Clinical manifestations are pruritus that worsens during the night and a papular rash. The pruritus is a result of a delayed type-IV hypersensitivity reaction to the mite, the mite’s feces or their eggs . Therefore symptoms may not appear until 4 to 6 weeks after infection.
During the incubation period, symptoms of scabies typically begin to present 3-6 weeks after the primary infection. In patients who have previously been infected by scabies, symptoms may appear earlier due to sensitization of the patient’s immune system.
During infestation period the lesion(s) are small, erythematous, nondescript papules, often excoriated and tipped with hemorrhagic crusts. The burrow is a thin, grayish, reddish or brownish line that is 2-15 mm long. Miniature wheals, vesicles, pustules, and rarely bullae may also be present.
The typical distribution of scabies is:
Usually the back and head are not involved. Young children and infants often have involvement of the palms and soles and all aspects of the fingers. Lesions in children are usually more inflammatory than in adults and often vesicular or bullous.
Norwegian Crusted Scabies (scabies crustosa)
This subtype of scabies commonly occurs in immunocompromised patients. These result in thick crusts of skin that contain large numbers of scabies, mites and eggs. The mites in the crusts are not any more virulent as the ones in non-crusted scabies. However they are significantly more numerous (up to 2 million per patient). The fissures associated with crusted scabies provide a portal of entry for bacteria.
In an immunocompromised person, this may lead to impetigo, severe infection and even sepsis. Crusted scabies begin with poorly defined erythematous patches that quickly develop prominent scales. Scalp, hands and feet are commonly affected. Lesions are malodorous. Nails may become distorted and discolored, itching may be minimal or absent.
Treatment with oral ivermectin and topical permethrin has been successful. In very severe cases, surgical debridement in combination with the ivermectin and permethrin, has been shown to be an effective treatment.
The diagnosis of scabies is usually determined from the patient’s history and the distribution of the lesions. Affirmative answers that my indicate scabies include: Wide spread itching that is worse at night everywhere on the body but the head? Any pruritic eruptions with characteristic lesions and distributions? Are there any other household members with similar symptoms?
Skin scraping – Skin scraping may allow direct observation of the mites, eggs or the mite’s feces pellets. This involves placing a drop of mineral oil over the skin lesion and scraping the area with a number 15 blade or pinching the area between the thumb and index finger and while shaving the top layer of the skin. The specimen is then placed on a slide and visualized under a microscope at 10x power for mite eggs or mites . Draw backs to this method are that special stains and equipment are required and children may not tolerate this well.
Dermoscopy – Dermoscopy may also allow direct observation of the mites or burrowing. This test involves an examination of the skin surface with a handheld dermatocsope which allows visualization of the dermal epidermis. The characteristic finding on dermoscopic examination is a dark, triangular shape that represents the mite’s head within a burrow, called the “delta wing” sign. The primary draw back to this method is the need to have specialized equipment and evaluation is more difficult in dark skinned patients.
Adhesive tape test – Transparent tape is firmly applied directly onto a lesion and then quickly removed. The tape is then applied to a glass and examined for mites and eggs. This test is most often used in c clinics because no special equipment is needed and children tend to tolerate this test better than skin scrapings.
Complete eradication of mites is essential for treatment. The patient as well as his/her close contacts must be treated simultaneously.
Both oral (e.g. ivermectin, thiabendazole, flubendazole) and topical creams (e.g. lindane, permethrin, sulfur containing products, crotamiton, malathion, benzyl benzoate are used to treat scabies mites .
There is no international consensus on the treatment of scabies. However, 5% permethrin with oral ivermectin are usually the first line choices for treatment. Clinical trials evaluating the toxicity of various therapies have indicated that topical permethrin 5% cream and oral ivermectin are reasonable first-line therapies, with minimal side effects.
In another clinical trial evaluating the efficacy between 5% permethrin cream or 1% lindane lotion found similar cure rates achieved in 4 weeks after a single whole body application of each. However, permethrin has less neurotoxicity than lindane, particularly in children, and therefore is preferred .
Oral ivermectin is an anthelmintic with a half-life of 36 hours. The advantage to an oral medication compared to a topical medication is its ease of use; lack of treatment associated dermatitis and increased compliance. Ivermectin is first line therapy in nursing home or other institutional facilities where topical therapy may not be practical .
Randomized clinical trials have shown that a single dose of ivermectin 200 mcg/kg is as or more effective than application of 1% lindane, but LESS effective than a single application of permethrin. Two doses of ivermectin achieved equivalent cure rates to a single application of permethrin .
The CDC recommends using ivermectin (200 mcg/kg by mouth as a single dose with a repeat dose 2 weeks later) as an equivalent option to topical permethrin .
Itching can be controlled with antihistamines. Itching may persist up to 2 weeks after treatment because of hypersensitivity reaction to mites, mites feces and eggs. High potency topical corticosteroids can also be used to control itching after eradication of mites.
The entire household and close contacts must also be treated in addition to the patient at the same time to prevent re-infection or cross contamination. Fomite transfer of scabies may also occur although it is not as much of a concern as person to person transmission.
There is a possibility that contaminated clothing can result in spread or reinfection with scabies. Such items should be placed in a plastic bag for 3 days (scabies mites cannot survive for more than 2-3 days away from human skin). Then machine washed with hot water and placed in a hot dryer or dry cleaned .
Scabies is curable with scabicide medications.
Scabies is caused by the host-specific mite Sarcopetes scabiei hominis, which is an obligate human parasite and a member of the family Sarcoptidae.
Almost 300 million people may be infected worldwide. The scabiei mite depends on humans for survival and infection occurs from human to human contact.
It is equally seen in men and women and in persons of all races. It is most prevalent in crowded conditions such as nursing homes, child care facilities, extended-care facilities and prisons.
Scabies is more prevalent during the winter than in the summer. This may be attributed to greater physical crowding in the winder and also because the mites can survive longer on fomites in colder temperatures .
Mites can survive off a host for 24 or 36 hours depending on environmental conditions . The mites mate on the surface of the skin and then the female burrows into the skin to lay the eggs. The eggs hatch a few days later and nymphs appear.
Burrowing is facilitated by secretion of enzymes which cause skin damage detectable at the microscopic level. The female mite burrows into the epidermis to the level of the granulosum and burrows down further about 2 mm a day, lays 10-25 eggs a day and then dies.
The larvae hatch in three to four days, leave the burrow for the surface of the skin, copulate and continue the cycle.
There are no guidelines for prevention of Scabies.
What are scabies?
Scabies is an infection caused by tiny mites that makes your skin very itchy. This happens when tiny insects called mites burrow under your skin to lay eggs each day for several weeks.
How do you get scabies?
Scabies is spread from people to people that are in close contact (skin to skin contact) and through shared bedding, clothing, towels of the infested person.
What are the symptoms of scabies?
The common symptom is severe itching that is worse at night and small red bumps that may be hard to see. The itching is caused by allergic reaction to the mites. Therefore, the itching may start a few weeks after a person is infected. The body parts impacted the most by scabies are:
Treatment and Control
If you have these symptoms, you should see your doctor. He/she will give you a medicine to cure the scabies mites. If you keep scratching, you may get infections. You can use anti-histamines (allergy pills) to stop the itching while you are undergoing treatment. Itching may last 2 weeks after you finish your treatment.
Once your doctor starts you on the medication, he/she will also ask the people in close contact with you to start the treatment as well. This is because they may be carrying scabies, even without any symptoms. The goal is to prevent re-infection.
Wash all clothes that you and others wore in the last week in hot water and dry on high heat in the dryer. Also wash bedding, towels, stuffed animals, etc. Dry cleaning will also get rid of the mites. If you are not able to wash or dry clean these items, place them in a plastic bag for 3 days. The scabies mites cannot live away from the body for more than 2-3 days.