Infectious Disease Online
Scabies - Causing Itchy Skin Lesions:
10 facts about Pathology of Scabies Infestation
[Pathology Infographic] - Scabies
1. Scabies is caused by Sarcoptes scabiei var hominis or the itch mite. It is an obligatory human parasite, which spreads from person to person by transmission of fertilised female mites by direct skin contact.
2. The leading risk factors identified are poor personal hygiene, living in overcrowded places or due to sexual contact.
3. A typical infestation involves a stable population of 15–20 adult female mites, which burrow in the stratum corneum where they deposit eggs and faeces.
4. The clinical symptoms of an intensely itchy eruption occur typically after a delay of two to six weeks in the case of an initial infestation and are caused by a host immune response to the mite and its faeces. The 3 clinical forms are: i) Papulovesicular lesions ; ii) Persistent nodules and iii) Norwegian (crusted) Scabies.
5. The diagnosis of scabies can be made either on clinical grounds or with confirmation using skin scraping, the adhesive tape test or dermatoscopy.
6. Microscopic features include superficial and deep infiltrate of lymphocytes, histiocytes, mast cells and eosinophils.
7. Spongiotic vesicles may be present in the epidermis containing eosinophils and neutrophils. Subepidermal bullae have also been reported. This may resemble bullous pemphigoid.
8. When the burrow is excised eggs, larva, mites and excreta may be present in the stratum corneum.
9. Lesions of persistent nodular scabies shows dense superficial and deep dermal infiltrate. Lymphoid follicles may be present in some cases.
10. Norwegian Scabies is characterized by prominent parakeratosis and orthokeratosis. Mites in various stages of development are present. There is pseudoepitheliomatous hyperplasia of the underlying epidermis, focal area of spongiosis and collection of eosinophils and neutrophils.
Prompt recognition of the condition on presentation, diagnosis and treatment is necessary to eliminate the risk of further transmission.
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