Organization:
The human body is home to a variety of organisms ranging from the minute bacteria to eukaryotic mites. Demodex folliculorum is a small arthropod that lives in human hair follicles and sebaceous glands. D. folliculorum and the closely related D. brevis live in a commensal relationship on humans and are harmless in the normal course of events. Demodex was first discovered by Henle in 1841 and described by Simon Akbulatova in 1842. The existence of the mite in cadavers was established by Stcherbatchoff in 1903 and later by Gmeiner in 1908. Riechers and Kopf in 1969 showed that maximum infestation of the mite is found in areas where sebum production is more. Norn in 1970 showed the presence of the mite in eyelash follicles and follicles of nasolabial folds (Rufli and Mumcuoglu, 1981).
The size of an adult D. folliculorum mite ranges from 03-0.4mm in length , the female mites being shorter and rounder than their male counterparts. The body is divided into two segments fused to each other with eight legs on the first segment that facilitate movement. The mite anchors itself to hair follicles by means of scales present all over its body. It feeds on skin cells, hormones, sebum and other secretions produced by the cells using pin-like structures (Rather and Hassan, 2014). Fertilization is internal and the eggs are laid and harbored on hair follicles and sebaceous openings. Three to four days after fertiliztion, a six-legged larval stage develops and achieves its complete growth in a span of seven days. The mite has a life-cycle of 14 days (Rather and Hassan, 2014). The genome size of Demodex was determined by flow cytometry to be 512Mb 9Lei et al, 2013). D. folliculorum has a mitochondrial genome of 14,150 bp with an AT percentage of 74.9%. The mitochondrial genome shows various gene rearrangements especially among the tRNA genes, a trait they share with other members of Acariformes (Palopoli et al, 2014)
Not much is known about the trasmission of the mite. It is known that in dogs, Demodex is transferred from mother to pup. This could be one probable method of transmission in humans also especially since microorganims are known to be transferred in this manner. However, some studies have found that the colonization of Demodex is higher in adults than in children suggesting some other means of transmission (Thoemmes et al, 2014).
In normal conditions,the presence Demodex does not manifest any symptoms. There are varied conditions that can lead to Demodex pathogenesis. Demodex turns parasitic when their numbers increase above normalcy. This condition is referred to as demodicosis. There are various conditions that manifest as a result of demodicosis. Demodex has even been associated with cancers and HIV infections. This is the major reason why I chose this organism. The following are some of the common conditions brought about by Demodex pathogenesis:
Rosacea
Rosacea is a facial condition characterized by redness, swelling, itching and stinging. Rosacea is thought to occur as a result of high acumulation of facial oil which leads to higher consumption of lipids by Demodex mites. The resulting proliferation of the mites result in blockage of facial pores leading to redness and swelling. Other factors that contribute to rosacea are sun exposure, weather extemities, wind, alcohol and emotional stress (Bhatia and Rosso, 2007, Rather and Hassan, 2014).
Blepharitis
Demodex is associated with the eyelash follicles and is thought to contribute to eye inflammatory disorders. A study conducted to formulate the relationship between blephairits and Demodex infestation included the collection eye lashes form 95 patients suffering from different disorders, and 1091 healthy individuals. Demodex infestation was found in patients suffering from hematologic disorders and cancer but the percentage wass comparable to that of the healthy controls. In the control individuals, the symptoms of Demodex infestation included itching, sensitivity to light and dandruff in lash roots. The cause of blepharitis associated with Demodex is speculated to be varied. It can be due to blockage of follicles, Demodex acting as a vector for pathogenic bacteria or by triggering the host’s immune response (Czepita et al, 2007, Danuta el al, 2012).
Demodex dermatitis
Demodex dermatitis is a condition separate from rosacea and seborrheic dermatitis. A study involving the treatment of patients reported to have dermatitis with crotamiton cream twce daily suggests the relationship between facial dermatitis and Demodex. The results of the treatment regimen did not correlate with the KOH test for Demodex suggesting that such tests are not always reliable and that the application of crotamiton might be useful for patients with dermatitis even when tested negative for Demodex ( Bikowski et al 2009).
Madarosis
Madarosis is the loss if eyelashes owing to various reasons. Many factors, genetic and environmental, have been associated with madarosis. Demodex infestation is one such reason that has been speculated to reuslt in madarosis. Patients with high prevalence of D. folliculorum has been shown to be affected with clinical dandruff and madarosis (Kumar and Karthikeyan, 2012).
Association of demodex with diabetes
Increased infestation of Demodex has been associated with diabetes. In a study, eyelashes of diabetes patients harboring clinical dandruff were aseptically removed and the presence of the mite was visualized under a microscope. The prevalance of the mite was found to be more common in dibetes patients as compared to the control (Yashamita et al, 2011). The correlation of gestational diabetes and Demodex infestation was studied by taking a group of 33 patients with gestational diabetes and 30 pregnant women was control. The Demodex population was higher in diabetes patients especially those with unregulates glucose levels ( Kurt et al, 2014). In another study, patients with type 2 diabetes were found to be more susceptible to Demodex infestation when there is improper regulation of blood glucose levels (Gökçe et al, 2013).
Miscellaneous facial dermatoses
In order to study the relationship between Demodex and various facial dermatoses, patients of ages ranging form 12 to 84 were oberved by four experienced dermatologists for conditions such as Steroid-induced dermatitis (SID), Seborrheic dermatitis (Seb D), primary irritation dermatitis (PID), sensitization dermatitis (SD) and Acne vulgaris (AV). A statistical correlation of Demodex was found in SID, Seb D, and PID but not in SD and AV ( Zhao et al, 2011).
Demodex and cancer
In order to find a possible relation between Demodex infestation and various forms of skin cancer, a population of 144 patients with different skin ailments including squamous cell carcinoma, melanoma and non-malignant discoid lupus erythematosus (DLE) was taken. A correlation of Demodex and rosacea was found. However, no significant correlation between the percentage of Demodex was found between patients with different skin cancers and healthy control subjects ( Talghini et al, 2014).
Cancer results in decreased immune activities. Immunocompromised patients are known to be more prone to various infections than healthy individuals. The same could hold true for Demodex infestation also. This hypothesis was put to test by a group of workers in 101 patients who were divided into four groups based on the type of cancer they were diagnosed with. The patients were aged between 38 and 82. 76.2% of the patients were found to have Demodex infestation. The rate of infestation did not differ according to the age of the patient or the status of chemotherapy (Sönmez et al, 2013).
This article has presented a short review of the human commensal Demodex folliculorum and the various pathological conditions that are associated with an abnormal count of the mite. However, the case of the mite becomes more interesting from an evolutionary point of view. Thedosius Dobzhansky said “ Nothing in biology makes sense except in the light of evolution”. This statement holds true in the case of this seemingly unimportant mite. A recent study demonstrated that human beings of different lineages hosted phylogentically distinct mite populations suggesting possible coevolution (Palopoli et al, 2015). Further studies in this direction might improve our understanding of human and associated microflora evolution.
References
Bhatia, N., Del Rosso, J. Q. (2007). Dispelling the mystery of Demodex. The dermatologist, 15(1).
Bikowski, J. B., & Del Rosso, J. Q. (2009). Demodex dermatitis: A retrospective analysis of clinical diagnosis and successful treatment with topical crotamiton. Journal of Clinical and Aesthetic Dermatology, 2(1), 20–25.
Czepita, D., Kuźna-Grygiel, W., Czepita, M., Grobelny, A.(2007).
Demodex folliculorum and Demodex brevis as a cause of chronic marginal blepharitis.
Ann Acad Med Stetin 53(1):63-7.
De Freitas Yamashita, L. S. F., Cariello, A. J., Geha, N. M. A., Yu, M. C. Z., & Hofling-Lima, A. L. (2011). Demodex folliculorum on the eyelash follicule of diabetic patients. Arquivos Brasileiros de Oftalmologia, 74, 422–424. doi:10.1590/S0004-27492011000600008
Gö Kçe, C., Aycan-Kaya, Z., Yula, E., Hsan Stü N, I. ˙, Yengil, E., Sefil, F., Bayram, F. (2015). The effect of blood glucose regulation on the presence of opportunistic Demodex folliculorum mites in patients with type 2 diabetes mellitus. Journal of International Medical Research, 41, 1752–1758. doi:10.1177/0300060513494730
Lei, S., Shu-Ling, G., Ke-Yuan, X., Xiao-li, Z., Fang-shu, Y. (2013). Determination of Demodex genome size by flow cytometry. Journal of Shadong University (Health Sciences), 51(6), 57-60
Keskin Kurt, R., Aycan Kaya, O., Karateke, A., Silfeler, D. B., Soylu Karapinar, O., Akkoca, A. N., & Hakverdi, A. U. (2014). Increased density of demodex folliculorum mites in pregnancies with gestational diabetes. Medical Principles and Practice, 23, 369–372. doi:10.1159/000363244
Kosik-Bogacka, D. I., Lanocha, N., Lanocha, A., Czepita, D., Grobelny, A., Zdziarska, B., & Kalisinska, E. (2012). Role of demodex folliculorum in the pathogenesis of blepharitis. Acta Ophthalmologica, 90(2003), 2012. doi:10.1111/j.1755-3768.2012.02391.x
Kumar, A., & Karthikeyan, K. (2012). Madarosis: A Marker of Many Maladies.International Journal of Trichology, 4(1), 3–18. http://doi.org/10.4103/0974-7753.96079
Palopoli, M. F., Minot, S., Pei, D., Satterly, A., & Endrizzi, J. (2014). Complete mitochondrial genomes of the human follicle mites Demodex brevis and D. folliculorum: novel gene arrangement, truncated tRNA genes, and ancient divergence between species. BMC Genomics, 15, 1124. doi:10.1186/1471-2164-15-1124
Palopoli, M. F., Fergus, D. J., Minot, S., Pei, D. T., Simison, W. B., Fernandez-Silva, I., Trautwein, M. (2015). Global divergence of the human follicle mite Demodex folliculorum: Persistent associations between host ancestry and mite lineages. Proceedings of the National Academy of Sciences of the United States of America, 112(52), 201512609. doi:10.1073/pnas.1512609112
Rather, P. A., & Hassan, I. (2014). Human Demodex Mite: The Versatile Mite of Dermatological Importance. Indian Journal of Dermatology, 59(1), 60–66. http://doi.org/10.4103/0019-5154.123498.
Rufli, T., Mumcuoglu,Y. (1981). The hair follicle mites Demodex folliculorum and Demodex brevis: Biology and medical importance. Dermatologica, 162,1-11
Sonmez, O. U., Yalcin, Z. G., Karakece, E., Ciftci, I. H., & Erdem, T. (2013). Associations between Demodex species infestation and various types of cancer. Acta Parasitol, 58(4), 551–555. doi:10.2478/s11686-013-0178-y
Talghini, S., Fouladi, D. F., Babaeinejad, S., Shenasi, R., & Samani, S. M. (2015). Demodex Mite, Rosacea and Skin Melanoma; Coincidence or Association? Türkiye Parazitolojii Dergisi / Türkiye Parazitoloji Derneği = Acta Parasitologica Turcica / Turkish Society for Parasitology, 39, 41–6. doi:10.5152/tpd.2015.3473
Thoemmes, M. S., Fergus, D. J., Urban, J., Trautwein, M., & Dunn, R. R. (2014). Ubiquity and diversity of human-associated Demodex mites. PLoS ONE, 9(8). doi:10.1371/journal.pone.0106265
Zhao, Y., Peng, Y., Wang, X., Wu, L., Wang, M., Yan, H., & Xiao, S. (2011). Facial dermatosis associated with Demodex: a case-control study. Journal of Zhejiang University. Science. B, 12(12), 1008–15. doi:10.1631/jzus.B1100179
