The role of demodex mites in the pathogenesis of skin disorders in humans is still debated in contrast to their well known role as causative agents of various diseases in veterinary medicine. The authors here take the opportunity to report a case of demodicidosis in a 28-year-old male.
Keywords: Demodicidosis, demodex brevis, demodex folliculorum
|How to cite this article:
Hasan M, Siddiqui FA, Naim M. Human demodicidosis. Ann Trop Med Public Health 2008;1:70-1
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Hasan M, Siddiqui FA, Naim M. Human demodicidosis. Ann Trop Med Public Health [serial online] 2008 [cited 2020 Aug 11];1:70-1. Available from: https://www.atmph.org/text.asp?2008/1/2/70/50690
Infectious folliculitis has various etiologies, including bacteria, viruses, fungi, and parasites. Demodex mites can normally be found during a skin biopsy, however, at times, it may cause an inflammatory reaction or folliculitis requiring treatment. Accurate morphological recognition of microorganisms carries paramount importance in the implementation of appropriate therapy.
A 28-year-old male presented to dermatological out-patient department, Jawaharlal Nehru Medical College and Hospital with a complaint of an itching reddish area on his left cheek for the last 1 month. No associated pain was felt. The patient had consulted a private practitioner but was not responding to treatment and was referred to this hospital.
On general examination, the patient was a middle-aged male of average built and nutrition. His vitals were normal and a systemic examination was not contributory. A local examination revealed an erythematous and papulopustular non tender eruption on his left cheek measuring 3×2 cms. Routine blood analysis and chest X-rays were normal. A serological test for HIV was negative.
The patient was given topical corticosteroids and metronidazole. However, the patient found no relief even after 4 weeks of treatment. A skin biopsy was performed, which revealed demodex mites in the follicular ostia surrounded by a dense lymphocytic infiltrate in the dermis [Figure 1] and [Figure 2]. The patient was diagnosed with a case of demodicidosis and was given topical crotamiton. He showed complete clearing after 4 weeks.
Demodicidosis or demodicosis are skin disorders in which increased amounts of demodex mites are seen. Demodicidosis was first reported by Ayres in 1930.  Demodex folliculorum and demodex brevis are human ectoparasites belonging to the democidae family of the subclass mites.  Demodex is a parasite of the pilosebaceous follicle and the sebaceous gland in the seborrheic regions such as the nose, temporal regions, nasolabial folds, periorbital areas, and less commonly in the upper and medial region of the chest and back.  Demodex folliculorum is more commonly localized on the face while demodex brevis is more commonly found on the neck and chest. 
The number of demodex mites present in the lesion increases with age.  Demodicidosis is exceptionally seen in children less than 5 years of age. Delfos, et al., have stated that the rate of infestation in healthy individuals is age dependent and is almost absent in healthy children.  In fact, Forton is of the opinion that colonization of skin by demodex mites usually starts after 10 years of age due to increased sebum production. 
The pathogenesis of demodicidosis is still debated. Many authors believe the growth of demodex mites is favoured by the altered immune system, especially in immunodeficient individuals, which eventually causes a skin disorder. However, some authors suspect an unusual hypersensitivity against the mite itself, as histopathological examination reveals a dermal infiltrate of lymphocytes, eosinophils, and typical granulomas predominantly composed of CD4+ T helper lymphocytes, which are often distributed around a Demodex body. 
Rosacea of demodicidosis needs to be differentiated from common rosacea. Demodex type rosacea is characterized by dryness, follicular scaling, superficial vesicles, and pustules, while common rosacea is characterized by oily skin, absent follicular scaling, and is more deeply seated. On microscopic examination, a large number of demodex mites are seen in demodicidosis. , Another useful feature is the complete resolution of demodicidosis on treatment with crotamiton or lindane, but not by drugs effective against rosacea, such as metronidazole, which have no direct action on demodex mites. 
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Source of Support: None, Conflict of Interest: None
[Figure 1], [Figure 2]