22135150.
- Zhao, Ya-e; Hu, Li; Wu, Li-ping; Ma, Jun-xian (March 2012). "A meta-analysis of association between acne vulgaris and Demodex infestation". Journal of Zhejiang University Science B. 13 (3): 192–202. doi:10.1631/jzus.B1100285. PMC 3296070. PMID 22374611.
- "2011-2012 Annual Evidence Update on Acne vulgaris" (PDF). University of Nottingham Centre of Evidence Based Dermatology. 2012. p. 10. Retrieved 23 September 2013.
- Douglas, Annyella; Zaenglein, Andrea L. (September 2019). "A case series of demodicosis in children". Pediatric Dermatology. 36 (5): 651–654. doi:10.1111/pde.13852. PMID 31197860. S2CID 189817759.
Papulopustular lesions predominate, prompting the advice 'pustules on noses, think demodicosis!'
- MacKenzie, Debora (August 30, 2012). "Rosacea may be caused by mite faeces in your pores". New Scientist. Retrieved August 30, 2012.
- Jarmuda, Stanisław; O'Reilly, Niamh; Żaba, Ryszard; Jakubowicz, Oliwia; Szkaradkiewicz, Andrzej; Kavanagh, Kevin (1 November 2012). "Potential role of Demodex mites and bacteria in the induction of rosacea". Journal of Medical Microbiology. 61 (11): 1504–1510. doi:10.1099/jmm.0.048090-0. PMID 22933353.
- Savla, Keyur; Le, Jimmy T; Pucker, Andrew D (9 June 2019). "Tea tree oil for Demodex blepharitis". The Cochrane Database of Systematic Reviews. 2019 (6): CD013333. doi:10.1002/14651858.CD013333. PMC 6556368.
- Zhu, Minyi; Cheng, Chao; Yi, Haisu; Lin, Liping; Wu, Kaili (31 July 2018). "Quantitative Analysis of the Bacteria in Blepharitis With Demodex Infestation". Frontiers in Microbiology. 9: 1719. doi:10.3389/fmicb.2018.01719. PMC 6079233. PMID 30108572.
- Palopoli, Michael F.; Fergus, Daniel J.; Minot, Samuel; Pei, Dorothy T.; Simison, W. Brian; Fernandez-Silva, Iria; Thoemmes, Megan S.; Dunn, Robert R.; Trautwein, Michelle (29 December 2015). "Global divergence of the human follicle mite Demodex folliculorum: Persistent associations between host ancestry and mite lineages". Proceedings of the National Academy of Sciences. 112 (52): 15958–15963. Bibcode:2015PNAS..11215958P. doi:10.1073/pnas.1512609112. PMC 4703014. PMID 26668374.
- "Scientists say face mites evolved alongside humans since the dawn of human origins". ScienceDaily (Press release). December 14, 2015.
- Bisbee, E; Rudnick, E; Loyd, A (October 2019). "Crusted demodicosis in an immunocompetent patient". Cutis. 104 (4): E9–E11. PMID 31774896.
- Miller, William H., Jr; Griffin, Craig E.; Campbell, Karen L. (2013). "Canine demodicosis". Muller & Kirk's small animal dermatology (7th ed.). St. Louis, Mo.: Elsevier. pp. 304–313. ISBN 978-1-4160-0028-0.
- Horvath, Christa; Neuber, Ariane (March 2007). "Pathogenesis of canine demodicosis". Companion Animal. 12 (2): 55–59. doi:10.1111/j.2044-3862.2007.tb00131.x.
- 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
- Ocular Demodicosis (Demodex Infestation) at eMedicine
- Demodetic Mange in Dogs, by T. J. Dunn, Jr. DVM