Q&A: Demodex mites may play role in rosacea development
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Researchers have long questioned whether the microscopic Demodex mite is a cause or effect of rosacea, a skin condition affecting 16 million Americans.
Now, evidence suggests Demodex may play a role in the development of the condition’s papules and pustules, according to a National Rosacea Society press release.
This evidence is based on research recently published by Fabienne Forton, MD, PhD, a dermatologist and clinical researcher in Brussels. Since 1989, Forton has dedicated her career to the study of Demodex and rosacea. She recently spoke with Healio regarding the background and clinical implications of her research.
Healio: What are Demodex mites and how do they affect the skin?
Forton: Demodex are small transparent vermiform mites that live exclusively in the pilosebaceous follicles of mammals. They cannot survive outside the skin and each mammal has its own species of Demodex. Human skin harbors two species: Demodex folliculorum, which lives mainly in the follicular canal, and Demodex brevis, which lives in the sebaceous gland. Acquired through direct skin-to-skin contact after birth, Demodex are ultimately present in the skin of all adults. They feed on our living cells and attack our epidermis, but this aggression does not cause us any problems if they are present in low density. However, when they multiply excessively, they cause a dermatosis called “demodicosis.”
In humans, Demodex does not cause a fatal disease but a skin disease that can be very disturbing because it affects (almost exclusively) the face and the scalp; moreover, serious complications can occur if ocular involvement is not treated. The most frequent demodicosis, but also the least diagnosed because it is the most discreet, is pityriasis folliculorum without erythema. It is characterized by tiny whitish follicular scales at the base of the facial hair, which may be accompanied by pruritus. Each scale is actually several parasite “tails” protruding from the hair orifice. These scales are hardly visible to the naked eye, but if the inflammation worsens, other symptoms are added, giving rise to inflammatory demodicosis: pityriasis folliculorum with erythema, demodectic folliculitis (of the face, beard, scalp), isolated inflammatory papule and also papulopustular rosacea. The same symptoms can occur at the free edge of the eyelids, giving rise to blepharitis, meibomitis and ocular rosacea.
Healio: Who is most susceptible to developing rosacea?
Forton: Rosacea can affect patients of all ages, both sexes and all phototypes, but it is more common after the age of 30 and in patients with fair skin. Its development is influenced by genetic factors, such as family history, fair skin and genetic abnormalities; and environmental factors, such as age, UV exposition and factors that favor erythema (ie, intense temperature variations, cold wind, consumption of alcohol and spicy food, etc).
The erythema probably favors the proliferation of the parasite, and this proliferation causes an inflammation that aggravates the initial erythema. But the parasite can also proliferate without pre-existing erythema under the influence of other factors, such as sebaceous hyperplasia, which offers it shelter and nourishment; a slight immune deficiency, such as hypothyroidism or pregnancy; and possibly other factors which are not yet known. Demodex can obviously also proliferate in the event of severe immunosuppression, which would be the case with AIDS or leukemia, but it should not be concluded that rosacea and other demodicoses are the prerogative of immunocompromised people. Demodicoses are very common dermatoses in the general population, which is in principle healthy.
Healio: Why do some patients successfully eliminate the mites while others favor its proliferation, causing rosacea?
Forton: As with all infections, there is a delicate balance between the parasites trying to grow as much as possible and the host’s immune system trying to keep them at normal/low density. This balance is influenced by many factors, which act either directly on the development of the parasites — such as the size of the sebaceous glands — or on the host’s defenses — such as age, hypervascular ground or the patient’s own genetic immune profile. If the balance of the different factors involved is more in favor of the parasite, they proliferate excessively.
Healio: What is the potential solution for the proliferation of mites that cause rosacea?
Forton: Ideally, it should be possible to eliminate the factor that favors their proliferation, that unbalances the balance in their favor. Most of the time, this factor is unknown or cannot be eliminated, so the best solution at present is to kill the parasite with a local acaricide treatment until a normal Demodex density is reached. Afterward, this low/normal density should be maintained with an acaricidal maintenance treatment.
Healio: What is the key take-away for clinicians that read your research?
Forton: Rosacea is not an inflammatory disease, as usually considered, but an infectious disease. Papulopustular rosacea should be considered as a chronic infection by Demodex mites with associated T-cell exhaustion. The diagnosis of rosacea and other demodicoses can be easily confirmed by a diagnostic test which can be performed in 5 minutes during the consultation, with the help of a microscope. Two consecutive standardized skin surface biopsies (SSSB), specifically SSSB1 and SSSB2, allow to confirm the diagnosis of demodicosis/rosacea when SSSB1 is greater than five Demodex per cm² or when SSSB2 is greater than 10 Demodex per cm².
Healio: With this new-found evidence, how should clinicians approach the treatment of rosacea?
Forton: The causal treatment of rosacea is therefore acaricidal, and the anti-inflammatory treatment becomes an aid to help controlling the symptoms of the disease. In case of mild to moderate rosacea, a suitable local acaricidal treatment is usually sufficient. In case of very inflammatory rosacea, a specific anti-inflammatory treatment will be added. For these severe rosacea cases, and particularly on the nose or in the case of rhinophyma, a very effective treatment is oral isotretinoin, which acts on both panels.
Healio: What are your future goals for further research in this issue?
Forton: Personally, I am coming to the end of my professional career and I will be happy to see the new generation of researchers take up the baton and continue to explore this exciting field.
There are many areas of research to explore. On the fundamental science side, I hope to see the identification of the Demodex antigens that stimulate host immunity, understand the molecular mechanisms of the immune response and confirm the role of vascular endothelial growth factor as a “traitress” of the defensive immune response of the host.
Additional goals include exploring ideas such as: the role of the dendritic cell in rosacea; the interactions of Demodex with Staphylococcus epidermidis and Malassezia furfur; the possible influences of the parasite on general immunity, in particular the potential influence of Demodex on the neuroendocrine functions of the sebaceous glands and hence on the neuro-immune inflammatory reflex; the reciprocal influences between Demodex proliferation and rosacea comorbidities; and a culture media in order to better study the parasite and acaricide treatments.
On the clinical research side, I hope to see a development of relevant and practical methods of detection and measurement of Demodex density which could allow to explore more deeply the impact of Demodex proliferation on the scalp. I would also like to see the study of the potential effect of zinc supplementation in hypothyroid patients and develop treatments that are always more efficient.
Reference:
- Which comes first, the rosacea blemish or the mite? http://www.rosacea.org/press/2022/september/which-comes-first-the-rosacea-blemish-or-the-mite. Published Sept. 14, 2022. Accessed Sept. 19, 2022.
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