Demodex [from gr demos (fat) dex (worm)] is a microscopic mite of animals (dogs,
cats, rodents) and humans. The Demodecidea family comprises 100 species but in
Poland 25 of them are noted (1). So far, 2 species characteristic for humans
are known: Demodex folliculorum and Demodex brevis. D. folliculorum was first
described in 1842 by Simon, who found mites in the follicles of the nose. D.
brevis was later identified in 1963 by Akbulatova. This parasite is found in
the follicular infundibulum (D. folliculorum) and sebaceous or meibomian glands
(D. brevis). D. folliculorum is more common than D. brevis and it is
characterized by a larger size – about 300-350 µm long and 40-50 µm wide
whereas D. brevis is 200-230 µm long (2). They have an elongated body that
consists of three segments: the gnathosoma, podosoma and opisthosoma. Adult
parasites have four pairs of short, reduced legs which is an adaptation to
parasitic existence (3). The mites can leave the hair follicles and walk around
on the human skin, at a speed of about 8-16 mm per hour, but only males move,
especially at night (4). The parasites are transferred through direct contact
between people or by indirect contact with eggs dispersed in dust. Mites are
more numerous in facial skin: the forehead, nose or chin. The risk of infection
increases with age. The presence of the mites on the skin of children is
uncommon because their sebum production is very low. Children with acute
lymphoblastic leukemia (ALL) are susceptible to proliferation of Demodex mites
(5). The pathogenic role of Demodex in humans is still controversial but the
number of reports about the role it plays in some ophthalmic and dermatological
diseases is increasing. Demodex has been implicated in rosacea (6), blepharitis
(7-9) and frequently in immunosuppressed patients with AIDS (10). The
infestation may be asymptomatic (11).
In this study we estimated the prevalence of Demodex in patients with
blepharitis, people who work with microscopes and compared them with groups
consisting of young and older persons.
Materials and methods
264 people (range 20-88 years) were enrolled in the study and they were divided
into 4 different groups. There were 2 criteria for classification: age and
diagnosed blepharitis. The first group consisted of young students, the second
of elder people. None of the individuals in these groups had any blepharitis
symptoms. People who work with microscopes were in the third group and in the
forth comprised of patients with diagnosed blepharitis.
The young individuals from group 1 were students of the Medical University of
Warsaw, 41 women and 53 men. The mean age in this group was 22. In the second
control group with older individuals, the mean age was 66 with 72 women and 21
men. Microscope users with a mean age of 44 consisted of 20 women and 3 men.
Patients in group 4 were recruited in the Department of Ophthalmology Medical
University of Warsaw. The mean age of blepharitis patients was 65 (range 26-88
years old) – 32 were women and 22 were men.
Each patient was examined by epilation of 3-4 eyelashes from upper and lower
lid margin of each eye. After epilation, the eyelashes were put on a slide with
one drop of Hoyer medium (50 cm3 distilled water, 30 g arabic gum, 200 g
chloral hydrate, 20 g glycerine) and covered with a cover slip (12). The
samples were studied under a light microscope at magnifications 10 x and 20 x.
A positive result was the presence of adults, larvae or Demodex’s eggs in the
material. We did not differentiate between the two Demodex species.
The results are presented in a table I.
The highest prevalence of Demodex sp. infection was observed in blepharitis
patients – 74%, the lowest prevalence was found in group 1 with young students,
only 5% of the individuals was infected. In the senior group with the mean age
close to that of blepharitis patients, only 34% had parasites. Infection in
group 2 was over two times less frequent than in group 4. People who had worked
with microscopes exhibited an almost identical percentage of infection as the
senior group. But the mean age was much lower: 44 years in group 3 compared to
66 in the seniors’ group.
The highest number of parasite was 18 mites and 6 eggs in one sample. It
belonged to a 76 year-old woman with blepharitis. In the other examined groups
the highest number of parasites was lower – in the young person’s group – 7
mites (22 year-old man), among the seniors – 15 mites (78 year old woman) and
among people who work with a microscope: 7 mites in a 56 year-old woman.
In cases of a positive result for Demodex infection, 35 patients were treated
with topical metronidazol in a gel or ointment applied to lid margin b.i.d. for
no less than 2 months. After the treatment, the patients had a follow up
examination. 45% patients adhered to the dosing scheme had no parasites in the
control examination or the number of parasites was significantly lower (30%).
In the second case the treatment was continued for the next few months and the
control examinations were repeated.
Logistic regression with two independent variables (age and sex) was used to
estimate probability of infection. Sex was insignificant for this model (p >
0.05) therefore in further analysis only one independent variable was tested –
age (p < 0.001).
Exp (B) was more than one (1.054), it means that age effect was positive for
probability to being infected with Demodex. Older patient had higher
probability of infection. R2 Nagelkerke’s coefficient of determination reached
0.293 – it showed significant relation between age and probability of Demodex
infection. For statistical analysis was used PASW Statistics 18 (Fig. 1-5).
Studies similar to ours were conducted at Pomeranian Medical University in
Szczecin (7,9). In 2003 they examined 5 different-age groups. In a group
comprising medical students (20-21 years old) they observed 30% infected
individuals whereas in similar group in our study we found parasites only in 5%
of the cases. In a senior group (71-96 years) the infection in Szczecin was
95.2% while in our work only 34%. In the next survey by these authors in 2005,
they obtained results similar to those from 2 years earlier. Despite the fact
that the percentage of infected individuals is higher in Szczecin, their
results demonstrated the same trend, that the prevalence of Demodex infection
increases with patients’ age.
In a study from Turkey (13) researchers obtained a prevalence of Demodex
infection of only 28.8% in blepharitis patients which is much lower than our
74% in a comparable group. However in the Turkish study blepharitis patients
were younger – the mean age was 36 years while in our study the mean age was 65
years. In another Turkish survey (14) the results were comparable – the
infection in blepharitis patients was 29.72%.
Epilation of eyelashes followed by microscopic examination is an easy and
effective method for detecting mites. Diagnosis towards Demodex infection could
be considered as an additional test in blepharitis patients. It was observed by
ophthalmologists that both antibacterial and antiparasitic treatment gave
better results than antibacterial treatment alone. Recently, more information
about Demodex and the role it could plays in ophthalmologic and dermatological
diseases has appeared.
In our study we examined people who work with microscopes because the
possibility to be infected could be much higher through using the same
equipment. Very often eyepieces are not cleaned before use which gives the
opportunity for transmission of parasites. The results in our study confirmed
this hypothesis. In the group consisting of people working with microscopes,
the infection was estimated to be 30% which was comparable to the prevalence of
infection in seniors, while the mean age of microscope operators was lower – 44
years compared to 66 in the senior group.
Demodex mites are an etiological factor of blepharitis.
There is a significant correlation between Demodex sp. infection and the age of
People who work with microscopes are at higher risk for Demodex infection.
We would like to thank dr Joanna Konieczna-Salamatin from Sociology Insitute (University
of Warsaw) for help in statistical analysis.
1. Izdebska JN: Nużeńcowate. W: Bogadowicz W., Chudzicka E., Filipiuk I.,
Skibińska E. (red.) Fauna Polski, Muzeum i Instytut Zoologii PAN 2008, Tom 3,
2. Desch C, Nutting WB: Demodex folliculorum (Simons) and D. brevis Akbulatova
of man: redescription and reevaluation. J Parasitology 1972, 58, 169-177.
3. Buczek A: Atlas pasożytów człowieka. Wydawnictwo Koliber
2005, Lublin, 146.
4. Gerkowicz M, Baltyziak L, Puacz E: Przewlekłe zapalenie brzegów powiek
wywołane przez nużeńca Demodex folliculorum. Klin Oczna 2005, 107(4-6),
5. Herron MD, O’Reilly MA, Vanderhooft SL: Refractory Demodex folliculitis in
five children with acute lymphoblastic leukemia. Pediatr Dermatol 2005, 22,
6. Bonnar E, Eustace P, Powell FC: The Demodex mite population in rosacea. J Am
Acad Dermatol 1993, 28, 443-448.
7. Czepita D, Kuźna-Grygiel W, Kosik-Bogacka D: Investigations on the
occurrence as well as the role of Demodex folliculorum and Demodex brevis in
the pathogensis of blepharitis. Klin Oczna 2005, 107(1-3), 80-82.
8. Czepita D, Kuźna-Grygiel W, Kosik-Bogacka D: Demodex as an etiological
factor in chronic blepharitis. Klin Oczna 2005, 107(10-12), 722-724.
9. Kuźna-Grygiel W, Kosik-Bogacka D, Czepita D: Demodex folliculorum i Demodex
brevis w etiologii zapalenia brzegów powiek. Materiały zjazdowe XVI Zjazdu
Polskiego Towarzystwa Epidemiologów i Lekarzy Chorób Zakaźnych, Białystok 2003,
10. Ashack RJ, Frost ML, Norins AL: Papular pruritic eruption of Demodex
folliculitis in patients with acquired immunodeficiency syndrome. J Am Acad
Dermatol 1989 Aug, 21, 306-307.
11. Humiczewska M, Kuźna W, Hermach U: Frequency of occurrence of symptomatic
and asymptomatic eyelids demodecosis among the inhabitants of Szczecin. Wiad
Parazytol 1994, 40, 69-71.
12. Cielecka D, Salamatin R, Garbacewicz A: Usage of the Hoyer’s medium for
diagnostics and morphological studies of some parasites. Wiad Parazytol 2009,
13. Kemal M, Sümer Z, Toker MI, Erdoğan H, Topalkara A, Akbulut M: The
Prevalence of Demodex folliculorum in blepharitis patients and the normal
population. Ophthalmic Epidemiol 2005Aug, 12(4), 287-290.
14. Türk M, Oztürk I, Sener AG, Küçükbay S, Afşar I, Maden A: Comparison of
incidence of Demodex folliculorum on the eyelash follicule in normal people and
blepharitis patients. Turkiye Parazitol Derg 2007, 31(4), 296-297.
The study was originally received 01.04.2010 (1209)/
Praca wpłynęła do Redakcji 01.04.2010 r. (1209)
Accepted for publication 04.10.2010/
Zakwalifikowano do druku 04.10.2010 r.
Fig. 1. Prediction of the probability of Demodex infection
dependent on age (based on logistic regression).
Ryc. 1. Przewidywane prawdopodobieństwo zarażenia nużeńcem w zależności od
wieku (na podstawie modelu logistycznego).
Fig. 2. Left eye 56 years old woman with blepharitis.
Ryc. 2. Lewe oko 56-letniej kobiety z zapaleniem brzegów powiek.
Fig. 3. Right eye 56 years old woman with blepharitis
Ryc. 3. Prawe oko 56-letniej kobiety z zapaleniem brzegów powiek.
Fig. 4. Arrowed-shaped egg of Demodex folliculorum. Technic:
Differential interference contrast.
Ryc. 4. Charakterystyczne jajo Demodex
folliculorum. Technika: kontrast interfazowy (DIC).
Fig. 5. Photograph of an adult and larva of Demodex. Technic:
Differential interference contrast.
Ryc. 5. Zdjęcie Demodex – osobnika dorosłego i larwy. Technika: kontrast