Scabies

The Seven Year Itch

          Recognized since biblical times, scabies is a contagious, itchy skin infection caused by the burrowing parasitic mite, Sarcoptes scabiei.  The name is derived from the Latin word scabere, meaning ‘to scratch’, and the infestation was known as the ‘seven year itch’ before effective treatment was available.  These tiny, eight-legged critters related to spiders and ticks are usually not visible to the naked eye.  It is the female who burrows into the outer layer of the host’s skin to lay her eggs which then hatch in three to ten days.  The movement of the mites under the skin cause severe itching which is allergic in nature.  Scabies is one of the most common skin diseases in children and it is estimated that 300 million cases occur throughout the world each year. 

Transmission 

          Scabies is transmitted by direct personal contact, particularly during sex, and is not necessarily prevented by the use of condoms.  Because sexual contact is one of the most common ways that scabies is transmitted, it is sometimes considered a sexually transmitted disease.  The longer the direct skin to skin contact the more likely the infestation will be spread.  While scabies can also be contracted from objects such as sheets, clothing and furniture, this is much less common than transmission through direct contact with skin.  The mites can survive away from the host for 24 to 36 hours, accounting for their ability to spread through contact with these inanimate objects.  Scabies can spread quickly in crowded environments like nursing homes and day care centers, but is less likely to do so in the school setting.  

Diagnosis 

          As with so many afflictions of the human body the presence of a scabies infestation can usually be diagnosed by a good history and physical examination.  The itching begins a month to six weeks after exposure and is typically worse at night and with exposure to warmth.  Often another member of the family will also complain of itching.  Typical areas of the body that are affected with the small red bumps and blisters typical of the rash include the soft skin webs between the fingers, the ventral wrist area (same side as the palm), the underarm area, the feet, buttocks and external genitals, particularly in males.  The hands are often the first site to become infected.  Sometimes burrows appearing like thin, curved pencil marks can be detected and excoriation of the skin is common due to scratching.  All of these signs can be magnified in elderly and in immunocompromised individuals.  A definitive diagnosis can be made from a skin scraping and identification of eggs and feces during examination under the microscope. 

Treatment and Prevention 

          Scabies can be effectively treated with the application of permethrin cream prescribed by your health care provider.  The cream is usually applied to the entire body from the neck down at bedtime and then washed off in the shower eight to fourteen hours later.  A full body treatment is necessary, regardless of where the rash is located.  In some cases the cream must also be applied to the head, scalp and face and occasionally it is necessary to repeat this application one week later.  Itching often persists for a week or so even after effective treatment and can be alleviated by the use of antihistamines.  To prevent reinfestation, any clothing, bed sheets or towels that the patient has used should be washed and dried using high heat.  It is often necessary to treat the entire household even if they do not have symptoms in order to irradiate scabies.  If you suspect that you might have scabies it is important to contact your healthcare provider for proper diagnosis and treatment.