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Under the lash: Demodex mites in human diseases

Authors:
Noreen Lacey at National University of Ireland, Maynooth
Noreen Lacey
Kevin Kavanagh at National University of Ireland, Maynooth
Kevin Kavanagh
Scheffer C G Tseng at TissueTech, Inc.
Scheffer C G Tseng
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Abstract and Figures

Demodex mites, class Arachnida and subclass Acarina, are elongated mites with clear cephalothorax and abdomens, the former with four pairs of legs. There are more than 100 species of Demodex mite, many of which are obligatory commensals of the pilosebaceous unit of mammals including cats, dogs, sheep, cattle, pigs, goats, deer, bats, hamsters, rats and mice. Among them, Demodex canis, which is found ubiquitously in dogs, is the most documented and investigated. In excessive numbers D. canis causes the inflammatory disease termed demodicosis (demodectic mange, follicular mange or red mange), which is more common in purebred dogs and has a hereditary predisposition in breeding kennels1. Two distinct Demodex species have been confirmed as the most common ectoparasite in man. The larger Demodex folliculorum, about 0.3-0.4 mm long, is primarily found as a cluster in the hair follicle (Figure 1a), while the smaller Demodex brevis, about 0.2-0.3 mm long with a spindle shape and stubby legs, resides solitarily in the sebaceous gland (Figure 1b). These two species are also ubiquitously found in all human races without gender preference. The pathogenic role of Demodex mites in veterinary medicine is not as greatly disputed as in human diseases. In this article, we review the key literature and our joint research experience regarding the pathogenic potential of these two mites in causing inflammatory diseases of human skin and eye. We hope that the evidence summarized herein will invite readers to take a different look at the life of Demodex mites in several common human diseases.
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Under the lash:
Demodex mites in human diseases
Noreen Lacey,
University of Ireland Maynooth
Kevin Kavanagh, and
University of Ireland Maynooth
Scheffer C.G. Tseng
Ocular Surface Center and Ocular Surface Research Education Foundation, Miami
Abstract
Demodex mites, class Arachnida and subclass Acarina, are elongated mites with clear
cephalothorax and abdomens, the former with four pairs of legs. There are more than 100 species
of Demodex mite, many of which are obligatory commensals of the pilosebaceous unit of
mammals including cats, dogs, sheep, cattle, pigs, goats, deer, bats, hamsters, rats and mice.
Among them, Demodex canis, which is found ubiquitously in dogs, is the most documented and
investigated. In excessive numbers D. canis causes the inflammatory disease termed demodicosis
(demodectic mange, follicular mange or red mange), which is more common in purebred dogs and
has a hereditary predisposition in breeding kennels1. Two distinct Demodex species have been
confirmed as the most common ectoparasite in man. The larger Demodex folliculorum, about 0.3–
0.4 mm long, is primarily found as a cluster in the hair follicle (Figure 1a), while the smaller
Demodex brevis, about 0.2–0.3 mm long with a spindle shape and stubby legs, resides solitarily in
the sebaceous gland (Figure 1b). These two species are also ubiquitously found in all human races
without gender preference. The pathogenic role of Demodex mites in veterinary medicine is not as
greatly disputed as in human diseases. In this article, we review the key literature and our joint
research experience regarding the pathogenic potential of these two mites in causing inflammatory
diseases of human skin and eye. We hope that the evidence summarized herein will invite readers
to take a different look at the life of Demodex mites in several common human diseases.
Keywords
Demodex; eye disease; eyelash; hair follicle; mite; skin disease
The life cycle of the Demodex mite is approximately 14–18 days from an egg to the larval
stage of protonymph to deutonymph and finally to the adult stage (see Figure 1)2. Because
all adult mites have a limited life cycle, their ability to expand in numbers in a human host
depends on successful copulation by adult male and female mites in the opening of the hair
follicle (near the skin surface). Afterwards, the gravid female moves to the sebaceous gland
to deposit eggs, each of which gives rise to a larva and then a protonymph in the sebaceous
canal. A protonymph is brought to the opening of the hair follicle and matures into a
deutonymph, which crawls on to the skin surface, then re-enters a hair follicle to become an
adult. Therefore, during a life cycle, if adults can successfully copulate and produce the next
generation, the extent of Demodex infestation will gradually increase in the host over time.
Scanning electron microscopy reveals the special piercing mouthparts of D. folliculorum as
a sharp offensive weapon capable of destroying adipose tissue. Although it has also been
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proposed that mites feed on follicular and glandular epithelial cells, sebum is thought to be
the mite’s main food source. As a result, both Demodex species often coexist at the same
skin area and gather in the face, cheeks, forehead, nose and external ear tract, where active
sebum excretion creates favourable habitats and breeding conditions. Because these mites
are susceptible to desiccation, their lifespan is limited outside the living body, and direct
contact is required for transmission of mites from one individual to another. Consequently,
an effective regimen in eradicating Demodex infestation should include killing as well as
prevention of their copulation and transmission.
Implication of Demodex mites in human diseases
Although Demodex mites have been implicated as a cause of many human skin disorders,
their pathogenic role has long been debated3. Such a concern has been raised in part because
some Demodex mites can be found in the skin of asymptomatic individuals. Most
researchers attribute some skin diseases to Demodex only when their numbers are elevated.
To quantify the extent of Demodex infestation in the skin, a surface biopsy has been
standardized as the main method4. After cleaning the patient’s skin and a glass slide with
ether to improve adherence, a spot of cyanoacrylate adhesive (superglue) is applied on the
skin surface of interest before being overlaid with a slide. After approximately 1 minute on
the skin, the slide is gently removed and covered by one drop of immersion oil before being
mounted with a coverslip. The density of D. folliculorum is measured by counting the
number of mites on the slide in a pre-marked surface area of 1 cm2 at a magnification of ×40
and ×100 under a microscope. Because hairs together with the superficial horny layer are
sampled with minimal sebaceous glands, D. folliculorum is primarily found. Using this
method, Demodex infestation is thought to be non-existent in healthy children of less than
one decade of life, increasing in an age-dependent manner, and found probably 100% in
elderly skin, unless some eradicating measures are taken. It remains unclear whether such an
age-dependent increase is due to cumulative colonization or an increase in sebum levels with
age. This quantitative biopsy method has also been used for monitoring the efficacy of
various therapies in eradicating D. folliculorum in the skin.
Since 1932, Demodex infestation has been implied as a causative role in rosacea, a chronic
inflammatory dermatosis of the convexities of the central face characterized by the presence
of multiple small dome-shaped erythematous papules and papulopustules arising on a
background of fixed inflammatory erythema. It has been proposed that the pathogenic
potential increases if a mite density is higher than five per cm2 1. Several studies have
shown a higher mite density on the faces of rosacea patients than on those of age- and sex-
matched non-rosacea controls4. It is intriguing that Demodex numbers increase when the
outside temperature elevates in spring and summer, coinciding with the time when rosacea is
exacerbated. Demodex mites have also been implicated as a cause of other skin diseases
such as pityriasis folliculorum (typically found in older women who do not use soap but
apply large amounts of makeup), perioral dermatitis (a facial rash typically occurring around
the mouth), scabies-like eruptions, facial pigmentation, eruptions of the bald scalp, Demodex
folliculitis (an inflammatory reaction in the superficial aspect of the hair follicle),
demodicosis gravis (dermal granulomas formed because of mite remnants phagocytosed by
foreign-body giant cells) and even basal cell carcinoma. Furthermore, the above skin
demodicosis is prone to develop in patients whose local or systemic immune status is
compromised by topical or systemic administration of steroids or other immunosuppressive
agents or by diseases such as leukaemia and HIV.
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Implication of Demodex mites in human eye diseases
Contiguous to the skin, the eye can also be infested by Demodex mites. In the eye, D.
folliculorum is found in the lash follicle, whereas D. brevis burrows deep into the lash
sebaceous gland and the meibomian gland, the latter of which produces meibum as the
superficial layer of the preocular tear film. Because the eye is surrounded by such protruding
body parts as the nose, the brow and the cheek, the eyelid is not as accessible as the face to
daily cleansing hygiene. Therefore, once Demodex mite infestation establishes in the face, it
is likely to spread and flourish in the eyelid. As a matter of fact, the first disorder that was
associated with Demodex, dated as early as 1899, was blepharitis (inflammation of the lid), a
disease that has continued to be a subject of investigation ever since5. However, as in the
skin, the pathogenic potential of these mites in blepharitis had been questioned because a
low number of Demodex was found in the lashes of asymptomatic individuals.
Cylindrical dandruff (CD) in eye lashes (Figure 2a) is a common finding in some blepharitis
patients. We speculated that the controversy of whether CD can be regarded pathognomonic
for Demodex infestation originated from errors of the previously published method in
sampling and counting mites. Besides errors in randomly epilating eyelashes and mounting
the slide using a drop of oil, the most important one was that Demodex embedded in
compact and opaque CD could not be fully counted unless 100% alcohol6 or a drop of
fluorescein7 is added to stimulate them to migrate out (Figure 3). Using the modified
method, we have confirmed that CD in eye lashes is indeed a reliable clinical sign indicative
of Demodex infestation of the eyelash6. Furthermore, we observed that Demodex infestation
can still be detected in 50% of patients despite daily lid scrub with Baby shampoo (a routine
regimen) for more than 1 year. This result together with those published earlier strongly
suggests that the conventional lid scrub with baby shampoo may not eradicate Demodex,
rendering it difficult to resolve whether Demodex is pathogenic or not.
Hence, we believe that one way of determining the pathogenic potential of Demodex
infestation in blepharitis and other ocular diseases is to identify a treatment that can kill
Demodex with a good safety profile. Using an in vitro microscopic observation for a period
of 150 minutes, we found that adult D. folliculorum is resistant to a wide range of common
antiseptic solutions including 75% alcohol and 10% povidone–iodine, but can dose-
dependently be killed by tea tree oil (TTO)8. TTO, a natural essential oil steam-distilled
from the leaf of the tea tree Melaleuca alternifolia, has long been used as an aboriginal
traditional medicine in Australia for wounds and cutaneous infection. Unlike Bbaby
shampoo, lid scrub with TTO not only cleanses CD from the lash root, but also stimulates
embedded mites to migrate out to the skin (Figure 4). As a result, weekly lid scrub with 50%
TTO and daily lid scrub with tea tree shampoo is effective in eradicating ocular Demodex
infestation in vivo, as is evident by bringing the Demodex count down to zero in 4 weeks in a
majority of patients9,10. Because refractory ocular surface inflammation resolved after
significant reduction of mite counts achieved by this new lid scrub regimen, we concluded
that ocular Demodex infestation in lashes can cause the lashes to become mal-aligned
(Figure 2a), turn in to touch the cornea (trichiasis) (Figure 2b) and fall off (madarosis)
(Figure 2c). Furthermore, its infestation in meibomian glands can cause meibomian gland
dysfunction (Figure 2d), leading to disturbance and deficiency of the lipid tear film and
blurry vision9. To our surprise, inflammation derived from lashes and meibomian glands (in
the context of blepharitis) may spread over to the conjunctiva, resulting in conjunctivitis
(Figure 2e) and even to the cornea, resulting in various blinding corneal lesions (Figure
2f)9,10. The tendency of inflammation spread to the conjunctiva and cornea depends on not
only the severity of the host inflammatory response, but also the distance from the site of
mite infestation. In this regard, the intriguing finding that the rate of detecting D. brevis is
much higher in patients who developed corneal lesions10, is consistent with the notion that
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D. brevis primarily residing in meibomian glands is easier to reach the conjunctiva and the
cornea. Future studies are needed to determine whether the pathogenicity of D. brevis differs
from that of D. folliculorum. Unlike what has been reported for skin demodicosis, we
recently discovered that ocular Demodex infestation could be detected in immune non-
compromised paediatric patients inflicted with refractory blepharoconjunctivitis (Liang L,
Safran S, Gao Y, Sheha H, Li J, and Tseng SCG, unpublished work). Therefore future
studies are also needed to determine whether eyelash sampling is more sensitive than skin
surface biopsy in detecting demodicosis in paediatric patients.
Pathogenic mechanism of Demodex mites
Because a high number of Demodex mites have been observed in the skin and eyelashes of
patients with the aforementioned diseases, several pathogenic mechanisms have been
postulated to support the notion that mites alone are able to inflict significant damage to the
habitat that they live in. Mechanically, the mites may block the hair follicles and sebaceous
ducts to induce epithelial hyperplasia and hyperkeratinization. The chitinous exoskeleton of
the mites may act as a foreign body and cause granulomatous reaction. Debris or wastes
generated by mites may elicit inflammatory responses via a delayed hypersensitivity
reaction or an innate immune response11.
Nevertheless, one cannot rule out the pathogenic role of microbial agents that may be
associated with Demodex infestation. The notion that microbes are involved in pathogenesis
of mite-infested diseases has long been suggested because the skin inflammation in rosacea
can be markedly improved by topical metronidazole or oral antibiotics including
tetracycline, i.e. treatments that do not kill mites. Because TTO also may exert antibacterial,
antifungal and anti-inflammatory actions, we cannot attribute its therapeutic benefit in
treating the above eye diseases solely to its effect of killing mites. In fact, it has been
postulated that the mites may act as vectors to bring in common skin bacterial flora12.
Scanning electron microscopy showed bacteria on the mite skin surface. Staphylococcus
albus was shown to be transported by these mites from follicle to follicle. Superantigens
produced by streptococci and staphylococci that are implicated in a number of diseases may
play a role in the induction of rosacea.
To reconcile the apparently disparate findings of increased numbers of D. folliculorum
mites, perifollicular inflammation and response of papulopustular rosacea to selective
antibiotic therapy in some patients, we have recently isolated Bacillus oleronius inside
Demodex mites from one patient with papulopustular rosacea13. We discovered further that
this bacterium produced antigens capable of stimulating proliferation of peripheral blood
mononuclear cells in patients with rosacea in a significantly higher frequency than in control
subjects13. The pooled serum from six patients with papulopustular rosacea exhibited
positive immunoreactivity to two pro-inflammatory 62-kDa and 83-kDa proteins produced
by this bacterium13. Lately, our collaborative and prospective study of 59 patients disclosed
further a strong correlation among positive serum immunoreactivity to these two bacillus
proteins, ocular Demodex infestation, facial rosacea and blepharitis (Li J, O’Reilly N, Sheha
H, Katz R, Raju VK, Kavanagh K, and Tseng SCG, unpublished work). If such a strong
correlation signifies a causative relationship, a new pathogenic paradigm emerges to link
both Demodex infestation and microbial infection through symbiotic Bacillus oleronius in
causing skin and ocular surface inflammation. Such co-morbidity between mites and
Bacillus rests in the symbiosis of the latter in the former, a scenario first reported in the
hindgut of a termite. This paradigm explains that the large numbers of dying mites in the
follicles or glands may increase the release of the 83-kDa and 62-kDa bacterial antigen load
to a critical level to trigger a cascade of host inflammatory responses. Furthermore, it also
predicts why such a host immune-inflammatory response might be modified or exaggerated
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in certain individuals who are allergic or immune-sensitive to mites as alluded to above11.
Because ocular surface inflammation is notably reduced by lid scrub with TTO, but not by
conventional treatments including lid hygiene with Bbaby shampoo, topical steroids and
antibiotics or systemic doxycycline in some rosacea patients that present with corneal
lesions10, the mite’s role in stirring up host inflammatory response cannot be ruled out. In
short, the co-morbidity based on a symbiotic relationship of B. oleronius in Demodex mites
also justifies the consideration of a therapeutic strategy directed to killing the symbiotic
bacterium via oral antibiotics such as tetracycline and to killing and preventing mating/
reinfestation of Demodex mites, e.g. lid scrub with TTO and general hygiene at the same
time. Future investigation into this co-morbidity between mites and microbes may shed new
light not only on the understanding of the pathogenesis of this century-old common ailment
of the skin and eye, but also other similar unresolved human diseases.
Acknowledgments
Dr Tseng has filed two patents for the use of TTO and its ingredients for treating demodicosis. Studies described in
this article are supported in part by a research grant 1R43 EY019586-01 from the National Institutes of Health,
National Eye Institute.
Biographies
Noreen Lacey is a graduate of National University of Ireland Maynooth, where she received
her BSc in Biology (2004) and PhD (2007). Her PhD research was focused on investigating
the factors involved in the induction and persistence of papulopustular rosacea, under the
supervision of Dr K. Kavanagh. Results from this study demonstrated a potential role for
Demodex mite-related bacterial antigens in the pathogenesis of rosacea. She is currently a
postdoctoral researcher at the UCD Clinical Research Centre at the Mater Misericordiae
University Hospital, Dublin. Her research interests remain focused on investigating the role
of Demodex mites in the biology of human skin. Noreen.lacey@ucd.ie
Kevin Kavanagh is a Senior Lecturer in the Department of Biology at the National
University of Ireland Maynooth. His research is focused on understanding the mechanisms
employed by microbes to regulate the innate immune response of the host to facilitate their
continued persistence. He also has interests in exploring the structural and functional
similarities between the immune system of vertebrates and invertebrates.
kevin.kavanagh@nuim.ie
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Scheffer Tseng was a chaired professor at Bascom Palmer Eye Institute University of Miami
School of Medicine until 2002, when he became Chief Scientific Officer leading a research
team of 12 people of Bio-Tissue, Inc., a leading tissue engineering company. He has been
specialized in ocular surface diseases and surgical reconstruction using stem cells and
amniotic membrane, and received research support from NIH, National Eye Institute for
over 25 years. For the last 5 years, he has been interested in understanding the pathogenic
role of Demodex mites. stseng@ocularsurface.com
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12. Wolf R, Ophir J, Avigad J, et al. Acta Derm. Venereol 1988;68:535–537. [PubMed: 2467494]
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17596156]
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Figure 1.
Microscopic features of adult D. folliculorum(a) and D. brevis (b). D. folliculorum tends to
gather as a group in the follicle area of the hair or lash (a). In contrast, D. brevis tends to be
in solitude and reside in the sebaceous gland. As a result, D. brevis is not readily detected
during sampling of the lash. Under scanning electron microscopy, several D. folliculorum
mites are together next to the hair follicle
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Figure 2.
Clinical features of Demodex infestation in the eye. The most common finding is CD on the
skin surface where lashes emit (a). As mites reside close to the follicle, the orientation of
lashes become disorganized (a), can turn in to touch the ocular surface (trichiasis) (b), and in
the extreme cases results in the loss of lashes (madarosis) (c). Besides lashes, meibomian
glands can be involved to manifest plugging of the orifices (d). The inflammation derived
from lashes or meibomian glands of the lid margin can be spill over to the conjunctiva (e)
and cause a number of corneal lesions, including nodular scar (f)
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Figure 3.
Unmasking embedded mites in CD by fluorescein solution. A representative lash with CD
(a), in which embedded mites are revealed only after application of a drop of an aqueous
solution containing fluorescein (b). An arrow marks the hidden mites (a) that are revealed by
fluorescein drops. Note that this procedure of dissolving CD frequently generates air
bubbles, and the change of colour is due to the presence of fluorescein
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Figure 4.
Migration of Demodex by lid scrub with TTO. In this eye with diffuse CD found in the
lashes before treatment (a), lash to be epilated (marked by arrow) showed a fragment of CD
attached to the lash and abundant Demodex embedded close to the lash follicle (d). After lid
scrub in the orifice with 50% TTO, the lashes became clean and totally free of CD, but tails
of Demodex were protruding from the lash roots (b, arrow). At 3 minutes after lid scrub, free
Demodex was found on the trunk close to the skin surface, i.e. away from the lash follicle in
the epilated lash (e). Rotating these lashes (shown in b) before epilation allowed us to detect
a group of Demodex migrating along the lash trunk (f and g). If no lid scrub was carried out
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at home for one week, CD returned to the lashes 1 week later (c). With permission from Br.
J. Ophthalmol.8
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... Pure air-water mists may commonly splash in the eyes, and even splash around the sides of their eyewear [8,9]. Further studies are needed to determine the method of spread of eyelash bacteria, mites and other viruses that may transmitted to clinicians and/or patients [8,10]. Aerosols generated during dental treatments can remain suspended in the air for a prolonged period, potentially promoting microbial growth, of which may occur along the surface of false eyelashes [8]. ...
... They can be found in the sebaceous glands of the scalp, face, and ears, and in glands of the eyelids and eyelash follicles, where they anchor themselves to the follicle head [10,17]. A high density of Demodex infestation has been implicated in a variety of ocular surface conditions such as blepharitis [2], and inflammation of the eyelids that can cause burning or itching sensations, redness and scaling [10]. ...
... They can be found in the sebaceous glands of the scalp, face, and ears, and in glands of the eyelids and eyelash follicles, where they anchor themselves to the follicle head [10,17]. A high density of Demodex infestation has been implicated in a variety of ocular surface conditions such as blepharitis [2], and inflammation of the eyelids that can cause burning or itching sensations, redness and scaling [10]. Demodex, a parasite has been implicated in a variety of ocular surface conditions such as blepharitis, and inflammation of the eyelids that can cause burning or itching sensations, and redness [10,17]. ...
View
... Demodex mites, class Arachnida and subclass Acarina, are common ectoparasites found in hair follicles and sebaceous glands of most mammals (Lacey et al., 2009;Wesolowska et al., 2014;Ferreira et al., 2015). The genus Demodex consists of more than 100 species (Lacey et al., 2009). ...
... Demodex mites, class Arachnida and subclass Acarina, are common ectoparasites found in hair follicles and sebaceous glands of most mammals (Lacey et al., 2009;Wesolowska et al., 2014;Ferreira et al., 2015). The genus Demodex consists of more than 100 species (Lacey et al., 2009). Only two species of Demodex mites are found in humans: Demodex folliculorum and Demodex brevis (also called eyelash, face, or skin mites) (García et al., 2019;Huang et al., 2021). ...
... D. brevis are found in the sebaceous glands and usually live singly in the sebaceous glands (formed from two species) (Elston and Elston, 2014;Sędzikowska et al., 2021). A small number of mites do not cause any symptoms, and previously they were considered non-pathogenic parasites to humans (Lacey et al., 2009;Huang et al., 2021). Demodex spp. ...
Identification of Demodex spp. mites on human eyelashes in Lithuania
Article
  • Dec 2023
The aim of the study was to identify the Demodex mites collected from the patients’ eyelashes from the X outpatient clinic in Lithuania and the bacteria they carry. A total of 62 mites were collected from 15 different patients who complained of redness and itchiness around the eyes, rubbing around the eye area. Morphological examination of mites was carried out with an optical microscope. The Mites’ DNA was isolated using a DNA isolation kit, bacterial amplification was performed using specific primers for amplification of the 16S RNA gene fragment. Demodex folliculiorum was identified in all the examined samples, Demodex brevis was detected in only one sample. No bacteria were detected in the analysed samples.
View
... 7 The incidence of Demodex infestation rises with age, with detection occurring in 84% of the population at the age of 60 and in 100% of individuals over 70 years old. 1,8 Moreover, the involvement of Demodex spp. is crucial in the development of numerous eye and skin disorders 1,9 such as perioral dermatitis, pustular folliculitis and rosacea or rosacea-like dermatitis. 7,10 The establishment of Demodex infestation on the face may lead to its spread and proliferation in the eyelids, causing blepharitis. ...
... 41,54 The present nomenclature in regard to demodicosis is not specific and includes numerous dermatological conditions such as rosacea-like (rosaceiform) dermatitis, pityriasis folliculorum, demodectic rosacea, granulomatous rosacea-like dermatitis, Demodex facial dermatitis, perioral/periorbital dermatitis-like demodicosis, pityriasis folliculitis, facial demodicosis, scalp folliculitis, Demodex abscess, favus-like scalp demodicidosis and facial abscess-like conglomerates. 9 To eliminate potentially confusing information in publications, Chen and Plewig (2014) categorized demodicosis into primary and secondary forms. Primary demodicosis includes pityriasis folliculorum, papulopustular/nodulocystic or conglobate demodicosis, auricular demodicosis and ocular demodicosis. ...
Beyond the Surface: Understanding Demodex and Its Link to Blepharitis and Facial Dermatoses
Article
Full-text available
Demodex represents the most frequent ectoparasite found in humans. Although Demodex mites are considered commensals of human pilosebaceous units, an abnormally high mite density can cause several ocular and cutaneous symptoms and signs, sometimes to a severe degree. Both Demodex spp. (folliculorum and brevis) play a significant part in eye pathology and facial dermatoses. These mites have been related to blepharitis, ocular rosacea, meibomian gland dysfunction and various skin diseases, including rosacea, demodicosis and seborrheic dermatitis. Understanding the importance of Demodex in both eye and skin conditions is crucial for accurate diagnosis and appropriate management strategies, which may involve targeted treatments to control the mite population and reduce associated symptoms.
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... Acariform mites include two major and distantly related lineages, Prostigmata and Astigmata, showing multiple independent origins of parasitism 38 and thus allowing phylogenetically independent comparisons, e.g., most prostigmatan families (n = 6) have colonized mammals independently, and astigmatan mammal mites are bi-or triphyletic 39 . Among these mites are relatively benign human-specific (single-host) symbionts, such as follicular mites, Demodex folliculorum and D. brevis 40 . Demodex mites are common components of healthy skin, acting as mostly harmless symbionts 41 . ...
Predicting host range expansion in parasitic mites using a global mammalian-acarine dataset
Article
Full-text available
  • Jun 2024
Multi-host parasites pose greater health risks to wildlife, livestock, and humans than single-host parasites, yet our understanding of how ecological and biological factors influence a parasite’s host range remains limited. Here, we assemble the largest and most complete dataset on permanently parasitic mammalian mites and build a predictive model assessing the probability of single-host parasites to become multi-hosts, while accounting for potentially unobserved host-parasite links and class imbalance. This model identifies statistically significant predictors related to parasites, hosts, climate, and habitat disturbance. The most important predictors include the parasite’s contact level with the host immune system and two variables characterizing host phylogenetic similarity and spatial co-distribution. Our model reveals an overrepresentation of mites associated with Rodentia (rodents), Chiroptera (bats), and Carnivora in the multi-host risk group. This highlights both the potential vulnerability of these hosts to parasitic infestations and the risk of serving as reservoirs of parasites for new hosts. In addition, we find independent macroevolutionary evidence that supports our prediction of several single-host species of Notoedres, the bat skin parasites, to be in the multi-host risk group, demonstrating the forecasting potential of our model.
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... The skin environment is dynamic and alive with many commensal microorganisms that may contribute to maintaining healthy [1][2][3] and desirable skin [4]. These microorganisms form the skin microbiota, which is comprised of diverse bacteria, fungi, yeasts, viruses [5,6], archaea [7] and mites, principally Demodex [8]. ...
Facial Skin Microbiome Composition and Functional Shift with Aging
Article
Full-text available
  • May 2024
The change in the skin microbiome as individuals age is only partially known. To provide a better understanding of the impact of aging, whole-genome sequencing analysis was performed on facial skin swabs of 100 healthy female Caucasian volunteers grouped by age and wrinkle grade. Volunteers’ metadata were collected through questionnaires and non-invasive biophysical measurements. A simple model and a biological statistical model were used to show the difference in skin microbiota composition between the two age groups. Taxonomic and non-metric multidimensional scaling analysis showed that the skin microbiome was more diverse in the older group (≥55 yo). There was also a significant decrease in Actinobacteria, namely in Cutibacterium acnes, and an increase in Corynebacterium kroppenstedtii. Some Streptococcus and Staphylococcus species belonging to the Firmicutes phylum and species belonging to the Proteobacteria phylum increased. In the 18–35 yo younger group, the microbiome was characterized by a significantly higher proportion of Cutibacterium acnes and Lactobacillus, most strikingly, Lactobacillus crispatus. The functional analysis using GO terms revealed that the young group has a higher significant expression of genes involved in biological and metabolic processes and in innate skin microbiome protection. The better comprehension of age-related impacts observed will later support the investigation of skin microbiome implications in antiaging protection.
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... As high numbers of Demodex mites have been observed on the skin and eyelashes of patients with infection, several pathogenic mechanisms have been proposed to support the idea that mites alone are able to cause significant damage to their habitat without excluding the pathogenic role of microbial agents potentially associated with Demodex infestation [13,15]. ...
Data on Demodex Ectoparasite Infestation in Patients Attending an Outpatient Clinic in Greece
Article
Full-text available
  • Apr 2024
Demodex mites are acari, common ectoparasites of humans and other mammalian pilosebaceous units. Demodicosis occurs when mites overpopulate the skin, causing several skin disorders. Our aim was to investigate the prevalence of demodicosis in patients with suspicious clinical features, such as cheek redness, itching, and skin sensitivity, who presented at the outpatient clinic of the Andreas Syggros Dermatology Hospital in Greece. We studied 184 individuals aged between 18 and 97 years and analyzed the content of pilosebaceous units by microscopy to determine the density of Demodex mites. Samples were evaluated as positive when Demodex spp. densities equaled or exceeded 5 mites per square cm. Sixty-six percent of the examined subjects were positive for demodicosis. The age distribution was statistically normal (p = 0.2), and the median age was 51.29 years. Seventy percent of the patients were females, and 30% were males, while 64.46% of the demodicosis-positive individuals were females, and 35.54% were males. We observed a rise in the percentage of males as the age of the patients increased. Demodicosis can be a challenging disease because it presents apart from the typical symptoms, with a variety of nonspecific symptoms mimicking other dermatological skin conditions. Therefore, it is important to investigate Demodex spp. in patients who present with common facial dermatological diseases to improve treatment results. Further studies could contribute to a better understanding of the pathogenic role of Demodex mites and how this role is affected by mite density, host sex and age.
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... Conversely, other studies have suggested that rotating the lash can help mechanically scrape out mites embedded deep in the follicle, which can stimulate the mites to migrate out along with the lash. 22,26,58 This observation seems to be supported with this study. Techniques B and C both had a higher mite count than technique A (where no manual rotation was involved). ...
Double-Blind Comparison of Eyelash Epilation Techniques for the Purpose of Demodex folliculorum Mite Retrieval
Article
  • Feb 2024
Objective Demodex folliculorum blepharitis is typically confirmed with lash epilation and microscopic identification of mites. However, mite counts may vary with the epilation technique. As there is no gold standard to epilating lashes for the purposes of mite counts, the aim of this study was to compare three epilation techniques. Method A prospective randomized double-blind study compared three epilation techniques on lashes with cylindrical dandruff. Techniques included (A) direct pulling of the lash; (B) rotating the lash before epilation; and (C) sliding the cylindrical dandruff away, lash rotation, and epilation. Mean mite counts were analyzed using a repeated-measures analysis of variance. Results Forty (n=40) participants (20 M: 20 F, mean age of 62.3±17.1 years) revealed similar mite counts between right (1.43±1.74) and left (1.35±1.59) eyes ( P =0.63). A significant difference ( P =0.03) in mite count was noted (technique A: 1.05 ± 1.60; technique B 1.76 ± 1.80; and technique C 1.36 ± 1.54) with technique B yielding the highest mite count ( P =0.04). Conclusion Demodex mite count is a key parameter in establishing infestation or to determine treatment efficacy. This study revealed that rotating the lash before epilation yielded the highest mite count. Future studies should report the epilation technique used to allow for study comparisons.
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... They are most abundant in the skin of the scalp, upper chest and face [9]. Demodex is recognized to colonize normal human skin ubiquitously; the Demodex population is around 5/cm 2 of the skin in the adult population [10]. They typically do not result in any dermatological diseases, but when the parasites enter the dermis, they can cause rosacea, acne, and folliculitis. ...
Preparation and Physicochemical Evaluation of Topical Cream Ivermectin 1% for Treatment of Rosacea
Article
Full-text available
  • Nov 2023
Background: Rosacea is a prevalent disease throughout the world. Various studies have shown that the hair follicle mites Demodex has a key role in the rosacea pathogenesis. The current study aims to formulate a formulation of ivermectin 1% for rosacea treatment. Methods: The researchers sought an ivermectin topical cream in following a stable preparation for the treatment of rosacea. Investigation of the active ingredient in the formulation was conducted according to standards. The formulation was monitored as an ICH guideline within six months. Results: The resulting formula did not show any physical instability during accelerated stability studies, and the appearance of the formula did not change. During the storage period, the preparation displayed no significant changes in density, viscosity, pH, and uniformity. Additionally, no microbial contamination was occurred in this formulation. Conclusion: The study data indicated that the proper o/w cream produced from the active ingredient Ivermectin. Administration of ivermectin topical dosage form reduces the chronic use of antibiotic in the rosacea treatment. Our data can aid physicians to prescribe high potential formulation for rosacea treatment. This topical ivermectin with the standard formulation assessments showed the preparation was sufficiently stable and can use in the treatment of rosacea.
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... One of the possible explanations for estimating a low Demodex prevalence may be climatic conditions. For example, Lacey, Kavanagh & Tseng [44] believed that Demodex mite numbers are affected by climatic conditions and are more prevalent during the warmer months of the year. Although the effect of climatic conditions on the prevalence of Demodex mites have been questioned [45]. ...
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... Conversely, other studies have suggested that rotating the lash can help mechanically scrape out mites embedded deep in the follicle, which can stimulate the mites to migrate out along with the lash. 22,26,58 This observation seems to be supported with this study. Techniques B and C both had a higher mite count than technique A (where no manual rotation was involved). ...
Financial Inequities in Optometric Education in Canada: A Comparison of Two Optometry Programs
Article
  • Sep 2023
Significance The advancing age of the population will require increased access to eyecare services to manage eye diseases and vision correction. Optometric education requires a sound financial plan to manage student debt. This study evaluates the financial inequalities of optometric programs in Canada, and how this may impact the provision of eyecare professionals. Purpose The objective of this study was to compare the financial inequities in Optometric education in Canada from the 2020 graduating class. Methods A cross-sectional study assessed monetary variables related to the study of optometry in Canada, including academic and personal expenses, and overall debt and expenses related to the COVID-19 lockdown for the 2020 graduating class. Results 108 optometry students from the 2020 graduating classes of the University of Montreal and the University of Waterloo responded, with 68 (53 F:15 M, age 25.66, SD = 2.01) completing the study. Waterloo students spent more years in university ( P < .001); had higher academic fees ( P < .001); spent more on travelling to their family residence (P = .007) and received more provincial ( P = .002) and federal ( P < .001) loans than Montreal students. Overall debt prior to optometry was similar amongst students but differed ( P < .001) at the end of their program, with Waterloo students having a higher debt burden. Conclusions There is a financial inequity in optometric education in Canada depending on the chosen program. Cumulative optometry student debt for the 2020 graduating class in Canada ranges from $CAN 0 to 189,000 with an average of $CAN 65,800 and a median of $CAN 50,000. The results of this study can assist financial, government agencies and future optometry students to better understand the financial burdens and establish a financial plan to study optometry in Canada, to respond to the growing eyecare needs of the public.
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The Hair Follicle Mites Demodex folliculorum and Demodex brevis: Biology and Medical Importance
Article
Full-text available
  • Feb 1981
The hair follicles mites D. folliculorum and D. brevis are the most common permanent ectoparasites of man, who is their exclusive host. Main habitats are the hair follicles and sebaceous glands of the facial skin. D. folliculorum lives in the follicular orifices, D. brevis deeper down in the sebaceous glands. The elongated, spindle-shaped form of the mites is adapted to these structures. The rate of infestation in healthy skin is age-dependent and reaches 100% in elderly people. The reliability of the quantitative assessment of mite populations in healthy skin and in lesions of rosacea and perioral dermatitis may be greatly enhanced by using acrylate adhesives ('skin surface biopsy') instead of the simple expressing of follicular material. As with animal demodicosis, the importance of quantative factors (numbers of affected follicles and numbers of mites per follicle) in the pathogenesis of the two facial dermatoses in man and of internal and external influences (corticosteroids!) must be evaluated. The study of the pathogenetic importance of the Demodex species in rosacea and perioral dermatitis and the integration of the results into modern clinical and epidermiological knowledge is needed, since the aetiology of both skin diseases is still not solved.
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Is Demodex really non-pathogenic?
Article
Full-text available
  • Jun 2000
Although usually considered a non-pathogenic parasite in parasitological textbooks, Demodex folliculorum has been implicated as a causative agent for some dermatological conditions, such as rosacea-like eruptions and some types of blepharitis. Several anecdotal reports have demonstrated unequivocal tissue damage directly related to the presence of the parasite. However, this seems to be exceedingly rare, in contrast with the marked prevalence of this infestation. We have had the opportunity to observe one of such cases. A 38-year-old woman presented with rosacea-like papular lesions in her right cheek. Histopathological examination revealed granulomatous dermal inflammation with a well-preserved mite phagocytized by a multinucleated giant cell. This finding may be taken as an evidence for the pathogenicity of the parasite, inasmuch as it does not explain how such a common parasite is able to produce such a rare disease.
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High Prevalence of Demodex in Eyelashes with Cylindrical Dandruff
Article
Full-text available
  • Oct 2005
  • INVEST OPHTH VIS SCI
To determine the prevalence of Demodex in eyelashes with cylindrical dandruff (CD). A modified sampling and counting method was applied to 55 clinical cases. Patients were divided in to group A (n = 20) with diffuse CD, group B (n = 12) with sporadic CD, and group C (n = 23) with clean lashes or greasy scales, of which the latter was divided into subgroup C1 (n = 15) without lid hygiene and subgroup C2 (n = 8) using daily lid hygiene for the past year. Each patient underwent a routine complete eye examination and modified counts of Demodex. Demodex was found in all group A and B patients (n = 32) with CD, which was significantly higher than the 22% of group C patients (n = 23) without CD (P < 0.001). The Demodex counts were 4.1 +/- 1.0 and 2.0 +/- 1.2 per epilated lash with retained CD, significantly higher than the 0.2 +/- 0.5 and 0.2 +/- 0.4 per lash without retained CD in groups A and B, respectively (each P < 0.001) and than the 0.01 +/- 0.09 and 0.12 +/- 0.41 per lash in subgroups C1 and C2, respectively (each P < 0.001). Demodex was still found in CD fragments left on the lid skin after epilation. Five Demodex brevis mites were found among the 422 Demodex specimens. The modified sampling and counting method showed that the prior controversy regarding Demodex has resulted from miscounting and confirmed that lashes with CD are pathognomonic for ocular Demodex infestation. Lid hygiene with shampoo reduces Demodex counts but does not eradicate the mites.
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In vitro and in vivo killing of ocular Demodex by tea tree oil
Article
Full-text available
  • Dec 2005
To compare the in vitro killing effect of different agents on Demodex and to report the in vivo killing effect of tea tree oil (TTO) on ocular Demodex. Survival time of Demodex was measured under the microscope. Sampling and counting of Demodex was performed by a modified method. Demodex folliculorum survived for more than 150 minutes in 10% povidone-iodine, 75% alcohol, 50% baby shampoo, and 4% pilocarpine. However, the survival time was significantly shortened to within 15 minutes in 100% alcohol, 100% TTO, 100% caraway oil, or 100% dill weed oil. TTO's in vitro killing effect was dose dependent. Lid scrub with 50% TTO, but not with 50% baby shampoo, can further stimulate Demodex to move out to the skin. The Demodex count did not reach zero in any of the seven patients receiving daily lid scrub with baby shampoo for 40-350 days. In contrast, the Demodex count dropped to zero in seven of nine patients receiving TTO scrub in 4 weeks without recurrence. Demodex is resistant to a wide range of antiseptic solutions. Weekly lid scrub with 50% TTO and daily lid scrub with tea tree shampoo is effective in eradicating ocular Demodex.
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The hair follicle mites (Demodex spp.). Could they be vectors of pathogenic microorganisms?
Article
  • Feb 1988
The hair follicle mites Demodex folliculorum and D. brevis are the most common permanent ectoparasites of Man. Ordinarily they are harmless to their human host and appear to be of no medical significance. We present, however, an unusual finding regarding this mite, namely, that in a potassium hydroxide mount of a skin scraping from a mycotic plaque we found numerous Demodex mites containing inside them spores of Microsporum canis. This could mean that the putatively inoffensive Demodex has the potential to ingest various microorganisms that are found in its niche and transport them to other areas of the skin or possibly to other individuals.
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Density of Demodex folliculorum in rosacea: A case-control study using standardized skin-surface biopsy
Article
  • Jul 1993
A standardized skin-surface biopsy (1 cm2) of the check was performed in 49 patients with rosacea [13 with erythemato-telangiectatic rosacea (ETR), three with squamous rosacea (SR), 33 with papulopustular rosacea (PPR)], and 45 controls. A mean density of 0.7 Demodex folliculorum/cm2 was found in controls, 98% of whom had less than five Demodex/cm2. When all clinical types of rosacea were considered collectively, the density of Demodex was significantly higher in patients with rosacea than in controls (mean = 10.8/cm2; P < 0.001). When the various clinical types of rosacea were considered separately, Demodex density was statistically significantly higher than in controls only in the PPR patients (mean = 12.8/cm2; P < 0.001). The same type of comparison was also made for three other groups of subjects--patients with isolated inflammatory papules (n = 4), rhinophyma (n = 3), and HIV infection (n = 21), respectively: in these groups, the Demodex density did not differ significantly from controls. The present study demonstrates a high density of D. folliculorum in PPR, and supports its pathogenic role in the papulopustular phase of rosacea. The study suggests that standardized surface biopsy could be a useful diagnostic tool for PPR, with a 98% specificity when Demodex density is higher than 5/cm2.
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Demodicidosis Revisited
Article
  • Feb 2002
Demodex mites are common commensals of the pilosebaceous unit in mammals. In humans, only two species (Demodex folliculorum and D. brevis) have been identified and have been implied to play a role in at least three facial conditions: pityriasis folliculorum, rosacea-like demodicidosis and so-called "demodicidosis gravis". However, there is no consensus to what degree the mites are causative of the skin pathology and how they might contribute to the disease. This review presents a demodicidosis case, discusses the clinical features of Demodex infestation in man and reviews its pathogenetic implications and the therapeutic options.
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Clinical Treatment of Ocular Demodecosis by Lid Scrub With Tea Tree Oil
Article
  • Mar 2007
  • CORNEA
To report clinical outcome of treating ocular demodecosis by lid scrub with tea tree oil (TTO). Retrospective review of clinical results in 11 patients with ocular Demodex who received weekly lid scrub with 50% TTO combined with daily lid hygiene with tea tree shampoo. These 11 patients also had meibomian gland dysfunction (n = 7) manifesting abnormal lipid film with slow lipid film spread, intermittent trichiasis (n = 5), and subjective lash loss (n = 4), suggesting damage to the meibomian glands and lash follicles. In addition, conjunctival inflammation (n = 8) was associated with conjunctivitis (n = 5), conjunctivochalasis (n = 3), findings suspicious for pemphigoid (n = 2), and recurrent pterygium (n = 2). After TTO lid scrub, the Demodex count dropped to 0 for 2 consecutive visits in less than 4 weeks in 8 of 11 patients. Ten of the 11 patients showed different degrees of symptomatic relief and notable reduction of inflammatory signs. Significant visual improvement in 6 of 22 eyes was associated with a stable lipid tear film caused by significant reduction of lipid spread time. Lid scrub with 50% TTO caused notable irritation in 3 patients. Demodex potentially causes ocular surface inflammation, meibomian gland dysfunction, and lash abnormalities. Lid scrub with TTO can effectively eradicate ocular Demodex and result in subjective and objective improvements. This preliminary positive result warrants future prospective investigation of Demodex pathogenicity.
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Corneal Manifestations of Ocular Demodex Infestation
Article
  • Jun 2007
  • AM J OPHTHALMOL
To report the corneal manifestations in eyes with Demodex infestation of the eyelids. Noncomparative, interventional case series. This retrospective review included six patients with Demodex blepharitis who also exhibited corneal abnormalities, which led to suspicion of limbal stem cell deficiency in three cases. All patients received weekly lid scrubs with 50% tea tree oil and a daily lid scrubs with tea tree shampoo for a minimum of six weeks. Improvement of symptoms and corneal and conjunctival signs were evaluated. All six patients exhibited ocular irritation and conjunctival inflammation, while meibomian gland dysfunction (n = 5), rosacea (n = 4), and decreased vision (n = 3) also were noted despite prior treatments with oral tetracycline, topical steroids with antibiotics, and lid scrub with baby shampoo. These patients were proven to have Demodex folliculorum (n = 6) and Demodex brevis (n = 3) by microscopic examination of epilated lashes. Their corneal manifestation included superficial corneal vascularization (six eyes of five cases), marginal corneal infiltration (two eyes of two cases), phlyctenule-like lesion (one eye of one case), superficial corneal opacity (two eyes of two cases), and nodular corneal scar (two eyes of two cases). After treatment, the Demodex count was reduced from 6.8 +/- 2.8 to 1 +/- 0.9 (standard deviation; P = .001). All patients showed dramatic resolution of ocular irritation, conjunctival inflammation, and all inflammatory, but not scarred, corneal signs; three patients showed improved vision. A variety of corneal pathologic features together with conjunctival inflammation, commonly noted in rosacea, can be found in patients with Demodex infestation of the eyelids. When conventional treatments for rosacea fail, one may consider lid scrub with tea tree oil to eradicate mites as a new treatment.
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