Scabies – Diagnosis, Symptoms and Treatment

What is Scabies?

Scabies is a skin disease characterized by the infestation of the mite Sarcoptes scabiei.  The condition is typically acquired by close contact with people who have an active infection.  Sometimes it is spread through infected linens and clothing.  Individuals with scabies infection typically have severe itching and rash that involve the webs between the fingers and toes and the belt-line, groin, and armpits.  Symptoms are usually worse at night.

Scabies is highly contagious and often transmitted to other family members in the household.  Although not life-threatening, the disease can be cosmetically, physically, and psychologically disturbing.

What Causes Scabies?

Scabies is caused by the mite Sarcoptes scabiei – this mite infests the skin in some regions of the body, resulting in an extremely itchy and red rash.  The mite burrows into the skin, resulting in irritation and inflammation of the epidermis.  This results in erythema (redness) and pruritus (itching).

Scabies is transmitted via close contact with infected individuals.  Patients and children often transmit the infection to each other.  Some patients may develop scabies due to sexual contact – this is usually seen in young, sexually active adults.  Sarcoptes scabiei mites can typically survive off their host for up to 2-3 days.

How Common is Scabies?

Scabies is common in the United States and frequently evaluated in the primary care clinic.  Atypical or severe cases may require referral to an infectious disease or dermatology specialist, especially if first-line measures are unsuccessful.

The prevalence of scabies is increased in crowded conditions– in fact, infestations often occur in institutional settings such as nursing homes.  Rates of scabies infection also increase during winter months, likely because people crowd indoors.

Signs and Symptoms

Symptoms and signs of scabies often include a severely itchy (pruritic) rash that may be red (erythematous), scaly, and typically involves the following locations:

•         Web-spaces between fingers and toes
•         Groin
•         Belt-line
•         Armpits

Patients often have the characteristic appearance of a mite burrow on a detailed inspection of the rash.  This often has a zig-zag appearance as the mite moves side to side to drive farther down the skin horizontally.  Individuals with crusted (Norwegian) scabies – a more aggressive form of the mite – typically develop more severe infestation and symptoms.  Crusted scabies typically affects individuals with immunosuppression, such as HIV/AIDS.

Diagnosis

Scabies is a clinical diagnosis based on the patient’s symptoms, history, and physical examination.  An itchy rash with the characteristic appearance and distribution is highly suggestive.  Family member involvement is even more strongly suggestive of the disease.

Occasionally, your doctor may confirm the diagnosis by obtaining skin scrapings or performing a dermoscopic examination.  Negative laboratory studies do not necessarily exclude the diagnosis of scabies.  If you have evidence of crusted (Norwegian) scabies, your doctor may perform tests to exclude immunodeficiency such as HIV/AIDS.

Scabies Medication and Treatment

Scabies are treated with symptom control and prescription medications to eradicate the infection and prevent further disease transmission.

Your doctor may recommend the following medications:

•       Nix, Elimite - permethrin 5% cream
•       Stromectol - oral ivermectin

Permethrin cream is applied all over the body from the neck down.  The cream should be removed by showing 8-14 hours after drug administration.  An additional application is typically performed one week later.  Similarly, ivermectin is given as a single dose and is repeated after 1-2 weeks.  Individuals with crusted scabies are typically treated with both oral ivermectin and topical permethrin 5% cream simultaneously.

Close contacts of infected individuals should also receive treatment.  Clothing and linens should also be washed in hot water and dried in a hot dryer.  As an alternative, clothing and linens can be bagged for several days.

References:

1.     Chosidow O. Clinical practices. Scabies. N Engl J Med 2006; 354:1718. - https://www.nejm.org/doi/full/10.1056/NEJMcp052784
2.     Fuller LC. Epidemiology of scabies. Curr Opin Infect Dis 2013; 26:123.  - https://www.thelancet.com/pdfs/journals/laninf/PIIS1473-3099(18)30558-9.pdf