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A transmissible parasitic skin infection (Sarcoptes scabiei, a mite), characterized by superficial burrows, intense pruritus and secondary infection

Clinical Features

  1. Small urticarial crusted papules, eczematous plaques, excoriations
  2. Intractable pruritus worse at night
  3. Sites: axillae, cubitus, wrist, side of palm, web spaces, groin, Buttocks, back of ankle, toes, penis.
             Predisposing factors: Sexual promiscuity, crowding, poverty, nosocomial
             Adults: scalp, face, upper back spared
    ​         Infants: scalp, face, palms/soles involved
    1. Immunocompromised: Norwegian Scabies = 
    2. Scabies mite remain alive 2-3 days on clothing/sheets
    3. Incubation = 1 month, then begin to itch re-infection followed by hypersensitivity in 24 hours
    4. Microscopic examination of root and content of burrow with KOH for mite, eggs, feces
  1. Morphology And Biology Of The Scabies Mite
    1. The adult female mite is 0.4 mm long while the male mite is 0.2 mm long. Copulation occurs in a small burrow excavated by the female mite.
    2. The fertilized female enlarges the burrow and begins egg-laying. About 50 eggs are laid by each female mite during its life span of 4 to 6 weeks. The mite shows a preference for certain sites to burrow. They tend to avoid area with a high density of pilosebaceous follicles. Infested patients harbour an average of 11 mites. [ But in Norwegian scabies – thousands of mites]
  2. Clinical Features
    1. Incubation period is 3 to 4 weeks.  Itchiness is the most obvious symptom of scabies. It is worst at night time when the patient is warm.
    2. The pathognomonic sign of scabies is a burrow; it is a short, wavy, dirty-appearing line crossing skin lines. They may occur on the wrists, the borders of the hands, the sides of the fingers and the finger web-spaces  , the feet particularly the instep and in male the genitalia and nodules on scrotum. Burrows are uncommon on the trunk in adult but they may be found in elderly and infants. Pruritic papules which accompany hypersensitivity reaction occur around axillae, peri-areolar regions, peri-umbilical regions, buttock and thighs. The lesions do not occur above the neck-line. Secondary change like eczematous change frequently give confusion to the clinical picture. Inappropriate use of topical steroid may change the clinical picture to mimic other dermatoses.
  3. Diagnosis
    Absolute confirmation can only be made by the discovery of the burrows and microscopic examination. Presence of mites, eggs or fragments of egg-shells confirms the diagnosis.
  4. Treatment
    1. It is important that all members of the household and all close contacts should be treated simultaneously.
    2. Treatment must be given on two consecutive nights but not for longer. This anointing is repeated on the following morning. On the following evening the patient should take a bath again and has the bed-linen and clothing changed which are then laundered in the usual way.
    3. After the scabicidal treatment, pruritus may persist for a further 2 weeks. A topical antipruritic such as crotamiton cream may be applied on residual itchy areas. Postscabetic eczema can be treated with topical steroid.
    4. Secondary infection should be treated with a systemic antibiotic. If eczematisation is severe, a non-irritant scabicide, preferably in an aqueous base, should be used.
    5. Treatment of neonates - 6.25% benzyl benzoate emulsion may be used. Other alternatives include 10% crotamiton cream (applied nightly for 2 nights and washed off after the second application), 10% sulphur in petrolatum (applied nightly for 3 nights and washed off 24 hours after the last application) and 5% permethrin cream.
  5. Other Drugs Used:
    1. 1% gamma benzene hexachloride - a single application wash off after 12-24 hours is usually recommended. It is not recommended to be used in young children, pregnant and nursing women, and those with neurological diseases.
    2. Malathion - Malathion 0.5% in aqueous base has been used as scabicide. It should be left on the skin for 24 hours. The advantage over BBE is that it is much less stinging and acceptable.
    3. Permethrin - 5% dermal cream employed as a single application, wash off 8-12 hours. It is of low toxicity, and a single application which is removed in 8-10 hours is adequate. The disadvantage is that it is much more expensive than BBE or malathion.
    4. Monosulfiram - 25% solution diluted with 2-3 parts of water to be applied daily for 2 or 3 days.
    5. Crotamiton - 10% crotamiton cream is not highly effective and should not be a first line treatment for scabies. It is at best an adjunctive treatment for post-treatment pruritus and an alternative for BBE in infants and pregnant ladies.
    6. Topical sulphur e.g. 10% sulphur in petrolatum.  
    7. Ivermectin in dose 200 μ g/kg stat.

All the following are used in scabies except: (AIIMS May 08)
B. Permethrin
C. Crotamiton
D. Cyclopirox oleamine


Ans. C. Cyclopirox oleamine

  1. Crusted Scabies (Norwegian Scabies)
    Crusted scabies is an infestation with Sarcoptes scabiei hominis in which huge number of mites were present. The grossly thickened horny layer is honeycombed with cavities which contain large number of mites, and these are shed into the environment of the patient. Crusted scabies is highly contagious; an undiagnosed case of crusted scabies may lead to large outbreak of common scabies.

Atypical types of Scabies
Type Feature
•  Infantile scabies Face, palms, soles and scalp are involved
•  Norwegian scabies
Crusted hyperkeratotic lesion on face, palms, sole, nails. Itching is not prominent. Mites are found in thousand. most sever form of scabies
•  Crusted scabies Extensive cursts
•  Nodular scabies Itchy nodule over scrotum and penis
•  Genital scabies Genitals affected
•  Animal scabies History of contact with cat or dog. Atypical lesions develop.

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