Demodex folliculorum

I first became familiar with this parasite about 10 years ago, when it was suggested to be an aggravating factor with an acne skin. At that time there was not much information about Demodex folliculorum or proof to back up the claim, so it slipped into the ever increasing pile of research material and forgotten.

Earlier this month, a colleague who had come across some recent information about Demodex folliculorum brought it to my attention. In addition Dr Des Fernandez made mention in his article about Rosacea that Demodex folliculorum was thought to be an aggravating factor with this skin condition. So I decided to update myself re this parasite and pass any new information on to you, we will begin with its physical appearance, where it lives and then discuss the skin conditions that are most often found in relation to its presence.

 

Geographic distribution

  • The mite Demodex spp., which belongs to Class Arachnida. In humans, the infestation is known as 'demodicosis' and occurs worldwide.

Morphology

  • Adults - The size of demodices varies from 0.1 mm to 0.4 mm. Adult parasites have four pairs of short legs. They can slowly move on the skin especially during the night. Larvae, Nymphs - similar to adults, but larvae are 6-legged.

Life cycle (stages)

  • Entire life cycle is spent on the host

  • Females lay 20-24 eggs in the hair follicle

  • Larvae and nymphs (protonymph, deutonymph) are swept by the sebaceous flow to the mouth of the follicle, where they mature

  • Life cycle is completed in 18-24 days

Sites of infestation

  • Lives around hair follicles (Demodex folliculorum hominis) or in the secretory ducts of sebaceous (fat) glands connected to the hair follicles (Demodex brevis) of humans. The preferred sites are facial skin, forehead, cheeks, nose wings, eyelashes and external ear channels. The incidence of demodicosis steadily increases with the individual's age. The infestation may be frequently free of symptoms. However, Demodicidosis is characterised by the presence of an erythematous papule-pustular rash mainly on the face and inflammation in acute and chronic forms may occur. 

Demodex folliculorum:

The parasites frequently lie in pairs; they are elongated organisms with an obvious head-neck part and a body-tail part.

They are covered by a cuticle surface.The body is mostly semi-transparent.

The cuticle covering of body-tail part shows numerous striations. Head-neck part contains four pairs of short legs.

High magnification of the head-neck part embedded in keratin-containing desquamated skin cells.

The body-tail part in high magnification.
 

Skin conditions aggravated by Demodex folliculorum

To date, all research I have conducted has shown that when the Demodex folliculorum mite is associated with eruptions and erythema, the most irritated areas are through the central facial area or where there is the greatest abundance of sebaceous glands (T zone). In addition the higher incidence is the older client with a denser facial hair distribution.

The eruptions are not always Rosacea, unless one uses the term to describe any form of permanent diffused redness that is graded 1-5. Many adult acne and peri- oral dermatitis conditions may be found to have an infestation of Demodex folliculorum and that instead of being a cause, are an aggravating factor. The itching and irritation sensations, coming from an over proliferation of the mite, that is normally found in the pilosebaceous duct in fewer quantities.

A mite obtained from a case of demodicidosis in a patient with rosacea.

 

 

 

A study on Demodex folliculorum in rosacea.
Abd-El-Al AM, Bayoumy AM, Abou Salem EA.
Department of Dermatology, Faculty of Medicine, Al-Azhar University, Nasr City, Cairo.

A random sample of 16 female patients suffering from papulopustular rosacea (PPR) as well as (16) normal female healthy subjects as control group were adopted in this study to assess of Demodex folliculorum pathogenesis. It was done through determination of mite density using a standard skin surface biopsy 10.5 cm2 from different designated 6 areas on the face, and scanning electron microscopic study (SEM) as well as total IgE estimation.

A trial of treatment using Crotamiton 10% cream with special program was also attempted. All subjects ranged between 35-55 years old. All patients with rosacea and 15 of the control group i.e. 75.93% were found to harbour mites. The mean mite counts by site distribution were 28.6 & 6.9 on the cheeks, followed by 14.5 & 3.0 on the forehead and lastly 6.8 & 0.8 on the chin in PPR and control groups respectively. The total mean mite count in patients was 49.9 initially and 7.9 after treatment. In the control group it was 10.7 & 10.6 respectively. The mean total IgE was 169.4 & 168.4 and 96.3 & 98.4 in PPR and control groups respectively.

Light and scanning electron microscopy revealed that all mites were pointing in one direction. Some of them were containing bacteria inside their gut and on their skin. After treatment 3 cases (18.75%) were completely cured, 10 cases (62.5%) gave moderate response while 3 cases (18.75) have no response. In conclusion, this study supports the pathogenic role of D. folliculorum in rosacea.