View source for Demodex

{{Short description|Genus of mites that live on mammals}}
{{Automatic taxobox
| image = Demodex folliculorum SEM crop.jpg
| taxon = Demodex
| authority = [[Richard Owen|Owen]], 1843<ref>{{cite book|last1=Owen|first1=Richard|last2=Cooper|first2=William White|title=Lectures on Comparative Anatomy|date=1843|publisher=Longman, Brown, Green, and Longmans|location=London|page=252|chapter-url=https://biodiversitylibrary.org/page/6256930|chapter=Lecture XIX. Arachnida}}</ref>
| type_species = ''[[Demodex folliculorum|Acarus folliculorum]]''
| type_species_authority = [[Gustav Simon (physician)|Simon]], 1842
| subdivision_ranks = Species
| subdivision = {{Plainlist|
* ''[[Demodex aries]]''
* ''[[Demodex aurati]]''
* ''[[Demodex brevis]]''
* ''[[Demodex bovis]]''
* ''[[Demodex#Demodex canis|Demodex canis]]''
* ''[[Demodex caprae]]''
* ''[[Demodex caballi]]''
* ''[[Demodex cati]]''
* ''[[Demodex conicus]]''
* ''[[Demodex cornei]]''
* ''[[Demodex criceti]]''
* ''[[Demodex cyonis]]''
* ''[[Demodex equi]]''
* ''[[Demodex folliculorum]]''
* ''[[Demodex foveolator]]''
* ''[[Demodex gapperi]]''
* ''[[Demodex gatoi]]''
* ''[[Demodex huttereri]]''
* ''[[Demodex injai]]''
* ''[[Demodex leucogasteri]]''
* ''[[Demodex microti]]''
* ''[[Demodex ovis]]''
* ''[[Demodex phyloides]]''
* ''[[Demodex ponderosus]]''
* ''[[Demodex vibrissae]]''
* ''[[Demodex zalophi]]''
}}
}}

'''''Demodex''''' {{IPAc-en|'|d|E|m|@|d|E|k|s}} is a [[genus]] of tiny [[mite]]s that live in or near [[hair follicles]] of [[mammal]]s. Around 65 species of ''Demodex'' are known.<ref>{{cite web |url=http://blogs.discovermagazine.com/notrocketscience/2012/08/31/everything-you-never-wanted-to-know-about-the-mites-that-eat-crawl-and-have-sex-on-your-face/#.UXeT_TcXekI |title=Everything you never wanted to know about the mites that eat, crawl, and have sex on your face |first=Ed |last=Yong |date=August 31, 2012 |access-date=April 24, 2013 |department=Not Exactly Rocket Science |magazine=[[Discover (magazine)|Discover]] |archive-date=November 7, 2019 |archive-url=https://web.archive.org/web/20191107094558/http://blogs.discovermagazine.com/notrocketscience/2012/08/31/everything-you-never-wanted-to-know-about-the-mites-that-eat-crawl-and-have-sex-on-your-face/#.UXeT_TcXekI |url-status=dead }}</ref> Two species live on [[human]]s: ''[[Demodex folliculorum]]'' and ''[[Demodex brevis]]'', both frequently referred to as '''eyelash mites''', alternatively '''face mites''' or '''skin mites'''.<ref>{{Cite web|url=https://www.npr.org/sections/health-shots/2019/05/21/725087824/meet-the-mites-that-live-on-your-face?t=1611010615097|title = Meet the Mites That Live on Your Face|website = [[NPR]]| date=21 May 2019 | last1=Cassidy | first1=Josh }}</ref>

Different species of animals host different species of ''Demodex''. ''[[Demodex#D. canis|Demodex canis]]'' lives on the domestic [[dog]]. The presence of ''Demodex'' species on mammals is common and usually does not cause any symptoms. ''Demodex'' is derived from [[Greek language|Greek]] {{lang|el|δημός}} ({{transliteration|el|dēmos}}) {{gloss|fat}} and {{lang|el|δήξ}}, δηκός ({{transliteration|el|dēx}}, ''dēkós'') {{gloss|woodworm}}.<ref>{{LSJ|dhmo/s|δημός|ref|mLSJ}}.</ref><ref>{{LSJ|D.H./c|δήξ|ref}}.</ref><ref>{{cite web | url = http://medicine.academic.ru/19095/Demodex | title = Demodex | work = Medical Dictionary (medicine.academic.ru) }}</ref>

==Notable species==
===''D. folliculorum'' and ''D. brevis''===
{{Main|Demodex folliculorum|Demodex brevis}}
''Demodex folliculorum'' and ''D. brevis'' are typically found on humans. The former was first described in 1842 by German physician and dermatologist [[Gustav Simon (physician)|Gustav Simon]],<ref>{{Cite book |last=Simon |first=Gustav |url=https://www.biodiversitylibrary.org/item/49986 |title=Archiv für Anatomie, Physiologie und Wissenschaftliche Medicin |publisher=Verlag von Veit & Comp. |year=1842 |editor-last=Müller |editor-first=Johannes |volume= |location=Berlin |pages=221 |language=DE |trans-title=Archive for Anatomy, Physiology and Scientific Medicine |chapter=Ueber eine in den kranken und normalen Haarsäcken des Menschen lebende Milbe |trans-chapter=On a Mite Living in the Diseased and Normal Hair Follicles of Humans}}</ref> with English biologist [[Richard Owen]] naming the genus ''Demodex'' the following year.<ref>{{Cite book |title=Rook's textbook of dermatology |date=2016 |publisher=John Wiley & Sons Inc |isbn=978-1-118-44117-6 |editor-last=Griffiths |editor-first=Christopher E. M. |edition=9th |location=Chichester, West Sussex Hoboken, NJ |editor-last2=Barker |editor-first2=Jonathan |editor-last3=Bleiker |editor-first3=Tanya |editor-last4=Chalmers |editor-first4=Robert J. G. |editor-last5=Creamer |editor-first5=Daniel |editor-last6=Rook |editor-first6=Graham Arthur}}</ref>

''Demodex brevis'' was identified as separate in 1963 by LK Akbulatova. While ''D. folliculorum'' is found in hair follicles, ''D. brevis'' lives in [[sebaceous gland]]s connected to [[hair follicle]]s. Both species are primarily found in the face {{emdash}} near the nose, the [[eyelash]]es, and [[eyebrow]]s {{emdash}} but also occur elsewhere on the body. ''Demodex folliculorum'' is occasionally found as a cause of [[Demodex folliculitis|folliculitis]], although most people with ''D. folliculorum'' mites have no obvious ill effects.

The adult mites are {{convert|0.3|-|0.4|mm|abbr=on|frac=256}} long, with ''D. brevis'' slightly shorter than ''D. folliculorum''.<ref name="rufli">{{cite journal |first1=T. | last1=Rufli | first2=Y. |last2=Mumcuoglu |date=1981 |title=The hair follicle mites ''Demodex folliculorum'' and ''Demodex brevis'': biology and medical importance. A review |journal=[[Dermatologica]] |volume=162 |issue=1 |pages=1–11 |pmid=6453029 |doi=10.1159/000250228}}</ref> Each has a [[transparency and translucency|semitransparent]], elongated body that consists of two fused parts. Eight short, segmented legs are attached to the first body segment. The body is covered with [[Scale (anatomy)|scales]] for anchoring itself in the hair follicle, and the mite has pin-like mouthparts for eating [[skin|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 {{convert|8|–|16|mm|abbr=on|frac=8}} per hour, especially at night, as they try to avoid light.<ref name="rufli"/>{{rp|page=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.<ref>{{cite web|last=Rush|first=Aisha|date=2000|title=ADW: Demodex folliculorum|url=https://animaldiversity.org/accounts/Demodex_folliculorum--Demodex/|url-status=live|archive-url=https://web.archive.org/web/20210125092156/http://animaldiversity.org/accounts/Demodex_folliculorum--Demodex/|archive-date=2021-01-25|access-date=2022-02-10|work=[[Animal Diversity Web]]|publisher=[[University of Michigan]]}}</ref> 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 the larvae develop into adults in about 7 days. The total lifespan of a ''Demodex'' mite is several weeks.<ref>{{cite journal |last1=Rather |first1=Parvaiz Anwar |last2=Hassan |first2=Iffat |date=Jan–Feb 2014 |title=Human ''Demodex'' Mite: The Versatile Mite of Dermatological Importance |journal=[[Indian Journal of Dermatology]] |volume=59 |issue=1 |pages=60–66 |publisher=[[Lippincott Williams & Wilkins]] |doi=10.4103/0019-5154.123498 |pmc=3884930 |pmid=24470662 |access-date=16 December 2023 |url=https://journals.lww.com/ijod/fulltext/2014/59010/human_demodex_mite__the_versatile_mite_of.11.aspx |doi-access=free }}</ref>

====Prevalence====
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.<ref>{{cite journal |first1=H. G. |last1=Sengbusch |first2=J. W. |last2=Hauswirth |date=1986 |title=Prevalence of hair follicle mites, ''Demodex folliculorum'' and ''D. brevis'' (Acari: Demodicidae), in a selected human population in western New York, USA |journal=[[Journal of Medical Entomology]] |volume=23 |issue=4 |pages=384–388 |pmid=3735343 |doi=10.1093/jmedent/23.4.384}}</ref> 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.<ref name=Thoemmes>{{cite journal |last1=Thoemmes |first1=Megan S. |last2=Fergus |first2=Daniel J. |last3=Urban |first3=Julie |last4=Trautwein |first4=Michelle |last5=Dunn |first5=Robert R. |last6=Kolokotronis |first6=Sergios-Orestis |title=Ubiquity and Diversity of Human-Associated ''Demodex'' Mites| journal=[[PLoS ONE]] |date=27 August 2014 |volume=9 |issue=8 |pages=e106265 |doi=10.1371/journal.pone.0106265 |pmid=25162399 |pmc=4146604|bibcode=2014PLoSO...9j6265T |doi-access=free }}</ref> 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.

====Research====
Research about human infestation by ''Demodex'' mites is ongoing:<ref>{{cite journal |first1=Jingbo |last1=Liu |first2=Hosam |last2=Sheha | first3=Scheffer C. G. |last3=Tseng |date=October 2010 |title=Pathogenic role of ''Demodex'' mites in blepharitis |journal=[[Current Opinion in Allergy and Clinical Immunology]] |volume=10 |issue=5 |pages=505–510 |pmid=20689407 |pmc=2946818 |doi=10.1097/ACI.0b013e32833df9f4}}</ref><ref name=yzhaocase>{{cite journal |first1=Ya-e |last1=Zhao | first2=Yan |last2=Peng |first3=Xiang-lan |last3=Wang |first4=Li-ping |last4=Wu |first5=Mei |last5=Wang |first6=Hu-ling |last6=Yan |first7=Sheng-xiang |last7=Xiao |date=December 2011 |title=Facial dermatosis associated with ''Demodex'': a case-control study |journal=[[Journal of Zhejiang University Science B]] |volume=12 |issue=8 |pages=1008–1015 |pmid=22135150 |doi=10.1631/jzus.B1100179 |pmc=3232434}}</ref><ref name="yzhaometa" /><ref name=nottinghamreview>{{cite web |publisher=University of Nottingham Centre of Evidence Based Dermatology |year=2012 |title=2011-2012 Annual Evidence Update on Acne vulgaris |page=10 |url=
http://www.nottingham.ac.uk/research/groups/cebd/documents/methodological-resources/2012-annual-evidence-update-on-acne-vulgaris.pdf |access-date=23 September 2013}}</ref>

* 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.<ref name=yzhaometa>{{cite journal |first1=Ya-e |last1=Zhao | first2=Li |last2=Hu |first3=Li-ping |last3=Wu |first4=Jun-xian |last4=Ma |date=March 2012 |title=A meta-analysis of association between acne vulgaris and ''Demodex'' infestation |journal=[[Journal of Zhejiang University Science B]] |volume=13 |issue=3 |pages=192–202 |pmid=22374611 |doi=10.1631/jzus.B1100285 |pmc=3296070}}</ref><ref>{{cite journal |last1=Douglas |first1=Annyella |last2=Zaenglein |first2=Andrea L. |title=A case series of demodicosis in children |journal=Pediatric Dermatology |date=September 2019 |volume=36 |issue=5 |pages=651–654 |doi=10.1111/pde.13852 |pmid=31197860 |s2cid=189817759 |quote=Papulopustular lesions predominate, prompting the advice 'pustules on noses, think demodicosis!'}}</ref>
* Several preliminary studies suggest an association between mite infestation and [[rosacea]].<ref name="MacKenzie">{{cite journal |first=Debora |last=MacKenzie |date=August 30, 2012 |url=https://www.newscientist.com/article/dn22227-rosacea-may-be-caused-by-mite-faeces-in-your-pores.html |title=Rosacea may be caused by mite faeces in your pores |access-date=August 30, 2012 |journal=[[New Scientist]]}}</ref><ref>{{cite journal |last1=Jarmuda |first1=Stanisław |last2=O'Reilly |first2=Niamh |last3=Żaba |first3=Ryszard |last4=Jakubowicz |first4=Oliwia |last5=Szkaradkiewicz |first5=Andrzej |last6=Kavanagh |first6=Kevin |title=Potential role of ''Demodex'' mites and bacteria in the induction of rosacea |journal=Journal of Medical Microbiology |date=1 November 2012 |volume=61 |issue=11 |pages=1504–1510 |doi=10.1099/jmm.0.048090-0 |pmid=22933353 |doi-access=free }}</ref>
*''Demodex'' mites can cause [[blepharitis]], which can be treated with solutions of [[tea tree oil]];<ref>{{Cite journal |last1=Liu |first1=Jingbo |last2=Sheha |first2=Hosam |last3=Tseng |first3=Scheffer CG |date=2010 |title=Pathogenic role of ''Demodex'' mites in blepharitis |url=https://journals.lww.com/co-allergy/Abstract/2010/10000/Pathogenic_role_of_Demodex_mites_in_blepharitis.16.aspx |journal=Current Opinion in Allergy and Clinical Immunology |language=en-US |volume=10 |issue=5 |pages=505–510 |doi=10.1097/ACI.0b013e32833df9f4 |issn=1528-4050 |pmc=2946818 |pmid=20689407}}</ref><ref>{{cite journal |last1=Zhu |first1=Minyi |last2=Cheng |first2=Chao |last3=Yi |first3=Haisu |last4=Lin |first4=Liping |last5=Wu |first5=Kaili |title=Quantitative Analysis of the Bacteria in Blepharitis With Demodex Infestation |journal=Frontiers in Microbiology |date=31 July 2018 |volume=9 |pages=1719 |doi=10.3389/fmicb.2018.01719 |pmid=30108572 |pmc=6079233 |doi-access=free }}</ref> there is no good evidence for its effectiveness.<ref>{{cite journal |last1=Savla |first1=Keyur |last2=Le |first2=Jimmy T |last3=Pucker |first3=Andrew D |title=Tea tree oil for Demodex blepharitis |journal=The Cochrane Database of Systematic Reviews |date=9 June 2019 |volume=2019 |issue=6 |pages=CD013333 |doi=10.1002/14651858.CD013333 |pmc=6556368 }}</ref>
* ''Demodex'' mites causing a reaction in healthy individuals depends on genealogy. Mites may evolve differently with different bloodlines.<ref>{{cite journal |last1=Palopoli |first1=Michael F. |last2=Fergus |first2=Daniel J. |last3=Minot |first3=Samuel |last4=Pei |first4=Dorothy T. |last5=Simison |first5=W. Brian |last6=Fernandez-Silva |first6=Iria |last7=Thoemmes |first7=Megan S. |last8=Dunn |first8=Robert R. |last9=Trautwein |first9=Michelle |title=Global divergence of the human follicle mite ''Demodex folliculorum'': Persistent associations between host ancestry and mite lineages |journal=Proceedings of the National Academy of Sciences |date=29 December 2015 |volume=112 |issue=52 |pages=15958–15963 |doi=10.1073/pnas.1512609112 |pmid=26668374 |pmc=4703014 |bibcode=2015PNAS..11215958P |doi-access=free}}
*{{cite press release |date=December 14, 2015 |title=Scientists say face mites evolved alongside humans since the dawn of human origins |website=ScienceDaily |url=https://www.sciencedaily.com/releases/2015/12/151214165733.htm}}</ref><ref>{{cite journal |last1=Bisbee |first1=E |last2=Rudnick |first2=E |last3=Loyd |first3=A |title=Crusted demodicosis in an immunocompetent patient |journal=Cutis |date=October 2019 |volume=104 |issue=4 |pages=E9–E11 |pmid=31774896 }}</ref>
* New studies suggest ''Demodex'' mites are involved in psoriasis, allergic rhinitis, and seborrheic dermatitis in immunosuppressed individuals.<ref>{{cite journal |
last1= Yengil |first1=Erhan |last2= Cevik |first2=Cengiz |last3=Aycan Kaya |first3= Özlem |last4= Taner |first4= Melis |last5=Akkoca |first5=Ayse |last6=Ozer |first6=Cahit |date=1 January 2014 |pages= 27–31 |title= Relationship between ''Demodex folliculorum'' and allergic rhinitis in adults |volume= 30 |journal= Acta Medica Mediterranea |url= https://www.researchgate.net/publication/288367546}}</ref><ref>{{cite journal |url= https://pubmed.ncbi.nlm.nih.gov/24314384/ |vauthors=Ramos-e-Silva M, Sampaio AL, Carneiro S |title= Red face revisited: Endogenous dermatitis in the form of atopic dermatitis and seborrheic dermatitis |journal=Clin. Dermatol. |year=2014  |volume=32 |issue=1 |pages=109–15 |doi= 10.1016/j.clindermatol.2013.05.032 |pmid= 24314384 }}</ref><ref>{{cite journal |title=Allergic Rhinitis and Asthma Among Adolescents with Psoriasis: A Population-based Cross-sectional Study |author1=Eran Galili |author2=Aviv Barzilai |author3=Gilad Twig |author4=Tomm Caspi |author5=Danny Daniely |author6=Rony Shreberk-Hassidim |author7=Nadav Astman|journal=Acta Dermato Venereologica |year=2020 |volume=100 |issue=10 |pages=adv00133-5 |doi=10.2340/00015555-3485 |pmid=32314795 |pmc=9137373 }}</ref>

===''D. canis''===
[[File:Demodex mite 1.JPG|thumb|''D. canis'']]
{{See also|Demodicosis|Canine demodicosis}}

The natural host of ''D. canis'' is the domestic [[dog]]. ''Demodex 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; 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.<ref>{{cite book|last1=Miller|first1=William H. Jr.|last2=Griffin|first2=Craig E.|last3=Campbell|first3=Karen L.|title=Muller & Kirk's small animal dermatology|date=2013|publisher=Elsevier|location=St. Louis, Mo.|isbn=978-1-4160-0028-0|pages=304–313|edition=7th|chapter=Canine demodicosis}}</ref> 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.

The species was first described by [[Franz Leydig]] in 1859.<ref>{{cite journal|last1=Horvath|first1=Christa|last2=Neuber|first2=Ariane|title=Pathogenesis of canine demodicosis|journal=Companion Animal|date=March 2007|volume=12|issue=2|pages=55–59|doi=10.1111/j.2044-3862.2007.tb00131.x}}</ref>

==References==
{{Reflist}}

==External links==
*{{Commons category-inline}}
*{{Wikispecies-inline}}
* [http://www.microscopy-uk.org.uk/mag/artmay00/demodex.html ''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
* {{EMedicine|article|1203895|Ocular Demodicosis (Demodex Infestation)}}
* [http://www.petmd.com/dog/general-health/evr_dg_demodectic_mange_in_dogs#.Un5eOJRc0dK ''Demodetic Mange in Dogs'', by T. J. Dunn, Jr. DVM]
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{{Pediculosis, acariasis and other infestations}}
{{Acari}}
{{Taxonbar|from=Q292297}}
{{Authority control}}

[[Category:Parasitic acari]]
[[Category:Parasitic arthropods of mammals]]
[[Category:Trombidiformes genera]]
[[Category:Human eyelashes]]