This month, I have decided to jump on the Demodex infestation bandwagon. The topic is germane due to the myriad ocular signs and symptoms that can result from mite infestation, ranging from seemingly harmless lash collarettes to corneal manifestations such as vascularization and opacity. Let’s consider the likely connection between mite infestation and rosacea, and Demodex’s potential to serve as a bacterial vector.

For over a century, mites have been seen in a variety of habitats and, for at least a few decades, linked to a form of blepharitis.1 Unfortunately, it was easy to dismiss Demodex, as it was thought to be only commensal, and not recognized as a potential human pathogen, in part because of its ubiquity, as well as the difficulty and rarity of visualizing the mites.1 (Most organisms living in or on the body represent commensals, but the designation might require some attention to microbial competition or antagonism.2)

Recently, there has been a resurgence of attention toward identifying Demodex mite infestation as a reason for significant ocular morbidity.1,3-5 But the mite’s ability to impart havoc depends on the host’s innate immunity and response (current state and HLA typing), and the surrounding flora in which the mites thrive.1-3
In humans, only two species of Demodex (folliculorum and brevis)4 have been identified and believed to play a role in three facial conditions: pityriasis folliculorum, rosacea-like democidosis and democidosis gravis.  

There is statistical association between Demodex mite density and rosacea, facial itching and blepharitis.4 Papulovesicular rosacea-like lesions and spiny blepharitis often respond to treatments that reduce the number of Demodex mites.3,4 Controversy exists in whether the mites play the main role in the pathophysiology or a more minor role as the player aggravating rosacea in some patients.2,4

The Missing Link?
It now appears that a link exists between the bacteria Bacillus oleronius, carried by Demodex, and rosacea. The strong correlation between ocular Demodex infestation and serum reactivity to Bacillus proteins provides a better understanding of comorbidity between Demodex mites and symbiotic Bacillus in facial rosacea and blepharitis.4 The bacterium isolated from the mites may enable follicular-based inflammatory changes in papulopustular rosacea; it also has the potential to involve deep sebaceous gland, and even subcutaneous, tissue.1,4,5

A timely diagnosis that includes simple lash epilation and viewing mites under light microscopy or rotation (twirling the lash to expose the cylindrical mites) is important.1

Treatment options, discussed in detail elsewhere,1,5 include ether, turpentine, sulfur preparations, Camphor oil, oil of oregano and tea tree oil. Unfortunately, all the above can be quite irritating to the ocular surface and skin. Compounded 1% ivermectin can be applied to the lash area in the evening for at least three to four weeks.1 Using a facial cleaner appears to be equally important to treating the lid area.

Immunocompromised patients or those on immunosuppression therapy have an increased number of mites on the skin and lid area.4 Demodex folliculorum were more frequently detected in patients who had previously been treated with topical corticosteroids.4 And, unfortunately, topical corticosteroid agents are often the mainstay of therapy in blepharitis patients.

It’s easy to dismiss Demodex as innocuous, since many patients will not be symptomatic with mite infestation. We must constantly be on the lookout for conditions like mite infestation—the often unseen pests that can either cause or contribute to ocular complications. Fortunately, attention has rebounded recently, bringing added awareness to this condition.

3.Forton F, Germaux MA, Brassuer T, et al: Demodicosis and rosacea: epidemiology and significance in daily dermatologic practice. J Am Acad Dermatol. 2005 Jan;52(1):74-87.
4.Li J, O’Reilly N, Sheha H, et al: Correlation between ocular Demodex infestation and serum immunoreactivity to Bacillus proteins in patients with facial rosacea. Ophthalmol. 2010 May;117(5):870-877.
5.Clyti E, Sayavong K, and Chanthavisouk K: Demodicosis in a patient with HIV: successful treatment with Ivermectin. Ann Dermatol Venereol. 2005 May;132(5):459-461.