“The controversy surrounding the role
of Demodex mites
in the pathophysiology of rosacea has been going on for over eight
decades,” said Dr. James Del Rosso, adjunct clinical professor of
dermatology at Touro University College of Osteopathic Medicine in
Henderson, Nev. “We are now finally seeing more research using
advanced technological methods to better evaluate and quantify the
potential connections between Demodex mites,
rosacea and other rosacea-form facial eruptions. This is great news
for dermatologists and their patients!"
Demodex mites
are a normal part of the human microbiome but have often been found
in more than four times greater numbers on the facial skin of
rosacea sufferers than in the normal population, according to Dr.
Frank Powell, consultant dermatologist at Mater Misericordiae
Hospital in Dublin and former president of the European Academy of
Dermatology and Venereology.
“Researchers have more recently discovered that
while Demodex
folliculorum and D.
brevis live in the hair follicles and
sebaceous glands of the facial skin, D.
folliculorum is also found in the meibomian
(tear) glands of ocular rosacea patients,” he said. “In the mites’
brief life span of 14 days, they live and reproduce in the
pilosebaceous units, subsisting on sebum and cellular contents, and
emerge from the follicles primarily at night.”
He
suggested that a genetic predisposition for rosacea may be
reflected in a different skin type with specific lipid qualities
that allows Demodex to
flourish in greater numbers.
Recent research has identified a host of microscopic elements and
interactions in the innate immune system that contribute to
rosacea's development, involving such substances as kallikreins,
cathelicidins and mast cells, said Dr. Diane Thiboutot, professor
of dermatology and vice chair for research at Pennsylvania State
University. Importantly, she noted, many of the triggers of rosacea
– ultraviolet light damage or bacterial antigens, as well
as Demodex, for example – have
one thing in common: They have been shown to activate the enzyme
toll-like receptor-2 (TLR-2) signaling, which initiates a cascade
of events that leads to the inflammatory signs and symptoms of
rosacea, including papules (bumps) and pustules
(pimples).1 The
challenge, however, is that TLR-2 activation is necessary to fight
off pathogens, so wiping out its function would be
counterproductive.
“The significance of the relationship
between Demodex and
rosacea has long been controversial, as it doesn’t fulfill certain
traditional parameters for a causal association between a pathogen
and a disease,” Dr. Thiboutot continued. “These parameters may have
been superseded by more recent findings, and a recent review of 48
articles in the Archives of
Dermatologyconcluded that the degree
of Demodex infestation,
as opposed to its simple presence, is an important factor in
rosacea.”
Dr. Del Rosso stressed that Demodex may
play a role in the pathophysiology of rosacea, at least in some
patients, and may influence the type and severity of visible
manifestations of rosacea in different individuals.
“The classic ‘subtypes’ of rosacea appear to reflect variations in
inflammatory and immunologic responses which in some cases may be
induced byDemodex mites,”
he said. “For example, in one study, individuals with
erythematotelangiectatic rosacea (subtype 1) were found to have
higher facial counts of Demodex mites
than those with papulopustular rosacea (subtype 2). It has been
suggested that the higher Demodex counts
lead to degradation of the follicular wall as the mites attempt to
improve their survival. This loss of follicular wall integrity then
triggers an immunologic response that reduces the number
of Demodex mites,
with papules and pustules subsequently emerging from the augmented
perifollicular inflammation that occurs.”
Dr. Del Rosso noted that he has observed cases of patients with a
more diffuse facial distribution of small papules, pustules and
fine scaling than what is typical of rosacea. He has previously
diagnosed these cases as demodicosis, as skin scrapings of the
facial lesions have easily revealed
multiple Demodexmites on light
microscopy.
The roundtable participants agreed that further studies should be
conducted to improve understanding of the presence
of Demodex and
its potential actions and interactions with other pathogenic
factors in rosacea. The roundtable was sponsored by the National
Rosacea Society with funding from Galderma Laboratories.
Reference:
1.
Murillo N, Aubert J, Raoult D. Microbiota
of Demodex mites
from rosacea patients and controls. Microb
Pathog 2014;71-72:37-40.
加载中…
喜欢