Demodex mites and blepharitis

Demodex mites are the most common microscopic ectoparasite found in the human skin.

• Rate of Demodex infestation increases with age, being observed in 84% of the population at age 60 and in 100% of those older than 70 years (1).
• Demodex infestation has a higher density in patients with rosacea.
• Demodex infestation also been suggested as a cause of other skin diseases such as:
  • pityriasis folliculorum
  • perioral dermatitis
  • scabies-like eruptions
  • facial pigmentation
  • eruptions of the bald scalp
  • demodicosis gravis
  • basal cell carcinoma (1)
• Eye is surrounded by protruding body parts such as the nose, the brow, and the cheek, hence, the eyelid is not as accessible as the face to daily cleansing hygiene.
  • Once Demodex infestation establishes in the face, it is likely to spread and flourish in the eyelids leading to blepharitis
• Clinical significance of Demodex infestation remains debatable in part because it can be found in asymptomatic subjects.

Two distinct Demodex species have been confirmed as a cause of blepharitis:

• in the eyelids, D. folliculorum can be found in the lash follicle, whereas D. brevis burrows deep into sebaceous glands and meibomian glands looking for sebum which is thought to be their main food source
  • been proposed that these mites might feed on follicular and glandular epithelial cells leading to direct damage of the lid margin
  • life cycle of the Demodex mite is approximately 14–18 days from the egg to the larval stage followed by 5 days in the adult stage. Females may live an additional 5 days after oviposition
  • direct contact is required for transmission of mites
    
• Demodex folliculorum can cause anterior blepharitis associated with disorders of eyelashes, and D. brevis can cause posterior blepharitis with meibomian gland dysfunction and keratoconjunctivitis

Treatment:

• various treatments have been used to control Demodex mites such as mercury oxide 1% ointment, pilocarpine gel, sulfur ointment, and camphorated oil
• tea tree oil treatments with either 50% lid scrubs or 5% lid massages are effective in eradicating mites and reducing ocular surface inflammation (1)
  • shows promising potential to treat Demodex blepharitis by reducing Demodex counts with additional antibacterial, antifungal, and anti-inflammatory actions (1)
  • effectiveness of tea tree oil is not well documented (2)

Reference:

• (1) Liu J et al. Pathogenic role of Demodex mites in blepharitis. Curr Opin Allergy Clin Immunol. 2010 Oct;10(5):505-10
• (2) Savla K, Le JT, Pucker AD. Tea tree oil for Demodex blepharitis. Cochrane Database Syst Rev. 2020 Jun 20;6(6):CD013333. doi: 10.1002/14651858.CD013333.pub2.