Demodex sp. infestation in anterior blepharitis, meibomian-gland dysfunction, and mixed blepharitis
- Angelito Braulio de Venecia III, MD
Ruben Lim Bon Siong, MDDepartment of Ophthalmology and
Visual Sciences
University of the Philippines–
Philippine General Hospital
Manila, Philippines
BELONGING to Phylum Arthropoda, Class Arachnida,
Order Acarina, Demodex mite is an external parasite that
can infest the meibomian and sebaceous glands. Although
they normally inhabit the hair and eyelash follicles in low
numbers, their over proliferation may lead to lid-margin
infection causing ocular-surface irritation and symptoms
of ocular discomfort like itching, foreign-body or stinging
sensation. It may also exacerbate coexisting lid-margin
diseases like anterior blepharitis (staphylococcal and
sebaceous) and posterior blepharitis (meibomian-gland
dysfunction). Demodex infestation is an often-overlooked
differential diagnosis in the clinical investigation of
blepharitis and may be a cause of treatment failure
when not specifically addressed. The exact relationship
of Demodex and blepharitis, however, is yet to be fully
explained.
The adult Demodex is cigar-shaped, with several pairs
of legs, and has a mouth with a biting apparatus. It
measures about 280 to 440 microns. Two distinct species
have been found on human skin: Demodex folliculorum and
Demodex brevis.1 Diagnosis of Demodex infestation is made
by identification of the parasite at the root of the lashes
using light microscopy.
Alejo and Valenton described Demodex folliculorum in
the lids of 50% of randomly chosen Filipino patients at
the Philippine General Hospital.2 Patients diagnosed
with blepharitis had Demodex in 88% of cases. The
authors, however, did not classify blepharitis according to
anatomic involvement or specific diagnosis of blepharitis,
and did not associate age, sex, ocular symptomatology
and clinical findings with the incidence and severity of
Demodex infestation. Such correlation will be useful to the
clinician in the diagnosis and treatment of blepharitis in
general and Demodex-related blepharitis in particular.
This study determined the incidence and density
of Demodex species found on the eyelashes of subjects
with normal eyelids, anterior blepharitis, meibomian
gland dysfunction, and mixed blepharitis. Specifically, it
determined the relationship of the incidence and density
of Demodex with age and sex, ocular symptoms related to
blepharitis, and clinical lid-margin findings (dandrufflike
material, collarette or cylindrical dandruff, scurf,
plugged meibomian gland orifices, crust).
METHODOLOGY
Consecutive patients who consulted at the General
Clinic and the External Disease Clinic of a tertiary public
hospital over a period of 3 months with the diagnosis of
meibomian-gland dysfunction (MGD), anterior blepharitis
(AB), or mixed blepharitis (MB) were recruited into
the study. One of the authors (ABDV) established the
diagnosis based on preset criteria of clinical findings
(Table 1) using a single slit lamp biomicroscope (Topcon
Slitlamp SLD7, Japan).
The diagnosis was confirmed by
one of the consultants of the External Disease Clinic
(RLBS included) using the same slitlamp biomicroscope.
Patients who were on topical ophthalmic medications
over the past 3 months, except for artificial tears; with history
of ocular or eyelid trauma and surgery; with previous
diagnosis of chemical burns; Steven-Johnson syndrome,
ocular cicatricial pemphigoid, and other similar conditions;
with eyelid malpositions like entropion, ectropion,
and dystrichiasis; or with signs of active ocular infection or
inflammation other than blepharitis were excluded from
the study. After the recruitment period for MGD, AB,
and MB, 50 age-matched patients who consulted at the
General Clinic for other eye complaints were recruited
to serve as controls (normal).
Table 1. Criteria for the diagnosis of MGD, anterior blepharitis
(AB), and mixed blepharitis (MB).
All patients underwent standard eye examinations.
Data gathered included demographics, ocular symptomatology,
and clinical findings. Digital photographs of the
lid margins were taken using the digital camera of the
same slitlamp biomicroscope. Lash sampling was done
using the Modified Coston Method for epilating lashes.6-7
The collected lashes were checked for Demodex based on
morphology (Figure 1) using a light microscope (Nikon
YS100) and the total number of Demodex identified were
tabulated for each eye. Patients in groups AB and MB underwent
eyelid culture using a standard procedure. Each
eye was swabbed with a sterile cotton tip applicator on the
upper and lower lid margins. Blood agar was used as the
culture medium. The cotton-tip applicators were applied to the blood agar plates. Specimen from the right eye
Figure 1. Appearance of Demodex folliculorum under the light microscope. The diagnosis of Demodex infestation is made by identification of the parasite under light
microscopy. Diagram of a typical parasite that is cigar-shaped and has 4 pairs of short legs on the right half and a mouth with a biting apparatus on the extreme right
(A). The parasite frequently appears in pairs and has an obvious head-neck part and body-tail part (B). The parasite is covered by a cuticle surface, and the body is
mostly semi-transparent (C). The body-tail part may show numerous striations, while the head-neck part contain 4 pairs of short legs (D). Demodex follicullorum in
clusters in a single hair follicle (E). Demodex embedded in dandruff-like debris (F).
was applied in the form of “R” and that of the left eye in
the form of “L”. Each plate was labeled with the patient’s
name and date of collection and sent to the Microbiology
Department of UP-PGH for incubation and identification.
All patients were referred back to either the General
Clinic or the External Disease Clinic for further treatment
and follow-up.
The main outcome measures were:
1. Incidence of Demodex infestation, taken as the
percentage of patients per group (Normal, MGD, AB,
MB) that had lashes with mites identified using the light
microscope, and
2. Mean Demodex count (MDC), taken as total number
of mites counted from both right and left eyes of all
patients of each group divided by the total number of
patients per group.
Data were tabulated using Microsoft Excel ver. 2008
(Microsoft Corporation, Redmond, WA, USA). They were
subjected to statistical analyses using one-way analysis of
variance, Dunnett’s method of comparison (comparison
with a control, p < 0.01), Tukey-Kramer HSD method,
chi-square analysis, and t-test.
The study was reviewed and approved by the Ethics Review Board of the University of the Philippines-Philippine
General Hospital. Informed consent was obtained
from all participants.
RESULTS
A total of 167 participants (334 eyes) were included,
22% males and 78% females with a mean age of 53.7
years (range, 20 to 85). Of the total, 50 (30%, 100 eyes)
were normal; 65 (40%, 130 eyes) had MGD; 20 (12%, 40
eyes) had anterior blepharitis; and 32 (19%, 64 eyes) had
mixed blepharitis.
Incidence of Demodex infestation
A total of 122 participants (73%) had Demodex infestation.
The incidence of Demodex infestation was as follows:
34% (17/50) in normal participants, 85% (55/65) in
MGD patients, 95% (19/20) in AB patients, and 97%
(31/32) in MB patients (Figure 2). Using one-way
ANOVA, there was a significant difference in the number
of patients with Demodex infestation in MGD, AB, and MB
compared to the normal group (p < 0.01).
There was a strong association between anterior
and posterior blepharitis and Demodex infestation. The
incidence was highest when both anterior and posterior
blepharitis were present (MB), followed by posterior
blepharitis (PB) and anterior blepharitis (AB).
Mean Demodex Count (MDC)
Patients with MB had the highest density of Demodex
infestation, with MDC of 13.63 (range, 0 to 27), followed
by AB with MDC of 8.95 (range, 0 to 22), and by MGD
with MDC of 3.83 (range, 0 to 11). The normal group had
the least density with MDC of 0.98 (range, 0 to 5) (Figure
3). The MDCs of MGD, AB, and MB were significantly
different from the MDC of the normal group using the
Dunnett’s method of comparison (p < 0.01). The MDCs
of MGD, AB, and MB were also statistically different from
each other.
The degree of blepharitis was directly proportional
to the density count of Demodex. Mixed blepharitis with
involvement of both anterior and posterior lid margins
had the highest density counts. Comparing the incidence
and MDC per diagnosis, it also showed a directly
proportional relationship.
Figure 2. Incidence of Demodex infestation by diagnosis.
Relationship with Age
Majority of patients were between 41 and 70 years old
(Figure 4). 58% of normal, 66% with MGD, 70% with
AB, and 82% with MB were within this age range. The
highest incidence of Demodex infestation was seen in the
61 to 70 age group (31%), followed by the 51 to 60 age
group (24%) (Figure 5). One-way ANOVA test, however,
showed no significant difference in the incidence of
Demodex infestation among the different age groups.
There was, likewise, a trend towards increasing density
of Demodex (MDC) with increasing age (Figure 6). Using
the Tukey-Kramer HSD Method, however, there was also
no significant difference in density of Demodex among
age groups.
Figure 3. Comparison of mean density count of Demodex species by diagnosis.
Figure 4. Age distribution of patients by diagnosis.
Figure 5. Relationship of age and incidence of Demodex infestation.
Figure 6. Relationship of age and density of Demodex infestation.
Figure 7. Gender distribution by study groups.
Figure 9. Gender distribution of patients with Demodex.
These results showed possible direct relationship
between age and incidence of Demodex infestation and
between age and density of Demodex.
Relationship with sex
In all 4 groups, there were more female than male
patients. The male: female ratio was 1:2 for normal, 1:5
for MGD, 1:5 for AB, and 1:3 for MB (Figure 7). The
incidence of Demodex infestation was expectedly higher
in females. However, taken as a percentage of patients
of the same sex, there were 27 out of the total 37 males
(73%) in the study found to be positive for Demodex.
In females, 95 out of the 130 females (73.10%) were found to be positive for Demodex (Figure 8). Result of the
one-way ANOVA test showed that the difference in the
incidence of Demodex infestation between genders was
not statistically significant. Similarly, one-way ANOVA test
comparing MDC in males (5.65) and MDC in females
(5.33) showed no significant difference.
These results showed that males and females, regardless
of type of blepharitis, were equally at risk for Demodex
infestation.
Relationship with ocular symptomatology
The most common eye symptoms were itchiness and
foreign-body sensation (Table 2). These and other symptoms
were nonspecific, appearing in all study groups.
Ocular symptomatology was compared with density
of Demodex infestation (MDC) divided into four density
ranges based on the data from Figure 3 (Table 2). Chisquare
analysis was used to test if there was a difference in
frequency of occurrence of symptom between the MDC
ranges. Analysis showed that 50% of the patients with
irritation had a MDC >9 mites (p = 0.05) and that 68.8%
of patients with no symptoms had a MDC of 0 to 2 mites
(p = 0.01). Other symptoms were similar in terms of their
distribution in each of the MDC subgroups.
The results showed that:
1. Severe Demodex infestation, defined as presence
of more than 9 mites, will probably result in lid irritation.
Presence of Demodex usually did not present with any
specific symptoms unless infestation was severe.
2. Individuals who were asymptomatic had no or
very mild Demodex infestation.
3. Symptoms in Demodex-related blepharitis was
not reflective of the severity of Demodex infestation. Relationship with clinical findings on slitlamp
examination
Among the 3 groups of patients with diagnosis of
blepharitis or MGD, the top 3 slitlamp lid-margin findings
were collarettes/cylindrical dandruff, plugged
meibomian gland orifices, and dandruff-like or scale-like
materials. Clinical findings of collarettes/cylindrical
dandruff had the highest association with the severity of
the MDC, followed by plugged meibomian gland orifices
(also seen in low MDC), while dandruff-like material
was not associated with the severity of the density count
(Table 3). Chi-square analysis showed that 68% of the
patients with collarettes/cylindrical dandruff (p < 0.001)
and 36.1% of plugged meibomian glands had a MDC >
9 mites (p < 0.001), and that 82.7% of patients with no
clinical findings had a MDC of 0 – 2 mites (p < 0.001).
Other clinical findings were similar in terms of their
distribution in each of the MDC subgroups.
These results showed that:
1. Patients with clinical findings of collarettes/cylindrical
dandruff or plugged meibomian gland orifices
will probably have severe Demodex infestation.
2. Individuals with no clinical findings will have no
or very mild Demodex infestation.
3. Clinical findings of dandruff-like materials are
not reflective of the severity of Demodex infestation.
Culture Studies
Over 90% of cases in the AB and MB groups were
positive for Staphylococcus aureus and epidermidis (Table
4). These findings supported the clinical diagnoses of
anterior and mixed blepharitis among these patients.
DISCUSSION
The general incidence rate of Demodex infestation in
this study was 73%, significantly higher than the 50% in
the study by Alejo and Valenton.2 This could be partly
due to the bigger sample size and the larger number of
patients with anterior and posterior blepharitis included
in the sampling. Among normal patients, the incidence
was lower at 34%. In patients diagnosed with blepharitis,
Alejo and Valenton found Demodex in 88% of cases, which
is consistent with our study (85 to 97%). Their study, however,
neither classified blepharitis according to anatomic
involvement nor determined the density of the Demodex. This study demonstrated the highest
incidence and density in patients
with mixed blepharitis, followed by
anterior blepharitis. MGD patients
have the lowest incidence and density
among the three. This can be explained
by the fact that patients with
mixed and anterior blepharitis have
involvement of the eyelashes because
Demodex mites tend to be clustered to
the roots of lashes.
Table 2. Comparison between ocular symptomatology and density of Demodex (MDC=mean density count).
Demodex infestation in humans was
once thought to be of no clinical significance
due to its nonpathogenic
nature. Several authors, however,
have concluded that Demodex infestation
or demodecosis is related to
blepharitis.3,8-11 But the exact pathogenic
potential of Demodex mites
remains unclear because a low
number of Demodex can be found in
the skin and lashes of asymptomatic
individuals. It is thought that Demodex
becomes pathogenic when it multiplies
to cause or exacerbate ocular
symptoms and lid-margin changes.
No prior research has convincingly
demonstrated whether a minimal
number of mites must be present to
produce symptoms. Of the ocular
symptoms investigated, only lid irritation
correlated with a high Demodex
count. The etiology of lid irritation
in Demodex infestation is an interplay
of different factors. First, the biting
apparatus of the parasite alone may
cause lid irritation. Second, lid irritation
is also caused by the lipolytic
enzymes produced by the parasite to
digest sebum, and by the accumulation
of parasite excreta, resulting in
the blockage of sebaceous glands that
may lead to infection or the stimulation
of the host’s humoral responses
and cell-mediated reaction. Third,
secondary or concomitant microbial
blepharitis is common in Demodex
infestation, as the microorganisms
may cling to the integuments of the
parasites.4
The incidence and density of
Demodex infestation tend to steadily
increase with the individual’s age.
This is consistent with the increasing
incidence of mixed blepharitis
and MGD in the older age groups.
Similar to the results of our study,
Özlem et al. reported no significant
difference between mite positivity
and negativity between genders.5
Gao, et al. noted that Demodex
infestation was more prevalent
in patients with clinically evident
cylindrical dandruff, which was seen
in anterior blepharitis.1 The severity
of Demodex infestation correlated
well with the clinical finding of
cylindrical dandruff. The Demodex
count was higher in lashes with
cylindrical dandruff compared to
those without. English proposed that
instead of just randomly choosing non-adjacent lashes, as done in the
conventional Coston Method, lashes
with dandruff-like material should
be picked over those without.6
This modification in the Coston
Method was applied in this study.
The conventional Coston method
of determining Demodex infestation
carried certain errors of under
detection: (1) Random epilation of
lashes may result in a lower count if
lashes without cylindrical dandruff
were epilated; (2) Demodex mites
were more adherent to cylindrical
dandruff and the non-adherent mites
in lashes without cylindrical dandruff
may get dislodge during mounting,
resulting in undercounting.
The conventional Coston method
of Demodex collection proposed in 1967 also advocated the use of peanut oil in mounting the
specimen prior to microscopic evaluation and counting.3
Placing oil did not promote instant breakdown of debris
and cuffs, resulting in undercounting of embedded mites.
The use of fluorescein in our study improved the microscopic
visibility and counting of Demodex by dissolution
and expansion of cuffs. The yellowish contrast provided
by the fluorescein also helped detect Demodex embedded
in compact and opaque cuffs of epilated lashes, resulting
in a more accurate Demodex count.7
Table 3. Comparison between clinical findings and density of Demodex.
*MDC = mean density count
Table 4. Culture results of anterior blepharitis (AB) and mixed blepharitis (MB) groups.
The modified Coston method may still result in some
under-counting especially in patients with MGD because it
may not detect Demodex brevis since they burrow deep into
the sebaceous and meibomian glands. Expressing sebum
from plugged meibomian glands, and detecting Demodex
microscopically, is a method to diagnose demodecosis
in posterior blepharitis, although there are no previous
studies to prove its efficacy. Biopsy of the lid margin is still
the gold standard in detecting demodecosis, but this is
an invasive procedure and not warranted for all forms of
blepharitis unless malignancy is a strong consideration.
Epilation of lashes is still a useful adjunctive tool to detect
Demodex when the clinical presentation may not warrant
the biopsy.
The incidence and density of Demodex infestation were
highest among patients with both anterior blepharitis
and meibomian-gland dysfunction. Symptom of lid irritation
and presence of cylindrical dandruff are indicative of high density count. These diagnoses and eye findings
should alert the clinician about Demodex infestation
of the eyelashes, especially in the elderly. Patients with
recurrent blepharitis not responsive to current blepharitis
treatment regimen should be investigated and treated
for Demodex infestation.