Scabies are tiny mites called Sarcoptes scabiei that burrow under the skin causing infection and intense itching. They lay eggs in the skin, leading to further infection and symptoms. It can take up to 8 weeks for any symptoms or rash to appear after the initial infestation.
Presentation
Scabies presents with incredibly itchy small red spots, possibly with track marks where the mites have burrowed. The classic location of the rash is between the finger webs, but it can spread to the whole body.
TOM TIP: Scabies is more common than you may think. When someone presents with an itchy rash, ask whether anyone they live with has a similar rash and check between their finger webs for little red dots and track marks that may indicate scabies.
Management
Treatment is with permethrin cream. This needs to be applied to the whole body, completely covering skin. It is best to do this when the skin is cool (i.e. not after a bath or shower) so that a layer of cream remains on top of the skin and does not get absorbed. The cream should be left on for 8 – 12 hours and then washed off. This should be repeated a week later to kill all the eggs that survived the first treatment and have now hatched.
Oral ivermectin as a single dose that can be repeated a week later is an option for difficult to treat or crusted scabies.
Scabies is contagious to all household and close contacts. When one person is diagnosed, all household and close contacts should also be treated in exactly the same way, even if asymptomatic. This is because they may be infected and not yet have symptoms.
All clothes, bedclothes, towels and other materials in contact with scabies need to be washed on a hot wash to destroy the mites. Thorough hoovering of carpets and furniture is also essential.
Itching can continue for up to 4 weeks after successful treatment. Crotamiton cream and chlorphenamine at night at night can help with the itching.
Crusted Scabies
Crusted scabies is also known as Norwegian scabies. It is a serious infestation with scabies in patients that are immunocompromised. These patient may have over a million mites in their skin. They are extremely contagious. Rather than individual spots and burrows, they have patches of red skin that turn into scaly plaques. These can be misdiagnosed as psoriasis. Immunocompromised patients may not have an itch as they do not mount an immune response to the infestation. They may need admission for treatment as an inpatient with oral ivermectin and isolation.
Last updated January 2020