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