Scabies
Overview:
Scabies is a contagious skin infestation caused by Sarcoptes scabiei var. hominis mite. It leads to severe pruritus and skin lesions due to the mite burrowing into the epidermis.
Epidemiology:
Scabies is a widespread condition affecting individuals of all ages, ethnicities, and socioeconomic groups. Factors contribute to its spread:
- Overcrowded living conditions
- Delayed diagnosis and treatment
- Limited public awareness
- Poor hygiene
Transmission can be through direct skin to skin contact, and indirectly through contaminated objects (fomites).
A severe form of scabies, crusted scabies (Norwegian scabies), occurs in immunocompromised individuals, and is highly contagious.
Pathogenesis:
The Incubation period varies:
- First time infestation: symptoms appear within 2 to 6 weeks,
- Reinfestation: symptoms develop faster, within 24 to 48 hours.
Scabies mites can survive outside the human body for up to 3 days. However, in crusted scabies, mites can survive up to 7 days.
Clinical features:
Itching (pruritus):
- Often severe and worse at night or with hot showers.
- It can be the first symptom before visible skin lesions appear.
Lesions distribution and appearance:
- Lesions present as small erythematous papules with varying degree of excoriations.
- Other possible lesions include nodules and vesicles.
- Symmetrically affects interdigital web spaces of the hands, wrists, axillae, waist, ankles, feet, and buttocks.
- The face and scalp are typically spared, except in infants, elderly, immunocompromised patients, and in crusted scabies cases.
- Burrows is a pathognomonic sign, representing the tunnels created by female mites as they lay eggs. Burrows appear as grayish-white, thread like lines, measuring 1 to 10 mm in length.
- Crusted scabies has a widespread involvement of thick scaling and crusting.
Diagnosis:
Diagnosis is clinically, based on history and physical examination. Can be confirmed using diagnostic methods include:
- Dermoscopy allows visualization of mites and eggs.
- Skin scraping and microscopy using mineral oil preparation.
Treatment:
First line treatment: Topical Permethrin 5%
- Applied from head to toe in infants and elderly. In other age groups, face and scalp are excluded from treatment. Applied overnight for 8 to 12 hours on day 1 and 8.
Environmental and Preventive Measures:
- Clothing, bedding, and towels should be washed in hot water and dried in high heat or sealed in a bag for 7 to 10 days.
- All close contacts, even asymptomatic, must be treated in the same way.
Post-Treatment:
- After successful treatment, pruritus and skin lesions may persist for 2 to 4 weeks, this is called post scabetic pruritus.
Oral ivermectin is an option for treatment failures, outbreaks, or non-adherence, with a repeat dose after two weeks. Other alternatives include 25% benzyl benzoate or 0.5% malathion lotion.
Done by:
Layan AlShehri, Medical Intern
Revised by:
Naif Alshehri, Medical Intern
Resources:
Bolognia 5th Edition.
DermNet