Overview
Scabies describes skin inflammation due to the mite Sarcoptes scabei, resulting in pruritic eruptions and burrows. The intense itching occurs due to a delayed type IV hypersensitivity reaction to the mites and eggs after infection, therefore, people can be infectious before the onset of symptoms.
Types
Classical (typical) scabies describe an infestation with a low number of mites (around 5-15).
Crusted (Norwegian) scabies describe hyperinfestation with thousands/millions of mites in exfoliating scales of skin. It occurs due to an insufficient immune response.
Transmission
Classical scabies are transmitted through prolonged skin contact with someone who has an infection. It can be sexually transmitted. Since mites can survive away from a host for up to 36 hours, transmission can also occur via shared bedding, towels etc.
Epidemiology
- Scabies is associated with poverty, overcrowding, poor hygiene, and malnutrition
- Scabies may be endemic in some areas, such as developing countries and subtropical locations
Risk Factors
General risk factors include:
- Close contact with an infected person
- Poverty, overcrowding, poor hygiene, and malnutrition
Risk factors of crusted scabies can include:
- Immunocompromised states – such as HIV and immunosuppressant drugs
- Reduced ability to scratch – such as disability, impaired sensation, learning difficulties, and dementia
However, up to 40% of people with crusted scabies may have no identifiable risk factor.
Presentation
Features of scabies include:
- Intense pruritus – often worse at night
- Linear burrows at the sides of fingers, finger webs, and flexor aspects of the wrist
- Excoriations and secondary infections can occur due to scratching
Features of crusted scabies include:
- Hyperkeratotic, crusted nodules or plaques
- Nail involvement may be present
Management
Overview
The management of scabies includes:
- Topical antiparasitic cream + repeat after 7 days – to ensure new mites that hatch are also killed:
- 1st-line: permethrin
- If ineffective/inappropriate: malathion
- Avoiding physical contact until treatment is complete
- Treating all household members/close contacts as well, even if asymptomatic
Itching may persist for up to 4 weeks post-treatment.
Complications
Secondary bacterial infection – such as impetigo, cellulitis, folliculitis, furunculosis etc.
Secondary eczematisation – this may occur due to scratching or irritation due to topical treatment
Nodular scabies – pruritic nodules that can form due to prolonged immune responses to mite antigens that can persist for weeks-months after treatment. Often found in the axillae, groin, and male genitalia.
Crusted (Norwegian scabies) – more common in immunocompromised people and requires prolonged and repeated treatment. The risk of the above complications is higher and also includes an increased risk of sepsis and death.
Prognosis
- Most people are cured after two treatments of topical permethrin, however, itching can persist for up to 4 weeks post-treatment
